DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting General Description Features The AAT1451 is a highly integrated, high efficiency LED backlight solution for notebook, netbook computers, monitors and portable TVs. The device operates from DC inputs, cigarette adapters and single to multi-cell Li-ion batteries in the voltage range from 2.7V to 26V. * VIN Range: 2.7V to 26V * Integrated 50V Boost Converter Maximum IOUT: 120mA Programmable Switching Frequency * 600kHz to 1MHz Up to 93% Efficiency High Efficiency Light-Load Mode * Four White LED Strings Programmable Max Current Sink up to 30mA Each 2% Accuracy (22mA) 1.5% Matching (22mA) * Direct PWM Dimming Automatic Phase Shifting Fast Turn-On/Off * Integrated Fault Protection for Independent Disable of Open/Shorted LED(s) String(s) Over-Voltage Over-Temperature * FAULT Indication for Shorted LED(s) and OverTemperature * Soft-Start Minimizes Inrush Current * TDFN34-16 Low Profile Package * -40C to +85C Temperature Range An integrated boost (step-up) converter provides a high voltage output up to 50V for driving series LEDs. Four precision current sinks are programmable up to 30mA per string through one external RSET resistor, supporting up to 481 white LEDs at 120mA total output current. The boost output voltage is determined by the highest total forward voltage of the LED strings, allowing for a wide range of LED characteristics. Each string is PWM dimmed with 90 degree phase shift to minimize ripple currents, and filter capacitor sizes. The PWM input frequency range is 100Hz to 10kHz with a dimming range of 256:1. The integrated boost regulator switching frequency is programmable from 600kHz to 1MHz by external resistor for optimum efficiency and the smallest external L/C filtering components. Boost current mode control provides fast response to line and load transients. Integrated light-load mode ensures highest efficiency across the entire load range. Fault tolerant circuitry extends system life by disabling open and shorted LED(s) strings. The unique high voltage current sinks prevent damage resulting from shorted LEDs. The FAULT pin indicates the presence of shorted LEDs or over-temperature conditions. Applications * * * * Tablets Notebook and Netbook Computers Portable Media Players Monitors The AAT1451 is available in a Pb-free, thermally enhanced 16-pin 3x4 TDFN package. 1. The maximum number of LEDs in each string is dependent upon the maximum VF of the diodes in that string. Under no event should the absolute maximum voltage at SW be exceeded. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 1 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Typical Application Circuit (VIN = 2.7V) VIN = 2.7-26V L1 4.7H D1 Up to 48 WLEDs VOUT: 45V at 120mA R1 CIN 2.2F/ 50V VIN SW COUT 2.2F/50V OVP R2 AAT1451 TDFN34-16 5V VDD CVDD 2.2F/6.3V C (GPIO) CCOMP FB1 FB2 FB3 FB4 SHDN PWM COMP VDD ISET RSET RCOMP R3 FSLCT RFS FAULT PGND GND Typical Application Circuit (VIN = 5.0V) VIN = 5V-26V L1 4.7H Up to 48 WLED Backlight D1 VOUT = 45V at 120mA COUT 2.2F/ 50V R1 CIN 2.2F/ 50V CVDD 2.2F/ 6.3V VIN VDD SW AAT1451 TDFN34-16 SHDN C (GPIO) FB1 FB2 FB3 FB4 PWM COMP CCOMP RCOMP 2 OVP ISET RSET FSLCT RFS R2 VDD R3 FAULT GND Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Pin Descriptions Pin # Symbol Function 1 2 3 4 5 6 7 8 PGND VIN FSLCT ISET FB1 FB2 FB3 FB4 GND I I I O O O O 9 FAULT O 10 VDD I/O 11 PWM I 12 SHDN I 13 COMP I 14 15 AGND OVP AGND I 16 SW O EP PGND Description Power Ground. Connect to GND underneath the IC. Input voltage to IC. Tied to input voltage source and input boost inductor. Connect an external resistor to set boost switching frequency from 600kHz to 1MHz. Connect resistor to ground to set maximum current up to 30mA through the LED strings. Output current sink 1. Connect to GND to disable channel 1. Output current sink 2. Connect to GND to disable channel 2. Output current sink 3. Connect to GND to disable channel 3. Output current sink 4. Connect to GND to disable channel 4. Open drain FAULT signal. Pull up to VDD with external resistor. Low indicates a shorted LED condition. Internal regulated voltage when operating from input voltage range 5.0V to 26.0V. De-couple with a 2.2F capacitor to ground. Do not source current from this node. Connect to 5.0V rail when operating from VIN less than 5.0V. PWM input pin. Connect logic level PWM input signal in the frequency range 100Hz-10kHz to this pin to enable PWM dimming. Logic high to enable the device. Logic low disables the device and minimizes quiescent current and also disables the internal linear regulator. Connect an external resistor in series with a capacitor to ground to compensate the boost converter. Connect to AGND Over-voltage protection pin. Connect to output of boost converter through a resistor divider. Switching node of boost converter. Connect an inductor between this pin and input voltage source. Connect the Schottky diode between this pin and boost output capacitor. Exposed paddle. Connect to PCB PGND plane. Input and output capacitor GND should connect to EP. Pin Configuration TDFN34-16 (Top View) PGND VIN FSLCT ISET FB1 FB2 FB3 FB4 1 16 2 15 3 14 4 13 5 12 6 11 7 10 8 9 SW OVP GND COMP SHDN PWM FAULT VDD Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 3 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Absolute Maximum Ratings1 Symbol VSW VIN VFBx VDD, VFAULT SHDN, COMP, PWM, ISET, FSLCT, OVP IOUT TJ TLEAD PD JA Description Value Voltage to GND Input Voltage to GND Output Current Sinks FB1 - FB4 to GND Low Voltage Pin to GND Voltage to GND Units 50 -0.3 to 30 -0.3 to 40 -0.3 to 7.0 V -0.3 to VDD + 0.3 Maximum DC Output Current Maximum Junction Operating Temperature Maximum Soldering Temperature (at leads, 10 sec.) Maximum Power Dissipation3 Thermal Resistance3,4 2 134 -40 to +150 300 2 50 mA O O C W C/W Recommended Operating Conditions Symbol VIN VOUT FPWM TA TJ Description Input Voltage Range Output Voltage Range PWM Dimming Frequency Range Operating Ambient Temperature Operating Junction Temperature Value 5 to 26 VIN + 3 to 45 0.1 to 10 -40 to 85 -40 to 130 Units V kHz O C 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. 2. Based on long-term current density limitation. 3. Mounted on an FR4 board. 4. Derate 20mW/C above 25C. 4 Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Electrical Characteristics1 VIN = 12V; CIN = 2.2F, COUT = 2.2F; CVDD = 2.2F; L1 = 4.7H; RSET =7.5k (IFBx = 22mA); RFSCLT = 20k; TA = -40C to 85C unless otherwise noted. Typical values are at TA = 25C. Symbol Description Conditions Power Supply, Current Sinks VIN Input Voltage Range VUVLO Under-Voltage Threshold VDD VDD Output Voltage VFBx Current Sink Voltage VFBx(SHORT) IQ FOSC FPWMI(MAX) FPWMO(MAX) TSS 26.0 4.3 V V mV V V 500 3.2 4.0 4.5 6.0 0.3 V 5 V FB1-FB4 = Open, SHDN= Logic low FB1-FB4 = Open, SHDN = VPWM = Logic low, does not include SW leakage current IFBx = 22mA, TA = 25C 3 mA -5 IFBx= 22mA VOUT Rising VOUT Falling VDD = 4.5V Current Sink Accuracy Current Matching Between Any Sink Channel Over Voltage Threshold Over Voltage Hysteresis Low Side Switch ON Resistance Maximum Duty Cycle Minimum On-Time Voltage at ISET Voltage at FSCLT Current Set Ratio Low Side Switch Current Limit SW Pin Leakage FBx Pin Leakage Oscillator Frequency Maximum Input PWM Frequency1 Maximum Output PWM Frequency Soft-Start Time ILEAK Units IFBx= 30mA IFBx RDS(ON)LO DMAX TMIN VISET VFSCLT IFBx / IRSET ILIMIT 5.0 VIN Rising Hysteresis VIN Falling SHDN = Logic High, IDD(OUT) = 0mA SHDN = Logic High, IFBx = 22mA (RSET = 7.5k) Max IN Quiescent Current IN Pin Shutdown Current VOVP Typ Shorted Diode(s) Detection Threshold ISD IFBx-Matching Min 40.0 A 2 +5 % -2 1.5 +2 % 1.1 1.2 100 500 1.3 V mV m % ns V V A/A A A A kHz Hz Hz ms 90 IFBx/IISET , VISET = 0.6V VIN = 5.0V to 26.0V SHDN = Logic Low, VSW = 45V VFBx = 30V, VPWM = logic high RFS = 20k 100 0.6 0.6 264 3.0 850 100 6750 VOUT = 35V, CCOMP = 18nF, RCOMP = 10k 1000 8000 1.5 5.0 1 10 1150 10000 9250 Logic Level Inputs: SHDN, PWM VLSHDN SHDN Threshold Low VL PWM Threshold Low VH PWM and SHDN Threshold High ILK DPWMI SHDN, PWM Input Leakage Current Input PWM Duty Cycle 0.4 V 0.8 V 99 A % 0.4 1 V A 2.2 VPWM = VSHLD = VDD V 10 0 FAULT Output VFAULTLOW FAULT Logic Output Low IFAULT FAULT Leakage Current Thermal Protection TJ(SD) TJ Thermal Shutdown Threshold TJ(SD-HYS) TJ Thermal Shutdown Hysteresis ISINK = 1mA VFAULT = 3.3V, No Faults Maintains previous dimming setting 150 15 C C 1. The AAT1451 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Output voltage must result in a voltage lower than the SW maximum ratings under all operating conditions. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 5 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Typical Characteristics Boost Efficiency vs Input Voltage Boost Efficiency vs Load Current (L = 4.7H; VDD = 5V; PWM = 5V; IOUT = 30mA/ch) 100 100 90 90 80 80 Efficiency (%) Efficiency (%) (L = 4.7H; VDD = 5V; PWM = 5V;IOUT = 30mA/ch) 70 60 50 40 VOUT = 40V 30 70 60 50 40 VIN = 12 V; VOUT = 40 V 30 VIN = 12 V; VOUT = 28 V VIN = 26 V; VOUT = 40 V 20 VOUT = 28V 10 20 6 8 10 12 14 16 18 20 22 24 26 0 30 60 Input Voltage (V) 210 240 270 300 (VIN= 12V; IOUT= 30mA/ch) Output Current (mA) 90 Efficiency (%) 180 120 100 80 70 60 VIN = 12 V; VOUT = 40V 50 VIN = 26 V; VOUT = 40V 40 VIN = 26 V; VOUT = 28V 30 0 10 20 30 40 50 60 70 80 90 100 80 60 40 20 0 100 0 20 PWM Duty Cycle (%) 40 60 80 100 Duty Cycle (%) UVLO vs Temperature Current Limit vs Temperature 4.4 3.95 4.2 3.9 4 3.85 Current Limit (A) UVLO (V) 150 Output Current vs PWM Duty Cycle (L = 4.7H; VDD = PWM = 5V; IOUT = 30mA/ch) 3.8 3.6 3.4 3.2 UVLO Rising 3 UVLO Falling -40 -15 10 35 Temperature (C) 60 3.8 3.75 3.7 3.65 3.6 3.55 2.8 6 120 Output Current (mA) Boost Efficiency vs PWM Duty Cycle 20 90 85 3.5 -40 -15 10 35 60 Temperature (C) Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 85 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Typical Characteristics Quiscent Current vs Input Voltage VDD Line Regulation vs Input Voltage (Non-Swtiching) 4.7 4.65 3.4 4.6 3.3 3.2 VDD (V) Quiescent Current (mA) 3.5 3.1 3 2.9 4.55 4.5 4.45 85C 4.4 2.8 85C 2.7 25C 4.35 2.6 -40C 4.3 25C -40C 6 2.5 6 8 10 12 14 16 18 20 22 24 8 10 26 16 14 12 10 8 25C 2 -40C 0 6 8 10 12 14 16 18 20 22 24 26 Switching Frequency Error(%) Shutdown Current (uA) 18 85C 1 0 -1 2 -3 -4 -40 -15 10 35 60 85 (VIN=12V; 30mA/ch) Current Sink Matching (%) Current Sink Accuracy (%) 26 Current Sink Matching vs Temperature 3 2 1 0 -1 -2 -3 -4 Temperature (C) 24 Temperature (C) 4 35 22 2 (VIN = 12V; 30mA/ch) 10 20 3 Current Sink Accuracy vs Temperature -15 18 (VIN = 12V) 4 Input Voltage (V) -40 16 Frequency vs Temperature Shutdown Current vs Input Voltage 4 14 Input Voltage (V) Input Voltage (V) 6 12 60 85 2 1.75 1.5 1.25 1 0.75 0.5 0.25 0 -40 -15 10 35 60 85 Temperature (C) Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 7 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Typical Characteristics Low Side Switch On Resistance vs Temperature Over Voltage Threshold vs Temperature VIN=12V 1.30 600 500 1.26 1.24 RDS(ON) (ms) OVP Threshold (V) 1.28 1.22 1.20 1.18 1.16 1.14 400 300 200 100 1.12 1.10 -40 -15 10 35 60 0 85 -40 -15 10 Temperature (C) Enable High Threshold Voltage vs. Input Voltage 1.4 1.4 1.3 1.3 Threshold Voltage (V) Threshold Voltage (V) 35 60 1.2 1.1 1.0 0.9 -40C 0.8 25C 0.7 85C 0.6 PWM, FSET Logic Low Threshold Voltage vs. Input Voltage 1.2 1.1 1.0 0.9 0.8 -40C 25C 0.7 85C 0.6 6 8 10 12 14 16 18 20 22 24 26 6 Input Voltage (V) Switching Waveforms (VIN = 12V; VOUT = 37V; IOUT = 80mA) VIN 50mV/div (AC) 8 10 12 14 16 12 20 Start UP VOUT 5V/div IOUT 50mA/div IL 0 500mA/div Time (400ns/div) 8 24 26 (VIN = 12V; VOUT = 40V; IOUT = 65mV; Duty Cycle = 50%) VSHDN IL 1A/div 22 Input Voltage (V) 20V/div VOUT 50mV/div (AC) 85 Temperature (C) Time (2ms/div) Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET PRODUCT DATASHEET AAT1451 AAT1451 SwitchRegTM Four LED Strings, Strings-High Efficiency White White LED LED Driver Driver for for LCD LCD Backlighting Backlighting Four-LED High Efficiency Typical Characteristics PWM Switching Waveforms PWM Switching Waveforms (VIN = 12V; VOUT = 40V; Duty Cycle = 30%) (VIN = 12V; VOUT = 40V; Duty Cycle = 80%) 60 VOUT (AC) 200mV/div 40 VOUT (AC) 200mV/div 5V VPWM 5V/div 0V IOUT 50mA/div 50mA IL 500mA/div 20 VPWM 5V/div 5V 0V 0 IOUT -20 50mA/div 100mA 0mA -40 50mA 500mA -60 500mA 0mA IL -80 500mA/div 0mA -100 Time (200s/div) Time (200s/div) PWM Switching Waveforms (VIN = 12V; VOUT = 40V; Duty Cycle = 50%) VOUT (AC) 200mV/div VPWM 5V/div 5V 0 0V 1.5 100mA IOUT 50mA/div -40 50mA 1.0 -60 500mA 0.5 IL -80 500mA/div 0.0 0mA -100 -0.5 Time (200s/div) Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 9 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Functional Block Diagram VIN SW Linear Reg VDD FB1 SHDN OVP VREF FB2 COMP Logic PWM FB3 FB4 Osc FSLCT PGND GND FAULT Functional Description The AAT1451 adopts a synchronous peak current detect step-up structure to drive up to 48 white LEDs with up to 30mA each (120mA total) for backlight solutions. The controller derives output feedback from the lowest sink voltage of the four LED sink channels while maintaining the programmed current accuracy and matching. This ensures the lowest possible output voltage, highest efficiency, and continuous operation with mismatched LED strings. LED dimming is controlled by an external 100Hz to 10kHz PWM signal. The LED current is on/off with fixed frequency of 8kHz with the same duty cycle as the PWM signal. This feature, together with the phase shifting feature, makes it easy to filter the LED current switching noise on the output when designing the system. The AAT1451 is designed for maximum flexibility allowing unused current sinks to be disabled by connecting them to ground. The unique high voltage current sinks support non-matching LED strings (LED quantity, type, etc.) 10 RSET The boost switching frequency is programmable from 600kHz up to 1MHz by external resistor for optimum efficiency and the smallest external filter components. Current mode control provides fast response to line and load transients. Integrated light-load mode ensures highest efficiency across the entire input voltage and load range. The AAT1451 integrates several fault protection features to deal with LED opens/shorts and thermal faults. Fault tolerant circuitry extends system life by disabling current sinks with open LEDs. The high voltage current sinks maintain normal operation with non-matched strings while also preventing damage due to shorted LEDs. When all LED sinks are open, the over voltage protection is active to prevent the boost output voltage from becoming too high by disabling power MOSFET switching when the OVP voltage threshold is exceeded. Boost switching is re-enabled when OVP hysteresis is satisfied. Over-current protection prevents inductor saturation and any resulting damage to the switching device occurring during an overload fault condition. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Boost Converter Switching Frequency The RSET value can be calculated as follows: The AAT1451's boost converter frequency can be adjusted between 600kHz to 1MHz using an external resistor (RFS). For maximum accuracy, a 1% tolerance resistor is recommended. Please refer to Table 1 and Figure 1 for RFS resistor values. 2 * 1010 FSW RFS = RSET = CurrentSetRatio * VISET IFB Where CurrentSetRatio = 264 and VISET = 0.6V. For example, if the maximum current for each string LEDs is 30mA, this corresponds to a minimum resistor of 5.23 k. RSET = RFS (k) Frequency (kHz) 20 22 24 26 28 30 33 1000 909 833 769 714 667 606 Switching Frequency (kHz) Table 1: Examples of Standard 1% RFS Values for Setting Switching Frequency. 264 * 0.6V = 5.23k 30mA Maximum LED Current (mA) RSET (k) 30 25 22 20 15 5.23 6.34 7.5 7.87 10.5 Table 2: Examples of Standard 1% RSET Values for Setting Maximum LED Current Levels. Please also refer to Figure 2 for quickly choosing a RSET value. 40 35 ICSx (mA) 30 25 20 15 18 20 22 24 26 28 30 32 34 RFS (k) Figure 1: Switch Frequency vs. RFS Maximum LED Current Selection 10 5 4 5 6 7 8 9 10 11 12 13 14 RSET (k) Figure 2: Choosing an RSET Value The current sink is controlled by the internal reference voltage (VISET) and the external resistor (RSET) at the ISET pin. The maximum LED current programmable range is from 15mA to 30mA by RSET. For maximum accuracy, a 1% tolerance resistor is recommended. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 11 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting PWM Dimming The AAT1451 integrates a clock hunting circuitry to derive the external PWM signal duty cycle to generate same duty cycle LED current on/off between the maximum current value and 0mA with fixed 8kHz frequency. It can work bi-directionally when the PWM signal increases or decreases to determine the duty cycle. PWM Duty Cycle FB1 - FB4 Current (mA) (RSET = 7.5K) 100% 95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 22 20 19 18 17 16 15 14 13 12 11 9 8 7 6 5 4 3 2 1 PWM Duty vs WLED Current AAT1451 35 30 Current per Channel (mA) The AAT1451 uses a simple PWM interface to control the effective LED current (RMS) at the current sinks. The PWM signal should fit the requirements listed in the electrical characteristic table for proper operation. After initial power-up and SHDN is pulled to high together with PWM high, the device is enabled with 100% brightness as determined by the RSET resistor value. For example, when the PWM pin is constantly pulled high, which means 100% duty ratio, the current per channel is typically 30mA with RSET =5.3k. By feeding the PWM pin with a proper PWM signal, the RMS current of each sink is proportional to the duty ratio of the PWM signal. Table 3 shows the average LED current of each channel at maximum 22mA as the PWM duty cycle change. 25 20 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 PWM Duty Ratio(%) Figure 3: PWM Duty Cycle vs. LED Current at Maximum 30mA Setting. Automatic Phase Shift PWM The AAT1451 has implemented an automatic phase shift PWM mechanism for FB1-FB4 current sources. It will automatically detect the number of operating channels and phase shift each channel, "n", by n relative to the PWM input. The phase shift and delay time TD are defined as: n = 360 * (n - 1) N TD = TPWM N Where N is the number of operating channels, and n is the target channel. The FB1-FB4 timing diagram is shown in Figure 4 to elaborate the automatic phase shift working waveform. Table 3: AAT1451 PWM Duty Cycle vs. LED Current at Maximum 22mA Setting 12 Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Duty Cycle = 50% PWM Input ICS1 0 TD ICS2 90 2TD ICS3 180 3TD ICS4 270 Figure 4: AAT1451 Automatic Phase Shift PWM Timing Diagram Open LED Protection and FAULT Indication for Shorted LEDs The AAT1451 device is protected from faults arising from LED opens and shorts. An open LED(s) condition will be detected by the controller at startup. The low voltage is detected by the controller which disables the given current sink. The remaining LED strings continue to operate normally. The controller re-enables the disabled current sink in the event that the LED open condition is removed during a power cycle or SHDN cycle. This feature extends backlight life and reliability. Under the condition that PWM duty cycle is less than 100%, shorted LEDs condition results in a higher voltage appearing on the affected channels' current-sink pin. The affected current sink automatically compensates for the additional voltage. This current sink can withstand a high voltage indefinitely. However, the increased voltage across the current sink causes an increase in power dissipation. The AAT1451 automatically monitors the current sink voltage for two or more shorted LEDs. To prevent thermal shutdown, the shorted LED string is disabled while the remaining strings continue to operate. The shorted LED string remains disabled until a power cycle or SHDN cycle. The open drain FAULT output is driven low to indicate thermal shutdown and shorted LED condition(s). The FAULT output is latched low during shorted LED fault, and is reset after a power cycle, SHDN cycle or thermal shutdown. To prevent damage, the backlight can be shutdown based on the FAULT output. OVP Protection Under all conditions, the over-voltage protection circuitry prevents the switching node (SW) from exceeding the maximum operating voltage prior to disabling the current sink. Over-voltage protection (OVP) disables boost switching while maintaining the programmed LED current. Boost switching is re-enabled when OVP hysteresis is satisfied. Thermal Protection for Over-Current and Short-Circuit The AAT1451 has a built-in thermal protection circuit that goes into shutdown when the die temperature rises above the thermal limit, as is the case during a LED short-circuit condition. Integrated over-current limit protection is provided. Over-current prevents inductor saturation and any resulting damage to the switching device occurring during an overload fault condition. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 13 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Application Information LED Selection The AAT1451 is specifically intended for driving white LEDs. However, the device design will allow the AAT1451 to drive most types of LEDs with forward voltage specifications typically ranging from 2.2V to 4.7V depending upon supply voltage. LED applications may include mixed arrangements for display backlighting, keypad display, and any other application that needs a constant current sink generated from a varying input voltage. Since the FB1 to FB4 constant current sinks are matched within 2% with negligible supply voltage dependence, the constant current channels will be matched regardless of the specific LED forward voltage (VF) levels. The low dropout current sinks in the AAT1451 maximize performance and make it capable of driving LEDs with high forward voltages. Shutdown To activate the shutdown operation, the SHDN input for the AAT1451 should be strobed low. In this case, the AAT1451 typically draws less than 40A from the input. Inductor Selection The white LED boost (step-up) converter is designed to operate with a 4.7H inductor for all input and output voltage combinations. The inductor saturation current rating should be greater than the NMOS current limit. DMAX = VOUT + VD - VIN(MIN) VOUT + VD Compensation Component Selection The AAT1451 Main Boost architecture uses peak current mode control to eliminate the double pole effect of the output L&C filter and simplifies the compensation loop design. The current mode control architecture simplifies the transfer function of the control loop to be a one-pole, one left plane zero and one right half plane (RHP) system in frequency domain. The dominant pole can be calculated by: The ESR zero of the output capacitor can be calculated by: fZ_ESR = COUT is the output filter capacitor; RO is the equivalent load resistor value; RESR is the equivalent series resistance of the output capacitor. The right half plane (RHP) zero can be determined by: fZ_ESR = 14 IOUT D * VIN(MIN) + MAX 1 - DMAX 2 * FS * L VIN2 2 * L1 * IOUT * VOUT It is recommended to design the bandwidth to one decade lower than the frequency of RHP zero to guarantee the loop stability. A series capacitor and resistor network (RCOMP and CCOMP) connected to the COMP pin sets the pole and zero which are given by: fP_COM = VOUT is the boost converter output voltage; VD is the forward voltage of Schottky diode; VIN(MIN) is the minimum input voltage. IPEAK = 1 2 * RESR * COUT Where: Where: The output inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load conditions. Peak current may be calculated from the following equation, again assuming continuous conduction mode. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Switching frequency is estimated at 600kHz with a 4.7H inductor. 1 2 * RO * COUT fP = fZ_COM = 1 2 * REA * CCOMP 1 2 * RCOMP * CCOMP Where: CCOMP is the compensation capacitor; RCOMP is the compensation resistor; REA is the output resistance of the error amplifier (M). A 15nF capacitor and a 20k resistor in series are chosen for optimum phase margin and fast transient response. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Capacitor Selection AAT1451 applications. Careful selection of the external capacitor CIN is important because it will affect turn-on time and transient performance. Optimum performance will be obtained when low equivalent series resistance (ESR) ceramic capacitor is used; in general, low ESR may be defined as less than 100m. A value of 2.2F for the input capacitor is a good starting point when choosing a capacitor. If the constant current sinks are only programmed for light current levels then the input capacitor size may be decreased. Capacitor area is another contributor to ESR. Capacitors that are physically large will have a lower ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. Capacitor Characteristics Ceramic composition capacitor is highly recommended over all other types of capacitors for use with the AAT1451. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lower cost, has a smaller PCB footprint, and is non-polarized. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. Ceramic Capacitor Materials Ceramic capacitor less than 0.1F are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U or Y5V dielectric materials. Large ceramic capacitors (i.e. larger than 4.7F) are often available in low cost Y5V and Z5U dielectrics, but capacitors larger than 4.7F are not typically required for PCB Layout Considerations When designing a PCB for the AAT1451, the key requirements are: 1. Place the input and output decoupling capacitors CIN and COUT as close to the chip as possible to reduce switching noise and output ripple. 2. Place the bypass capacitor CVDD as close to the chip as possible. 3. Keep the power traces (GND, SW, and VIN) short, direct, and wide to allow large current flow. Place sufficient multiple-layer pads when needed to change the trace layer. 4. Connect the output capacitor COUT, output inductor L1 and Schottky diode DS1 as close as possible. Use connections as short as possible for L1 to the SW pins and place no signal lines under the inductor. 5. Place the peripheral components like RCOMP, CCOMP, RSET and RFS as close to the chip as possible. Evaluation Board User Interface The user interface for the AAT1451 evaluation board is provided by three buttons and two connection terminals. The board is operated by supplying external power and pressing individual buttons. Table 4 indicates the function of each button or button combination. To power-on the evaluation board, connect a power supply or battery to both the VIN (with 5 to 26V) and the VCC (with 2.2 to 5V) terminals. A red LED indicates that VCC power is applied which is necessary to enable the AAT1451. Once one button is pressed, the green LED will flash once to indicate that the related action is processed. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 15 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting User Interface Functionality Button(s) Pushed UP DOWN CYCLE Description [Push/Release once] Channels FB1 to FB4 are turned on with 1mA per channel. With every push/release the current is increased according to Table 3. [Push/Release once] Channels FB1 to FB4 are turned on with 22mA per channel. With every push/release the current is decreased according to Table 3. [Push/Release once] Auto cycling up and down. Table 4: AAT1451 Evaluation Board User Interface. SW DS1 SS16L L1 4.7H U1 AAT1451 J1 VIN 5V-26V DC+ 1 2 2 VIN 9 VDD 3 CIN 2.2F/50V GND CVDD 2.2F 6.3V EN SHDN 11 R4 10k C2 0.1F PWM VCC 2.2V-5V VCC RCOMP 20k DOWN S2 CYCLE S3 ISET 3 FSLCT PGND RFS 20k COUT 2.2F 50V R2 1.2k 15 1 R3 10k 10 FB1 5 FB1 1 FB2 6 FB2 2 FB3 7 FB3 3 FB4 8 FB4 0 4 VCC 5 J3 EP GND 14 MCU VMCU R8 R9 R10 1k 1k 1k UP S1 COMP 4 RSET 7.5k FAULT PWM 13 CCOMP 15nF OVP VOUT FLT 12 R5 10k R1 42.7k 16 SW VOUT U2 PIC12F675 1 S1 2 3 4 S2 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 C1 0.1F 8 R7 1k 7 6 5 R6 330 LED1 Red LED2 Green S3 Figure 5: AAT1451 Evaluation Board Schematic. 16 Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting a: Top Side b: Bottom Side Figure 6: AAT1451 Evaluation Board Layout. Component Part Number Description Manufacturer U1 U2 S1 - S3 RCOMP, RFS RSET R1 R2 R3, R4, R5 R6 R7, R8, R9, R10 CIN, COUT CVDD CCOMP C1, C2 L1 DS1 LED1 LED2 AAT1451 PIC12F675 PTS645TL50 Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor GRM31CR71H225KA88 GCM188R70J225KE22 GRM188R71H153KA01 GRM188R71H104KA93 SD53-4R7-R SS16L CMD15-21SRC/TR8 CMD15-21UGC/TR8 High Efficiency White Backlight LED Driver 8-bit CMOS, FLASH-based C; 8-pin PDIP package Switch Tact, SPST, 5mm 20k, 1%, 1/4W; 0603 7.5k, 1%, 1/4W; 0603 42.7k, 1%, 1/4W; 0603 1.2k, 1%, 1/4W; 0603 10k, 1%, 1/4W; 0603 330, 1%, 1/4W; 0603 1k, 1%, 1/4W; 0603 2.2F, 50V, X7R, 1206 2.2F, 6.3V, X7R, 0603 15nF, 50V, X7R, 0603 0.1F, 50V, X7R, 0603 4.7H, 45m, 2.01A, 20% 1.0A, 60V Surface Mount Schottky Barrier Rectifier Red LED; 1206 Green LED; 1206 Skyworks Microchip ITT Industries Vishay Vishay Vishay Vishay Vishay Vishay Vishay Murata Murata Murata Murata Coiltronics TSC Chicago Miniature Lamp Chicago Miniature Lamp Table 5: AAT1451 Evaluation Board BOM List. Manufacturer Murata Coiltronics Part Number L (H) Max DCR (m) Saturation Current (A) LQH6PPN4R7M43 LQH6PPN6R8M43 SD53-4R7-R SD53-6R8-R 4.7 6.8 4.7 6.8 20 28 45 68 3.2 2.8 2.01 1.65 Size WxLxH (mm) 6.0x6.0x4.3 5.2x5.2x3.0 Table 6: Surface Mount Inductors. Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 17 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Manufacturer Murata AVX KEMET Part Number Value (F) Voltage (V) Tolerance Temp. Co. Case GCM188R70J225KE22 GRM188R71H153KA01 GRM188R71H104KA93 GRM31CR71H225KA88 06036C225KAT 06035C163KAT 06035C104KAT 12065C225KAT C0603C225K9RAC C0603C153K5RAC C0603C104K5RAC C1206C225K5RAC 2.2 0.015 0.1 2.2 2.2 0.015 0.1 2.2 2.2 0.015 0.1 2.2 6.3 50 50 50 6.3 50 50 50 6.3 50 50 50 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% X7R X7R X7R X7R X7R X7R X7R X7R X7R X7R X7R X7R 0603 0603 0603 1206 0603 0603 0603 1206 0603 0603 0603 1206 Table 7: Surface Mount Capacitors. 18 Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Single Li-ion Cell Powered Application: plus AAT3110 solution is adopted to drive 6 series-4 parallel (6S4P) to 8 series-4 parallel (8S4P) typical of 13" and smaller sized displays. Figure 8 shows the efficiency. Figure 7 demonstrates a backlight solution for single cell Li-ion battery powered application using the AAT1451 to drive the WLEDs and the AAT3110 regulated charge pump to supply the internal regulator of AAT1451. The AAT1451 DS1 SS16L L1 4.7H Battery 2.7-4.2V CIN 4.7F 2 CIN1 2.2F U2 AAT3110IJS-5.0-T1 1 COUT2 10F VIN GND C+ 3 SHDN 6 VDD 12 SHDN 11 CFLY 1F 13 CCOMP 15nF CIN2 10F C- 4 VIN 9 R1 42.7k 16 SW OVP 15 1.2k R2 CVDD 2.2F 5 4 3 RSET 7.5k RCOMP 20k FAULT PWM FB1 COMP FB2 ISET FB3 FSLCT FB4 PGND EP 1 0 RFS 20k 10 LED 6S4P~8S4P 10k VCC R3 5 6 7 8 GND 14 Figure 7: Schematic of AAT1451 plus AAT3110 Efficiency 100 95 90 Efficiency (%) ON/OFF signal 2 VOUT U1 AAT1451 VOUT COUT1 2.2F/50V 85 80 75 70 VIN = 3V 65 VIN = 3.6V 60 VIN = 4.2V 55 50 0 5 10 15 20 25 ILED (mA) Figure 8: Efficiency vs ILED for driving 8series - 4parallel (8S4P) LEDs Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012 19 DATA SHEET AAT1451 Four-LED Strings, High Efficiency White LED Driver for LCD Backlighting Ordering Information Package Part Marking1 Part Number (Tape and Reel)2 TDFN34-16 N5XYY AAT1451IRN-T1 Skyworks GreenTM products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of GreenTM, document number SQ04-0074. Package Information TDFN34-16 3.000 0.050 0.450 0.050 1.600 0.050 Detail "A" 0.230 0.050 0.450 0.050 3.300 0.050 4.000 0.050 Index Area Top View Bottom View 0.750 0.050 Detail "A" 0.000 + 0.100 -0.000 0.203 REF Side View All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. Copyright (c) 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. ("Skyworks") products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. 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Skyworks assumes no liability for applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters. Skyworks, the Skyworks symbol, and "Breakthrough Simplicity" are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 20 Skyworks Solutions, Inc. * Phone [781] 376-3000 * Fax [781] 376-3100 * sales@skyworksinc.com * www.skyworksinc.com 202306A * Skyworks Proprietary Information * Products and Product Information are Subject to Change Without Notice. * August 24, 2012