LT8490 High Voltage, High Current Buck-Boost Battery Charge Controller with Maximum Power Point Tracking (MPPT) Description Features VIN Range: 6V to 80V nn V BAT Range: 1.3V to 80V nn Single Inductor Allows V Above, Below, or Equal IN to VBAT nn Automatic MPPT for Solar Powered Charging nn Automatic Temperature Compensation nn No Software or Firmware Development Required nn Operation from Solar Panel or DC Supply nn Input and Output Current Monitor Pins nn Four Integrated Feedback Loops nn Synchronizable Fixed Frequency: 100kHz to 400kHz nn 64-Lead (7mm x 11mm x 0.75mm) QFN Package nn Applications Solar Powered Battery Chargers Multiple Types of Lead-Acid Battery Charging nn Li-Ion Battery Charger nn Battery Equipped Industrial or Portable Military Equipment nn The LT(R)8490 is a buck-boost switching regulator battery charger that implements a constant-current constantvoltage (CCCV) charging profile used for most battery types, including sealed lead-acid (SLA), flooded, gel and lithium-ion. The device operates from input voltages above, below or equal to the output voltage and can be powered by a solar panel or a DC power supply. On-chip logic provides automatic maximum power point tracking (MPPT) for solar powered applications. The LT8490 can perform automatic temperature compensation by sensing an external thermistor thermally coupled to the battery. STATUS and FAULT pins containing charger information can be used to drive LED indicator lamps. The device is available in a low profile (0.75mm) 7mm x 11mm 64-lead QFN package. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. nn Typical Application Simplified Solar Powered Battery Charger Schematic Maximum Power Point Tracking FULL PANEL SCAN GATEVCC GATEVCC VPANEL 6V/DIV SOLAR PANEL LOAD TG1 BOOST1 SW1 BG1 CSP CSN BG2 SW2 BOOST2 TG2 IPANEL 1.36A/DIV VBAT CSNIN CSPIN VIN CSPOUT CSNOUT EXTVCC LT8490 GATEVCC AVDD TEMPSENSE + PERTURB & OBSERVE PERTURB & OBSERVE - RECHARGABLE BATTERY 0.5s/DIV 8490 TA01b BACK PAGE APPLICATION THERMISTOR GATEVCC INTVCC STATUS AVDD FAULT GND AVDD 8490 TA01a 8490fa For more information www.linear.com/LT8490 1 LT8490 Absolute Maximum Ratings Pin Configuration (Note 1) 64 IOR 63 CHARGECFG2 62 GND 61 CHARGECFG1 60 NC 59 GND 58 AVDD 57 FBOR 56 CLKDET 55 GND 54 VINR 53 IIR TOP VIEW 52 NC 51 STATUS 50 IOW 49 SWENO 48 ECON FBIR 1 FAULT 2 TEMPSENSE 3 VDD 4 FBOW 5 FBIW 6 INTVCC 7 SWEN 8 MODE 9 IMON_IN 10 SHDN 11 CSN 12 CSP 13 LDO33 14 FBIN 15 FBOUT 16 IMON_OUT 17 VC 18 SS 19 CLKOUT 20 46 VIN 45 CSPIN 44 CSNIN 65 GND 42 CSPOUT 41 CSNOUT 40 EXTVCC 38 SRVO_FBOUT 37 SRVO_IOUT 36 SRVO_IIN 35 SRVO_FBIN SW1 31 TG1 32 BOOST2 27 TG2 28 SW2 29 33 BOOST1 SYNC 21 RT 22 BG1 23 GATEVCC 24 BG2 25 VCSP - VCSN, VCSPIN - VCSNIN, VCSPOUT - VCSNOUT.................................... -0.3V to 0.3V SS, CLKOUT, CSP, CSN Voltage ................... -0.3V to 3V VC Voltage (Note 2).................................... -0.3V to 2.2V LDO33, VDD, AVDD Voltage........................... -0.3V to 5V RT, FBOUT Voltage........................................ -0.3V to 5V IMON_IN, IMON_OUT Voltage ..................... -0.3V to 5V SYNC Voltage............................................. -0.3V to 5.5V INTVCC, GATEVCC Voltage ............................ -0.3V to 7V VBOOST1 - VSW1, VBOOST2 - VSW2................. -0.3V to 7V SWEN, MODE Voltage .................................. -0.3V to 7V SRVO_FBIN, SRVO_FBOUT Voltage............ -0.3V to 30V SRVO_IIN, SRVO_IOUT Voltage.................. -0.3V to 30V FBIN, SHDN Voltage.................................... -0.3V to 30V CSNIN, CSPIN, CSPOUT, CSNOUT Voltage... -0.3V to 80V VIN, EXTVCC Voltage................................... -0.3V to 80V SW1, SW2 Voltage ...................................... 81V (Note 5) BOOST1, BOOST2 Voltage ......................... -0.3V to 87V BG1, BG2, TG1, TG2............................................ (Note 4) IOW, ECON, CLKDET Voltage .......... -0.3V to VDD + 0.5V SWENO, STATUS Voltage................. -0.3V to VDD + 0.5V FBOW, FBIW, FAULT Voltage ........... -0.3V to VDD + 0.5V VINR, FBOR, IIR, IOR Voltage.......... -0.3V to VDD + 0.5V TEMPSENSE Voltage....................... -0.3V to VDD + 0.5V CHARGECFG2, CHARGECFG1 Voltage...................... -0.3V to VDD + 0.5V UKJ PACKAGE 64-LEAD (7mm x 11mm) PLASTIC QFN TJMAX = 125C, JA = 34C/W EXPOSED PAD (PIN 65) IS GND, MUST BE SOLDERED TO PCB Operating Junction Temperature Range LT8490E (Notes 1, 3).......................... -40C to 125C LT8490I (Notes 1, 3)........................... -40C to 125C Storage Temperature Range .................. -65C to 150C Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8490EUKJ#PBF LT8490EUKJ#TRPBF LT8490UKJ 64-Lead (7mm x 11mm) Plastic QFN -40C to 125C LT8490IUKJ#PBF LT8490IUKJ#TRPBF LT8490UKJ 64-Lead (7mm x 11mm) Plastic QFN -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 2 8490fa For more information www.linear.com/LT8490 LT8490 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, VDD = AVDD = 3.3V, SHDN = 3V unless otherwise noted. (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS Voltage Supply and Regulators VIN Operating Voltage Range (Note 7) l 6 VIN Quiescent Current Not Switching, VEXTVCC = 0, VDD = AVDD = Float VIN Quiescent Current in Shutdown VSHDN = 0V VDD Quiescent Current IAVDD + IVDD, VDD = AVDD = 3.3V l 2.5 EXTVCC Switchover Voltage IINTVCC = 20mA, VEXTVCC Rising l 6.15 EXTVCC Switchover Hysteresis V 2.65 4.2 mA 0 1 A 4 6.5 mA 6.4 6.6 V 0.18 LDO33 Pin Voltage 5mA from LDO33 Pin LDO33 Pin Load Regulation ILDO33 = 0.1mA to 5mA LDO33 Pin Current Limit LDO33 Pin Undervoltage Lockout 80 l l LDO33 Falling 3.23 V 3.295 3.35 V -0.25 -1 % 12 17.25 22 mA 2.96 3.04 3.12 LDO33 Pin Undervoltage Lockout Hysteresis 35 V mV Switching Regulator Control SHDN Input Voltage High SHDN Rising to Enable the Device l 1.184 1.234 1.284 SHDN Input Voltage High Hysteresis 50 SHDN Input Voltage Low Device Disabled, Low Quiescent Current SHDN Pin Bias Current VSHDN = 3V VSHDN = 12V SWEN Rising Threshold Voltage l 0 11 l MODE Pin Thresholds 0.35 V 1 22 A A 1.156 1.206 1.256 SWEN Threshold Voltage Hysteresis V mV 22 V mV 2.3 V V 195 224 mV 122 150 mV Discontinuous Mode Forced Continuous Mode l l 0.4 IMON_OUT Rising threshold for CCM Operation MODE = 0V l 168 IMON_OUT Falling threshold for DCM MODE = 0V l 95 Regulation Voltage for FBOUT VC = 1.2V, EXTVCC = 0V l 1.193 1.207 1.222 V Regulation Voltage for FBIN VC = 1.2V, EXTVCC = 0V l 1.184 1.205 1.226 V FBOUT Pin Bias Current Current Out of Pin 15 nA FBIN Pin Bias Current Current Out of Pin 10 nA Voltage Regulation Current Regulation Regulation Voltage for IMON_IN and IMON_OUT VC = 1.2V, EXTVCC = 0V IMON_IN Output Current VCSPIN - VCSNIN = 50mV, VCSPIN = 5.025V VCSPIN - VCSNIN = 50mV, VCSPIN = 5.025V VCSPIN - VCSNIN = 0mV, VCSPIN = 5V IMON_IN Overvoltage Threshold IMON_OUT Output Current VCSPOUT - VCSNOUT = 50mV, VCSPOUT = 5.025V VCSPOUT - VCSNOUT = 50mV, VCSPOUT = 5.025V VCSPOUT - VCSNOUT = 5mV, VCSPOUT = 5.0025V VCSPOUT - VCSNOUT = 5mV, VCSPOUT = 5.0025V IMON_OUT Overvoltage Threshold l 1.187 1.208 1.229 V l l 54 53 2.5 57 57 7 60 61 11.5 A A A l 1.55 1.61 1.67 V l 47.5 47 3.25 2.75 50 50 5 5 52.5 54.25 6.75 8 A A A A l 1.55 1.61 1.67 V l 8490fa For more information www.linear.com/LT8490 3 LT8490 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, VDD = AVDD = 3.3V, SHDN = 3V unless otherwise noted. (Note 3) PARAMETER CONDITIONS MIN Switch Frequency Range Syncing or Free Running 100 Switching Frequency, fOSC RT = 365k RT = 215k RT = 124k TYP MAX UNITS 400 kHz 142 235 400 kHz kHz kHz Switching Regulator Oscillator (OSC1) l l l 102 170 310 SYNC High Level for Synchronization l 1.3 SYNC Low Level for Synchronization l VSYNC = 0V to 2V SYNC Clock Pulse Duty Cycle 120 202 350 V 0.5 V 80 % 2.45 2.55 V 25 100 mV 20 Recommended Min SYNC Ratio, fSYNC / fOSC 3/4 CLKOUT Output Voltage HIGH 1mA Out of CLKOUT Pin CLKOUT Output Voltage LOW 1mA into CLKOUT Pin CLKOUT Duty Cycle TJ = -40C TJ = 25C TJ = 125C 2.3 22.7 44.1 77 % % % Charging Control STATUS, FBOW, FBIW, SWENO, IOW, ECON Output Low Voltage IOL = 5mA l STATUS, FBOW, FBIW, SWENO, IOW, ECON Output High Voltage IOH = -5mA l FAULT Output Voltage Low IOL = 0.5mA l FAULT Output Voltage High IOH = -0.1mA 0.22 0.5 V 2.7 3.0 l 1.7 2.2 l 155 174 mV 29 mV 0.1 V 0.25 V V Power Supply Mode Detection Threshold (Note 6) VINR Pin Falling Power Supply Mode Detection Threshold Hysteresis (Note 6) VINR Pin Minimum VINR Voltage for Start-Up (Note 6) Not in Power Supply Mode Low Power Mode Enabled Low Power Mode Disabled l l 380 213 High Charging Current Threshold on IOR (Note 6) IOR Rising g ECON Rising l 168 195 224 mV Low Charging Current Threshold on IOR (Note 6) IOR Falling g ECON Falling l 95 122 150 mV Minimum CHARGECFG1 % of AVDD to Disable Stage 3 (Note 6) Temperature Compensation Enabled l 94 95 96 % Maximum CHARGECFG1 % of AVDD to Disable Stage 3 (Note 6) Temperature Compensation Disabled l 4 5 6 % Minimum CHARGECFG2 % of AVDD to Disable Time Limits (Note 6) Wide Valid Temperature Range l 94 95 96 % Maximum CHARGECFG2 % of AVDD to Disable Time Limits (Note 6) Narrow Valid Temperature Range l 4 5 6 % l 94.5 96 97.5 % Minimum TEMPSENSE % of AVDD to Detect Battery Disconnected (Note 6) 395 225 410 237 mV mV VCSPOUT - VCSNOUT Threshold for C/5 Detection (Note 6) VCSxOUT Common Mode = 5.0V, RTOTAL from IMON_OUT to Ground = 24.3k 9 10 11 mV VCSPOUT - VCSNOUT Threshold for C/10 Detection (Note 6) VCSxOUT Common Mode = 5.0V, IOR Falling, RTOTAL from IMON_OUT to Ground = 24.3k 4.25 5 5.75 mV FBIW, FBOW PWM Frequency (OSC2) 31.25 FBIW, FBOW PWM Resolution 8 STATUS UART Bit Rate l Internal A/D Resolution 4 kHz 2160 2400 10 Bits 2640 Baud Bits 8490fa For more information www.linear.com/LT8490 LT8490 Electrical Characteristics Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Do not force voltage on the VC pin. Note 3: The LT8490E is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT8490I is guaranteed over the full -40C to 125C junction temperature range. Note 4: Do not apply a voltage or current source to these pins. They must be connected to capacitive loads only, otherwise permanent damage may occur. Note 5: Negative voltages on the SW1 and SW2 pins are limited in the applications by the body diodes of the external NMOS devices M2 and M3 or parallel Schottky diodes when present. The SW1 and SW2 pins are tolerant of these negative voltages in excess of one diode drop below ground, guaranteed by design. Note 6: These thresholds are measured by the internal A-D converter. The A-D reference voltage is AVDD. AVDD, VDD and an additional 2.8mA load are regulated by LDO33 to create the AVDD reference for these measurements. The absolute threshold voltages will shift with corresponding changes in the AVDD voltage. Note 7: 10V minimum VIN required for solar powered start-up if low power mode is enabled. 8490fa For more information www.linear.com/LT8490 5 LT8490 Typical Performance Characteristics 17.5 Solar Powered Charging Lead Acid Battery "B" 17.5 PARTLY CLOUDY VBAT 10.0 IBAT 7.50 5.00 SOME TRANSIENTS 2.50 FROM FULL PANEL SCANS REMOVED 0 FOR CLARITY. 7.50 0 0 6PM 9AM IBAT 2.50 3 STAGE SUNSET 5.00 VBAT 5.00 VOH 25C 2 1 8490 G03 3 VFAULT (V) VSTATUS (V) VBAT (V) AND IBAT (A) 7.50 25C 125C 2 -40C 125C 25C 1 25C 2.50 VOL VIN = 36V 0 12 0 0 BACK PAGE APPLICATION 8490 G04 LDO33 Load Regulation (Not Connected to AVDD and VDD) VOL -40C 5 CHARGING TIME (HOURS) 3.4 0 5PM FIGURE 34 APPLICATION -40C 125C IBAT 0 UART AND STATUS 2 INDICATE < C/10 FAULT VOH and VOL (VDD = AVDD = 3.3V) VOH 10.0 4 TIME OF DAY 8490 G02 3 STAGE 3 6 SOME TRANSIENTS FROM FULL PANEL SCANS REMOVED FOR CLARITY. 24 STATUS VOH and VOL (VDD = AVDD = 3.3V) 15.0 STAGE 2 IBAT TIME OF DAY BACK PAGE APPLICATION Power Supply Mode Charging Lead Acid Battery "B" STAGE 1 26 20 1PM 0 6PM 10AM 8490 G01 BACK PAGE APPLICATION 12.5 VBAT 3 STAGE TIME OF DAY 8 28 SOME TRANSIENTS FROM FULL PANEL SCANS REMOVED FOR CLARITY. 10.0 STAGE 2 IBAT (A) SUNSET VBAT (V) AND IBAT (A) 12.5 10 PARTLY CLOUDY STAGE 1 VBAT CHARGING STAGE 12.5 30 CLOUDY DAY 15.0 CHARGING STAGE VBAT (V) AND IBAT (A) 15.0 Solar Powered Charging Lithium Ion Battery VBAT (V) Solar Powered Charging Lead Acid Battery "A" TA = 25C, unless otherwise noted. 10 |ISTATUS| (mA) 0 20 15 0 125C -40C 1 8490 G05 3 2 |IFAULT| (mA) 8490 G06 FBOUT, FBIN, IMONIN, IMONOUT Voltage Rise vs Power IMON Output Currents 1.0 200 175 125C -40C 3.1 IMON_IN 125 VOLTAGE RISE (%) 25C 3.2 PIN CURRENT (A) LDO33 (V) 0.8 150 3.3 100 75 IMON_OUT 50 25 INTVCC REGULATED FROM VIN 0.6 0.4 INTVCC REGULATED FROM EXTVCC 0.2 0 3 0 4 8 12 16 LOAD CURRENT (mA) 20 8490 G07 6 -25 -100 -50 0 50 100 CSxIN-CSxOUT (mV) 150 200 8490 G08 0 0 1 1.5 0.5 INTVCC REGULATOR POWER (W) 2 8490 G09 8490fa For more information www.linear.com/LT8490 LT8490 Typical Performance Characteristics Maximum Power Point Tracking VPANEL 5V/DIV TA = 25C, unless otherwise noted. Perturb and Observe Perturb and Observe VPANEL 5V/DIV PERTURB & OBSERVE FULL PANEL SCANS VPANEL 5V/DIV IMON_OUT 200mV/DIV IMON_OUT 100mV/DIV IMON_OUT 500mV/DIV 8490 G10 30s/DIV 8490 G11 0.5s/DIV 0.5s/DIV 8490 G12 FIGURE 34 APPLICATION FIGURE 34 APPLICATION FIGURE 34 APPLICATION Perturb and Observe Maximum Power Point Tracking Full Panel Scan Single Power Peak Full Panel Scan--Partially Shaded with Dual Power Peaks ROTATE PANEL TOWARDS THE SUN. PANEL VOLTAGE AND CURRENT ARE AUTOMATICALLY ADJUSTED TO NEW MAX. VPANEL 6V/DIV IMON_OUT 100mV/DIV VPANEL 10V/DIV VPANEL 10V/DIV POWER PEAK IMON_OUT 500mV/DIV IMON_OUT 200mV/DIV 0.5s/DIV 0.5s/DIV 8490 G15 FIGURE 34 APPLICATION Panel Voltage in Low Power Mode IMON_OUT 50mV/DIV 8490 G14 FIGURE 34 APPLICATION FIGURE 34 APPLICATION MAX POWER PEAK IMON_IN 200mV/DIV IMON_IN 500mV/DIV 8490 G13 5s/DIV LOWER POWER PEAK Panel Voltage in Low Power Mode 10.6mV IMON_OUT 50mV/DIV 10.6mV 17.6V VPANEL 5V/DIV SWEN 5V/DIV 3.3V SWEN 5V/DIV 40ms/DIV FIGURE 34 APPLICATION 10.1V VPANEL 5V/DIV 10.4V 3.3V 8490 G16 40ms/DIV 8490 G17 FIGURE 34 APPLICATION 8490fa For more information www.linear.com/LT8490 7 LT8490 Pin Functions FBIR (Pin 1): A/D Input Pin. Connects to FBIN pin to measure input feedback voltage. CSN (Pin 12): The (-) Input to the Inductor Current Sense and Reverse Current Detect Amplifier. FAULT (Pin 2): FAULT Pin. This pin generates an active high digital output that, when used with an LED, provides a visual indication of a fault event. CSP (Pin 13): The (+) Input to the Inductor Current Sense and Reverse Current Detect Amplifier. The VC pin voltage and built-in offsets between the CSP and CSN pins set the current trip threshold. TEMPSENSE (Pin 3): A/D Input Pin. Connects to a thermistor divider network for sensing battery temperature or a resistor divider if unused. This pin is frequently monitored for temperature compensation and enforcing temperature limits. VDD (Pin 4): Control Logic Power Supply Pin. Connect this pin to LDO33 and AVDD. FBOW (Pin 5): PWM Digital Output Pin. Connects to FBOUT through an RCR network to temperature compensate the battery voltage. FBIW (Pin 6): PWM Digital Output Pin. Connects to FBIN through an RCR network to adjust the solar panel voltage for MPPT. INTVCC (Pin 7): Internal 6.35V Regulator Output Pin. Connects to the GATEVCC pin. INTVCC is powered from EXTVCC when the EXTVCC voltage is higher than 6.4V, otherwise INTVCC is powered from VIN. Bypass this pin to ground with a minimum 4.7F ceramic capacitor. See Switching Configuration - MODE Pin for additional details. SWEN (Pin 8): Switch Enable Pin. Tie to the SWENO pin. MODE (Pin 9): Mode Pin. The voltage applied to this pin sets the operating mode of the switching regulator. Tie this pin to INTVCC to make discontinuous current mode active. Tie this pin to ground to operate in discontinuous current mode for low battery charging currents and continuous current mode for high battery charging currents. Do not float this pin. See Switching Configuration - MODE Pin for additional details. IMON_IN (Pin 10): Input Current Monitor Pin. The current out of this pin is proportional to the input current. See the Applications Information section for more information. SHDN (Pin 11): Shutdown Pin. In conjunction with the UVLO (undervoltage lockout) circuit, this pin is used to enable/disable the chip. Do not float this pin. 8 LDO33 (Pin 14): 3.3V Regulator Output. This supply provides power to the VDD and AVDD pins. Bypass this pin to ground with a minimum 4.7F ceramic capacitor. FBIN (Pin 15): Input Feedback Pin. This pin is connected to the input error amplifier input. FBOUT (Pin 16): Output Feedback Pin. This pin connects the error amplifier input to an external resistor divider from the output. IMON_OUT (Pin 17): Output Current Monitor Pin. The current out of this pin is proportional to the average output current. See the Applications Information section for more information. VC (Pin 18): Error Amplifier Output Pin. Tie the external compensation network to this pin. SS (Pin 19): Soft-Start Pin. Place 100nF of capacitance from this pin to ground. Upon start-up, this pin will be charged by an internal resistor to 2.5V. CLKOUT (Pin 20): Switching Regulator Clock Output Pin. CLKOUT will toggle at the same frequency as the switching regulator oscillator (OSC1 on the Block Diagram) or as the SYNC pin, but is approximately 180 out-of-phase. CLKOUT can also be used as a temperature monitor of the switching regulator since the CLKOUT duty cycle varies linearly with the junction temperature of the switching regulator. It is connected to CLKDET through an RC filter. The CLKOUT pin can drive capacitive loads up to 200pF. SYNC (Pin 21): To synchronize the switching frequency to an outside clock, simply drive this pin with a clock. The high voltage level of the clock needs to exceed 1.3V, and the low level should be less than 0.5V. Drive this pin to less than 0.5V to revert to the internal free-running clock (OSC1 in the Block Diagram). 8490fa For more information www.linear.com/LT8490 LT8490 Pin Functions RT (Pin 22): Timing Resistor Pin. Adjusts the switching regulator frequency (OSC1) when SYNC is not driven by a clock. Place a resistor from this pin to ground to set the free-running frequency of OSC1. Do not float this pin. BG1, BG2 (Pin 23/Pin 25): Bottom Gate Drive. Drives the gates of the bottom N-channel MOSFETs between ground and GATEVCC. GATEVCC (Pin 24): Power Supply for Gate Drivers. Must be connected to the INTVCC pin. Do not power from any other supply. Locally bypass to ground. BOOST1, BOOST2 (Pin 33/Pin 27): Boosted Floating Driver Supply. The (+) terminal of the bootstrap capacitor connects here. The BOOST1 pin swings from a diode voltage below GATEVcc up to VIN + GATEVCC. The BOOST2 pin swings from a diode voltage below GATEVCC up to VBAT + GATEVCC. TG1, TG2 (Pin 32/Pin 28): Top Gate Drive. Drives the top N-channel MOSFETs with voltage swings equal to GATEVCC superimposed on the switch node voltages. SW1, SW2 (Pin 31/Pin 29): Switch Nodes. The (-) terminal of the bootstrap capacitors connect here. SRVO_FBIN (Pin 35): Open-Drain Logic Output. This pin is pulled to ground when the input voltage feedback loop is active. This pin is unused for most LT8490 applications and can be floated. SRVO_IIN (Pin 36): Open-Drain Logic Output. This pin is pulled to ground when the input current feedback loop is active. This pin is unused for most LT8490 applications and can be floated. SRVO_IOUT (Pin 37): Open-Drain Logic Output. This pin is pulled to ground when the output current feedback loop is active. This pin is unused for most LT8490 applications and can be floated. SRVO_FBOUT (Pin 38): Open-Drain Logic Output. This pin is pulled to ground when the output voltage feedback loop is active. This pin is unused for most LT8490 applications and can be floated. EXTVCC (Pin 40): External VCC Input. When EXTVCC exceeds 6.4V (typical), INTVCC will be powered from this pin. When EXTVCC is lower than 6.22V (typical), INTVCC will be powered from VIN. See Switching Configuration - MODE Pin for additional details. CSNOUT (Pin 41): The (-) Input to the Output Current Sense Amplifier. CSPOUT (Pin 42): The (+) Input to the Output Current Sense Amplifier. This pin and the CSNOUT pin measure the voltage across the sense resistor to provide the output current signals. CSNIN (Pin 44): The (-) Input to the Input Current Sense Amplifier. This pin and the CSPIN pin measure the voltage across the sense resistor to provide the instantaneous input current signals. CSPIN (Pin 45): The (+) Input to the Input Current Sense Amplifier. VIN (Pin 46): Main Input Supply Pin. Must be bypassed to local ground plane. ECON (Pin 48): Digital Output Pin. Optional control output signal used to disconnect EXTVCC from the battery when the average charge current drops below a predetermined threshold. SWENO (Pin 49): Digital Output Pin. Connect to SWEN. Enables the switching regulator. A 200k pull-down resistor is required from this pin to ground. IOW (Pin 50): Digital Output Pin. Connects to IMON_OUT through a resistor. By switching the pin between logic low and high impedance, the total RIMON_OUT changes, which changes the output current limit. STATUS (Pin 51): Digital Output Pin. When used with an LED, this signal provides a visual indication of the progress of the charging algorithm. In addition, STATUS transmits two UART bytes (8 bits, no parity, one stop bit, 2400 baud) every 3.5 seconds (typical), which indicates status and fault information. IIR (Pin 53): A/D Input Pin. Connects to IMON_IN to read input current. Used to manage MPPT. 8490fa For more information www.linear.com/LT8490 9 LT8490 Pin Functions VINR (Pin 54): A/D Input Pin. Connects to resistive divider on VIN to measure input voltage. Used to manage MPPT and start-up. CHARGECFG1 (Pin 61): A/D Input Pin. Used to configure the float voltage, temperature compensation and enable stage 3 charging. CLKDET (Pin 56): A/D Input Pin. Connects to CLKOUT through an RC filter to detect the duty cycle of CLKOUT. Used to manage start-up. CHARGECFG2 (Pin 63): A/D Input Pin. Used to configure time limits and the valid battery temperature range. FBOR (Pin 57): A/D Input Pin. Connects to FBOUT pin to read charger output voltage. Used to manage the charging algorithm. AVDD (Pin 58): A/D Positive Reference Pin. Tie this pin to VDD and LDO33. 10 IOR (Pin 64): A/D Input Pin. Connects to IMON_OUT pin to read the charger output current. Used to manage the charging algorithm. GND (Exposed Pad 65 and Pins 55, 59, 62): Ground. Tie directly to local ground plane. NC (Pins 52, 60): Not connected. 8490fa For more information www.linear.com/LT8490 LT8490 Block Diagram BOOST1 13 12 9 CSP + A8 - - +A5 CSN MODE OT OI_IN GATEVCC OI_OUT BG1 46 VIN BUCK,BOOST LOGIC START-UP AND FAULT LOGIC SS BG2 56 8 49 NC 36 44 45 10 + A9 - SYNC RT VIN SOLAR PANEL 1 6 EXTVCC SWEN INTVCC REG 3.3V REG LDO33 INTERNAL SUPPLY2 SWENO VDD SRVO_IIN 10 CSNIN SRVO_IOUT IMONIN AVDD IIR ADC - +EA2 + A6 - 10 AVDD VINR ADC FBIN EA1 10 CONTROL, CHARGING, MPPT LOGIC + EA3 - CSPOUT CSNOUT IMONOUT 1.208V IOW AVDD 10 IOR ADC OSC2 SRVO_FBIN FBOUT EA4 AVDD FBIR 10 ADC FBIW 3 AVDD AVDD NTC 61 63 TEMPSENSE AVDD CHARGECFG1 CHARGECFG2 AVDD ADC ADC ADC 27 18 40 7 14 4 ECON FBOW AVDD 10 10 37 NC 42 41 17 50 64 16 FBOR ADC + - SRVO_FBOUT PWM AVDD 28 1.207V PWM AVDD 29 AVDD 58 - +A7 CSPIN 25 6.35V REG INTERNAL SUPPLY1 ADC 23 RECHARGEABLE BATTERY NC 35 6.4V 24 305k 6.35V REG AVDD CLKDET 1.205V - 31 VBAT 15 VC CLKOUT + 54 BOOST2 OSC1 1.208V 53 TG2 + - 20 SW2 UV_LDO33 + + - 22 UV_GATEVCC - 21 - 1.234V SHDN UV_VIN + 11 32 2.5V UV_INTVCC 19 TG1 SW1 33 38 NC 48 5 57 10 10 55 GND AVDD Figure 1. Block Diagram For more information www.linear.com/LT8490 51 STATUS 2 FAULT AVDD 8490 BD 8490fa 11 LT8490 Operation Overview The LT8490 is a powerful and easy to use battery charging controller with automatic maximum power point tracking (MPPT) and temperature compensation. The LT8490 is based on the LT8705 buck-boost controller with additional battery charging and MPPT control functions. Refer to the LT8705 data sheet for more detailed information about the switching regulator portions of the LT8490. Several reference applications are included in this data sheet to simplify system design. Many battery charging applications can be implemented using one of the reference applications with little or no modification required. Configuration for the various charging parameters is implemented in the hardware. No software or firmware development is required. The LT8490 includes four different forms of regulation: output current, input current, input voltage and output voltage (EA1-EA4 respectively as shown in Figure 1). Whichever form of regulation requires the lowest voltage on the VC pin limits the commanded inductor current. When powered by a solar panel, the MPPT function uses input voltage regulation to locate and track the maximum power point of the panel. Input current regulation is used to limit the maximum current drawn from the input supply. The output current regulation limits the battery charging current, and the output voltage regulation is used to set the maximum battery charging voltage. The LT8490 offers user configurable timers that can be enabled with the appropriate resistor divider on the CHARGECFG2 pin. If a timer has been set and expires, the LT8490 will halt charging and communicate this through the STATUS and FAULT pins. Options for automatic restart of the charge cycle are discussed later in the Automatic Charger Restart and Fault Recovery section. The LT8490 also includes a TEMPSENSE pin, which can be connected to an NTC resistor divider network thermally coupled to the battery pack. When connected, the 12 TEMPSENSE pin can provide temperature compensated charging and/or can be used to disable charging when the battery is outside of safe temperature limits. The presence of the NTC resistor can also give an indication to the charger if the battery is connected or not. The LT8490 also provides charging status and fault indicators through the STATUS and FAULT pins. The behavior of these pins is described in the STATUS and FAULT Indicators section. Battery Charging Algorithm The LT8490 implements a CCCV charging algorithm. The idealized charging profile is shown in Figure 2 and assumes constant temperature and adequate input power. As battery temperature and illumination conditions on the panel change, the actual current and voltage seen by the battery will vary accordingly. After start-up, the LT8490 frequently measures the battery voltage and charging current to determine the proper charging stage. STAGE 0 STAGE 1 TRICKLE CONSTANT CHARGE CURRENT STAGE 2 CONSTANT VOLTAGE STAGE 3 REDUCED CONSTANT VOLTAGE MAXIMUM CHARGING CURRENT (C) STAGE 2 VOLTAGE LIMIT VS2 BATTERY VOLTAGE VS3 STAGE 3 VOLTAGE LIMIT (OPTIONAL) CHARGING CURRENT CHARGING TIME 8490 F01 Figure 2. Typical Battery Charging Cycle 8490fa For more information www.linear.com/LT8490 LT8490 Operation STAGE 0: In Stage 0 (reduced constant-current/trickle charge) the LT8490 charges the battery with a hardware configurable reduced constant current. This trickle charge stage occurs for battery voltages between 35% to 70% (typical) of the Stage 2 voltage limit (VS2). STAGE 1: In Stage 1 (full constant-current) the LT8490 charges the battery with a hardware configurable constant current equal to or higher than in Stage 0. This constant current stage occurs for battery voltages between 70% to 98% (typical) of the Stage 2 voltage limit. This charging stage is often referred to as bulk charging. This charging stage will be called Stage 1 for the remainder of this document. Table 1. Description of LT8490 Charging Stages STAGE NAME METHOD DURATION 0 Trickle Charge Constant Current at a Configured Fraction of Full Charge Current Until Battery Voltage Rises Above VS0 (70% of Stage 2 Voltage Limit) Constant Full Charge Current Until Battery Voltage Rises Above VS1 (98% of Stage 2 Voltage Limit) 1 Constant Current Optional Max Time Limit for Stage 1 + Stage 2 2 Constant Constant Voltage Voltage 3 Reduced Constant Voltage (Optional) Constant at a Configured Voltage Fraction of Stage 2 Constant Voltage If the optional Stage 3 is enabled, the LT8490 will proceed from Stage 2 to Stage 3 when the charging current drops below C/10. Other conditions for exiting Stage 2 depend on whether time limits are enabled for the charger. See the Charging Time Limits section for more details about Stage 2 termination. Maximum Power Point Tracking Charging will automatically restart if, during Stage 3, the charging current exceeds C/5 or the battery voltage falls below 96% (typical) of the Stage 3 voltage limit (VS3). In addition, an optional time limit can be enabled to terminate charging in Stage 3. See the Charging Time Limits section for more details about Stage 3 termination. Until Charging Current Falls Below C/10 or Optional Indefinite Charging Optional Max Time Limit for Stage 1 + Stage 2 STAGE 2: In Stage 2 (constant-voltage) the LT8490 charges the battery with a hardware configurable constant voltage. This constant voltage stage occurs for battery voltages above 98% (typical) of the Stage 2 voltage limit. This charging stage is often referred to as float charging for lithium-ion batteries and absorption charging for lead-acid batteries. To avoid confusion, this charging stage will be called Stage 2 for the remainder of this document. STAGE 3 (OPTIONAL): Stage 3 is optional as configured with the CHARGECFG1 pin. In Stage 3 the LT8490 charges the battery with a hardware configurable reduced constant voltage. This charging stage is often referred to as float charging in lead-acid battery charging. This charging stage will be called Stage 3 for the remainder of this document. Optional Max Time Limit Until Battery Voltage Falls below 96% of VS3 (Stage 3 Voltage Limit - Configurable) or Charging Current Rises Above C/5 Optional Max Time Limit. The same duration as the Stage 1 + Stage 2 Time Limit. When powered by a solar panel, the LT8490 employs a proprietary Perturb and Observe algorithm for identifying the maximum power point. This algorithm provides accurate MPPT for slow to moderate changes in panel illumination. The panel is also scanned periodically to avoid settling on a false maximum power point for long periods of time, in the case of non-uniform panel illumination. Fault Conditions The LT8490 can indicate the presence of a fault condition through the STATUS and FAULT pins. These faults include: battery undervoltage, battery overtemperature, battery under temperature and timer expiration. Following a fault, the LT8490 will discontinue charging until the fault condition is removed, at which point it will continue or restart the charging cycle. See the Automatic Charger Restart and Fault Recovery section for more information. 8490fa For more information www.linear.com/LT8490 13 LT8490 Applications Information Input Voltage Sensing and Modulation Network The passive component network shown in Figure 3 is required to properly measure and modulate the input supply voltage. This network is required whether the supply is a solar panel or a DC voltage source. VIN VIN R RFBIN1 VX2 = 1.205 * + FBIN1 + 1 RDACI1 +RDACI2 RFBIN2 LT8490 FBIR RFBIN1 Due to the granularity of standard resistor values, simply rounding the calculated results to their nearest standard values may result in unwanted errors. Consider using multiple resistors in series to more closely match the calculated results. Otherwise, use standard resistor values and check the final results with the following equations: FBIN RDACI2 RFBIN2 RDACI1 CDACI FBIW GND 8490 F03 Figure 3. Input Feedback Resistor Network Choosing the components requires knowing the maximum panel open-circuit voltage (VOCMAX) as well as the maximum DC input supply voltage (VDCMAX) desired (see the DC Supply Powered Charging section for more information). VOCMAX typically occurs at cold temperatures and should be specified in the panel manufacturer's data sheet. Use the following equations to determine proper component values: 4.470V 1+ VMAX - 6V RFBIN1 = 100k * 5.593 1+ VMAX - 6V VX2 indicates the actual VMAX using the selected resistors. Make sure this result is greater than or equal to the desired VMAX for the application. RFBIN1 VX1 = VX2 - 3.3 * RDAC1 +RDAC2 VX1 should be as close to 6V as possible. Iterations may be required to determine the best standard resistor values. Table 2 shows good sets of standard value components for maximum input voltages of 20V, 40V, 60V and 80V. Iterative calculations were required to select these values that achieve the best overall results. Table 2. Input Feedback Network vs Panel Voltage VMAX (V) RFBIN1 (k) RFBIN2 (k) RDACI1 (k) RDACI2 (k) CDACI (nF) 20 95.3 40 107 8.45 3.4 19.1 270 4.87 1.69 8.66 560 60 105 3.24 1.05 5.36 1000 80 133 3.09 1.05 4.87 1000 R RDACI2 = 2.75 * FBIN1 VMAX - 6V 1 RFBIN2 = 1 1 - 100k -RFBIN1 RDACI2 As discussed later in DC Supply Powered Charging, arbitrarily setting VMAX to 80V may not result in the best operation of the LT8490 for all conditions, particularly at low input voltages. Be sure to give proper consideration to the required voltage range for each application. RDACI1 = 0.2 * RDACI2 Solar Powered Charging CDACI = 1 F 1000 * RDACI1 where VMAX is the greater of VOCMAX and VDCMAX with some additional margin. These resistors should have a 1% tolerance or better. 14 VINR DIVIDER NETWORK: The LT8490 can be powered by a solar panel or a DC power supply. As discussed later in DC Supply Powered Charging, the VINR pin must be pulled low when being powered by a DC supply. Otherwise, VINR must be connected to the resistor divider network as shown in Figure 4. 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information 1. LOW POWER MODE ENABLED: Low power mode allows additional power to be recovered from the solar panel under very weak lighting conditions. When low power mode is enabled, the panel voltage must initially exceed 10V (typical - as measured through the VINR pin) before the charger will attempt to charge the battery. Read the Optional Low Power Mode section for more details. LT8490 VIN 196k VINR 8.06k GND 8490 F04 Figure 4. VINR Resistor Divider Circuit The LT8490 uses this divider network to measure absolute panel voltage (as part of its maximum power point calculations) and to check for adequate input voltage to operate the charger. These resistors should have a 1% tolerance or better. TIMER TERMINATION DISABLED: When powered by a solar panel, the timer termination option (see the Charging Time Limits section for more detail) is automatically disabled. This is due to the inability to guarantee full charging current during the entire charging cycle in cases where the panel illumination conditions change. In addition, the timers can reset if all power to the charger is lost due to insufficient lighting. This makes the use of timer termination potentially unreliable in solar powered applications. C/10 DETECTION: When powered by a solar panel, charging current may drop below C/10 because the battery is approaching full charge, or because the solar panel has insufficient lighting. If sufficient panel power is available, the LT8490 can determine if the charging current has dropped below C/10 due to the battery approaching full charge. In this case, the charger will proceed from Stage 2 to the next appropriate stage. If the LT8490 is able to determine that the charging current has dropped below C/10 due to insufficient panel power, the charger will continue operating in Stage 2. MINIMUM PANEL VOLTAGE REQUIREMENT: A minimum panel voltage of 6V is required to operate the charger. However, higher panel voltages are required in various other cases. 2. LOW POWER MODE DISABLED: If low power mode is disabled the charger will attempt to charge the battery as long as the panel is above 6V. However, if sufficient panel current is not detected the LT8490 will temporarily stop charging. The charger will check for sufficient panel current at 30 second intervals (typical) or will check sooner if the LT8490 detects either a significant rise in panel voltage or a significant fall in battery voltage. 3. LOW INPUT VOLTAGE EFFECTS: Figure 5 shows the minimum input voltage, below which the maximum charging current can be reduced. This limit is a function of the input VMAX as discussed previously in the Input Voltage and Modulation Network section. Maximum charging current can reduce as FBIN gets closer to its regulation voltage of 1.205V (typical). This is not normally a significant issue unless 1) the charger is powered by a low voltage DC power supply or 2) a low voltage panel is used with a charger that was configured for a much higher voltage panel. The farther that VIN is below the Normal Configuration line in Figure 5 the more the current can reduce. 25 MINIMUM FULL-CHARGING CURRENT VIN VOLTAGE (V) VIN 20 NORMAL CONFIGURATION 15 10 5 0 DC SUPPLY ONLY WITH FBIN = LDO33 0 10 20 30 40 50 VMAX (V) 60 70 80 8490 F05 Figure 5. Minimum Full Charging Current VIN Voltage 8490fa For more information www.linear.com/LT8490 15 LT8490 Applications Information When VIN is powered by a DC voltage supply, maintain VIN higher than the Normal Configuration line in Figure 5. Operating VIN below this line can reduce the maximum charging current and the VS2 and VS3 charging voltages. If VIN is never going to be supplied by a solar panel then FBIN can be disconnected from FBIR (see Figure 3) and reconnected to the LDO33 pin. This allows the charger to operate with VIN as low as 6V with no charging current or voltage reduction. When using a solar panel supply, choose a panel having a maximum open-circuit voltage (VOC) close to VMAX (discussed in the prior Input Voltage Sensing and Modulation Network section). The maximum power point voltage is typically well above the voltage limit in Figure 5 and current limiting is rarely an issue. Avoid using solar panels that operate dramatically below VMAX, particularly if the maximum power point voltage is typically below the Normal Configuration line in Figure 5. DC Supply Powered Charging SELECTING POWER SUPPLY MODE: When powered by a DC voltage source, the VINR pin must be pulled below 174mV (typical) to activate power supply mode. This disables unnecessary solar panel functions and allows the LT8490 to operate properly from a DC voltage source. If the application is never powered by a solar panel, VINR can be grounded. If the application is only powered by a solar panel, then connect VINR as shown in Figure 4. Otherwise, see the Optional DC Supply Detection Circuit section for a method to pull down the VINR pin when a DC supply is detected. MINIMUM INPUT VOLTAGE REQUIREMENT: When power supply mode is enabled, the LT8490 will operate from an input as low as 6V. However, charging current capability can become limited at low input voltages depending on the VMAX voltage used to select the input voltage sensing network (see previous Input Voltage Sensing and Modulation Network section). Figure 5 shows the minimum input supply voltage required, below which charging current can become less than the maximum output current limit. If the LT8490 is powered by a DC supply only, the minimum input voltage shown in Figure 5 can be reduced to 6V by 16 (1) disconnecting FBIN from FBIR and (2) connecting the FBIN pin directly to LDO33. INPUT CURRENT LIMITING: Input current limiting should be considered when using DC power supplies. This is discussed later in the Input Current Limiting section. In Situ Battery Charging The LT8490 can be used to charge a battery while the battery is powering a load. The load should be directly connected to the battery terminals as shown in Figure 6. The variable nature of some loads can make charging times unpredictable. Due to this unpredictability it is recommended that charging time limits be disabled (see Charger Configuration - CHARGECFG2 Pin section for more information). Because a load connected to the battery may draw more power than provided by the charger, the battery may discharge while the LT8490 is charging the battery. If this case occurs and the battery voltage falls below 31% (typical) of the Stage 2 voltage limit, the undervoltage fault will become active and the charger will halt until the battery voltage rises above 35% (typical) of the Stage 2 voltage limit. Consider automatically disabling the load if the battery depletes below an unacceptably low voltage. The arrow in Figure 6 shows the proper disconnect point if removing the battery from the charger in an in situ battery charging application. This disconnect point is specified because the LT8490 is not designed to provide power directly to a load without the presence of a battery. + LT8490 BASED CHARGER LOAD VBAT CABLE TO/FROM CHARGER - 8490 F06 Figure 6. Load Connection to Battery in LT8490 Application 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Stage Voltage Limits The Stage 2 voltage limit (VS2) is the maximum battery charging voltage. The voltage limits for Stages 0, 1 and 3 are all related to the Stage 2 limit as shown in Table 3 and Figure 11. If temperature compensated charging is enabled, then VS2 will change with temperature as shown in Figure 13. As such, the limits for the other stages will also change with temperature since they are a constant proportion of VS2. Table 3. Typical Charging Stage Voltage Thresholds VBAT RISING OR FALLING TYPICAL VBAT/VS2 TYPICAL VBAT /VS3 VBAT Undervoltage Fault STAGE 0 Rising 35% - STAGE 0 STAGE 1 Rising 70% - STAGE 1 STAGE 2 Rising 98% - STAGE 3 STAGE 0 Falling - 96% STAGE 2 STAGE 1 Falling 95% - STAGE 1 STAGE 0 Falling 66% - STAGE 0 VBAT Undervoltage Fault Falling 31% STAGE TRANSITION LT8490 VBAT FBOUT FBOR FBOW GND RFBOUT1 RDACO1 RDACO2 CDACO RFBOUT2 8490 F07 Figure 7. Output Feedback Resistor Network SETTING THE STAGE 2 VOLTAGE LIMIT: The resistor network shown in Figure 7 is used to set the Stage 2 voltage limit. Battery manufacturers typically call for a higher Stage 2 voltage limit than the nominal battery voltage. For example, a 12V lead-acid battery used in automotive applications commonly has a Stage 2 charging voltage limit of 14.2V. If temperature compensated charging will be used (see Temperature Measurement, Compensation and Fault section) then use the 25C value for VS2 in the equations below. RFBOUT2 is often chosen between 4.99k and 49.9k. Choosing higher values for RFBOUT2 reduces the amount of current draw from the battery through the feedback network. 1.241 RFBOUT1 = RFBOUT2 * VS2 * - 0.128 -1 1.211 RFBOUT1 * RFBOUT2 * 0.833 RDACO2 = 1.241 RFBOUT2 * VS2 * -RFBOUT2 -RFBOUT1 1.211 RDACO1 = 0.2 * RDACO2 CDACO = 1 F 500 * RDACO1 For greater charging voltage accuracy, it is recommended that 0.1% tolerance resistors be used for the output feedback resistor network. Due to the granularity of standard resistor values, simply rounding the calculated results to their nearest standard values may result in unwanted errors. Consider using multiple resistors in series to match the calculated results. Otherwise, use standard resistor values and check the final results with the following equations. RFBOUT1 VX3 = * ( X - 1.89) RDACO1 +RDACO2 where R R +R +R X = 1.211* 1+ DACO1 DACO2 + DACO1 DACO2 RFBOUT2 RFBOUT1 VX3 indicates the actual 25C VS2 voltage using the selected resistors. N1= X - 1.89 X - 3.3 N1 should be as close as possible to 1.22. N2 = 1- 1.89 X N2 should be as close as possible to 0.805. Iterations may be required to determine best standard resistor values. 8490fa For more information www.linear.com/LT8490 17 LT8490 Applications Information Table 4. Standard Value Output Feedback Network vs Output Regulation Voltage BATTERY VOLTAGE TARGET VS2 (V) RFBOUT1 RFBOUT2 (k) (k) RDACO1 (k) RDACO2 (k) CDACO (nF) 12 14.2 274 23.2 26.1 124 82 24 28.4 487 20 28 107 68 36 42.6 787 21 22.6 121 100 48 56.8 1000 20 22.6 115 100 60 71.0 866 13.7 13.3 80.6 150 SETTING THE STAGE 3 VOLTAGE LIMIT: When enabled, Stage 3 charging maintains the battery voltage at 85% to 99% of VS2. This proportion is adjustable and is discussed in the Charger Configuration - CHARGECFG1 Pin section. BATTERY UNDERVOLTAGE LIMIT: Upon start-up, the LT8490 checks for battery voltage above 35% (typical) of the Stage 2 voltage limit. If the battery voltage is less than this, charging will not start and a battery undervoltage fault will be indicated on the FAULT pin. Charging will begin after the battery voltage rises above 35% (typical) of the Stage 2 voltage limit. If the battery voltage subsequently falls below 31% (typical), charging will again stop and the fault will be indicated on the FAULT and STATUS pins. IMON_OUT voltages above 1.208V (typical) cause VC to reduce due to EA1, and thus limit the output current. IOW is either driven to ground or floated depending on charging conditions. This allows the current limit for Stage 0 (IOUT(MAXS0)) to be set independently of the remaining Stages (IOUT(MAX)) with proper selection of RIOW and RIMON_OUT. Use the following equations to configure the charging current limits: RSENSE2 = 0.0497 IOUT(MAX) RIMON _ OUT = RIOW = 1208 IOUT(MAXS0) * RSENSE2 24.3k * RIMON _ OUT RIMON _ OUT - 24.3k RIOR = 3.01k CIMON _ OUT = read below where IOUT(MAX) is the maximum charging current in Amps, IOUT(MAXS0) is the maximum trickle charging current in Stage 0 and IOUT(MAXS0) is no greater than IOUT(MAX). For cases where IOUT(MAX) = IOUT(MAXS0), it is OK to exclude RIOW and float the IOW pin. IOUT(MAXS0) must be at least 20% of IOUT(MAX). RSENSE2 FROM CONTROLLER VOUT1 Charge Current Limiting The maximum charging current is configured with the output current limiting circuit. The output current is sensed through RSENSE2 and converted to a proportional current flowing out of the IMON_OUT pin (see Figure 8). OUTPUT CURRENT CSPOUT LT8490 CSNOUT + gm =1m A6 - FAULT CONTROL TO BATTERY 1.61V - Table 4 shows good sets of standard value components for charging nominal battery voltages of 12V, 24V, 36V, 48V and 60V. Iterative calculations were required to select these values that achieve the best overall results. + 1.208V - + EA1 IMON_OUT IOW RIOW RIMON_OUT IOR VC RIOR 3.01k CIMON_OUT 8490 F08 Figure 8. Output Current Regulation Loop 18 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Input Current Limiting SOLAR PANEL SUPPLY: Solar panels are inherently current limited and may not be able to provide maximum charging power at the lowest input voltages. The LT8490 uses its MPPT algorithm to sweep the panel voltage as low as 6V to find the maximum power point. Make sure that the input current limit is set higher than the maximum panel current capability, plus at least 20% to 30% margin, in order to achieve the maximum charging capability of the system. In addition, note that the LT8490 uses the same circuit (shown in Figure 9) to measure the input current as to limit it. The input current is measured by an A/D conversion of the IIR pin voltage which is connected to IMON_IN and is proportional to input current. The digitized input current is used to locate the maximum power point of the solar panel. Setting a higher input current limit reduces the resolution of the digitized reading of the input current. Avoid setting the input current limit dramatically higher than necessary, as this may affect the accuracy of the maximum power point calculations. DC POWER SUPPLY: When charging a battery at maximum current, and thus power, a low voltage supply must provide more current than a high voltage supply. This can be seen by equating output power to input power, less some efficiency loss. where the efficiency factor is typically between 0.95 and 0.99. When powered by a DC supply, appropriate input current limiting is recommended for supplies that might (1) become overloaded as the supply ramps up or down through 6V or (2) provide more input current than the charger components can tolerate. SETTING THE INPUT CURRENT LIMIT: The input current is sensed through RSENSE1 as shown in Figure 9. The current through RSENSE1 is converted to a voltage on the IMON_IN pin according to the following equation: I * R VIMON _IN = IN SENSE1 + 7A * RIMON _IN V 1000 IMON_IN voltages exceeding 1.208V (typical) cause the VC voltage to reduce, thus limiting the input current. RIMON_IN should be 21k 1% or better. Using this information, the appropriate value for RSENSE1 can be calculated using the following equation: 1.208V - 7A 1000 * 21k 0.0505 RSENSE1 = = IIN(MAX) IIN(MAX) where IIN(MAX) is the maximum input current limit in Amps. RSENSE1 values greater than 25m are not recommended. CSPIN LT8490 - + + CSNIN 7mV gm =1m A7 - FAULT CONTROL 1.61V 1.208V + - EA2 IMON_IN 21k RIMON_IN VBAT *IBAT(MAX) - + IIR or VIN(MIN) * TO REMAINDER OF SYSTEM OUTPUT CURRENT VIN * IIN * = VBAT * IBAT IIN(MAX) = RSENSE1 FROM SOLAR PANEL OR DC POWER SUPPLY CIMON_OUT reduces IMON_OUT ripple and stabilizes the constant charging current control loop. Reducing CIMON_OUT improves stability and minimizes inductor current overshoot that can occur if a discharged battery is quickly disconnected then reconnected to the charger. However, this is at the expense of increased IMON_OUT ripple that can introduce more noise into the ADC measurements. The higher frequency pole created at IMON_OUT must be adequately separated from the lower frequency pole at the VC pin for proper stability. A CIMON_OUT capacitor in the range of 4.7nF to 22nF is adequate for most applications. VC CIMON_IN 8490 F09 Figure 9. Input Current Regulation Loop 8490fa For more information www.linear.com/LT8490 19 LT8490 Applications Information 100 95 90 NON-TEMPERATURE COMPENSATED CHARGING LIMITS 85 0 5 Input and Output Current Sense Filtering CC1 and CC2 may be required, depending on board layout, to reduce common mode noise that may reach the LT8490 pins. 100nF ceramic capacitors, with the appropriate voltage ratings, work well in most cases. Be sure to place all of the filter components (CSX, RSX, CCX) close to the LT8490 for best performance. Finally, note that a small voltage drop (typically ~0.25mV per 10) will occur across RS1 and RS2 due to the input bias currents of CSNOUT and CSNIN. This represents a ~0.5% reduction in the maximum current limit which typically occurs with ~50mV across RSENSE. The C/10 threshold (typically when 5mV is measured across CSPOUT and CSNOUT) will also reduce to C/10.5 due to the 0.25mV drop across RS2. CS1 RSENSE2 RS1 CC1 CS2 RS2 CC2 CSPIN CSNIN LT8490 TEMPERATURE COMPENSATED CHARGING LIMITS 45 50 55 95 100 8490 F11 CHARGECFG1 PIN VOLTAGE (% OF AVDD) The CSX and RSX current sense filtering shown in Figure 10 can improve the accuracy of the input and output current measurements at low average current levels. Amplifiers A7 and A8 (Figures 8 and 9) can only amplify positive RSENSE voltages. Although the average RSENSE voltage is always positive, the voltage ripple at low average current levels may contain negative components that are averaged out by the filter. Recommended values for RS1, RS2 and CS1, CS2 are 10 and 470nF. RSENSE1 S3 DISABLED S3 DISABLED VS3 / VS2 (%) CIMON_IN reduces IMON_IN ripple and stabilizes the input current limit control loop. Reducing CIMON_IN improves stability and minimizes possible inductor current overshoot. However, this is at the expense of increased IMON_IN ripple that can introduce more noise into the ADC measurements. The higher frequency pole created at IMON_IN must be adequately separated from the lower frequency pole at the VC pin for proper stability. A CIMON_IN capacitor of 4.7nF to 22nF is adequate for most applications. CSPOUT CSNOUT Figure 11. CHARGECFG1 Pin Configuration Charger Configuration - CHARGECFG1 Pin The CHARGECFG1 pin is a multifunctional pin as shown in Figure 11. Set this pin using a resistor divider totaling no less than 100k to the AVDD pin (see the Typical Applications section for examples). The voltage on CHARGECFG1, as a percentage of AVDD, makes the selections discussed below. Avoid setting the divider ratio directly at any of the inflection points on Figure 11 (e.g. 5%, 45%, 50%, 55% or 95%) ENABLE/DISABLE TEMPERATURE COMPENSATED VOLTAGE LIMITS: Setting the CHARGECFG1 pin in the upper half of the voltage range (> 50%) enables battery voltage temperature compensation, while using the bottom half (< 50%) disables the temperature compensation, even if a thermistor is coupled to the battery pack. The next section provides more detailed information. DISABLE STAGE 3: Setting the CHARGECFG1 pin to AVDD or 0V disables Stage 3. When the CHARGECFG1 pin is set in this manner, the charging algorithm will never proceed to Stage 3. Stage 3 is commonly used for lead-acid battery charging but is not typically used for lithium-ion battery charging. ENABLE STAGE 3: Setting the CHARGECFG1 pin between 5% to 95% of AVDD enables Stage 3 charging and sets the Stage 3 voltage limit (VS3) as a percentage of the Stage 2 voltage limit (VS2) according to the following formulas. LT8490 8490 F10 Figure 10. Recommended Current Sense Filter 20 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information When temperature compensated charging and Stage 3 are enabled, use: V CHARGECFG1% = 2.67 * S3 - 0.85 + 0.55 * 100% VS2 When temperature compensated charging is disabled and Stage 3 is enabled, use: V CHARGECFG1% = 2.72 - 2.67 * S3 * 100% VS2 where VS3 /VS2 should be between 0.86 to 0.99. For example, to enable temperature compensated charging with VS3 set to 93% of VS2, choose a divider that puts CHARGECFG1 at 76% of AVDD. For best accuracy use resistors that have a 1% tolerance or better. Temperature Measurement, Compensation and Fault The LT8490 can measure the battery temperature using an NTC (negative temperature coefficient) thermistor thermally coupled to the battery pack. The temperature monitoring function is enabled by connecting a 10k, = 3380 NTC thermistor from the TEMPSENSE pin to ground and an 11.5k (1% tolerance or better) resistor from AVDD to TEMPSENSE (as shown in Figure 12). If battery temperature monitoring is not required, then use a 10k resistor in place of the thermistor. This will indicate to the LT8490 that the battery is always at 25C. 112 110 AVDD 11.5k TEMPSENSE GND 2. BATTERY VOLTAGE TEMPERATURE COMPENSATION: Some battery chemistries charge best when the voltage limit is adjusted with battery temperature. Lead-acid batteries, in particular, experience a significant change in the ideal charging voltage as temperature changes. If enabled with the CHARGECFG1 pin, the battery charging voltage and all related voltage thresholds are automatically adjusted with battery temperature. As the voltage on the TEMPSENSE pin changes, the PWM duty cycle from the FBOW pin changes such that the voltage limits of the LT8490 follow the curve shown in Figure 13. CABLE TO/FROM CHARGER LT8490 100nF 1. INVALID BATTERY TEMPERATURE FAULT: A temperature fault occurs when the battery temperature is outside of the valid range as configured on the CHARGECFG2 pin (-20C to 50C or 0C to 50C). The temperature fault condition remains until the temperature returns within -15C to 45C or 5C to 45C (5C of hysteresis). During a temperature fault, charging is halted and the STATUS and FAULT pins follow the pattern described in Table 6. If timer termination is enabled with the CHARGECFG2 pin, the timer count is paused during the temperature fault and resumes when the fault state is exited. % OF VS2 AT 25C (%) TO CHARGER OUTPUT AT RSENSE2 The LT8490 monitors the voltage on the TEMPSENSE pin to determine the battery temperature and also to detect if the thermistor is connected or not. A TEMPSENSE voltage greater than 96% of AVDD (typical) indicates that the thermistor has been disconnected. Three charger functions rely on the TEMPSENSE information. 10k NTC THERMISTOR THERMALLY COUPLED WITH BATTERY PACK 108 106 104 102 100 98 96 -25 -15 8490 F12 Figure 12. Battery Temperature Sensing Circuit -5 5 15 25 35 40 BATTERY TEMPERATURE (C) 55 8490 F13 Figure 13. Stage 2 Voltage Limit vs Temperature When Temperature Compensation Is Enabled 8490fa For more information www.linear.com/LT8490 21 LT8490 Applications Information 3. BATTERY DISCONNECT SENSING: The LT8490 detects if the battery and thermistor have been disconnected from the charger by monitoring the TEMPSENSE pin voltage. When the connection to the battery is severed, as shown by the arrow in Figure 12, the connection to the thermistor is also severed and the TEMPSENSE voltage rises up to AVDD through the 11.5k resistor. During the time when the battery is not present, the LT8490 halts charging. The charger automatically restarts the charging at Stage 0 when a battery (along with integrated thermistor or resistor) is sensed through the TEMPSENSE pin. Charger Configuration - CHARGECFG2 Pin The CHARGECFG2 pin is a multifunctional pin as shown in Figure 14. Set this pin using a resistor divider totaling no less than 100k to the AVDD pin (see the Typical Applications section for examples). The voltage on CHARGECFG2, as a percentage of AVDD, makes the selections discussed below. Avoid setting the divider ratio directly at any of the inflection points on Figure 14 (e.g. 5%, 10%, 45%, 50%, 55%, 90% or 95%) TIME LIMITS ONLY AVAILABLE IN POWER SUPPLY MODE STAGE 1 AND 2 COMBINED TIMER AND STAGE 3 TIMER NO TIME LIMIT TIME (HRS) 3 2 0.5 STAGE 0 TIMER NARROW VALID BATTERY TEMP. RANGE 0 5 10 CHARGECFG2% = 3.5% * (TS1S2 - 2) + 55% where TS1S2 is the desired Stage 1 + Stage 2 time limit in hours between 2.1 and 11.9. When the narrow valid battery temperature range (0C to 50C) is desired use: Setting CHARGECFG2 below 4% (i.e., ground) or above 96% of AVDD (i.e., tie to AVDD) disables the time limits, allowing the charging to run indefinitely in lieu of any fault conditions. 90 95 100 8490 F14 Figure 14. CHARGECFG2 Pin Voltage Settings ENABLE/DISABLE CHARGING TIME LIMITS: The LT8490 supports charging time limits only when power supply mode is enabled (see the DC Supply Powered Charging section). When power supply mode is disabled, any finite time limit setting on CHARGECFG2 is interpreted as no time limit. This section discusses how to configure the time 22 When the wide valid battery temperature range (-20C to 50C) is desired use: where TS1S2 is the desired Stage 1 + Stage 2 time limit in hours between 2.1 and 11.9. WIDE VALID BATTERY TEMP. RANGE 45 50 55 CHARGECFG2 PIN VOLTAGE (% OF AVDD) Setting the CHARGECFG2 pin between 5% to 95% of AVDD allows for time limit settings between 0.5 hours to 3 hours for Stage 0, 2 hours to 12 hours for Stage 1 and 2 combined and 2 hours to 12 hours for Stage 3. The Stage 0 time limit is always 1/4th of the Stage 1 + Stage 2 time limit and the Stage 3 time limit is always the same length as the Stage 1 + Stage 2 limit. When choosing a Stage 1 + Stage 2 time limit of 12 hours, choose a divider ratio very close to 7.5% or 92.5%. When choosing a Stage 1 + Stage 2 time limit of 2 hours, choose a divider ratio very close to 47.5% or 52.5%. For time limits in between, use one of the following formulas. CHARGECFG2% = 45% - 3.5% * (TS1S2 - 2) NO TIME LIMIT 12 limits using the CHARGECFG2 pin. For more information about the operation of the time limits see the Charging Time Limits section. SELECT THE VALID BATTERY TEMPERATURE RANGE: Setting the CHARGECFG2 pin in the top half of the voltage range (> 50%) selects a wider valid battery temperature range (-20C to 50C), while using the bottom half of the voltage range (< 50%) selects a narrower valid battery temperature range (0C to 50C). Generally, lead-acid batteries would use the wide range, while lithium-ion batteries would use the narrow range. See the Temperature Measurement, Compensation and Fault section for more information about the invalid battery temperature fault. 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Charging Time Limits Charging time limits can be enabled only in power supply mode by properly configuring the CHARGECFG2 pin (see the Charger Configuration - CHARGECFG2 Pin section). Charging time limits are not recommended for use when a load is present on the battery due to the unpredictable amount of time that may be required to achieve full charge. When enabled, the appropriate timers start at the beginning of Stages 0, 1 and 3. If the timer expires while operating in its respective stage or the LT8490 returns to a charging stage after its respective timer has expired, charging stops immediately. As shown in Table 5, expiration of a timer is treated as either a fault or as done charging depending on the timer that expired and the configuration of the charger. In any case, when charging stops, the fault or done charging status is indicated on the STATUS and FAULT pins as described in the STATUS and FAULT Indicators section. Table 5. Charger Conditions and Timer Expiration Results CHARGING STAGE WHEN TIMER EXPIRES STAGE 3 ENABLED? TIMER USED RESULT OF TIMER EXPIRATION 0 - Stage 0 Fault 1 - Stage 1 + Stage 2 Fault 2 - Stage 1 + Stage 2 Fault 3 Yes Stage 3 Done Charging STAGE 2 TERMINATION (TIME LIMITS ENABLED): Timer expiration in Stage 2 causes a fault and charging stops immediately with a fault indication on the STATUS and FAULT pins. If the Stage 2 output current drops below C/10 before the timer expires and Stage 3 is disabled then charging stops and done charging is indicated on the STATUS pin. STAGE 2 TERMINATION (TIME LIMITS DISABLED): If time limits are disabled, Stage 2 can only terminate if Stage 3 is also enabled. After charging current falls below C/10, charging will proceed to Stage 3. If Stage 3 is also disabled then the charger will operate in Stage 2 indefinitely unless the battery voltage falls enough for charging to revert back to Stage 1. During the indefinite Stage 2 charging, the STATUS pin will indicate if Stage 2 current is below C/10 or above C/5 (as shown in Tables 6 and 7). STAGE 3 TERMINATION CONDITIONS: If Stage 3 is enabled and time limits are disabled, the LT8490 will remain in Stage 3 forcing reduced constant-voltage indefinitely unless the battery voltage falls below 96% of VS3 or charging current rises above C/5 causing the charger to revert back to Stage 0. If Stage 3 is enabled and time limits are enabled, timer expiration in Stage 3 will stop charging and communicate the done charging state through the STATUS pin (as shown in Tables 6 and 7). Lithium-Ion Battery Charging The LT8490 is well suited to charge lithium-ion batteries. Connecting the CHARGECFG1 and CHARGECFG2 pins to ground puts the LT8490 into a typical configuration for lithium-ion battery charging (0C to 50C valid battery temperature, Stage 3 disabled, no temperature compensation, no time limits). Figure 15 shows a typical lithium-ion charging cycle in this configuration. If no timer termination has been selected, the LT8490 will charge the lithium-ion battery stack to the desired Stage 2 voltage limit, maintaining that limit indefinitely. When the charging current is < C/10, the STATUS pin will go high as described in Table 6. NOTE: When solar charging a Li-Ion battery without time limits it is recommended that the Stage 2 voltage limit not exceed 95% of the lithium-ion maximum cell voltage. Since this configuration can charge indefinitely, following this guideline keeps the lifetime of the batteries from degrading quickly. STAGE 0 STAGE 1 TRICKLE CONSTANT CHARGE CURRENT MAXIMUM CHARGING CURRENT (C) STAGE 2 VOLTAGE LIMIT STAGE 2 CONSTANT VOLTAGE (FLOAT) BATTERY VOLTAGE CHARGING CURRENT CHARGING TIME 8490 F15 Figure 15. Lithium-Ion Battery Charging Cycle 8490fa For more information www.linear.com/LT8490 23 LT8490 Applications Information Lead-Acid Battery Charging STATUS and FAULT Indicators The LT8490 can be used to charge lead-acid batteries. Setting the CHARGECFG1 pin to 87.6% of AVDD and CHARGECFG2 pin equal to AVDD configures the LT8490 for typical lead-acid battery charging (-20C to 50C valid battery temperature, Stage 3 enabled with VS3 /VS2 = 97.2%, temperature compensated voltage limits, no time limits). Figure 16 shows a typical lead-acid charging cycle. The LT8490 reports charger status through two outputs, the STATUS and FAULT pins. These pins can be used to drive LEDs for user feedback. In addition, the STATUS pin doubles as a UART output to send status information to a peripheral device. Table 6 describes the LED behavior of these pins in relationship to the charger status. If time limits have been disabled, the LT8490 will charge the lead-acid battery stack to the desired Stage 3 voltage limit and restart the charging cycle if 1) the battery voltage falls below 96% of the Stage 3 voltage limit (VS3) or 2) the charging current rises above C/5. While the LT8490 is operating, the STATUS pin toggles on a 3.5 sec (typical) interval as shown in Figure 17. The three pulses shown in Figure 17 represent the charger operating in Stage 3. The STATUS and FAULT pins pull up to turn the LEDs on and drive to ground to turn the LEDs off. Table 6. STATUS and FAULT LED INDICATORS STAGE 0 STAGE 1 TRICKLE CONSTANT CHARGE CURRENT MAXIMUM CHARGING CURRENT (C) (BULK) STAGE 2 VOLTAGE LIMIT STAGE 2 CONSTANT VOLTAGE STAGE 3 REDUCED CONSTANT VOLTAGE (ABSORPTION) CHARGER STATUS (FLOAT) LED PULSES/3.5s, APPROXIMATE ON-TIME PER PULSE STATUS FAULT Stage 0 1, 10ms OFF Battery Charging Algorithm Stage 1 1, 250ms OFF Battery Charging Algorithm Stage 2 and (Stage 3 Enabled or Time Limits Enabled or IOUT Rising Above C/5) 2, 250ms OFF Battery Charging Algorithm and Charger Configuration Sections Stage 2 and Stage 3 Disabled and Time Limits Disabled and IOUT Falling Below C/10 ON OFF Battery Charging Algorithm and Charger Configuration Sections Stage 3 3, 250ms OFF Battery Charging Algorithm Done Charging ON OFF Charging Time Limits Battery Present Detection Fault 1, 10ms 1, 250ms Temperature Measurement, Compensation and Fault Invalid Battery Temperature Fault 1, 10ms 2, 250ms Temperature Measurement, Compensation and Fault Timer Expiration Fault 1, 10ms 3, 250ms Charging Time Limits Battery Undervoltage Fault 1, 10ms 4, 250ms Stage Voltage Limits BATTERY VOLTAGE STAGE 3 VOLTAGE LIMIT CHARGING CURRENT 8490 F16 CHARGING TIME Figure 16. Lead-Acid Battery Charging Cycle 3.5s 0.5s LED ON LED OFF 8490 F17 A Figure 17. Example Waveform for STATUS Pin in STAGE 3 24 FOR MORE INFORMATION SEE SECTION 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Driving LEDs with the STATUS and FAULT Pins The STATUS and FAULT pins on the LT8490 can be used to drive LED indicators. Figure 18 shows the simplest configuration for driving LEDs from these two pins. The STATUS pin can drive up to 2.5mA into an LED. Choose RDSA to limit the LED current to 2.5mA or less when STATUS is driven close to 3.3V. Choose RDSB to conduct a current equivalent to the LED current when STATUS is driven close to ground and RDSB has ~3.3V across the terminals. DS, in Figure 18, conducts ~2.5mA when STATUS is driven high. RDSB conducts ~2.5mA when the STATUS is driven low. The FAULT pin has a weak pull up in comparison to the STATUS pin (see the Typical Performance Characteristics section). The LED current is typically self-limited to less than 1mA by the FAULT pin driver. RDFB in Figure 18 is typically 3.32k and increases the FAULT LED current. When configured as shown in Figure 18, the DF LED current should be limited to less than 1.5mA. For driving higher current LEDs, the circuit in Figure 19 can be used. Note that the LED current for DF is provided by the INTVCC regulator in this case. Excessive LED current can overload the INTVCC regulator and/or cause excessive heating in the LT8490. 7.5mA is a good starting point when using this circuit. Higher currents can be possible LT8490 with careful board evaluation. Transistor Q2 must have a collector-emitter breakdown voltage greater than INTVCC. The MMBT3646 has a breakdown voltage of 15V and is well suited for this application. The LED current for DS is provided by VIN in this case. Do not draw current for DS from INTVCC since this increases power dissipation in the LT8490. Transistor Q1 must have a collector-emitter breakdown greater than VIN. The MMBT5550L has a breakdown voltage of 140V and is suitable for most applications. To properly set the resistors shown in Figure 19, use the following equations: RE1 2.6 ID I NTVCC - VF RC1 ID 50 RB1 = ID where INTVCC is typically 6.35V, VF is the forward voltage of the LED (often about 1.7V) and ID is the desired bias current through the LED. LDO33 VDD STATUS VDD RDSB 1.3k DS FAULT LT8490 RDFB VIN VIN RC1 DS RDSA 549 DF DF RDFA 549 STATUS Q1 RE1 DS: OSRAM, LGL29KF2J124Z DF: OSRAM, LGL29K-H1J2-1-Z INTVCC FAULT Q1: MMBT5550L Q2: MMBT3646 RB1 Q2 8490 F19 8490 F18 Figure 18. Default STATUS/FAULT LED Indicators Figure 19. Higher Current Drive for STATUS/FAULT LEDs 8490fa For more information www.linear.com/LT8490 25 LT8490 Applications Information STATUS Pin UART The STATUS pin also provides a UART (transmit only) communication function. This feature allows for remote monitoring of the LT8490. Immediately after each initial pulse described in Table 6 the STATUS pin sends out a synchronizing byte (0x55) followed by a status byte. UART data is transmitted with the LSB first. Figure 20 shows the zoomed in region labeled (A) from Figure 17. UART START BIT UART STOP BIT UART START BIT UART STOP BIT LP: "0" if in low power mode (see the Low Power Mode section) S2/S1/S0: Stage description (see Table 7) F2/F1/F0: Fault description (see Table 8) Table 7. Stage Description STAGE CONDITIONS S2 S1 S0 Stage 0 - 0 0 0 Stage 1 - 0 0 1 Stage 2 Stage 3 Enabled 0 1 0 Timers and Stage 3 Disabled, Charging Current Falls Below C/10 1 0 0 Stage 3 - 0 1 1 Done Charging - 1 0 1 FAULT INFORMATION F2 F1 F0 No Faults Present 0 0 0 Battery Disconnected (Thermistor Disconnected) 0 0 1 Invalid Battery Temperature 0 1 0 Timer Fault 0 1 1 Battery Undervoltage 1 0 0 Timers and Stage 3 Disabled, Charging Current Has Risen Above C/5 8490 F20 SYNC BYTE 0x55 LSB STATUS 0x14 MSB Figure 20. UART Transmission Waveform from Figure 17 Label (A) The status byte shown in Figure 20 has information regarding the present charging stage as well as fault information. The data format for each UART byte is 8 data bits, no parity, with one stop bit. The baud rate is 2400 baud 10% which may require auto baud rate detection, using the sync byte, for proper data reception. Figure 21 defines each bit present in the status byte. The status byte always contains an MSB of 0. Status bytes containing an MSB of 1 should be disregarded. MSB LSB 0 LP S2 S1 S0 F2 F1 F0 Table 8. Fault Description If multiple faults are present, the fault listed highest in Table 8 is reported through the STATUS and FAULT pins. 8490 F20 Figure 21. Status Byte Decode 26 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Automatic Charger Restart and Fault Recovery The LT8490 employs many features and checks that may cause the charger to stop until favorable operating conditions return. Table 9 summarizes the typical cause for the LT8490 to stop charging along with the conditions under which it will automatically restart charging. Upon automatic restart all timers are reset except when resuming from an invalid battery temperature fault. Done Charging 1. Stage 3 disabled and narrow battery temperature range selected and temperature compensated battery voltage not selected. 2. Not operating in power supply mode. Table 9. Automatic Restart Conditions CAUSE FOR CHARGING TO STOP The charger will attempt to restart every hour (typically) after having stopped due to a timeout fault in Stage 0, Stage 1 or Stage 2. Configuring the charger in any of the following ways prevents the charger from automatically restarting every hour: RESTART OR RESUME CHARGING REQUIREMENT FOR RESTART Stage 3 disabled and VBAT drops below 95% of VS2 Restart Stage 3 enabled and VBAT drops below 96% of VS3 Restart Battery Undervoltage Fault VBAT rises to 35% of VS2 Restart Stage 0 Timeout VBAT rises to 70% of VS2 or every hour after stopping (read below) Restart Stage 1 Timeout VBAT rises 5% or VBAT rises to 98% of VS2 or every hour after stopping (read below) Restart Stage 2 Timeout VBAT falls below 66% of VS2 or every hour after stopping (read below) Restart Invalid Battery Temperature Battery temperature returns within the valid temperature range with 5C hysteresis Resume Battery Disconnected Fault Re-Connect Thermistor Restart 3. Timer limits disabled. SHDN Pin Connection The LT8490 requires 1.234V (typical) on the SHDN pin to start-up. A minimum of 5V on VIN is also required for proper start-up operation; therefore, a resistor divider from VIN to the SHDN pin is used to set this threshold. Connect the SHDN pin as shown in Figure 22 (1% resistor tolerance or better required). VIN LT8490 VIN 110k SHDN 35.7k GND 8490 F22 Figure 22. SHDN Pin Resistor Divider 8490fa For more information www.linear.com/LT8490 27 LT8490 Applications Information Switching Configuration - MODE Pin The LT8490 has two modes of switching behavior controlled by the state of the MODE pin. Tying MODE to a voltage above 2.3V (i.e., VDD or INTVCC) configures the part for discontinuous conduction mode (DCM) which allows only positive current flow to the battery. More information about this mode of operation can be found in the LT8705 data sheet. Tying the MODE pin below 0.4V (i.e. ground) changes the configuration as follows: 1. AUTOMATIC CCM/DCM MODE SWITCHING: Very large inductor current ripple can lead the LT8490 to operate at high currents while still in DCM. In this case, the M4 switch (highlighted in Figure 23) can become hot due to the battery charging current flowing through the body diode of this device. VIN TG1 M1 SW1 BG1 VOUT M2 M4 L TG2 SW2 M3 BG2 RSENSE 8490 F23 Figure 23. Simplified Diagram of Switches Connecting the MODE pin low can reduce the M4 heating by activating the continuous conduction threshold mode (CCTM). In this mode the average charging current is monitored by the IMON_OUT pin. The LT8490 will operate in conventional DCM while the battery charging current, and thus IMON_OUT, is low (below 122mV typically). As the charging current increases, IMON_OUT will eventually rise above ~195mV signaling the LT8490 to enter CCM operation that will turn on M4 and reduce heating. While the average charging current will be positive, this mode does allow some negative current flow within each switching cycle. Use DCM operation if this behavior is not desired. 2. AUTOMATIC EXTVCC REGULATOR DISCONNECT: As discussed in more detail in the LT8705 data sheet, the INTVCC pin is regulated to 6.35V from one of two possible input pins, VIN or EXTVCC. The EXTVCC pin is often connected to the battery allowing INTVCC to be regulated from a low voltage supply which minimizes power loss and heating in the LT8490. However, EXTVCC should be disconnected from the battery when charging current is low to avoid discharging the battery. When MODE is low, the LT8490 automatically forces the INTVCC regulator to use VIN instead of EXTVCC for the input supply when charging current becomes low. Charging current is monitored on the IMON_OUT pin. When IMON_OUT falls below 122mV (typical) the INTVCC regulator uses VIN as the input supply. When IMON_OUT rises above ~195mV INTVCC will regulate from EXTVCC if EXTVCC is also above 6.4V (typical). This same functionality can be achieved when MODE is tied high by using the external circuit discussed in the Optional EXTVCC Disconnect section. Finally, a 305k (typical) resistor is connected from EXTVCC to ground inside the LT8490. This resistor can draw current from the battery unless EXTVCC is disconnected. See the Optional EXTVCC Disconnect section for a way to automatically disconnect EXTVCC when charging current becomes low or charging stops. 28 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Optional Low Power Mode When current from the solar panel is not high enough to reliably measure the maximum power point, the LT8490 may automatically begin operating in low power mode. Low power mode is automatically disabled when operating from a DC supply in power supply mode. Otherwise, the low power mode feature is enabled by default and allows the LT8490 to charge a battery under very low light conditions that would otherwise cause the LT8490 to stop charging. Low power mode can also be disabled with a method discussed later in this section. In low power mode, the LT8490 momentarily stops charging, allowing the panel voltage to rise. When the panel has sufficiently charged the input capacitor, the LT8490 transfers energy from the input capacitor to the battery while drawing down the panel voltage. This behavior repeats rapidly, delivering charge to the battery as shown in the Panel Voltage in Low Power Mode plots in the Typical Performance Characteristics section. MINIMUM INPUT CAPACITANCE FOR LOW POWER MODE: A minimum amount of energy must be transferred from the input capacitor to the battery during each charge transfer cycle. Otherwise the battery may be drained instead of being charged. Figure 24 shows the minimum input capacitance required when the charger is operating near the 10V minimum input voltage. As the panel voltage rises, due to increased illumination, more energy is stored in the input capacitor and a corresponding increase of energy is delivered to the battery. Carefully check the solar panel voltage for good stability and minimal ripple when operating with low input capacitance. MINIMUM INPUT VOLTAGE: With low power mode enabled, the panel voltage must initially exceed 10V (typical - as measured through the VINR pin) before the charger will attempt to charge the battery. If adequate charge is not being delivered to the battery, the charger may temporarily wait for even more input voltage before transferring the input charge to the battery. EXITING LOW POWER MODE: The charger will automatically exit low power mode and resume normal charging after adequate input current is detected. The charger typically requires the input current to exceed 2.5% to MINIMUM INPUT CAPACITANCE (F) 250 200 150 100 50 0 0 10 20 30 40 50 60 BATTERY VOLTAGE (V) 70 80 8490 F24 Figure 24. Minimum Input Capacitor Required for Low Power Mode 3% of the maximum input current limit to make a valid power point reading and exit low power mode. The panel voltage may be adjusted as low as 6V when searching for the maximum power point. DISABLING LOW POWER MODE: If the minimum input capacitance, or 10V minimum start-up voltage are not suitable for the application, low power mode can be disabled by including the resistor RNLP = 3.01k as shown in Figure 25. When low power mode is disabled, the LT8490 will attempt to charge the battery after 6V or more is detected on the panel. If the input current is too low (typically less than 1.5% of the maximum input current limit) charging is temporarily halted. The LT8490 will attempt to charge the battery on 30 second intervals or when the LT8490 measures a significant rise in the panel voltage. When the LT8490 determines that there is sufficient panel current, normal charging operation will automatically resume. VIN RNLP 3.01k RFBIN1 VIN LT8490 FBIR FBIN RDACI2 RFBIN2 RDACI1 CDACI FBIW GND 8490 F25 Figure 25. Disabling Low Power Mode with Resistor RNLP 8490fa For more information www.linear.com/LT8490 29 LT8490 Applications Information Optional Output Feedback Resistor Disconnect To measure and regulate the battery voltage, the LT8490 uses a resistor feedback network connected to the battery. Unless these resistors are disconnected from the battery, they will draw current from the battery even when it is not being charged as seen in Figure 26. This may be undesirable when using small capacity batteries. If desired, the resistors can be automatically disconnected from the battery when charging stops by using the circuit shown in Figure 27. This circuit is controlled by the SWENO signal from the LT8490 and connects the resistor feedback network when charging is taking place. When charging stops, the network is disconnected and current draw from the battery becomes negligible. IDRAIN LT8490 FBOUT + FBOR FBOW RDACO1 RFBOUT1 RDACO2 VBAT RFBOUT2 CDACO SWEN 200k GND 8490 F26 Figure 26. Battery Discharge When Not Charging TO CHARGER OUT AT RSENSE2 RVGS1 100k LT8490 FBOUT RFBOUT1 FBOR FBOW RDACO1 RDACO2 CDACO SWEN SWENO GND Z1 (OPT.) M5 RFBOUT2 OPTIONAL FEEDBACK RESISTOR DISCONNECT CIRCUIT + VBAT - SELECTING RLIM3: Using VGSon and setting RVGS1 to 100k R RLIM3 = VGS1 * 2.6V VGSon where VGSon is the desired gate to source voltage needed to turn on M5. If M5 is not properly selected, the on resistance may be large enough to cause a significant voltage drop across the drain-source terminal of this device. Check this voltage drop to determine if the application can tolerate this error. ALTERNATE CIRCUIT: For lower battery voltages (< 20V), Q3 in Figure 27 can saturate. To avoid this, consider connecting the emitter of Q3 directly to ground by removing RLIM3 and adding resistor RLIM4 to the base of Q3 as shown in Figure 28. Employing the optional feedback resistor disconnect at arbitrarily low battery voltages will be limited by the required gate to source voltage of M5. Use the following equation to properly set RLIM4: RLIM4 = 91* Q3 200k SELECTING Q3: This NPN must have a collector to emitter breakdown voltage greater than the maximum VBAT. The MMBT5550L is also suitable for most applications due to its 140V breakdown rating. SELECTING Z1: Due to the transients that may occur during hot-plugging of a battery, this Zener diode is recommended to protect device M5 from excessive gate to source voltage. If using device Z1, the reverse breakdown voltage should be selected such that VGSon < VZ1breakdown < VGSMAX where VGSMAX is the maximum rated gate to source voltage specified by the device manufacturer. The BZT52C13 has a reverse breakdown voltage of 13V making it suitable for the RLIM3 value shown in Figure 27. - SWENO SELECTING M5: This PMOS must have a drain to source breakdown voltage greater than the maximum VBAT. The ZVP3310F is rated for 100V making it suitable for most applications. RLIM3 26.1k RVGS1 VBAT 8490 F27 Figure 27. Optional Feedback Resistor Disconnect Circuit 30 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information Optional EXTVCC Disconnect TO CHARGER OUT AT RSENSE2 RVGS1 100k M5 LT8490 FBOUT FBOW RDACO1 RDACO2 CDACO SWEN SWENO GND OPTIONAL FEEDBACK RESISTOR DISCONNECT CIRCUIT RFBOUT1 FBOR RFBOUT2 + VBAT - Q3 RLIM4 200k 8490 F29 The LT8490, via the ECON signal, disconnects EXTVCC from the battery when charging current becomes low. Charging current is monitored by measuring the IMON_OUT pin voltage with the IOR pin's A/D input. When IMON_OUT falls below 122mV (typical) the ECON signal goes low and EXTVcc is disconnected from the battery. When IMON_OUT rises above 195mV (typical) the ECON signal goes high and EXTVCC is reconnected to the battery. Figure 28. Optional Low Battery Voltage Feedback Resistor Disconnect Circuit TO CHARGER OUT AT RSENSE2 RVGS2 100k Z2 (OPT.) M6 LT8490 + OPTIONAL EXTVCC DISCONNECT CIRCUIT 10 EXTVCC 1F VBAT - Q4 ECON 200k GND The LT8490 measures the battery voltage continually during charging. The apparent battery voltage is sensed from ground of the LT8490 to the top of RFBOUT1. During charging, resistance in the battery cables (RCABLE+/ RCABLE- in Figure 30) causes the apparent voltage to be higher than the actual battery voltage by 2 * VIR. 8490 F29 Figure 29. Optional EXTVCC Disconnect Circuit ICHARGE + LT8490 FBOR FBOW GND RFBOUT1 RDACO1 RDACO2 CDACO VIR - + FBOUT RCABLE+ RCABLE- VBAT - RFBOUT2 - Follow the same recommendations and equations from the previous section for choosing components for the optional EXTVCC disconnect circuit. Optional Remote Battery Voltage Sensing RLIM4 26.1k M6: ZVP3310F Q4: MMBT5550L Z2: BZT52C13 TO CHARGER OUT AT RSENSE2 It is often desirable to connect EXTVCC to the battery to reduce power loss (increase efficiency) and heating in the LT8490. However, the LT8490 draws current into the EXTVCC pin that can drain the battery when charging currents are low or when charging stops. Tying the MODE pin low, as discussed in the Switching Configuration - MODE Pin section, eliminates most of the current draw from EXTVCC when the charging current becomes low. However, there is a 305k (typical) path from EXTVCC to ground through the LT8490 at all times. If MODE is tied high or if the 305k load is undesirable, EXTVCC can be disconnected with the optional circuit shown in Figure 29. VIR The effects of this cable drop are most significant when charging low voltage batteries at high currents. As an example, a 4 foot battery cable using 14 AWG wire can have a voltage drop exceeding 0.5V at 15A of current. Note however that the voltage drop, along with the charging current, reduces automatically as the battery approaches full charge. + 8490 F30 Figure 30. IR Drop Present in Battery Connection 8490fa For more information www.linear.com/LT8490 31 LT8490 Applications Information The most significant effects from the VIR voltage drops are as follows: using a (-) terminal sensing cable, the LT1636, Q5 and R5. RFBOUT, RFBOUT and R5 are determined as follows: 1. When approaching full charge in Stage 2, the VIR error causes the charger to reduce the charging current earlier than otherwise necessary. This increases the total charging time. RFBOUT1 = 0.5 * RFBOUT1 VS2 - 1.211 RFBOUT1 = (RFBOUT1 -RFBOUT1) R5 = RFBOUT1 2. Terminating at C/10 in Stage 2 will occur at a reduced battery voltage equal to C/10 * (RCABLE+ + RCABLE-) which is 10% of the voltage drop at full charging current. where VS2 is the room temperature Stage 2 voltage limit and the solution for RFBOUT1 was discussed previously in the Stage Voltage Limits section. Solutions for determining RDACO1, RDACO2, RFBOUT2 and CDACO are also discussed in the Stage Voltage Limits section. 3. The STATUS pin will indicate a transition from Stage 1 to Stage 2 earlier than would otherwise occur without the cable drop. Due to its low current draw (< 1mA) Q5 can be a small signal device with a collector-emitter breakdown voltage at least as high as the battery voltage. The MMBT3904 is a good BJT rated to 40V. Alternatively, the MMBT5550L is rated for 140V. Again, these effects become less significant at higher battery voltages because the charging current is typically lower and the cable drop becomes a smaller percentage of the total battery voltage. Using thicker and/or shorter battery cables is the simplest method for reducing these effects. Otherwise, the remote battery sensing circuit in Figure 31 can correct for these effects. R3 is for safety in case the (+) battery sensing cable becomes disconnected. R3 prevents overcharging the battery in such an event by creating an alternate path to pull up the RFBOUT1 battery voltage sensing resistor. The R3 resistance should be less than 1% of RFBOUT1. Selecting R3 as a 100 resistor is often a good choice. During The RCABLE+ measurement error is eliminated by including an additional (+) terminal sensing cable. The negative cable error is eliminated by subtracting the RCABLE- drop from the voltage measured at the positive battery terminal RCABLE+ TO CHARGER OUT AT RSENSE2 D2A D2B D2C RFBOUT1 10 RFBOUT1 LT8490 VBAT + FBOR GND + INTVCC 1F FBOUT FBOW R3 RDACO1 RDACO2 CDACO Q5 LT1636 R4 - - RFBOUT2 R2 R5 D3A D3B RCABLE- 8490 F31 Figure 31. Remove (+) and (-) Cable VIR Measurement Errors 32 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information R2 maintains a negative voltage reference in case RCABLE- becomes disconnected. Selecting R2 as a 100 resistor is often a good choice. During normal operation the voltage across R2 is about the same as across RCABLE-. However, R2 may experience voltage in excess of VS2-VBAT across its terminals if RCABLE- becomes disconnected. R2 should be selected with an appropriate power rating, often at least 1W due to the case where the (+) and (-) wires of the remote sense circuit are first connected to the battery to address hot plugging issues (see the Hot Plugging Considerations section for more detail). normal operation the voltage across R3 is about the same as across RCABLE+. However, R3 may experience voltage up to VS2 -VBAT across its terminals if RCABLE+ becomes disconnected. R3 should be selected with an appropriate power rating, often at least 1W. D2A-D2C protect the charger if the positive charging cable (RCABLE+) becomes disconnected while the others remain intact. Without the diodes, the output of the charger may overvoltage and become damaged. BAV99 diodes are a good choice and are available in a dual-diode package to minimize board space. Note that the diodes limit the maximum RCABLE+ error to 0.3V to 0.5V. If a greater voltage drop is typical in the positive cable then place more diodes in series. D2D protects the M5 device by limiting the gate to source voltage when making the remote sense connection. Figure 32 shows how to combine the remote sensing circuit (Figure 31) and the feedback resistor disconnect (Figure 27) for applications that require the most accurate battery voltage sensing and negligible battery drain when charging completes. The RVGS1 resistor can no longer connect to the source of M5 (as in Figure 27) since the RVGS1 current would also flow through RFBOUT1 causing an error in the measured battery voltage. Figure 31 shows that RVGS1 has been reconnected to the (+) battery sensing terminal. D3A, D3B and R4 protect the input of the LT1636 from possible voltage extremes at the (-) battery terminal sensing connection. The dual-diode BAV99 is also suitable in this case. 4.99k is a good value for R4. RCABLE+ TO CHARGER OUT AT RSENSE2 D2A D2B D2C D2D R3 RFBOUT1 RVGS1 100k M5 LT8490 10 RFBOUT1 FBOUT 1F VBAT FBOR FBOW + RDACO1 RDACO2 Q5 CDACO RFBOUT2 SWEN SWENO GND + INTVCC - LT1636 R4 - R2 Q3 200k RLIM3 26.1k R5 D3A D3B RCABLE- 8490 F32 Figure 32. How to Combine Figure 27 and Figure 30 8490fa For more information www.linear.com/LT8490 33 LT8490 Applications Information Optional DC Supply Detection Circuit Board Layout Considerations A dual input application can be configured where the charger can be supplied by either a solar panel or a DC supply. When powered by a DC supply, the VINR pin must be pulled low to activate power supply mode. In addition, blocking diodes should be incorporated to prevent the supplies from back-feeding into each other. The circuit shown in Figure 33 shows a way to incorporate those features. For all power components and board routing associated with the LT8705 portion of the LT8490, please refer to the LT8705 documentation for which a circuit board layout checklist and drawing is provided. As shown in Figure 33, when the DC supply is connected the Q6 NPN pulls VINR below 174mV (typical) to activate the Power Supply Mode of the LT8490. Be sure to choose an NPN that can pull VINR below the power supply mode threshold before fully saturating. Alternatively, Q6 can be replaced with an NMOS device with proper care taken to avoid overvoltage of the NMOS gate. Depending on the current limit settings, diodes DPANEL and DVDC can incur significant current and heat. Consider the use of Schottky diodes or an appropriate ideal diode such as the LTC4358, LTC4412, LTC4352, etc. to minimize heating. DPANEL VPANEL DVDC VDC TO RSENSE1 VIN LT8490 196k VINR 100k 8.06k Q6 33k GND 8490 F33 Q6: 2SD2704K Figure 33. Optional DC Supply Detection Circuit 34 Hot Plugging Considerations When connecting a battery to an LT8490 charger, there can be significant inrush current due to charge equalization between the partially charged battery stack and the charger output capacitors. To a lesser extent a similar effect can occur when connecting an illuminated panel or powered DC supply to the input. The magnitude of the inrush current depends on (1) the battery, panel or supply voltage, (2) ESR of the input or output capacitors, (3) initial voltage of the capacitors, and (4) cable impedance. Excessive inrush current can lead to sparking that can compromise connector integrity and/or voltage overshoot that can cause electrical overstress on LT8490 pins. Excessive inrush current can be mitigated by first connecting the battery or supply to the charger through a resistive path, followed quickly by a short circuit. This can be accomplished using staggered length pins in a multi-pin connector. This can also be accomplished through the use of the optional circuit shown in Figure 31 by first connecting the (+) and (-) battery remote sense connections, which allow the charger output capacitors to charge through resistors R2 and R3. Alternatively, consider the use of a Hot SwapTM controller such as the LT1641, LT4256, etc. to make a current limited connection. Design Example In this design example, the LT8490 is paired with a 175W/5.4A panel (VMAX < 53V) and a 12V flooded leadacid battery. The desired maximum battery charging current (C) is 10A with a trickle charge current of 2.5A (C/4). Charger settings are as follows: -20C to 50C valid battery temperature range, temperature compensated charging limits, no time limits and Stage 3 is enabled with VS3 /VS2 = 97.2%. In this example resistors are rounded to the nearest standard value. If better accuracy is required then multiple resistors in series may be required. 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information * With RFBOUT2 set at 20k and a desired Stage 2 voltage limit of 14.2V, the top output feedback resistor, RFBOUT1, is calculated according to the following equation: 1.241 RFBOUT1 = RFBOUT2 * VS2 * - 0.128 - 1 1.211 1.241 - 0.128 - 1 = 20k * 14.2 * 1.211 = 234,684 Choose RFBOUT1 = 237k which is the closest standard value resistor. * Following the calculation of RFBOUT1, solve for RDACO1, RDACO2 and CDACO according to the following formulas: RFBOUT1 * RFBOUT2 * 0.833 1.241 RFBOUT2 * VS2 * -RFBOUT2 -RFBOUT1 1.211 234,684 * 20k * 0.833 = 1.241 20k * 14.2 * - 20k - 234,684 1.211 = 107,556 RDACO2 = Choose RDACO2 = 107k which is the closest standard value resistor. RDACO1 = (0.2 * RDACO2) = 0.2 * 107,556 = 21,511 1 F 500 * RDACO1 1 F 500 * 21,511 = 93nF = VX3 = 14.31V N1 = 1.22 N2 = 0.804 * In order to find a resistor combination that yields VX3 closer to the desired 14.2V, RFBOUT2 is increased to the next higher standard value and the above calculations are repeated. * Iterations of the previous step are performed that include adjustments to RFBOUT1, RDACO1 and RDACO2 until the following standard value feedback resistors were chosen: RFBOUT1 = 274k RFBOUT2 = 23.2k RDACO1 = 26.1k RDACO2 = 124k CDACO = 0.082F where: VX3 = 14.27V N1 = 1.22 N2 = 0.805 Choose RDACO1 = 21.5k which is the closest standard value resistor. CDACO = * Using the standard value resistors calculated above, the VX3, N1 and N2 checking equations yield the following: * With the output feedback network determined, use VMAX and solve for the input resistor feedback network according to the following formulas: 4.47V 1+ VMAX - 6V RFBIN1 = 100k * 5.593V 1+ VMAX - 6V 4.47V 1+ 53V - 6V = 100k * 1+ 5.593V 53V - 6V = 97,865 8490fa For more information www.linear.com/LT8490 35 LT8490 Applications Information The closest standard value for RFBIN1 is 97.6k. R RDACI2 = 2.75 * FBIN1 VMAX - 6V 97,865 = 2.75 * 53V - 6V = 5,726 RFBIN1 = 93.1k RFBIN2 = 3.24k Choose RDACI2 = 5.76k which is the closest standard value. RFBIN2 = 1 1 1 - 100k -RFBIN1 RDACI2 = 1 1 1 - 100k - 97,865 5,726 = 3,404 * Similar to the output feedback resistors, the final input feedback resistors were chosen to be standard values using an iterative process. The VX1 and VX2 equations in the Input Voltage Sensing and Modulation Network section were used to validate the selections: RDACI1 = 1.05k RDACI2 = 5.49k CDACI = 1F where: VX1 = 6V VX2 = 53V * The 10A maximum charge current limit and 2.5A trickle charge current limit are set by choosing RSENSE2, RIMON_OUT and RIOW using the following formulas: Choose RFBIN2 = 3.4k which is the closest standard value. RDACI1 = 0.2 * RDACI2 RSENSE2 = = 1,145 1 F = 1000 * 1,145 = 873nF = 0.0497 5m 10 1208 IOUT(MAXS0) * RSENSE2 1208 2.5 * 5m = 96.64k = Choose RDAC1 = 1.1k which is the closest standard value. 1 F 1000 * RDACI1 IOUT(MAX) RIMON _ OUT = = 0.2 * 5,726 CDACI = 0.0497 where the nearest standard value is 97.6k. RIOW = 24.3k * RIMON _ OUT RIMON _ OUT - 24.3k 24.3k * 47.6k 97.6k - 24.3k = 32,356 = where the nearest standard value is also 32.4k. 36 8490fa For more information www.linear.com/LT8490 LT8490 Applications Information * The input current limit is set by properly choosing RSENSE1. In this example, the panel can deliver up to 5.4A. Choosing a margin of 30% yields: RSENSE1 = 0.0505 0.0505 = = 7.2m IIN(MAX) 1.3 * 5.4 * To enable temperature compensated charging limits and allow a Stage 3 regulation voltage of 97.2% of Stage 2, use VS3 / VS2 = 0.972 in the following equation: V CHARGECFG1% = 2.67 * S3 - 0.85 + 0.55 * 100% VS2 Standard resistor values of 90.9k (from CHARGECFG1 to ground) and 13k (from AVDD to CHARGECFG1) can be used to set CHARGECFG1. * To set no time limits with a -20C to 50C valid battery temperature range requires CHARGECFG2 to be tied to AVDD. * For greater charging voltage accuracy, it is recommended that 0.1% tolerance resistors be used for the output feedback resistor network. * Please reference the LT8705 data sheet for completing the remaining power portions of the LT8490. CHARGECFG1% = 87.6% 8490fa For more information www.linear.com/LT8490 37 38 3.24k For more information www.linear.com/LT8490 21k 10nF 220nF DB1 LT8490 3.3nF 10 10 DS 2 549 DF DB2 549 3.32k AVDD CHARGECFG1 SWEN SWENO ECON VDD LDO33 SRVO_IIN SRVO_FBIN SRVO_FBOUT SRVO_IOUT TEMPSENSE AVDD FBOR FBOUT FBOW CSPOUT CSNOUT EXTVCC BOOST2 TG2 1.3k FAULT COUT3 10F x2 GATEVCC 220nF GND BG2 SW2 6m M3 M4 200k 24.3k COUT4 1F 4.7F 10k 1F 102k CCSPOUT 100nF COUT2 10F x2 11.5k 10 82nF 470nF 1/2W 10m Figure 34. 27.4V Lithium-Ion Polymer Battery Charger M1, M2: INFINEON BSC028N06NS M3, M4: INFINEON BSC059N04LSG L1: 10H COILCRAFT SER2915H-103KL DB1, DB2: CENTRAL SEMI CMMR1U-02 CIN1: 33F, 63V, SUNCON 63HVH33M CIN2, CIN3, CIN4: 2.2F, 100V, AVX 12101C225KAT2A COUT1: 150F, 50V PANASONIC EEU-FR1H151 COUT2, COUT3: 10F, 35V, MURATA GRM32ER7YA106KA12 COUT4: 1F, 50V, TDK CGA6L2X7R1H105K CCSPOUT: 100nF, 50V, AVX 08055C10 68nF 8.2nF 220pF CSN 3.3nF M2 L1 10H CLKDET CLKOUT CHARGECFG2 STATUS 53.6k SYNC 10k VC IOR IMON_OUT IOW RT SS IIR IMON_IN SHDN VINR FBIR FBIN FBIW MODE INTVCC TG1 BOOST1 SW1 BG1 CSP CSNIN CSPIN VIN GATEVCC 2 3.01k 1.05k 60.4k 40.2k 0.82F 4.7F x2 4 470nF 10 M1 GATEVCC CIN3 2.2F x2 27.4V STAGE 2 (FLOAT) CHARGE VOLTAGE (VS2) STAGE 3 DISABLED 5A CHARGING CURRENT LIMIT 2A TRICKLE CURRENT LIMIT 7.2A INPUT CURRENT LIMIT 53V MAXIMUM PANEL VOLTAGE (VMAX) NO TIMER LIMITS TEMPERATURE COMPENSATION DISABLED 202kHz SWITCHING FREQUENCY EXAMPLE SOLAR PANEL: SHARP NT-175UC1 175W 10nF 100nF 215k 5.49k 35.7k 8.06k 93.1k 110k GATEVCC CIN4 2.2F CIN1 33F x3 CIN2 2.2F x2 196k - VOC < 53V SOLAR PANEL + 1/2W 7m 100nF COUT1 150F 8490 F34 18.7k 442k 100 - + TENERGY 31417 Li-Ion POLYMER 10Ah 7S1P LOAD LT8490 Applications Information 8490fa 3.09k For more information www.linear.com/LT8490 21k 68nF 220pF CSN 10nF 10 10 LT8490 10nF M2 L1 15H DB2 GATEVCC EXTVCC SWEN SWENO ECON VDD LDO33 SRVO_IIN SRVO_FBIN SRVO_FBOUT SRVO_IOUT TEMPSENSE AVDD FBOR FBOUT FBOW CSPOUT CSNOUT DS 3.32k 1.3k 549 DF 549 90.9k 13k AVDD 200k 10 4.7F 10k AT 25C = 3380 NTC 1F 115k CCSPOUT 100nF COUT2 4.7F x2 11.5k 0.1F 470nF 1/2W 10m M1: INFINEON BSC046N10NS M2: INFINEON BSC109N10NS M3, M4: INFINEON BSC057N08NS L1: 15H COILCRAFT SER2915H-153KL DB1, DB2: CENTRAL SEMI CMMR1U-02 CIN1, COUT1: 220F, 100V, UNITED CHEMI-CON EKZE101ELL221MK255 CIN2, CIN3, CIN4: 2.2F, 100V, AVX 12101C225KAT2A COUT2, COUT3: 4.7F, 100V, TDK C4532X7S2A475M230KB COUT4: 1F, 100V AVX 12101C105KAT2A CCSPOUT: 100nF, 50V, AVX 08055C10 AVDD COUT4 1F 22.6k COUT3 4.7F x2 BOOST2 TG2 220nF GND BG2 SW2 6m M3 M4 CLKDET CLKOUT CHARGECFG2 STATUS FAULT CHARGECFG1 10nF SYNC 53.6k VC IOR IMON_OUT IOW RT SS IIR IMON_IN SHDN VINR FBIR FBIN FBIW MODE INTVCC TG1 BOOST1 SW1 BG1 CSP CSNIN CSPIN VIN GATEVCC 220nF DB1 11.3k 3.01k 1.05k 97.6k 32.4k 8.2nF 1F 4.7F x2 4 470nF 10 GATEVCC CIN3 2.2F x2 M1 56.8V STAGE 2 (ABSORPTION) CHARGE VOLTAGE (VS2) AT 25C 55.2V STAGE 3 (FLOAT) CHARGE VOLTAGE (VS3) AT 25C 5A CHARGING CURRENT LIMIT 1.25A TRICKLE CURRENT LIMIT 11.4A INPUT CURRENT LIMIT 80V MAXIMUM PANEL VOLTAGE (VMAX) NO TIMER LIMITS TEMPERATURE COMPENSATION ENABLED -20C TO 50C BATTERY TEMPERATURE RANGE 145kHz SWITCHING FREQUENCY EXAMPLE SOLAR PANEL: SHARP NT-175UC1 175W, SHARP NU-U235F3 235W 10nF 100nF 301k 4.87k 35.7k 8.06k 133k 110k GATEVCC CIN4 2.2F CIN1 220F CIN2 2.2F x2 196k - SOLAR PANEL VOC < 80V + 1/2W 5m 56.8V Lead-Acid Battery Charger (Four 12V Batteries in Series) 100nF COUT1 220F 8490 TA02 20k 1M 100 - + FLOODED LEAD ACID LOAD LT8490 Applications Information 8490fa 39 LT8490 Package Description Please refer to http://www.linear.com/product/LT8490#packaging for the most recent package drawings. UKJ Package Variation: UKJ64(58) UKJ Package 64(58)-Lead Variation: Plastic QFN (7mm x 11mm) UKJ64(58) (Reference LTC DWG 05-08-1922 O) 64(58)-Lead Plastic# QFN (7mm xRev 11mm) (Reference LTC DWG # 05-08-1922 Rev O) 0.70 0.05 1.80 0.05 1.50 0.05 9.38 0.05 3.60 0.05 7.50 0.05 5.50 REF 0.45 3.83 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 9.50 REF 10.10 0.05 11.50 0.05 APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.75 0.05 7.00 0.10 5.50 REF 0.00 - 0.05 PIN 1 TOP MARK (SEE NOTE 6) PIN 1 NOTCH R = 0.30 TYP OR 0.35 x 45 CHAMFER 53 63 64 1 52 2 0.325 REF 1.50 0.10 44 11.00 0.10 11.00 0.10 1.20 0.10 9.50 REF 9.38 0.10 40 0.45 0.10 3.83 0.10 3.60 0.10 35 33 20 0.50 REF 0.40 0.10 0.200 REF 31 27 0.25 0.05 25 21 0.50 BSC (UKJ64(58)) QFN 0412 REV O BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 40 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 8490fa For more information www.linear.com/LT8490 LT8490 Revision History REV DATE DESCRIPTION A 11/15 Changed diode type symbol. PAGE NUMBER 1, 38, 39, 42 Modified the Block Diagram. 11 8490fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. For more information www.linear.com/LT8490 41 LT8490 Typical Application 14.2V Flooded Lead-Acid Battery Charger 1/2W 7m + CIN3 2.2F x2 CIN2 2.2F x2 SOLAR PANEL VOC < 53V - 10 2 CIN4 2.2F 8.06k 110k GATEVCC CSN GND BG2 SW2 EXTVCC 3.01k 21k 100nF 4.7nF 11.5k 4.7F + FLOODED LEAD ACID 10k AT 25C = 3380 NTC 100nF SWEN SWENO SYNC 1F - ECON 8.45k 124k 23.2k VDD LDO33 SRVO_IIN SRVO_FBIN SRVO_FBOUT SRVO_IOUT IOR IMON_OUT VC LOAD 0.082F 26.1k TEMPSENSE AVDD LT8490 IOW 97.6k 8.2nF 274k FBOR FBOUT FBOW RT SS IIR IMON_IN 32.4k 470nF BOOST2 TG2 1.05k 249k COUT4 1F CSPOUT CSNOUT SHDN VINR FBIR FBIN FBIW 1F 5.49k DB2 2 COUT1 150F 10 220nF MODE 93.1k 3.24k 5m INTVCC 4.7F x2 35.7k COUT2 10F x2 GATEVCC 3.3nF TG1 BOOST1 SW1 BG1 CSP CSNIN CSPIN VIN GATEVCC 4 M3 10 3.3nF 220nF VBAT COUT3 10F x2 10 DB1 1W 5m M4 M2 GATEVCC CIN1 33F x3 470nF 196k L1 15H M1 CLKDET CLKOUT CHARGECFG2 STATUS FAULT CHARGECFG1 53.6k AVDD 1.3k 13k AVDD 200k 3.32k 68nF 10nF DS 470pF 90.9k DF 549 549 8490 TA03 14.27V STAGE 2 (ABSORPTION) CHARGE VOLTAGE (VS2) AT 25C 13.87V STAGE 3 (FLOAT) CHARGE VOLTAGE (VS3) AT 25C 10A CHARGING CURRENT LIMIT 2.5A TRICKLE CURRENT LIMIT 7.2A INPUT CURRENT LIMIT 53V MAXIMUM PANEL VOLTAGE (VMAX) NO TIMER LIMITS TEMPERATURE COMPENSATION ENABLED -20C TO 50C BATTERY TEMPERATURE RANGE 175kHz SWITCHING FREQUENCY EXAMPLE SOLAR PANEL: SHARP NT-175UC1 175W M1, M2: INFINEON BSC028N06NS M3, M4: INFINEON BSC042N03LSG L1: 15H COILCRAFT SER2915H-153KL DB1, DB2: CENTRAL SEMI CMMR1U-02 CIN1: 33F, 63V, SUNCON 63HVH33M CIN2, CIN3, CIN4: 2.2F, 100V, AVX 12101C225KAT2A COUT1: 150F, 35V NICHICON UPJ151MPD6TD COUT2, COUT3: 10F, 35V, MURATA GRM32ER7YA106KA12 COUT4: 1F, 25V AVX 12063C105KAT2A Related Parts PART NUMBER DESCRIPTION COMMENTS LT3652/LT3652HV Power Tracking 2A Battery Charger for Solar Power VIN Range = 4.95V to 32V (LT3652), 4.95V to 34V (HV), MPPC LTC4000-1 High Voltage, High Current Controller for Battery Charger with MPPC VIN and VOUT Range = 3V to 60V, MPPC LTC4020 55V VIN/VOUT Buck-Boost Multi-Chemistry Battery Charging Controller Li-Ion and Lead-Acid Algorithms, MPPC 42 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT8490 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LT8490 8490fa LT 1115 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2014