AAT2862IMK-T1

DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit General Description Features The AAT2862 is a highly integrated charge pump-based lighting management unit with four linear regulators optimized for single-cell lithium-ion/polymer systems. The charge pump provides power for all LED outputs and multiple LED configurations are available. The LED outputs can be programmed up to 30mA each. In addition the two auxiliary LED output current levels can be independently programmed. An I2C serial digital interface is used to enable, disable, and set the current to one of 32 levels. Current matching is better than 3% for uniform display brightness. • Input Voltage Range: 2.7V to 5.5V • Tri-Mode Charge Pump ▪ Drives up to Eight LEDs ▪ 32 Programmable Backlight Current with Auto-fade ▪ Settings Ranging From 500μA to 30mA ▪ Two Independently Controlled Auxillary LED Outputs ▪ 1MHz Switching Frequency ▪ Automatic Soft Start ▪ I2C Selectable Drivers • Four Linear Regulators ▪ 200mA Output Current ▪ 200mV Dropout ▪ I2C Programmable Output Voltage from 1.2V to 3.3V ▪ Output Auto-Discharge for Fast Shutdown • Built-In Thermal Protection • Automatic Soft Start • -40°C to +85°C Temperature Range • TQFN34-24 Package The AAT2862 also offers four high-performance lownoise MicroPower™ low dropout (LDO) linear regulators. The regulators are enabled and their output voltages are set through the I2C serial interface. Each LDO can supply up to 200mA load current and ground-pin current is only 80μA making the AAT2862 ideal for battery-operated applications. The AAT2862 is available in a Pb-free, space saving TQFN34-24 package and operates over the -40°C to +85°C ambient temperature range. Applications • Camera Enabled Mobile Devices • Digital Still Cameras • Multimedia Mobile Phones Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 1 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Typical Application CF1 1µF CF2 1µF WLEDs VOUT C1+ C1- C2+ C2IN OUT VBAT 3.6V CIN 2.2µF COUT 2.2µF IN ENABLE I2C Serial Interface EN SDA SDA SCL SCL BL1 BL2 BL3 BL4 BL5 BL6 BL7/AUX1 BL8/AUX2 LDOA VLDOA at 200mA CLDOA 2.2µF LDOB AAT2862 LDOC VLDOB at 200mA CLDOB 2.2µF VLDOC at 200mA CLDOC 2.2µF LDOD VLDOD at 200mA CLDOD 2.2µF AGND 2 PGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Pin Descriptions Pin # Symbol Function 1 OUT O 2 C2+ I 3 4 SDA SCL I I 5 EN I 6 7 AGND IN G PI 8 LDOC O 9 LDOB O 10 LDOA O 11 LDOD O 12 BL1 O 13 BL2 O 14 BL3 O 15 BL4 O 16 17 BL8/ AUX2 BL7/ AUX1 O O 18 BL6 O 19 BL5 O 20 21 22 PGND C2C1- G I I 23 IN PI 24 C1+ I EP Description Charge pump output. OUT is the output of the charge pump and supplies current to the backlight and flash LEDs. Connect the backlight and flash LED anodes to OUT. Bypass OUT to PGND with a 2.2μF or larger ceramic capacitor as close to the AAT2862 as possible. Positive terminal of charge pump capacitor 2. Connect the 1μF charge pump capacitor 2 from C2+ to C2-. I2C serial data input. SDA is the data input of the I2C serial interface. Drive SDA with the I2C data. I2C serial clock input. SCL is the clock input of the I2C serial interface. Drive SCL with the I2C clock. Programming Enable Input. When EN is strobed high, the backlight and LDO registers can be programmed via the I2C serial interface. When EN is strobed low, all backlight and LDO outputs are turned off and the backlight and LDO registers are reset to their default (POR) values and forces all LDO outputs to 0 (zero) volts. Analog ground. Connect to PGND as close to the AAT2862 as possible. Input power pin for all four LDOs. Connect Pin 7 to Pin 23 with as short a PCB trace as practical. LDO C regulated voltage output. Bypass LDOC to AGND with a 2.2μF or larger ceramic capacitor as close to the AAT2862 as possible. LDO B regulated voltage output. Bypass LDOB to AGND with a 2.2μF or larger capacitor as close to the AAT2862 as possible. LDO A regulated voltage output. Bypass LDOA to AGND with a 2.2μF or larger capacitor as close to the AAT2862 as possible. LDO D regulated voltage output. Bypass LDOD to AGND with a 2.2μF or larger ceramic capacitor as close to the AAT2862 as possible. Backlight LED 1 current sink. BL1 controls the current through backlight LED 1. Connect the cathode of backlight LED 1 to BL1. If not used, connect BL1 to OUT. Backlight LED 2 current sink. BL2 controls the current through backlight LED 2. Connect the cathode of backlight LED 2 to BL2. If not used, connect BL2 to OUT. Backlight LED 3 current sink. BL3 controls the current through backlight LED 3. Connect the cathode of backlight LED 3 to BL3. If not used, connect BL3 to OUT. Backlight LED 4 current sink. BL4 controls the current through backlight LED 4. Connect the cathode of backlight LED 4 to BL4. If not used, connect BL4 to OUT. Backlight or Auxiliary LED 8 current sink. BL8 controls the current through backlight LED 8. Connect the cathode of backlight LED 8 to BL8. If not used, connect BL8 to OUT. Backlight or Auxiliary LED 7 current sink. BL7 controls the current through backlight LED 7. Connect the cathode of backlight LED 7 to BL7. If not used, connect BL7 to OUT. Backlight LED 6 current sink. BL6 controls the current through backlight LED 6. Connect the cathode of backlight LED 6 to BL6. If not used, connect BL6 to OUT. Backlight LED 5 current sink. BL5 controls the current through backlight LED 5. Connect the cathode of backlight LED 5 to BL5. If not used, connect BL5 to OUT. Power ground. Connect to AGND as close to the AAT2862 as possible. Negative terminal of charge pump capacitor 2. Negative terminal of charge pump capacitor 1. Power input for the charge pump. Connect IN to the input source voltage. Bypass IN to PGND with a 2.2μF or larger ceramic capacitor as close to the AAT2862 as possible. Positive terminal of charge pump capacitor 1. Connect the 1μF charge pump capacitor 1 from C1+ to C1-. Exposed paddle (bottom) Connect to PGND/AGND as close to the AAT2862 as possible. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 3 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Pin Configuration TQFN34-24 (Top View) PGND C2C1IN C1+ 24 OUT C2+ SDA SCL EN AGND IN 23 22 21 20 1 19 2 18 3 17 4 16 5 15 6 14 7 13 8 9 10 11 BL5 BL6 BL7/AUX1 BL8/AUX2 BL4 BL3 BL2 12 BL1 LDOD LDOA LDOB LDOC Programmable Options1 Main Channels Sub Channels Independent AUX Channels 8* 6 5 5 4 4 4 0* 2 3 2 4 3 2 0* 0 0 1 0 1 2 1. "*" denotes default values. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Absolute Maximum Ratings1 TA = 25OC unless otherwise noted. Symbol Description IN, OUT, BL1, BL2, BL3, BL4, BL5, BL6, BL7/AUX1, BL8/AUX2 Voltage to PGND and AGND C1+, C2+ Voltage to PGND and AGND C1-, C2-, LDOA, LDOB, LDOC, LDOD, EN, SDA, SCL Voltage to PGND and AGND PGND to AGND Value Units -0.3 to 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -0.3 to + 0.3 V V V V Value Units Thermal Information2, 3 Symbol JA PD TJ TLEAD Description Thermal Resistance Maximum Power Dissipation Operating Junction Temperature Range Maximum Soldering Temperature (at Leads) 50 2 -40 to 150 300 O C/W W 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. Only one Absolute Maximum Rating should be applied at any one time. 2. Derate 20mW/°C above 25°C ambient temperature. 3. Mounted on a FR4 circuit board. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 5 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Electrical Characteristics1 VIN = 3.6V; CIN = COUT = 2.2μF; C1 = C2 = 1μF; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25C. Symbol VIN IIN(CP) Description Max Units 5.5 0.20 3.0 5.0 V mA mA mA 225 μA 2.7  VIN  5.5; Any One LDO ON; No Load 80 μA EN = GND 1.0 μA IN Operating Voltage Range Charge Pump IN Operating Current (Pin 23) LDOA, LDOB, LDOC and LDOD IN Operating Current (Pin 7) LDOA or LDOB or LDOC or LDOD IIN(LDOx) IN Operating Current (Pin 7) IN Shutdown Current IIN(SHDN) Over-Temperature Shutdown TSD Threshold Over-Temperature Shutdown TSD(HYS) Hysteresis Charge Pump Section VOUT OUT Output Voltage OUT Maximum Output Current IOUT(MAX) BL1-BL8 Charge Pump Mode VIN(TH_H, BL) Transition Hysteresis fOSC Charge Pump Oscillator Frequency tCP(SS) Charge Pump Soft-Start Time BL1-BL6, BL7/AUX1, BL8/AUX2 LED Drivers tLED(SU) LED Output Current Startup Time IBL_(MAX) BL1-BL8 Maximum Current IBL_(DATA29) BL1-BL8 Current BL1-BL8 Charge Pump Transition VBL_(TH) Threshold IIN(LDO) Conditions Min Typ 2.7 1x Mode; 3.0  VIN  5.5; LDOs OFF; No Load 1.5x Mode; 3.0  VIN  5.5; LDOs OFF; No Load 2x Mode; 3.0  VIN  5.5; LDOs OFF; No Load 0.15 2.7  VIN  5.5; All LDOs ON; No Load 140 °C 15 °C VIN = 3.0V, VOUT = 4.0V 5.2 800 V mA EN/SET = IN; VIN – VF = 1V 300 mV Address 07h Data=20 (0010 0000); TA = 25°C TA = 25°C 1.2 100 MHz μs OUT: 0V to IN Address 03h Data=E0 (1110 0000) Address 03h Data=FD (1111 1101) Address 03h Data=E0 (1110 0000) 27 1.75 20 30 1.94 33 2.13 180 us mA mA mV 1. The AAT2862 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Current matching is defined as the deviation of any sink current from the average of all active channels. 6 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Electrical Characteristics1 VIN = 3.6V; CIN = COUT = 2.2μF; C1 = C2 = 1μF; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol Description Linear Regulators LDOA, LDOB, LDOC, LDOD Output ΔVLDO[A/B/C,D] /VLDO[A/B/C,D] Voltage Tolerance LDOA, LDOB, LDOC, LDOD Maximum ILDO[A/B/C,D](MAX) Load Current LDOA, LDOB, LDOC, LDOD Dropout VLDO[A/B/C,D](DO) Voltage2 VLDO/ LDOA, LDOB, LDOC, LDOD Line VLDO*VIN Regulation LDOA, LDOB, LDOC, LDOD Power SupPSRR[A/B/C,D] ply Rejection Ratio LDOA, LDOB, LDOC, LDOD AutoROUT_(DCHG) Discharge Resistance I2C Logic and Control Interface VIL SDA, SCL, EN Input Low Threshold VIH SDA, SCL, EN Input High Threshold VOL SDA Output Low Voltage IIN SDA, SCL, EN Input Leakage Current fSCL SCL Clock Frequency tLOW SCL Clock Low Period tHIGH SCL Clock High Period tHD_STA Hold Time START Condition Setup Time for Repeat START tSU_STA tSU_DAT SDA Data Setup Time tHD_DAT SDA Data HOLD Time tSU_STO Setup Time for STOP Condition Bus Free Time Between STOP and tBUF START Conditions Conditions Min IOUT = 1mA to 200mA; TA = 25°C IOUT = 1mA to 200mA; TA = -40°C to +85°C -1.5 -3.0 Typ Max Units 1.5 3.0 % % 200 VLDO[A/B/C/D] ≥ 3.0V; IOUT = 150mA 75 VLDO = (VOUT[A/B/C/D] + 1V) to 5V ILDO[A/B/C/D] =10mA, 1kHz 2.7V ≤ VIN ≤ 5.5V 2.7V ≤ VIN ≤ 5.5V IPULLUP = 3mA VSDA = VSCL = VLED_SEL = VLDO_SEL = IN = 5V mA 200 mV 0.09 %/V 50 dB 20 Ω 0.4 1.4 -1 0 1.3 0.6 0.6 0.6 100 0 0.6 0.4 1 400 0.9 1.3 V V V μA kHz μs μs μs μs ns μs μs μs 1. The AAT2862 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. VDO[A/B/C/D] is defined as VIN – LDO[A/B/C/D] when LDO[A/B/C/D] is 98% of nominal. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 7 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit I2C Interface Timing Details t t t 8 t t t t t t Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Typical Characteristics Backlight Efficiency vs. Input Voltage Backlight Current Matching vs. Temperature 100 Efficiency (%) 90 80 70 60 50 30mA/ch, VF = 3.85V 20.32mA/ch, VF = 3.55V 4.84mA/ch, VF = 3.0V 40 30 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Backlight Output Current (mA) (VIN = 3.6V; 30mA/ch) 33 32 31 30 29 28 Channel 1 - Channel 8 27 26 25 -40 -15 10 35 60 Temperature (°C) Input Voltage (V) Charge Pump Output Turn On Characteristic Turn On to 1x Mode Backlight (VIN = 3.6V; ILED = 0mA; COUT = 2.2µF) (VIN = 4.5V; 30mA/ch) VEN (top) (V) 2.0 4.0 3.0 2.0 1.0 0.0 Charge Pump Output (bottom) (V) 4.0 0.0 SDA (2V/div) 0V VOUT (2V/div) VSINK (2V/div) 0V IIN (100mA/div) 0A Time (50µs/div) Time (200µs/div) Turn On to 1.5x Mode Backlight Turn On to 2x Mode Backlight (VIN = 3.5V; 30mA/ch) (VIN = 3.2V; 30mA/ch) SDA (2V/div) 85 SDA (2V/div) 0V 0V VOUT (2V/div) VOUT (2V/div) VSINK (2V/div) 0V VSINK (2V/div) 0V IIN (100mA/div) 0A IIN (200mA/div) 0A Time (200µs/div) Time (200µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 9 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Typical Characteristics (VIN = 3.3V; 30mA/ch Backlight; 1.5x Mode; COUT = 2.2µF; fOSC = 1.2MHz) Input Voltage (AC coupled) (top) (mV) Operating Characteristic (VIN = 3.5V; 30mA/ch) 0V VDIODE (2V/div) 0V IIN (200mA/div) 20 10 0 50 0 -50 0A Time (500ns/div) Time (200µs/div) 20 10 0 20 10 0 -10 -20 LDO Output Voltage Deviatoin (%) LDOA/B/C/D Output Voltage vs. Temperature Charge Pump Output Voltage (AC coupled) (bottom) (mV) Input Voltage (AC coupled) (top) (mV) Operating Characteristic (VIN = 3.0V; 30mA/ch Backlight; 2x Mode; COUT = 2.2µF; fOSC = 1.2MHz) (VIN = 3.6V; ILDO = 0mA) 1.5 1 0.5 0 -0.5 VOUT = 1.8V VOUT = 3.3V -1 -1.5 -40 -15 10 85 LDO A/B/C/D Line Regulation (VIN = 3.6V) (ILDO = 10mA) 1.5 VOUT = 1.2V VOUT = 3.3V 1.0 0.5 0.0 -0.5 -1.0 -1.5 1 10 100 1000 LDO Output Voltage Deviation (%) LDO Output Voltage Deviation (%) 60 LDO A/B/C/D Load Regulation Load Current (mA) 10 35 Temperature (°C) Time (500ns/div) 0.1 Charge Pump Output Voltage (AC coupled) (bottom) (mV) VEN (2V/div) Turn Off from 1.5x Mode Backlight 1.5 VOUT = 1.8V VOUT = 3.3V 1.0 0.5 0.0 -0.5 -1.0 -1.5 2.7 3.1 3.5 3.9 4.3 4.7 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 5.1 5.5 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Typical Characteristics LDO A/B/C/D Line Transient Response (VIN = 3.6V to 4.2V; ILDO = 10mA; VOUT = 1.8V; CLDO = 2.2µF) 0 2.00 1.90 1.80 1.70 4.4 Input Voltage (top) (V) 100 4.0 3.6 1.82 1.81 1.80 1.79 1.78 1.60 Time (20µs/div) Time (1ms/div) LDO A/B/C/D Turn On Characteristic LDO A/B/C/D Turn On Characteristic (VIN = 3.6V; VOUT = 1.8V; CLDO = 2.2µF) (VIN = 3.6V; VOUT = 3.3V; CLDO = 2.2µF) 1.5 1.0 0.5 0.0 VSDA (top) (V) VSDA (top) (V) 2.0 4.0 2.0 3.0 2.0 1.0 0.0 Time (20µs/div) Time (20µs/div) EN, SDA, SCL Input Low Threshold Voltage vs. Input Voltage 1.4 1.2 1.3 1.1 1.2 1.1 1.0 0.9 0.8 -40°C 25°C 85°C 0.6 0.5 0.4 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 Input Voltage (V) 4.7 4.9 5.1 5.3 5.5 VEN(L), VSDA(L), VSCL(L) (V) VEN(H), VSDA(H), VSCL(H) (V) EN, SDA, SCL Input High Threshold Voltage vs. Input Voltage 0.7 4.0 0.0 LDO Output (bottom) (V) 2.0 LDO Output (bottom) (V) 4.0 0.0 LDO Output Voltage (bottom) (V) 200 LDO Output Voltage (bottom) (V) LDO Output Current (top) (mA) LDO A/B/C/D Load Transient Response (ILDO = 10mA to 200mA; VIN = 3.6V; VOUT = 1.8V; CLDO = 2.2µF) 1.0 0.9 0.8 0.7 0.6 0.5 -40°C 25°C 85°C 0.4 0.3 0.2 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 11 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Functional Block Diagram IN IN LDOA C1C1+ C2- 1x/1.5x/2x Tri-mode Charge Pump C2+ LDOB OUT LDOC LDOD REF 8 BL1 SDA BL2 SCL BL3 BL4 EN Control Logic BL5 BL6 BL7/AUX1 BL8/AUX2 PGND 12 AGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Functional Description LED Current Control The AAT2862 is a highly integrated backlight driver with four LDO regulators. The charge pump LED driver powers the backlight LEDs from the 2.7V to 5.5V input voltage. The LDO regulators get their power from the same input and produce regulated output voltage between 1.2V and 3.3V. Control of the LEDs and the LDO output voltage is through an I2C serial interface for easy programming. The eight backlight LED channels are programmed through the I2C serial interface and can be set between 0.5 and 30mA in ~1mA steps. The currents match to within typically 3%. There are fade-in and fade-out timers that can be programmed through the interface as well. See the “I2C Serial Interface” section for more information on setting the LED currents. LDO Regulators LED Drivers The AAT2862 drives up to eight backlight LEDs up to 30mA each. The LEDs are driven from a charge pump to insure that constant current is maintained over the entire battery voltage range. The charge pump automatically switches from 1x, to 1.5x, to 2x modes and back to maintain the LED current while minimizing power loss for high efficiency. The charge pump operates at the high 1MHz switching frequency allowing the use of small 1μF ceramic capacitors. Depending on the battery voltage and LED forward voltage, the charge pump drives the LEDs directly from the input voltage (1x or bypass mode) or steps up the input voltage by a factor of 1.5 (1.5x mode) or 2 (2x mode). The charge pump requires only two tiny 2.2μF ceramic capacitors, making a more compact solution than an inductor-based step-up converter solution. Each individual LED is driven by a current sink to GND, allowing individual current control with high accuracy over a wide range of input voltages and LED forward voltages while maintaining high efficiency. The charge pump is controlled by the voltage across the LED current sinks. When any one of the active backlight current sink voltages drops below 180mV, the charge pump goes to the next higher mode (from 1x to 1.5x or from 1.5x to 2x mode) to maintain sufficient LED voltage for constant LED current. The AAT2862 continuously monitors the LED forward voltages and uses the input voltage to determine when to reduce the charge pump mode for better efficiency. There is also a 300mV modetransition hysteresis that prevents the charge pump from oscillating between modes. The AAT2862 includes four low dropout (LDO) linear regulators. These regulators are powered from the battery and produce a fixed output voltage set through the I2C serial interface. The output voltages can be programmed to one of 16 output voltages between 1.2V and 3.3V. The LDOs can also be turned on/off through the I2C serial interface. The LDO regulators require only a small 2.2μF ceramic output capacitor for stability. If improved load transient response is required, larger-valued capacitors can be used without stability degradation. I2C Serial Interface The AAT2862 uses an I2C serial interface to set the LED currents, the LDO's output voltages, and to turn on/off all LDOs, as well as other housekeeping functions. The I2C interface takes input from a master device while the AAT2862 acts as a target to the master. The I2C protocol uses two open-drain inputs; SDA (serial data line) and SCL (serial clock line). Both inputs require an external pull up resistor, typically to the input voltage. The I2C protocol is bidirectional and allows target devices and masters to both read and write to the bus. The AAT2862 only supports the write protocol; therefore, the Read/Write bit must always be set to “0”. The timing diagram in Figure 1 shows the typical transmission protocol. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 13 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit start msb Chip Address lsb w AAT2862 Device Address = 60 h w ack msb Register Add lsb ack msb DATA lsb ack stop SCL SDA start ack Addr = 00h ack Data = 06 h ack stop Figure 1: Typical I2C Timing Diagram. I2C Serial Interface Protocol START and STOP Conditions The I2C serial interface protocol is shown in Figure 1. Devices on the bus can be either master or target devices. Both master and target devices can both send and receive data over the bus, with the difference being that the master device controls all communication on the bus. The AAT2862 acts as a target device on the bus and is only capable of receiving data and does not transmit data over the bus. START and STOP conditions are always generated by the master. Prior to initiating a START, both the SDA and SCL pin are inactive and are pulled high through external pullup resistors. As shown in Figure 1, a START condition is when the master pulls the SDA line low and, after the start condition hold time (tHT_STA), the master strobes the SCL line low. A START condition acts as a signal to devices on the bus that the device producing the START condition is active and will be communicating on the bus. The I2C communications begin with the master making a START condition. Next, the master transmits the 7-bit device address and a Read/Write bit. Each target device on the bus has a unique address. The AAT2862 device address is 60h. If the address transmitted by the master matches the device address, the target device transmits an Acknowledge (ACK) signal to indicate that it is ready to receive data. Since the AAT2862 only reads from the master, the Read/Write bit must be set to “0”. Next, the master transmits the 8-bit register address, and the target device transmits an ACK to indicate that it received the register address. Next, the master transmits the 8-bit data word, and again the target device transmits an ACK indicating that it received the data. This process continues until the master is finished writing to the target device, at which time the master generates a STOP condition. 14 A STOP condition, as shown in Figure 1, is when SCL changes from low to high followed after the STOP condition setup time (tSU_STO), by an SDA low-to-high transition. The master does not issue an ACK and releases SCL and SDA. Transferring Data Addresses and data are sent with the most significant bit first transmitted and the least significant bit transmitted last. After each address or data transmission, the target device transmits an ACK signal to indicate that it has received the transmission. The ACK signal is generated by the target after the master releases the SDA data line by driving SDA low. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit STOP START SDA SDA SCL SCL Figure 2: I2C STOP and START Conditions; START: A High “1” to Low “0” Transition on the SDA Line While SCL is High “1” STOP: A Low “0” to High “1” Transition on the SDA Line While SCL is High “1”. SCL 1 2 3 4 5 6 7 MSB SDA A6 8 9 LSB A5 A4 A3 A2 A1 A0 R/W ACK Device Address Figure 3: I2C Address Bit Map; 7-bit Slave Address (A6-A0), 1-bit Read/Write (R/W), 1-bit Acknowledge (ACK). SCL 1 2 3 4 5 6 7 MSB SDA D7 8 9 LSB D6 D5 D4 D3 D2 D1 D0 ACK Register Address / Data Figure 4: I2C Register Address and Data Bit Map; 8-bit Data (D7-D0), 1-bit Acknowledge (ACK). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 15 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Applications Information Backlight Control Registers The AAT2862 has five backlight registers: I2C Serial Programmed Registers • REG3 (I2C address 03h) • REG4 (I2C address 04h) • REG5 (I2C address 05h) backlight. • REG6 (I2C address 06h) backlight. • REG7 (I2C address 07h) and fade-out function. The AAT2862 I2C programmable registers are listed in Table 1. There are eight registers, five for the backlight LED control, and three to control the four LDOs. All backlight channels can be easily configured in many different ways through the I2C interface. The default assignment for the drivers is four backlight for Main, two backlight for Sub, and two extra that can be applied to Main, Sub, or Auxiliary. All eight backlight channels can be driven to the same current level by writting the MEQS = 1 bit in REG3. The Main and Sub backlights can be programmed independently to one of 32 levels described in Table 2. controls Main backlight. controls Sub backlight. controls auxiliary Aux1 controls auxiliary Aux2 controls backlight fade-in Register Number Hex Address REG0 00h REG1 01h REG2 02h REG3 03h REG4 04h REG5 05h REG6 06h REG7 07h Functional Description LDO A & B Output Voltage Control LDO C & D Output Voltage Control LDO EN control Backlight Current Control MAIN Backlight Current Control SUB Backlight Current Control AUX1 Backlight Current Control AUX2 Backlight Fade Control Data Bit7 Data Bit6 Data Bit5 Data Bit4 Data Bit3 Data Bit2 Data Bit1 Data Bit0 LDOA[3] LDOA[2] LDOA[1] LDOA[0] LDOB[3] LDOB[2] LDOB[1] LDOB[0] LDOC[3] LDOC[2] LDOC[1] LDOC[0] LDOD[3] LDOD[2] LDOD[1] LDOD[0] X X X X ENLDO_D ENLDO_C ENLDO_B ENLDO_A MEQS DISABLE FADE_ MAIN MAIN_ON BLM[4] BLM[3] BLM[2] BLM[1] BLM[0] X DISABLE FADE_SUB SUB_ON BLS[4] BLS[3] BLS[2] BLS[1] BLS[0] AUX1[1] AUX1[0] AUX1_ON BLA1[4] BLA1[3] BLA1[2] BLA1[1] BLA1[0] AUX2[2] AUX2[0] AUX2_ON BLA2[4] BLA2[3] BLA2[2] BLA2[1] BLA2[0] X X FADE_ TIME[1] FADE_TIME[0] FADE_MAIN FADE_SUB FLOOR[1] FLOOR[0] Table 1: AAT2862 Configuration/Control Register Allocation (“X” = “Reserved”). 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Data Bit4 Data Bit3 Data Bit2 Data Bit1 Data Bit0 LED Current (mA) BLM[4] BLM[3] BLM[2] BLM[1] BLM[0] REG3 BLS[4] BLS[3] BLS[2] BLS[1] BLS[0] REG4 BLA1[4] BLA1[3] BLA1[2] BLA1[1] BLA1[0] REG5 BLA2[4] BLA2[3] BLA2[2] BLA2[1] BLA2[0] REG6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 30* 29.03 28.06 27.10 26.13 25.16 24.19 23.23 22.26 21.29 20.32 19.35 18.38 17.42 16.45 15.48 14.52 13.55 12.58 11.61 10.65 9.68 8.71 7.74 6.77 5.81 4.84 3.87 2.9 1.94 0.97 0.48 Table 2: Main/Sub/Aux Backlight LED Current - BLM/BLS/BLA1,2[4:0]. Table 3 describes the floor current per channel for the fade-in and fade-out functions. In fade-out sequence floor will be the final current that will continue to be present until the Main, Sub or Aux1,2 channels are disabled by writing MAIN_ON = 0 to REG3, SUB_ON = 0 to REG4, A1_ON = 0 to REG5, and/or A2_ON = 0 to REG6. In fade-in sequence floor is the direct current all chan- nels will be turned on by writing MAIN_ON = 1 to REG3, SUB_ON = 1 to REG4, A1_ON = 1 to REG5, and/or A2_ON = 1 to REG6. Fade-out can be initiated only after the fade in sequence has been programmed first by writing FADE_MAIN = 1 and/or FADE_SUB = 1 as is shown in Table 4. *Denotes default (power-on-reset) value. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 17 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Data Bit1 Data Bit0 Fade In and Out Current Level (mA) FLOOR[1] FLOOR[0] REG7 0* 0 1 1 0* 1 0 1 0.48* 0.97 1.94 2.90 Table 3: Main/Sub LED Current Fade In and Out Level Control. Data Bit6 of REG3 and REG4 enables the fade in and out control of the Main and Sub channels. Fade function is enabled by default and can be explicitly disabled by writing DISABLE FADE_MAIN = 1 and/or DISABLE FADE_SUB = 1 as shown in Table 6. Data Bit6 Backlight Channel Fade In and Out Enable/Disable DISABLE FADE_MAIN REG3 DISABLE FADE_SUB REG4 0* 1 Enable* Disable Fade In and Out Control Data Bit3 Data Bit2 FADE_MAIN FADE_SUB Main Sub 0* 0 1 1 0* 1 0 1 Fade Out* Fade Out Fade In Fade In Fade Out* Fade In Fade Out Fade In REG7 Table 6: Main/Sub Current Fade ON/OFF Control. Table 4: Main/Sub LED Current Fade In and Out Control. Data Bit5 of REG3, REG4, REG5 and REG6 controls the turn on and off of the Main, Sub, Aux1 and Aux2 channels according to Table 5. Both Aux1 and Aux2 channels are considered part of the Sub backlight channels unless explicitly turned on as part of the Main backlight or independently. Data Bit5 Backlight Channel ON/OFF MAIN_ON REG3 SUB_ON REG4 AUX1_ON REG5 AUX2_ON REG6 0* 1 OFF* ON Table 5: Main/Sub/Aux1/Aux2 LED Current ON/OFF Control. Data Bit7=1 of REG3 programs all Sub channels as Main backlight as described in Table 7. If the Main fade-in or fade-out function is enabled; all eight Main and Sub channels will be faded-in or out simultaneously. Data Bit7 MAIN Equal SUB (MEQS) MEQS REG3 0* 1 False* True Table 7: Main/Sub Current Fade ON/OFF Control. Data Bit4 and Data Bit5 of REG7 control the duration of the fade-in/out function. The default timing is 850ms with options for 650ms and 425ms according to Table 8. The charge pump oscillator frequency is related to the fade-in/out timing as follows: For the 850ms fade-in/out timer, typical fOSC = 600kHz For the 650ms fade-in/out timer, typical fOSC = 800kHz For the 425ms fade-in/out timer, typical fOSC = 1.2MHz respectively. Data Bit5 Data Bit4 FADE_TIME[1] FADE_TIME[0] Fade In and Out Timing (ms) 0* 0 1 1 0* 1 0 1 850* 650 425 850 Table 8: Main/Sub LED Current Fade In and Out Timing *Denotes default (power-on-reset) value. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Examples of Fade-Out Programming Examples of Fade-In/Out Programming Main Only (Sub is OFF): Main Only (Sub is OFF): Address Address Address Address Address 03h, Data 40: Disable fade 07h, Data 08: Fade-in is programmed 03h, Data 6F: Turn on directly to 15.48mA/ch 03h, Data 20: Re-enable fade 07h, Data 00: Fade-out to 0.48mA/ch Sub Only (Main is OFF): Address Address Address Address Address 04h, Data 40: Disable fade 07h, Data 04: Fade-in is programmed 04h, Data 6F: Turn on directly to 15.48mA/ch 04h, Data 2F: Enable fade 07h, Data 02: Fade-out to 1.94mA/ch Main and Sub (as shown in Figure 5): Address Address Address Address Address 03h, 07h, 03h, 03h, 07h, Data Data Data Data Data C0: 0C: 60: 20: 03: Address 03h, Data 20: Main backlight is turned on with 0.48mA/ch Address 07h, Data 08: Fade-in to 30mA/ch Address 07h, Data 03: Fade-out to 2.90mA/ch Sub Only (Main is OFF): Address 07h, Data 02: Fade-in is programmed to 1.94mA/ch Address 04h, Data 2E: Sub backlight is turned on with 1.94mA/ch Address 07h, Data 04: Fade-in to 16.45mA/ch Address 07h, Data 02: Fade-out to 1.94mA/ch Main and Sub (as shown in Figure 6): Disable fade Fade-in is programmed Turn on directly to 30mA/ch Enable fade Fade-out to 2.90mA/ch Address 07h, Data 01: Fade-in is programmed to 0.97mA/ch Address 03h, Data AA: Main and Sub backlight is turned on with 0.97mA/ch Address 07h, Data 0C: Fade-in to 20.32mA/ch Address 07h, Data 01: Fade-out to 0.97mA/ch Main and Sub Fade Out Only Max. 30mA /ch to 2.90mA/ch I2C Sequence: AAT2862 Chip Address 60h REG3 Address 03h, Data C0(0100 0000): Disable fade function REG7 Address 07h, Data 0C(0000 1100): Fade-in is programmed REG3 Address 03h, Data 60(0110 0000): Main/Sub is turned on with 30mA/ch Main/Sub Backlight 30mA/ch REG3 Address 03h, Data 20(0010 0000): Enable fade function REG7 Address 07h, Data 03(0000 0011): Fade-out is programmed to 2.90mA/ch Main/Sub Backlight 2.90mA/ch REG3 Address 03h Data 00(0000 0000 ) REG3 Address 03h, Data 20(0010 0000): Enable fade function REG3 Address 03h, Data 60(0110 0000): Main/Sub is turned on with 30mA/ch REG7 Address 07h, Data 08(0000 1000): Fade-in is programmed REG3 Address 03h, Data C0(0100 0000): Disable fade function REG7 Address 07h, Data 0C(0000 1100): Fade-in is programmed REG3 Address 03h, Data 60(0110 0000): Main/Sub is turned on with 30mA/ch Main/Sub Backlight Off Figure 5: Example of AAT2862 Fade Out Programming. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 19 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Main and Sub Fade In/Out Max. 20.32mA/ch to 0.97mA/ch I2C Sequence: AAT2862 Chip Address 60h REG7 Address 07h, Data 01(0000 0001): Fade-in is programmed as 0.97mA/ch REG3 Address 03h, Data AA(1010 1010): Main/Sub backlight is turned on with 0.97mA/ch REG7 Address 07h, Data 0C(0000 1100): Fade-in programmed to 20.32mA/ch Main/Sub Backlight 20.32mA/ch REG7 Address 07h, Data 01(0000 0001): Fade-out is programmed to 0.97mA/ch REG7 Address 07h, Data 0C(0000 1100): Fade-in is programmed as 20.32mA/ch Main/Sub Backlight 0.97mA/ch REG3 Address 03h Data 80(1000 0000) REG7 Address 07h, Data 01(0000 0001): Fade-in is programmed as 0.97mA/ch REG3 Address 03h, Data AA(1010 1010): Main/Sub backlight is turned on with 0.97mA/ch REG7 Address 07h, Data 0C(0000 1100): Fade-in is programmed to 20.32mA/ch Main/Sub Backlight Off Figure 6: Example of AAT2862 Fade In/Out Programming. LDO Control Registers The four LDO regulators have three dedicated control registers: • REG0 (I2C address 00h) and REG1 (I2C address 01h) set the output voltages of LDOA/B/C/D to one of 16 pre-set values according to Table 9 and Table 10. • REG2 (I2C address 02h) controls turning on/off of LDOA/B/C/D regulators according to Table 11. 20 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Data Bit7 Data Bit6 Data Bit5 Data Bit4 LDO VLDO[A/C] (V) Data Bit3 Data Bit2 Data Bit1 Data Bit0 LDO VLDO[B/D] (V) LDOA[3] LDOA[2] LDOA[1] LDOA[0] REG0 LDOB[3] LDOB[2] LDOB[1] LDOB[0] REG0 LDOC[3] LDOC[2] LDOC[1] LDOC[0] REG1 LDOD[3] LDOD[2] LDOD[1] LDOD[0] REG1 0* 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0* 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0* 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0* 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1.2* 1.3 1.5 1.6 1.8 2.0 2.2 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 0* 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0* 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0* 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0* 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1.2* 1.3 1.5 1.6 1.8 2.0 2.2 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 Table 9: LDOA/LDOC Output Voltage Control Data. Table 10: LDOB/LDOD Output Voltage Control Data. Data Bit3 Data Bit2 Data Bit1 Data Bit0 ENLDO_D ENLDO_C ENLDO_B ENLDO_A LDOD Output LDOC Output LDOB Output LDOA Output 0* 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0* 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0* 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0* 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Off* Off Off Off Off Off Off Off On On On On On On On On Off* Off Off Off On On On On Off Off Off Off On On On On Off* Off On On Off Off On On Off Off On On Off Off On On Off* On Off On Off On Off On Off On Off On Off On Off On Table 11: LDOA/LDOB/LDOC/LDOD ON/OFF Control Data. *Denotes default (power-on-reset) value. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 21 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit Auxillary Backlight Selection Each of the auxiliary drivers (Aux1, Aux2) can also be programmed to one of the 32 levels described in Table 2. The auxiliary drivers can be driven independently, or combined with the main or sub by changing Data Bit6 and Data Bit7 in REG5 (I2C address 05h) and REG6 (I2C address 06h) according to Table 12. Data Bit7 Data Bit6 Auxillary Channel Assignment AUX1[1] AUX1[0] REG5 AUX2[1] AUX2[0] 0* 0* 0 1 1 0 1 1 REG6 IAUX1 = Sub* IAUX2 = Sub* IAUX1 = Main IAUX2 = Main IAUX1 = Aux1 IAUX2 = Aux2 The low-dropout current sinks in the AAT2862 maximize performance and make it capable of driving LEDs with high forward voltages. Multiple channels can be combined to obtain a higher LED drive current without complication. Device Switching Noise Performance The AAT2862 operates at three fixed frequencies, typically 600kHz, 800kHz, and 1.2MHz, in order to help control noise and limit harmonics that can interfere with the RF operation of cellular telephone handsets or other communication devices. Back-injected noise appearing on the input pin of the charge pump is 20mV peak-topeak, typically ten times less than inductor-based DC/DC boost converter white LED backlight solutions. The AAT2862 soft-start feature prevents noise transient effects associated with in-rush currents during the start up of the charge pump circuit. Reserved Table 12: Auxiliary Channel Assignment. LED Selection The AAT2862 is specifically intended for driving white LEDs. However, the device design will allow the AAT2862 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.7V. LED applications may include mixed arrangements for display backlighting, color (RGB) LEDs, infrared (IR) diodes and any other load needing a constant current source generated from a varying input voltage. Since the D1 to D8 constant current sinks are matched with negligible voltage dependence, the constant current channels will be matched regardless of the specific LED forward voltage (VF) levels. Power Efficiency and Device Evaluation Charge-pump efficiency discussion in the following sections accounts only for the efficiency of the charge pump section itself. Due to the unique circuit architecture and design of the AAT2862, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT2862 outputs are pure constant current sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output (BL1 to BL8) to derive an overall output power measurement. For any given application, white LED forward voltage levels can differ, yet the output drive current will be maintained as a constant. This makes quantifying output power a difficult task when taken in the context of comparing to other white LED driver circuit topologies. A better way to quantify total device efficiency is to observe the total input power to the device for a given LED current drive level. The best White LED driver for a given application should be based on trade-offs of size, external component count, reliability, operating range and total energy usage...not just “% efficiency”. *Denotes default (power-on-reset) value. 22 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202071A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2862 Backlight LED Driver and Multiple LDO Lighting Management Unit The AAT2862 efficiency may be quantified under very specific conditions and is dependent upon the input voltage versus the output voltage seen across the loads applied to outputs D1 through D8 for a given constant current setting. Depending on the combination of VIN and voltages sensed at the current sinks, the device will operate in load switch mode. When any one of the voltages sensed at the current sinks nears dropout the device will operate in 1.5x or 2x charge pump mode. Each of these modes will yield different efficiency values. Refer to the following two sections for explanations of each operational mode. 1x Mode Efficiency The AAT2862 1x mode is operational at all times and functions alone to enhance device power conversion efficiency when VIN is greater then the voltage across the load. When in 1x mode, the voltage conversion efficiency is defined as output power divided by input power: η= POUT PIN The expression to define the ideal efficiency () can be rewritten as: η= POUT VOUT · IOUT VOUT = = PIN VIN · IOUT VIN -or- η(%) = 100 ⎛ VOUT ⎞ ⎝ VIN ⎠ In addition, with an ideal 1.5x charge pump, the output current may be expressed as 2/3 of the input current. The expression to define the ideal efficiency () can be rewritten as: η= POUT VOUT · IOUT VOUT = = VIN · 1.5IOUT 1.5VIN PIN η(%) = 100 ⎛ VOUT ⎞ ⎝ 1.5VIN⎠ For a charge pump with an output of 5V and a nominal input of 3.5V, the theoretical efficiency is 95%. Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 93%. These figures are in close agreement for output load conditions from 1mA to 100mA. Efficiency will decrease substantially as load current drops below 1mA or when level of VIN approaches VOUT. The same calculations apply for 2x mode where the output current then becomes 1/2 of the input current. Capacitor Selection Careful selection of the four external capacitors CIN, C1, C2, and COUT is important because they will affect turn on time, output ripple and transient performance. Optimum performance will be obtained when low ESR (