Compact, 1.5 A Linear Charger for Single-Cell Li+ Battery ADP2291 FEATURES GENERAL DESCRIPTION Simple, safe linear charger for single-cell lithium battery 4.5 V to 12 V input voltage range Adjustable charging current up to 1.5 A Low cost PNP external pass element Automatic reverse isolation with no external blocking diode Output overshoot protection Deep discharge precharge mode Thermal shutdown Automatic recharge Programmable termination timer LED charging status indicator 4.2 V output voltage with 1% accuracy over line and temperature 1 A shutdown supply current Small, 8-lead MSOP and 3 x 3 mm LFCSP packages The ADP2291 is a constant-current/constant-voltage linear charger for a single-cell, lithium ion battery, requiring just a few components to provide a simple and safe charging system that operates from a wide 4.5 V to 12 V input voltage range. It features an internally controlled, multistep charging cycle that improves battery life. An external, low cost PNP provides the charging current to the battery, and an external resistor sets the maximum charge current. A small, external capacitor programs the maximum charge time. The controller includes an LED driver to indicate the battery charging status. Safety features include charging stop mode for battery faults, output overshoot protection, and thermal shutdown. The ADP2291 also features automatic reverse isolation, which does not require an additional blocking diode. APPLICATIONS The multistep charge cycle optimizes the battery charging time in a safe manner. It features a trickle charge mode for a deeply discharged cell and a fast charging mode with a maximum current of 1.5 A. The ADP2291 controls the end of charge with a 4.2 V output voltage that is 1% accurate over line and temperature. It automatically recharges the battery if the cell voltage drops. When the input supply is removed, the part enters a low current state and reduces the current drawn from the battery to below 1 A. Wireless handsets Smart handhelds and PDAs Digital cameras Single-cell, lithium ion-powered systems Cradle chargers The ADP2291 is available in both a small, 8-lead MSOP package and a 3 x 3 mm LFCSP package that is ideally suited for small, portable applications. TYPICAL OPERATING CIRCUIT RS INPUT 4.6V-12V Q1 + COUT CIN CS DRV IN BAT ADP2291 CHG GND CTIMER ADJ SHUTDOWN 04873-001 TIMER Figure 1. Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c) 2005 Analog Devices, Inc. All rights reserved. ADP2291 TABLE OF CONTENTS Features .............................................................................................. 1 Overshoot Protection................................................................. 10 Applications....................................................................................... 1 Power Supply Checks................................................................. 10 General Description ......................................................................... 1 Thermal Shutdown .................................................................... 11 Typical Operating Circuit................................................................ 1 Application Information................................................................ 12 Specifications..................................................................................... 3 Setting the Maximum Charge Current.................................... 12 Absolute Maximum Ratings............................................................ 5 Setting the Maximum Charge Time ........................................ 12 ESD Caution.................................................................................. 5 External Capacitors.................................................................... 12 Pin Configurations and Function Descriptions ........................... 6 Reverse Input Protection........................................................... 12 Typical Performance Characteristics ............................................. 7 External Pass Transistor ............................................................ 13 Theory of Operation ...................................................................... 10 Typical Application Circuit....................................................... 14 Precharge Mode.......................................................................... 10 Charge Termination................................................................... 14 End-of-Charge Mode................................................................. 10 Selectable Charge Current......................................................... 14 Shutdown Mode.......................................................................... 10 Thermal Protection.................................................................... 14 Charge Restart............................................................................. 10 Printed Circuit Board Layout Considerations ....................... 16 Programmable Timer................................................................. 10 LFSCP Layout Considerations.................................................. 16 Charge Status Indicator ............................................................. 10 Outline Dimensions ....................................................................... 17 Automatic Reverse Isolation ..................................................... 10 Ordering Guide .......................................................................... 17 REVISION HISTORY 11/05--Rev. 0 to Rev. A Changes to Equation 7 ................................................................... 13 Changes to Figure 26...................................................................... 15 Changes to Table 7.......................................................................... 16 Changes to Ordering Guide .......................................................... 17 Updated Outline Dimensions ....................................................... 17 10/04--Initial Version: Revision 0 Rev. A | Page 2 of 20 ADP2291 SPECIFICATIONS VIN = 5.5 V, VBAT = 4.2 V, RADJ open, TA = -40C to +85C, typical values are at 25C, unless otherwise noted.1 Table 1. Parameter POWER SUPPLY, IN Input Voltage Current Draw BATTERY VOLTAGE, BAT Voltage Accuracy, End-of-Charge (VBAT, EOC) Load Regulation, No Battery Current Draw Current Draw Reverse Leakage Current FAST CHARGE MODE Sense Voltage Setpoint (VRS) Sense Voltage Setpoint (VRS) Current Regulation Adjustment PRECHARGE MODE Sense Voltage Setpoint (VRS) Sense Voltage Setpoint (VRS) BAT Precharge Threshold Hysteresis SHUTDOWN MODE ADJ Shutdown Threshold Hysteresis Pull-Up Current from ADJ POWER-DOWN MODE VIN Power-Down Threshold Hysteresis VIN_Good Comparator Threshold (VIN > VBAT) Hysteresis EOC COMPARATOR Current Threshold Current Threshold Hysteresis RESTART COMPARATOR BAT Restart Threshold Conditions Min Typ Max Unit 6 1.4 12 9 1.8 V mA mA 4.2 4.242 V 45 1 mV A A A 4.5 Fast charge/precharge/end-of-charge modes Timeout/shutdown/battery fault TA = 0C to +50C VIN = 4.5 V to 12 V VIN - VCS = VRS/10 VIN - VCS = 0 to VRS Timeout mode, VIN = 4.5 V to 12 V Battery fault/shutdown mode, VIN = 4.5 V to 12 V Power-down mode: VIN = float, VBAT = 4.2 V 4.158 VIN - VCS, RADJ = open VIN = 4.5 V to 12 V VBAT = 3.6 V VIN - VCS, RADJ = 100 k VIN = 4.5 V to 12 V VBAT = 3.6 V Per V of (3 V - VADJ) 140 150 160 mV 40 50 60 mV VIN - VCS, RADJ = open VIN = 4.5 V to 12 V VBAT = 2 V VIN - VCS, RADJ = 100 k VIN = 4.5 V to 12 V VBAT = 2 V VBAT rising 10 15 20 mV 5 10 15 mV 2.85 V mV 0.45 V mV A 4 V mV -80 0.1 0.1 67 2.65 mV/V 70 VADJ falling, VIN = 4.5 V 0.30 40 40 VADJ = 0 VIN rising 3.6 220 VIN rising 125 170 110 220 mV mV VIN - VCS falling, RADJ = open, relative to VRS VIN - VCS falling, RADJ = 100 k, relative to VRS 7 6 10 10 12 13 16 % % mV VIN > 4.5 V, VBAT falling, relative to VBAT, EOC -170 Rev. A | Page 3 of 20 mV ADP2291 Parameter BATTERY CHARGE TIMER Charge/Discharge TIMER Current Low Threshold High Threshold High-Low Threshold Delta2 OVERSHOOT PROTECTION BAT Threshold Current Sink CHG OUTPUT Output Voltage Low Output Leakage Current BASE DRIVE CAPABILITY Maximum Base Drive Current THERMAL SHUTDOWN Shutdown Threshold Hysteresis 1 2 Conditions Min Typ Max Unit 21.0 24.0 1.2 2.0 27.0 A V V mV 750 4.7 850 <2 ms duration 5 1.5 Current = 20 mA VCHG = 5 V 0.1 40 TA rising V A 0.45 1 V A mA 135 35 All limits at temperature extremes are guaranteed via correlation using standard statistical quality control (SQC). Typical values are at TA = 25C. Guaranteed by design; not tested in production. Rev. A | Page 4 of 20 5.3 C C ADP2291 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter IN, DRV,1 CS, CHG to GND BAT, ADJ, TIMER to GND Operating Ambient Temperature Operating Junction Temperature JA, 2-layer MSOP-8 JA, 4-layer MSOP-8 JA, 2-layer LFCSP-8 JA, 4-layer LFCSP-8 Storage Temperature Range Lead Temperature Soldering (10 sec) 1 Rating -0.3 V to +13.5 V -0.3 V to (VIN + 0.3 V) -40C to +85C -40C to +125C 220C/W 158C/W 62C/W 48C/W -65C to +150C 300C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other condition s above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in combination. Unless otherwise specified all other voltages referenced to GND. Pulling current from the DRV pin by driving it below ground while VIN is applied can cause permanent damage to the device. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. A | Page 5 of 20 ADP2291 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS CS 4 TOP VIEW (Not to Scale) 8 CHG 7 TIMER 6 IN 5 ADJ DRV 1 GND 2 BAT 3 CS 4 PIN 1 INDICATOR ADP2291 TOP VIEW (Not to Scale) Table 3. Pin Function Descriptions Mnemonic DRV GND BAT CS ADJ IN TIMER CHG 7 TIMER 6 IN 5 ADJ Figure 3. 8-Lead LFCSP Pin Configuration Figure 2. 8-Lead MSOP Pin Configuration Pin No. 1 2 3 4 5 6 7 8 8 CHG 04873-003 BAT 3 ADP2291 04873-002 DRV 1 GND 2 Description Base Driver Output. Controls the base of an external PNP pass transistor. Ground. Battery Voltage Sense Input. Current Sense Resistor Negative Input. Charging Current Adjust and Charger Shutdown Input. Power Input and Current Sense Resistor Positive Input. Timer Programming Input/Disable. LED Charge Status Indicator. This is an open-collector output. Rev. A | Page 6 of 20 ADP2291 TYPICAL PERFORMANCE CHARACTERISTICS 800.0 4.21 700.0 4.205 600.0 ICHG (mA) VBAT (V) 500.0 4.20 400.0 300.0 4.195 200.0 4.19 4 6 8 VIN (V) 10 04873-007 04873-004 100.0 0.0 2.50 12 Figure 4. Battery Voltage vs. Input Voltage 3.00 3.50 IBAT (V) 4.00 4.50 Figure 7. Charge Current vs. Battery Voltage RS = 200 m, VADJ = 3 V 4.21 250 200 IREVERSE (nA) VBAT (V) 4.205 4.20 150 100 4.195 -25 0 25 50 TEMPERATURE (C) 75 100 0 -50 125 Figure 5. Battery Voltage vs. Temperature -25 0 25 50 75 TEMPERATURE (C) 100 125 Figure 8. Battery Reverse Current vs. Temperature VIN = float, VBAT = 4.2 V 4.22 4.10 4.09 VRESTART (V) 4.21 4.20 4.08 4.07 4.19 4.06 4.18 0 200 400 ICHG (mA) 600 4.05 -40 800 Figure 6. Battery Voltage vs. Charge Current RS = 200 m, VADJ = 3 V 04873-009 04873-006 VBAT (V) 04873-008 4.19 -50 04873-005 50 -20 0 20 40 60 TEMPERATURE (C) Figure 9. Restart Threshold Rev. A | Page 7 of 20 80 100 16.0 153 15.8 152 15.6 151 VRS (mV) 15.4 150 04873-010 15.0 4 6 8 VIN (V) 10 04873-013 149 15.2 148 4 12 15.5 152 15.4 151 15.3 15.2 10 12 150 149 04873-011 15.1 -50 8 VIN (V) Figure 13. Fast Charge VRS vs. Input Voltage VRS (mV) VRS (mV) Figure 10. Precharge VRS vs. Input Voltage 6 -25 0 25 50 75 TEMPERATURE (C) 100 148 -50 125 Figure 11. Precharge VRS vs. Temperature 04873-014 VRS (mV) ADP2291 -25 0 25 50 75 TEMPERATURE (C) 100 125 Figure 14. Fast Charge VRS vs. Temperature 160 16 140 14 VRS (mV) 12 100 80 10 8 100 1k RADJ (k) 40 100 10k Figure 12. Precharge VRS vs. RADJ 04873-015 60 04873-012 VRS (mV) 120 1k RADJ (k) Figure 15. Fast Charge VRS vs. RADJ Rev. A | Page 8 of 20 10k ADP2291 135 CH1 = VBAT 4.18V OFFSET 130 BASE DRIVE (mA) 1 125 CH2 = VIN 5V OFFSET VIN = 5V TO 8V 04873-016 120 4 6 8 VIN (V) 10 2 04873-018 115 12 CH1 10.0mV BW CH2 1.00V Figure 16. Base Drive vs. Input Voltage BW M200s CH2 6.18V Figure 18. Line Transient Response IBAT = 350 mA 122 120 CH1 = VBAT 4.18V OFFSET 1 116 114 112 110 108 106 104 -40 -20 0 20 40 60 TEMPERATURE (C) 80 04873-019 CH3 = IBAT 200mA/DIV IBAT = 70mA TO 700mA 04873-017 BASE DRIVE (mA) 118 3 CH1 20.0mV BW CH3 10.0mV 100 M100s CH3 Figure 19. Load Transient Response VIN = 5 V Figure 17. Base Drive vs. Temperature VIN = 5 V Rev. A | Page 9 of 20 10.0mV ADP2291 THEORY OF OPERATION The ADP2291 is intended to charge a single-cell, lithium battery from a supply voltage or wall adapter providing 4.5 V to 12 V. The charge controller adjusts the base current of an external PNP transistor to optimize current and voltage applied to the battery during charging. A low value resistor placed in series with the battery charging current provides current measurement for the ADP2291. CHARGE RESTART To ensure safety and long battery lifetime, the ADP2291 charges the battery using a simple step-by-step cycle, as shown in Figure 26. The normal charge cycle begins by measuring the battery voltage to determine charge level. If the battery is deeply discharged, then low current precharge is initiated. Once precharge is complete, normal fast charge at the maximum current (denoted as IMAX) begins. This maximum current can be adjusted by varying the sense resistor value or by varying the voltage at the adjust pin. As the battery approaches full capacity, the charging current is reduced until the end-of-charge condition is reached. Batteries that are not deeply discharged skip the precharge mode and immediately begin fast charging. Each of these modes and associated fault conditions is discussed in detail. PROGRAMMABLE TIMER PRECHARGE MODE For deeply discharged cells, the ADP2291 charges at a reduced rate when the battery voltage VBAT < 2.8 V. This reduced rate is IMAX/10 when the ADJ pin voltage is 3 V and IMAX/5 when the ADJ pin voltage is 1.5 V. For ADJ pin voltages in between 3 V and 1.5 V, the charge current can be interpolated. If the battery voltage does not increase past 2.8 V before the precharge timer elapses (typically 30 minutes), a battery fault is assumed and the ADP2291 shuts down and does not restart until the input voltage is cycled off and then back on. Note that in this mode, shutdown commands are ignored. Once the charge is complete in the end-of-charge or timeout mode, the ADP2291 continually monitors the cell voltage and charge current. When the cell voltage falls by 100 mV or the charge current increases beyond the EOC hysteresis, the ADP2291 initiates another charge cycle to keep the cell fully charged. See Figure 26. The on-chip timer, controlled by an external capacitor CTIMER, determines the timeout intervals of the various charger modes. For example, a CTIMER value of 0.1 F results in a precharge timeout interval of 30 minutes, a fast charge timeout of 3 hours, and an end-of-charge timeout of 30 minutes. The ratio between precharge and end-of-charge to fast charge timeout is always 1/6. All these time intervals are proportional to the CTIMER capacitor value, allowing them to be adjusted over a wide range. Connecting the TIMER pin to ground disables the timer. CHARGE STATUS INDICATOR The ADP2291 contains a charge status output, CHG, that sinks current when the ADP2291 is charging the battery. This output can be used as a visual signal by connecting it to an LED, or it can be used to generate a logic-level charge status signal by connecting a resistor between CHG and logic high. AUTOMATIC REVERSE ISOLATION When the voltage on the BAT pin is higher than the voltage on IN, the ADP2291 automatically connects the base of the pass device to BAT. This removes the necessity of having an external diode between the pass device and battery, further reducing the charger's footprint and component count. END-OF-CHARGE MODE OVERSHOOT PROTECTION Once the voltage loop reduces the charge current to 1/10 of its nominal value, IMAX (irrespective of the ADJ voltage), the ADP2291 detects the end-of-charge (EOC) state, and the charge status indicator becomes high impedance. In the event of a battery disconnect during charging, a voltage overshoot condition on BAT could occur. The ADP2291 includes an overshoot protection circuit that activates when VBAT rises to 5 V and sinks up to 1.5 A to protect the external components. Low level charging continues until the timer terminates the charge (nominally 30 minutes). POWER SUPPLY CHECKS SHUTDOWN MODE When the ADJ input is pulled below 0.4 V, the ADP2291 is put into shutdown mode. When in this mode, the charger is disabled; the current drawn from the battery falls to less than 1 A; and the current drawn from IN falls to 0.7 mA. When the charger is re-enabled, the charger returns to the start state but quickly sequences through the states until the proper charge mode is reached. To ensure proper operation, the ADP2291 checks the absolute voltage level of the input supply and the supply voltage relative to the battery. When the supply IN is below 3.8 V, the chip is internally powered down and does not respond to external control. In this power-down mode, the device draws less than 1 A from the battery. The VIN good comparator halts operation if the supply voltage is less than 165 mV above the battery voltage, ensuring that charging occurs only if the supply voltage is sufficient. Rev. A | Page 10 of 20 ADP2291 THERMAL SHUTDOWN A 35C temperature hysteresis is included so that the ADP2291 does not return to operation during thermal shutdown until the on-chip temperature drops below 100C. If the ADP2291 junction temperature rises above 135C, thermal shutdown occurs. Extreme junction temperatures can be the result of excessive current operation and/or high ambient temperatures. IN CS DRV BAT 3V 5V GM GM GM ADJ 1.2V VOLTAGE REFERENCE TEMP SHUTDOWN RESTART 0.4V IN 4.1V VIN_GOOD BAT IN BAT CONTROL LOGIC PRECHARGE BAT 2.5V POWER_DOWN 3.8V C/10 CHG END_OF_CHARGE TIMER TIMER Figure 20. Functional Block Diagram Rev. A | Page 11 of 20 04873-020 IPNP ADP2291 APPLICATION INFORMATION SETTING THE MAXIMUM CHARGE CURRENT SETTING THE MAXIMUM CHARGE TIME The maximum charge current is set by choosing the proper current sense resistor, RS, and the voltage on the ADJ input. The charger nominally regulates its output current at the point where the voltage across the current sense resistor VIN - VCS (defined as VRS) is 150 mV. This setpoint voltage can be adjusted by pulling down on the ADJ input, which is internally attached through a 100 k pull-up resistor to 3 V. Each volt of pull-down from 3 V reduces VRS by 67 mV during fast charge. A minimum of 50 mV is reached when a 100 k resistor is attached between ADJ and ground. During slow charge, the voltage across the current sense resistor is 15 mV with no connection to ADJ, and it drops to 10 mV with a 100 k resistor attached to ground. Therefore, the maximum charge rate IMAX is calculated as The maximum charge time is intended as a safety mechanism to prevent the charger from trickle charging the cell indefinitely. It does not terminate charging under normal charging conditions, but only when there is a failure to reach end-of-charge. A typical cell charges at a 1 C rate in about 1.5 hours, depending on the cell type, temperature, and manufacturer. Generally, a three-hour time limit is sufficient to prevent a normal charge cycle from being interrupted by the charge timer. It is recommended that the cell manufacturer be consulted for timing details. I MAX CTIMER = tCHG(minutes) x V (mV) = RS RS (m) (1) where 50 mV VRS 150 mV. After determining suitable values for VRS and RS, the value of VADJ and RADJ are calculated as VADJ = VRS (mV ) + 50 mV V 66.7 mV (2) VADJ RADJ = 100 k x 3 V - VADJ (3) Examples of resistor combinations are shown in Table 4. Table 4. Examples of RS and RADJ Selection IMAX 1.5 A 1A 750 mA 500 mA 750 mA 500 mA 375 mA 250 mA 500 mA 333 mA 250 mA 167 mA RS m 100 100 100 100 200 200 200 200 300 300 300 300 The maximum charge time is set by selecting the value of the CTIMER capacitor. Calculate the timer capacitance using VRS mV 150 100 75 50 150 100 75 50 150 100 75 50 VADJ V 3 2.25 1.87 1.5 3 2.25 1.87 1.5 3 2.25 1.87 1.5 RADJ Open 300 K 167 K 100 K Open 300 K 167 K 100 K Open 300 K 167 K 100 K 1 F 1800 minutes (4) The precharge and end-of-charge periods are 1/6 the duration of the fast charge time limit. The charge timers are completely disabled by connecting the TIMER pin to ground. If the timers are disabled, the FAULT and TIMEOUT states are never reached, so the timers should only be disabled if charging is monitored and controlled externally. EXTERNAL CAPACITORS Use an input supply capacitor (CIN) with a value in the 1 F to 10 F range and place it close to the ADP2291. This should provide adequate input bypassing, but the selected capacitor should be checked in the actual application circuit. Check that the input voltage does not droop or overshoot excessively during the start-up transient. Use a battery output capacitor (COUT) with a value of at least 10 F. This capacitance provides compensation when no battery load is present. In addition, the battery and interconnections appear inductive at high frequencies and must be accounted for when the charger is operated with a battery load. Therefore, a small amount of output capacitance is necessary to compensate for the inductive nature of the battery and connections. Use a minimum output capacitance value of 1 F for applications where the battery cannot be removed. REVERSE INPUT PROTECTION The Diode D1, shown in Figure 22 through Figure 25, is optional. It is required only if the input adapter voltage can be applied with a reverse polarity. If the adapter voltage is high enough, a Schottky diode is recommended to minimize the voltage difference from the adapter to the charger input and the power dissipation. Choose a diode with a continuous current rating high enough to handle battery charging current at the maximum ambient temperature. Use a diode with a voltage rating greater than the maximum adapter voltage. Rev. A | Page 12 of 20 ADP2291 In cases where the voltage drop across the protection device must be kept low, a P MOSFET is recommended. Connect the MOSFET as shown in Figure 21. The power handling capability of the PNP pass transistor is another important parameter. The maximum power dissipation of the pass transistor is estimated using RS INPUT 4.6V-12V PDISS (W) = IMAX x (VADAPTER(MAX) - VPROTECT - VRS - VBAT) (7) CIN CS where VRS = 50 mV to 150 mV at VADJ = 1.5 V to 3.0 V, VBAT = 2.8 V, the lowest cell voltage where fast charge can occur. DRV IN 04873-021 ADP2291 CHG Figure 21. Reverse Input Protection EXTERNAL PASS TRANSISTOR Choose the external PNP pass transistor based on the given operating conditions and power handling capabilities. The pass device is determined by the base drive available, the input and output voltage, and the maximum charge current. Select the pass transistor with a collector-emitter breakdown voltage that exceeds the maximum adapter voltage. A VCEO rating of at least 15 V is recommended. Note that the adapter voltage can be either preregulated or unregulated. In the preregulated case, the difference between the maximum and minimum adapter voltage is small. In this case, use the maximum regulated adapter voltage to determine the maximum power dissipation. In the unregulated case, the adapter voltage can have a wide range specified. However, the maximum voltage specified is usually with no load applied. Therefore, the worst-case power dissipation calculation often leads to an over-specified pass device. In either case, it is best to determine the load characteristics of the adapter to optimize the charger design. For example: VADAPTER(MIN) = 5.0 V VADAPTER(MAX) = 6.0 V IMAX = 500 mA VPROTECT = 0.2 V at 500 mA VADJ = 3 V VRS = 150 mV Providing a charge current of IMAX with a minimum base drive of 40 mA requires a PNP beta of at least MIN = IMAX = IMAX I 40 mA (5) Note that the beta of a transistor drops off with collector current. Therefore, make sure the beta at IMAX meets the minimum requirement. MIN = IMAX = 500 mA = 12.5 I 40 mA VCE(SAT) = VADAPTER(MIN) - VPROTECT - VRS - VBAT = 5.0 V - 0.2 V - 0.15 V - 4.2 V = 0.45 V For cases where the adapter voltage is low (less than 5.5 V), calculate the saturation voltage by VCE(SAT) = VADAPTER(MIN) - VPROTECT - VRS - VBAT (6) PDISS (W) = IMAX x (VADAPTER(MAX) - VPROTECT - VRS - VBAT) = 0.50 A x (6.0 V - 0.2 V - 0.15 V - 2.8 V) = 1.4 W where VPROTECT is the forward drop of the reverse input protection. A guide for selecting the PNP pass transistor is shown in Table 5. Table 5. PNP Pass Transistor Selection Guide Vendor Fairchild ON Semiconductor(R) Philips ZETEX Part Number FSB6726 NZT45H8 MTB35200 BCP53T1 MMJT9435 BCP51 ZXT10P20DE6 ZXT2M322 FZT549 FMMT549 Package SuperSOT SOT223 TSOP-6 SOT223 SOT223 SOT223 SOT23-6 2 mm x 2 mm MLP SOT223 SOT23 Rev. A | Page 13 of 20 Max PD @ 25C 0.5 W 1.5 W 0.625 W 1.5 W 1.6 W 1.3 W 1.1 W 1.5 W 2W 0.5 W Beta @ 1 A 150 110 200 35 200 50 270 270 130 130 VCE (SAT) 0.5 V 0.1 V 0.175 V 0.3 V 0.18 V 0.5 V 0.17 V 0.17 V 0.25 V 0.25 V ADP2291 TYPICAL APPLICATION CIRCUIT INPUT 4.6V-12V D1 BAT1000 RS 200m Q1 FZT549 + CIN 2.2F CS IN RS 200m BAT CHG Q1 FZT549 GND CS COUT 10F DRV IN ADJ R2 100k CTIMER 100nF + CIN 2.2F LI-ION CELL ADP2291 TIMER D1 BAT1000 COUT 10F DRV Q2 2N7002 LOW/HIGH 04873-024 A typical application circuit is shown in Figure 22. The circuit is capable of a 750 mA charge current for an input voltage of 4.5 V to 6 V. Higher input voltages can be used, but the increased power dissipation of the pass device must be taken into account. INPUT 4.6V-12V BAT ADP2291 CHG Figure 24. Selectable Charge Current Circuit GND ADJ CTIMER 100nF Figure 22. Typical Application Circuit CHARGE TERMINATION In some applications, the charger is required to terminate charging when the EOC threshold is reached. Automatic charger restart is not desired. Adding components R1, C1, and Q2 terminates charging when the CHG pin opens and prevents further charging until the adapter is removed and reasserted. INPUT 4.6V-12V D1 BAT1000 RS 200m THERMAL PROTECTION In applications where the overall size must be small or the input voltage range is wide, adding thermal regulation is suggested. This allows the charger to monitor the temperature of the pass device and decrease the charge current as the temperature increases. By adding an NTC thermistor to the ADJ pin, it is possible to accomplish this; however, care is still required to ensure that the power dissipation of the pass device is not exceeded. INPUT 4.6V-12V Q1 FZT549 CS R1 500k COUT 10F DRV IN RS 200m Q1 FZT549 + CIN 2.2F + CIN 2.2F D1 BAT1000 LI-ION CELL CS BAT CHG GND TIMER GND CTIMER 100nF ADJ CTIMER 100nF ADJ R1 470k NTC LOCATED NEAR Q1 R2 100k 04873-023 C1 100nF Q2 2N7002 LI-ION CELL ADP2291 BAT TIMER DRV IN ADP2291 CHG COUT 10F 04873-025 04873-022 TIMER Figure 25. Thermal Regulation Circuit Figure 23. Self-Termination Circuit Some suggested NTC thermistor suppliers are listed in Table 6. SELECTABLE CHARGE CURRENT Table 6. NTC Thermistor Manufacturers In applications where the charge current needs to be selectable, use the circuit shown in Figure 24. This circuit allows a processor to determine if the charge current needs to be reduced due to an input source limitation or a different battery capacity option or simply to reduce the stress on the pass transistor. R2 and Q2 allow the charge current to be selected between high, which results in a charge current of 750 mA; and low, which results in a charge current of 250 mA. Vendor BetaTHERM Murata Panasonic Vishay Rev. A | Page 14 of 20 Part Number SMD2500KJ435J NCP18WM474J ERTJ0EV474J 2322 615 1.474 Website www.betatherm.com www.murata .com www.panasonic.com www.vishay.com ADP2291 VIN < 3.8V FROM ANYWHERE ASYNCHRONOUSLY POWER-DOWN VRS = 0mV CHG = OPEN VIN > 3.8V START VRS = 0mV CHG = OPEN START SEQUENCE ENDS VBAT > 2.8V PRECHARGE VRS = 15mV CHG = LOW VBAT < 2.8V FAST CHARGE VRS = 150mV CHG = LOW IPNP < C/10 AND VBAT > 4.1V T = 30 MIN VBAT < 4.1V OR IPNP > C/10 VADJ < 0.4V BATTERY FAULT VRS = 0mV CHG = OPEN END OF CHARGE VRS = 15mV CHG = OPEN T = 3 HOUR T = 30 MIN VADJ < 0.4V SHUTDOWN VRS = 0mV CHG = OPEN VADJ < 0.4V TIME OUT VRS = 0mV CHG = OPEN TEMP > 135C FROM ANYWHERE ASYNCHRONOUSLY Figure 26. State Diagram for the ADP2291 CTIMER = 0.1 F Rev. A | Page 15 of 20 VBAT < 4.1V 04873-026 VADJ > 0.4V AND TEMP < 100C ADP2291 PRINTED CIRCUIT BOARD LAYOUT CONSIDERATIONS Note that the via diameter is small to prevent the solder from flowing through the via and leaving voids in the thermal pad solder joint. Use the following general guidelines when designing printed circuit boards: * Keep the output capacitor as close to the BAT and GND pins as possible. * Keep the input capacitor as close to the IN and GND pins as possible. * PC board traces with larger cross-sectional areas remove more heat from the pass transistor. For optimum heat transfer, specify thick copper and use wide traces. * Use additional copper layers or planes to reduce thermal resistance. When connecting to other layers, use multiple vias if possible. Note also that the thermal pad is attached to the die substrate; therefore, the thermal planes to which the vias attach the package must be electrically isolated or connected to GND. * The solder mask opening should be about 120 microns (4.7 mils) larger than the pad size, resulting in a minimum of 60 microns (2.4 mils) clearance between the pad and the solder mask. * The paste mask opening is typically designed to match the pad size used on the peripheral pads of the LFCSP package. This should provide a reliable solder joint as long as the stencil thickness is about 0.125 mm. The paste mask for the thermal pad needs to be designed for the maximum coverage to effectively remove the heat from the package. However, due to the presence of thermal vias and the size of the thermal pad, eliminating voids may not be possible. * The recommended paste mask stencil thickness is 0.125 mm. Use a laser cut stainless steel stencil with trapezoidal walls. * Use a no-clean, Type 3 solder paste for mounting the LFCSP package. A nitrogen purge during the reflow process is recommended. * The package manufacturer recommends that the reflow temperature not exceed 220C and the time above liquidus be less than 75 seconds. Make sure the preheat ramp is 3C/second or lower. The actual temperature profile depends on the board's density and should be determined by the assembly house. LFSCP LAYOUT CONSIDERATIONS The LFCSP package has an exposed die paddle on the bottom that efficiently conducts heat to the PCB. To achieve the optimum performance from the LFCSP package, give special consideration to the layout of the PCB. Use the following layout guidelines for the LFCSP package: * The pad pattern is shown in Figure 27. Follow the pad dimension closely for reliable solder joints, while maintaining reasonable clearances to prevent solder bridging. * The thermal pad of the LFCSP package provides a low thermal impedance path (approximately 20C/W) to the PCB; therefore, a properly designed PCB effectively conducts the heat away from the package. This is achieved by adding thermal vias to the PCB that provide a thermal path to the inner or bottom layers. Table 7. Variables Description 2x VIAS, 0.250 35m PLATING Variable Name VX VRS 0.73 0.30 1.80 0.90 2.36 VBAT, EOC 0.50 IMAX 1.40 3.36 C rate 04873-027 1.90 Figure 27. 3 mm x 3 mm LFCSP Pad Pattern (Dimensions in millimeters) Rev. A | Page 16 of 20 Description The voltage on Pin X. The regulation setpoint for the voltage across the sense resistor (RS). The battery voltage at the point charging current is 1/10 the current setpoint. The charge current corresponding to VRS, including the effects of ADJ pin voltage. The charge current (mA) expressed as a multiple of the nominal battery capacity (mAh). A 900 mAh capacity battery, charged at a 1/10 C rate, is equivalent to a 90 mA charge current. ADP2291 OUTLINE DIMENSIONS 3.00 BSC SQ 0.50 0.40 0.30 0.60 MAX 1 8 PIN 1 INDICATOR 0.90 MAX 0.85 NOM 2.75 BSC SQ TOP VIEW 0.50 BSC 1.50 REF 1.89 1.74 1.59 4 5 1.60 1.45 1.30 0.70 MAX 0.65 TYP 12 MAX PIN 1 INDICATOR 0.05 MAX 0.01 NOM SEATING PLANE 0.30 0.23 0.18 0.20 REF Figure 28. 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] 3 mm x 3 mm Body, Very Thin, Dual Lead (CP-8-2) Dimensions shown in millimeters 3.20 3.00 2.80 8 3.20 3.00 2.80 5 1 5.15 4.90 4.65 4 PIN 1 0.65 BSC 0.95 0.85 0.75 1.10 MAX 0.15 0.00 0.38 0.22 0.23 0.08 COPLANARITY 0.10 0.80 0.60 0.40 8 0 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 29. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters ORDERING GUIDE Model ADP2291ARMZ-R71 ADP2291ACPZ-R71 ADP2291-EVAL 1 Temperature Range -40C to +85C -40C to +85C Package Description 8-Lead MSOP 8-Lead LFCSP_VD Evaluation Board Z = Pb-free part. Rev. A | Page 17 of 20 Package Option RM-8 CP-8-2 Branding P08 P08 ADP2291 NOTES Rev. A | Page 18 of 20 ADP2291 NOTES Rev. A | Page 19 of 20 ADP2291 NOTES (c) 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04873-0-11/05(A) Rev. A | Page 20 of 20