AAT2847

PRODUCT DATASHEET AAT2847 ChargePumpTM General Description The AAT2847 is a highly integrated power solution for single cell Li-Ion/Polymer based liquid crystal display (LCD) display applications. It includes a four channel light emitting diode (LED) backlight driver and two integrated 200mA low dropout voltage regulators (LDOs) as additional power supplies for display and camera related chipsets. The backlight driver in the AAT2847 is a low noise trimode DC/DC charge pump converter. Each of the four channels of the backlight driver is capable of delivering up to 20mA of bias currents for white LEDs. The white LED (WLED) backlight bias current matching is 1% which helps provide uniform display brightness. AnalogicTech’s AS2Cwire™ (Advanced Simple Serial Control™) serial digital interface is used to enable, disable, and set the current for each backlight LED channel. Each LED channel has sixteen available current level settings in three separate current scales, plus four available current level settings on a low level current scale. Each LED channel is equipped with built-in short circuit protection and auto disable functionality. A low shutdown current feature disconnects the load from the input and reduces quiescent current to less than 1µA. The AAT2847 is available in the thermally enhanced 20-pin 3x4x0.75mm TQFN package. Four-Channel Backlight Driver with Dual LDOs Features • Input Supply Voltage Range: 2.7V to 5.5V • Tri-Mode (1X/1.5X/2X) Charge Pump: ▪ Delivers up to 120mA of Output Current • Integrated LCD Display Solution: ▪ Four-Channel WLED Backlight • User-Programmable WLED Current Scales: 30mA, 20mA and 15mA. ▪ Sixteen Programmable Current Level Settings • User Selectable Low Level Current Scale ▪ Four Programmable Current Level Settings Dual 200mA LDOs (w/Separate Enables) ▪ • Single-Wire AS2Cwire Serial Interface for Configuration/ Control ▪ Four Addressable Registers ▪ Fast, 1MHz Serial Interface • > 90% Peak Efficiency • LDO Output Voltages: ▪ AAT2847-EE: User-Programmable ▪ AAT2847-QG: 2.8V and 1.5V ▪ AAT2847-QI: 2.8V and 1.8V • Over-Temperature Protection • Available in 3x4x0.75mm TQFN34-20 Package • -40°C to +85°C Temperature Range Applications • • • • Camera Function Power Supplies Camera Phone Displays LCD Modules White LED Backlighting Typical Application C1 1µF C2 1µF C2+ C1- C1+ C2C2+ OUT COUT 1µF WLEDs OSRAM LW M673 or equivalent C1 1µF C2 1µF C1- C1+ C2- OUT C OUT 1µF D1 D2 D3 D4 IN LDOA IN WLEDs OSRAM LW M673 or equivalent IN AAT 2847-EE VBAT 3.6V C IN 2.2µF VBAT 3.6V CIN 2.2µF AAT 2847-QI D1 D2 D3 D4 IN LDOA CLDOA 2.2µF VOUTB 1.8V, 200mA CLDOB 2.2µF GND PGND VOUTA 2.8V, 200mA 200mA C LDOA 2.2µF AS2Cwire Backlight control LDO A Enable LDO B Enable EN/SET ENA ENB LDOB AS2Cwire Backlight Control LDO A Enable LDO B Enable FBA EN/SET ENA ENB FBB GND PGND LDOB 200mA C LDOB 2.2µF 2847.2008.05.1.2 www.analogictech.com 1 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Pin Descriptions Symbol Pin # 1 2 3 4, 6 5 7 8 9 10 11 12 13 14 15 16 17 18 19 20 EP AAT2847-EE D2 D1 LDOB IN PGND FBA LDOA C2C2+ OUT C1C1+ EN/SET ENB D4 D3 GND ENA FBB AAT2847-QG/QI D2 D1 LDOB IN PGND NC LDOA C2C2+ OUT C1C1+ EN/SET ENB D4 D3 GND ENA N/C Four-Channel Backlight Driver with Dual LDOs Function LED2 current channel input. Connect to the cathode of backlight LED 2. If not used, connect D2 to the OUT pin. LED1 current channel input. Connect to the cathode of backlight LED 1. If not used, connect D1 to the OUT pin. Output of LDOB. Input voltage supply connection. Power Ground. AAT2847-EE: Feedback pin of LDOA. Internally regulated at 1.2V. AAT2847-QG/QI: No connection. Do not make any connection to this pin. Output of LDOA. Negative terminal of flying capacitor 2. Positive terminal of flying capacitor 2. Charge pump output to drive load circuit. Connect a 1µF or larger ceramic capacitor between OUT and PGND. Negative terminal of flying capacitor 1. Positive terminal of flying capacitor 1. AS2Cwire control pin for backlight LED current profile selection and control. Enable pin for LDOB. Active logic high. LED4 current channel input. Connect to the cathode of backlight LED 4. If not used, connect D4 to the OUT pin. LED3 current channel input. Connect to the cathode of backlight LED 3. If not used, connect D3 to the OUT pin. Ground. Enable pin for LDOA. Active logic high. AAT2847-EE: Feedback pin of LDOB. Internally regulated at 1.2V. AAT2847-QG/QI: No connection. Do not make any connection to this pin. Exposed pad (bottom). Pin Configuration AAT2847-EE TQFN34-20 (Top View) AAT2847-QG/QI TQFN34-20 (Top View) D3 GND ENA FBB 20 19 18 17 D3 GND ENA N/C 20 19 18 17 D2 D1 LDOB IN PGND IN 1 2 3 4 5 6 10 9 7 8 16 15 14 13 12 11 D4 ENB EN/SET C1+ C1OUT D2 D1 LDOB IN PGND IN 1 2 3 4 5 6 10 9 7 8 16 15 14 13 12 11 D4 ENB EN/SET C1+ C1OUT C2+ C2LDOA FBA www.analogictech.com C2+ C2LDOA N/C 2 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Absolute Maximum Ratings1 TA = 25°C, unless otherwise noted. Pin descriptions below apply to AAT2847-EE (AAT2847-QG/QI) Symbol VN VN VN TJ TLEAD Four-Channel Backlight Driver with Dual LDOs Description [IN, OUT, D1, D2, D3, D4] to GND [C1+, C1-, C2+, C2-] to GND [LDOA, LDOB, FBA, FBB, EN/SET, ENA, ENB] to GND Operating Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value -0.3 to 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -40 to 150 300 Units V V V °C °C Thermal Information2, 3 Symbol θJA PD Description Thermal Resistance Maximum Power Dissipation Value 50 2 Units °C/W W 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 in not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Derate 20mW/°C above 40°C ambient temperature. 3. Mounted on a FR4 circuit board. 2847.2008.05.1.2 www.analogictech.com 3 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Electrical Characteristics1 VIN = 3.6V; CIN = CLDOA = CLDOB = 2.2µF; COUT = 1µF; C1 = C2 = 1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions Min 2.7 VEN/SET = VENA = VENB = 0V 1x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load, VENA = VENB = 0V 1.5x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load, VENA = VENB = 0V 2x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load, VENA = VENB = 0V DATA 1, 20mA Range DATA 2, ADDRESS 4 DATA 1, 30mA Range DATA 1, 15mA Range VIN - VF = 1.5V, 20mA Range 20mA Range Four-Channel Backlight Driver with Dual LDOs Typ Max 5.5 1.0 1.0 4.0 5.0 Units V µA Power Supply Input Voltage Range VIN ISHDN Total Shutdown Current at IN Charge Pump IIN Input Operating Current mA IDX I(D-Match) Average Current Accuracy 18 0.9 Current Matching2 1x to 1.5x or 1.5x to 2x Transition VTH Threshold at Any DX Pin fCLK Clock Frequency TSD Over-Temperature Shutdown Threshold THYS Over-Temperature Shutdown Hysteresis EN/SET Logic Control TEN/SET LO EN/SET Low Time TEN/SET_HI_MIN Minimum EN/SET High Time TEN/SET_HI_MAX Maximum EN/SET High Time TOFF EN/SET Off Timeout TLAT EN/SET Latch Timeout VIL(EN/SET) EN/SET Logic Low Threshold Voltage VIH(EN/SET) EN/SET Logic High Threshold Voltage IEN/SET EN/SET Input Leakage 20 1.0 30 15 0.5 150 1 140 15 22 1.1 mA % mV MHz °C °C 1 0.3 50 75 75 500 500 0.4 VEN/SET = VIN = 5V 1.4 -1 1 µs ns µs µs µs V V µA 1. The AAT2847 is guaranteed to meet performance specifications over the –40°C to +85°C operating temperature range 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. 4 www.analogictech.com 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Electrical Characteristics1 VIN = 3.6V; CIN = CLDOA = CLDOB = 2.2µF; COUT = 1µF; C1 = C2 = 1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol IIN Four-Channel Backlight Driver with Dual LDOs Description IN Operating Current Conditions VENA = VENB = VIN, VEN/SET = 0V, No Load VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load ILDO[A/B] = 1mA to 200mA ILDO[A/B] = 150mA VIN = (VLDO[A/B] + 1V) to 5V ILDO[A/B] =10mA, 1kHz VENA = VENB = VIN, VEN/SET = 0V, No Load VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load ILDOA = 1mA to 150mA ILDOB = 1mA to 150mA ILDOA = 150mA VIN = (LDOA + 1V) to 5V; VIN = (LDOB + 1.2V) to 5V ILDO[A/B] =10mA, 1kHz VENA = VENB = VIN, VEN/SET = 0V, No Load VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load ILDOA = 1mA to 150mA ILDOB = 1mA to 150mA ILDOA = 150mA VIN = (LDO[A/B] + 1V) to 5V ILDO[A/B] = 10mA, 1kHz Min Typ 80 60 1.2 150 0.09 50 80 60 2.8 1.5 150 0.09 50 80 60 2.8 1.8 150 0.09 50 Max 150 112 1.23 300 Units µA V mV %/V dB LDOs: AAT2847-EE Feedback Voltage VFBA, VFBB VDO Dropout Voltage ∆VOUT/ Line Regulation VOUT*∆VIN PSRR Power Supply Rejection Ratio LDOs: AAT2847-QG IIN LDOA LDOB VDO ∆VLDO[A/B]/ VLDO[A/B]*∆VIN PSRR IN Operating Current LDOA Voltage Tolerance LDOB Voltage Tolerance LDOA Dropout Voltage2 LDOA, LDOB Line Regulation 1.17 2.716 1.455 150 112 2.884 1.545 300 µA V V mV %/V dB LDOA, LDOB Power Supply Rejection Ratio LDOs: AAT2847-QI IIN LDOA LDOB VDO ∆VLDO[A/B]/ VLDO[A/B]*∆VIN PSRR IN Operating Current LDOA Voltage Tolerance LDOB Voltage Tolerance LDOA Dropout Voltage2 LDOA, LDOB Line Regulation 2.716 1.746 150 112 2.884 1.854 300 µA V V mV %/V dB LDOA, LDOB Power Supply Rejection Ratio LDO Logic Control – All Options VIL(ENA), ENA, ENB Input Logic Low VIL(ENB) Threshold Voltage VIH(ENA), ENA, ENB Input Logic High VIH(ENB) Threshold Voltage ENA, ENB Input Leakage IEN[A/B] 0.4 1.4 VEN[A/B] = VIN = 5V -1 1 V V µA 1. The AAT2847 is guaranteed to meet performance specifications over the –40˚C to +85°C operating temperature range is assured by design, characterization and correlation with statistical process controls. 2. VDO is defined as VIN - LDOA when LDOA is 98% of nominal. 2847.2008.05.1.2 www.analogictech.com 5 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Typical Characteristics Backlight Efficiency vs. Input Voltage 100 90 Four-Channel Backlight Driver with Dual LDOs Backlight Current Matching vs. Temperature (IOUT = 20mA/Channel; VIN = 4.2V) 21 Efficiency (%) 80 70 60 50 40 30 2.7 3.1 3.5 3.9 20mA/Channel LED Current (mA) 5.5 20.5 20 19.5 19 18.5 -40 1mA/Channel 14.5mA/Channel 4.3 4.7 5.1 -15 10 35 60 85 Input Voltage (V) Temperature (°C) EN/SET Latch Timeout vs. Input Voltage 350 300 400 EN/SET Off Timeout vs. Input Voltage -40°C TOFF (µs) 350 300 250 200 150 100 4.3 4.7 5.1 5.5 50 2.7 3.1 -40°C TLAT (µs) 250 200 150 100 50 85°C 25°C 85°C 3.5 3.9 25°C 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Input Voltage (V) Logic High Threshold Voltage vs. Input Voltage 1.2 Logic Low Threshold Voltage vs. Input Voltage 1.2 VIH(ENA/ENB), VIH(EN/SET) (V) VIL(ENA/ENB), VIL(EN/SET) (V) 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 3.1 -40°C 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 3.1 3.5 -40°C 25°C 85°C 25°C 85°C 3.5 3.9 4.3 4.7 5.1 5.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Input Voltage (V) 6 www.analogictech.com 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Typical Characteristics Shutdown Current vs. Input Voltage (VEN/SET = VENA/ENB = 0V) 20 Four-Channel Backlight Driver with Dual LDOs Backlight Operating Characteristic (VIN = 3.7V; 1.5X Mode; 20mA/Channel Load; AC Coupled) VIN (20mV/div) VOUT (40mV/div) Shutdown Current (nA) 15 -40°C 10 5 25°C 85°C VDX (20mV/div) 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Time (500ns/div) Backlight Operating Characteristic (VIN = 3.5V; 1.5X Mode; 14mA/Channel Load; AC Coupled) VIN (20mV/div) VOUT (40mV/div) VIN (20mV/div) VOUT (40mV/div) Backlight Operating Characteristic (VIN = 2.9V; 2X Mode; 20mA/Channel Load; AC Coupled) VDX (20mV/div) VDX (40mV/div) Time (500ns/div) Time (500ns/div) Backlight Operating Characteristic (VIN = 2.9V; 2X Mode; 14mA/Channel Load; AC Coupled) VIN (20mV/div) VOUT (40mV/div) VDX (40mV/div) Time (500ns/div) 2847.2008.05.1.2 www.analogictech.com 7 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Typical Characteristics Turn On to 1X Mode Backlight (20mA/Channel; Address 0, Data 1; VIN = 4.2V) VEN/SET (2V/div) VOUT (2V/div) VDX (500mV/div) IIN (100mA/div) Time (500ns/div) Four-Channel Backlight Driver with Dual LDOs Turn On to 1.5X Mode Backlight (20mA/Channel; Address 0, Data 1; VIN = 3.5V) VEN/SET (2V/div) VOUT (2V/div) VDX (500mV/div) IIN (200mA/div) Time (200µs/div) Turn On to 2X Mode Backlight (20mA/Channel; Address 0, Data 1; VIN = 3.2V) VEN/SET (2V/div) VOUT (2V/div) VDX (500mV/div) IIN (200mA/div) Time (200µs/div) Turn Off from 1.5X Mode Backlight (20mA/Channel; Address 0, Data 1; VIN = 3.6V) VEN/SET (2V/div) VOUT (2V/div) ILED (20mA/div) Time (100µs/div) LDOA/LDOB Load Regulation Output Voltage Error (%) Output Voltage Error (%) 1.0 1.000 LDOA/LDOB Line Regulation 0.5 LDOA 0.500 LDOA 0.0 0.000 -0.5 LDOB -0.500 LDOB -1.0 0.1 1 10 100 1000 -1.000 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Load Current (mA) Input Voltage (V) 8 www.analogictech.com 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Typical Characteristics LDOA/LDOB Quiescent Current vs. Input Voltage (VOUT = 1.2V) 120 Four-Channel Backlight Driver with Dual LDOs LDOA Load Transient Response (VIN = 3.6V; VLDOA = 1.2V) 200mA Quiescent Current (µA) 100 80 60 40 20 0 2.7 85°C 25°C ILDOA (100mA/div) 10mA -40°C VLDOA (100mV/div) 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Time (20µs/div) LDOB Load Transient Response (VIN = 3.6V; VLDOB = 1.2V) 200mA LDOA Line Transient Response (10mA Load) VIN = 4.2V ILDOB (100mA/div) 10mA VIN (400mV/div) VIN = 3.6V VLDOB (100mV/div) VLDOA (20mV/div) Time (20µs/div) Time (40µs/div) LDOB Line Transient Response (10mA Load) VIN = 4.2V VIN (400mV/div) VIN = 3.6V VLDOB (20mV/div) Time (40µs/div) 2847.2008.05.1.2 www.analogictech.com 9 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Typical Characteristics LDOA/LDOB Turn On (VIN = 3.6V; VLDO(A/B) = 2.8V; DC Coupled) Four-Channel Backlight Driver with Dual LDOs LDOA/LDOB Turn On (VIN = 3.6V; VLDO(A/B) = 1.8V; DC Coupled) VEN(A/B) (2V/div) VEN(A/B) (2V/div) VLDO(A/B) (1V/div) VLDO(A/B) (1V/div) Time (40µs/div) Time (40µs/div) LDOA/LDOB Turn On (VIN = 3.6V; VLDO(A/B) = 1.5V; DC Coupled) LDOA/LDOB Turn On (VIN = 3.6V; VLDO(A/B) = 1.2V; DC Coupled) VEN(A/B) (2V/div) VEN(A/B) (2V/div) VLDO(A/B) (500mV/div) VLDO(A/B) (500mV/div) Time (40µs/div) Time (40µs/div) 10 www.analogictech.com 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 AAT2847 ChargePumpTM Functional Block Diagram C1+ AAT 2847-EE (AAT 2847-QG/-QI) IN C1- C2+ C2- Four-Channel Backlight Driver with Dual LDOs Tri-Mode (1x, 1.5x and 2x) Charge Pump OUT 1MHz Oscillator Voltage Reference 1.2V Reference D/A D/A D1 D2 D3 D4 EN/SET AS Cwire Interface 2 6 x16 bit ROM D/A D/A IN LDO A LDOA (2.8V/2.8V) FBA (NC) LDOB (1.5V/1.8V) FBB (NC) ENA LDO B ENB (AAT 2847-QG/-QI) GND PGND Functional Description The AAT2847 is an integrated solution for LCD display applications with a built-in four channel white LED driver (charge pump) and dual 200mA LDO voltage regulators. The AAT2847 incorporates a tri-mode charge pump with load switch (1X) functionality and high efficiency (1.5X or 2X) performance. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required at each white LED cathode input pin (D1-D4) and sets the load switch and charge pump mode based on the input battery voltage and the white LED cathode pin voltage. The voltage threshold for 1X to 1.5X and 1.5X to 2X mode transitions is VTH. The charge pump in the AAT2847 starts-up in 1X mode (default); under this condition, if the LED cathode input pin voltage is below VTH the AAT2847 will transition into 1.5X mode. When 1.5X mode does not provide enough current through the white LEDs for backlight applications, which occurs during the normal discharge of the input battery power source, the LED cathode input pin voltage will drop below VTH and the AAT2847 will transition into 2X mode. The charge pump requires only four external capacitors, 1µF ceramic capacitors for the flying (C1 and C2), input (CIN), and output (COUT) capacitors. The four LED cathode input pins (D1-D4) can drive individual LEDs with a maximum current of 30mA each. The unused LED cathode input pins have to be connected to the OUT pin, otherwise the AAT2847 will operate in 2X mode only. Operating in 2X mode when it is not necessary will result in a significant reduction in efficiency. The AS2Cwire serial interface enables the charge pump and sets the current flowing into the LED cathode input pins. The AAT2847 also contains dual LDO voltage regulators that have separate enable pins from each other and the charge pump. The separate enable pins for each DC/DC device in the AAT2847 allow for every possible device operational combination. The two LDO regulators require 2.2µF output capacitors for stable operation. 2847.2008.05.1.2 www.analogictech.com 11 PRODUCT DATASHEET AAT2847 ChargePumpTM 30.0 25.0 Four-Channel Backlight Driver with Dual LDOs AS2Cwire Serial Interface Addressing Address 0 3 4 5 Address 4 LED Current (mA) EN/SET Edges 17 20 21 22 Addressed Register D1-D4 Current Control Current Scale Low Current Control Independent LED Control 20.0 15.0 10.0 5.0 0.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4 Address 0 Table 1: AS2Cwire Serial Interface Addressing. Code Current Operation (Address 0) Use Address 0 to program all four LED channels with the current values in Table 2. All four white LED channels are programmed to the same current level by writing to Address 0 followed by any Data between, and including, 1 to 16. Figure 1: LED Current Control Profile. AS2Cwire Serial Interface Each white LED channel input on the AAT2847 (D1-D4) is controlled by AnalogicTech’s AS2Cwire serial digital interface. The AS2Cwire interface uses the number of rising edges on the EN/SET pin to address and load the LED configuration registers. AS2Cwire latches data or addresses after the EN/SET pin has been held logic high for longer than TLAT (500µs). Addresses and data are differentiated by the number of EN/SET rising edges. Since the data registers are 4 bits each, the differentiating number of pulses is 24 or 16, so that Address 0 is signified by 17 rising edges, Address 1 by 18 rising edges, Address 2 by 19 rising edges, and so on. Data is set to any number of rising edges between, and including, 1 to 16. A typical write protocol consist of the following: First a burst of EN/SET rising edges that identify/target a particular address followed by EN/SET being held logic high for the TLAT timeout period to latch the address value in the address register, then another burst of rising edges that signify data with the accompanying TLAT timeout period to latch the data value in the data register. Once an address is set, then multiple writes to the corresponding data register are allowed without having to write to the address for every value change in the data register. When EN/SET is held low longer than TOFF (500µs), the AAT2847 enters shutdown mode operation and draws less than 1µA from the input supply voltage. Data and address registers are cleared (0 for the address register and 1 for the data registers) in shutdown mode operation. Current Scale (Address 3) The AAT2847 has three selectable current scales for the four white LED channels: 30mA, 20mA, and 15mA. Only one of the three current scales can be active at any given time. By default, the 20mA current scale is active upon start-up. To change to the 30mA or 15mA current scale, or go back to the 20mA scale, write to Address 3 with the appropriate Data between, and including, 1 to 3. To enable low current mode, write Data 4 to Address 3. Low current mode results in the four white LED channels reverting to the current set by the low current settings in Address 4. 30mA Scale 30.0 28.5 26.6 25.2 23.3 21.8 19.8 18.5 16.5 15.0 13.1 11.6 9.8 8.3 6.3 4.8 Data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 20mA Scale 20.0 19.0 17.7 16.8 15.5 14.5 13.2 12.3 11.0 10.0 8.7 7.7 6.5 5.5 4.2 3.2 15mA Scale 15.0 14.3 13.3 12.6 11.6 10.9 9.9 9.2 8.3 7.5 6.5 5.8 4.9 4.1 3.2 2.4 Table 2: Current Settings—Address 0. 12 www.analogictech.com 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Address T HI T LO TLAT TLAT Data EN/SET 1 2 19 20 1 2... n ≤ 16 Address 0 3 DATA3 1 n DATA0 1 Figure 2: AS2Cwire Serial Interface Timing. Data 1 2 3 4 Current Scale 20mA Scale 30mA Scale 15mA Scale Low Current Mode Independent LED Current Control (Address 5) Independent LED control allows for individual LEDs to be enabled and disabled to form custom arrangement of active LEDs. To enable independent control write Address 5 with Data between, and including, 1 to 16. Data D4 on on on on on on on on off off off off off off off off Table 3: Current Scale Settings—Address 3. D3 on on on on off off off off on on on on off off off off D2 on on off off on on off off on on off off on on off off D1 on off on off on off on off on off on off on off on off Low Current Operation (Address 4) All four LED channels are programmed to the same low current level by writing to Address 4 followed by any Data between, and including, 1 to 4. This operational mode is especially useful for low current applications where a continuous low current state is maintained for a substantial length of time. Data 1 2 3 4 mA 0.5 1.0 1.5 2.0 Table 4: Low Current Settings—Address 4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Table 5: Independent LED Control Settings— Address 5. 2847.2008.05.1.2 www.analogictech.com 13 PRODUCT DATASHEET AAT2847 ChargePumpTM Auto Disable Feature The charge pump in the AAT2847 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and successively starts-up, a test current of 100µA (typical) is forced through each LED channel. The channel will be disabled if the voltage on that particular DX pin does not drop to certain threshold. This feature is convenient for disabling an unused channel or during an LED short circuiting event. Four-Channel Backlight Driver with Dual LDOs Applications Information LED Selection The charge pump in the AAT2847 is specifically intended for driving white LEDs. However, the AAT2847 can 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 D4 constant current channels are matched with negligible voltage dependence, the constant current channels will be matched regardless of the specific LED forward voltage (VF) levels. Multiple channels can be combined to obtain a higher LED drive current without complication. Low Dropout Regulators The AAT2847 incorporates two LDO voltage regulators. The two regulators run from the same 2.7V to 5.5V input voltage as the charge pump and have separate ON/OFF control inputs, ENA and ENB. For the AAT2847-EE, the LDO output voltages are set through a resistive voltage divider from the output (LDOA or LDOB) to the feedback input (FBA or FBB). The ratio of the voltage divider resistor values determines the LDO output voltage. For the AAT2847-QG option, LDOA is internally set to 2.8V and LDOB is internally set to 1.5V. For the AAT2847-QI option, LDOA is also 2.8V and LDOB is internally set to 1.8V. Each LDO regulator can supply a continuous load current up to 200mA, and both LDOs include current limiting and thermal overload protection to prevent damage to the load or to the LDO. AAT2847-EE LDO Output Voltage Programming The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown in Figure 3, the selection of R1 and R2 is a straightforward matter. R1 is chosen by considering the tradeoff between the feedback network bias current and resistor value. Higher resistor values allow stray capacitance to become a larger factor in circuit performance, whereas lower resistor values decrease efficiency. LDO(A/B) R2(A/B) FB(A/B) VREF = 1.2V R1(A/B) VLDO(A/B) Thermal Protection The charge pump has built-in thermal protection circuitry that will shut down the charge pump and the LDOs if the die temperature rises above the thermal limit, as is the case during an OUT pin short circuit event. Figure 3: Selection of External Resistors. To select appropriate resistor values, first choose a value for R1 that will produce a reasonable feedback network bias current. Then, according to the desired VLDO(A/B), calculate R2 according to the equation below. An example calculation follows. R1 is chosen to be 120kΩ, resulting in a small feedback network bias current of 10µA (VFB(A/B)/R1 = 1.2V/120kΩ). The desired output voltage is 1.8V. From this information, R2 is calculated from the equation below: 14 www.analogictech.com 2847.2008.05.1.2 PRODUCT DATASHEET AAT2847 ChargePumpTM R2(A/B) = R1(A/B)(VLDO(A/B) - 1.2V) 1.2V Four-Channel Backlight Driver with Dual LDOs With an ideal 1.5X charge pump, the input current is 1.5X of the output current. The expression to define the estimated ideal efficiency (η) for the AAT2847 in 1.5X mode is as follows: The result is R2 = 60kΩ. Since 60kΩ is not a standard 1% resistor value, 60.4kΩ is selected. From this example calculation, for VOUT = 1.8V, use R1 = 120kΩ and R2 = 60.4kΩ. A table of example output voltages and corresponding resistor values is provided below. R2 Standard 1% Values (R1 = 120kΩ) VLDO(A/B) (V) 2.8 2.5 2 1.8 1.5 η= η= PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4 = PIN VIN · IIN 4 · VLEDX · ILEDX ; x = 1, 2, 3 or 4 and IIN = 1.5(4 · ILEDX) VIN · IIN IN R2 (Ω) 160k 130k 79.6k 60.4k 30.1k VLEDX η = 1.5V Table 6: Example Output Voltages and Corresponding Resistor Values. The same calculations apply for the AAT2847 in 2X mode where for an ideal 2X charge pump, the input current is 2X of the output current. The expression for the estimated ideal efficiency (η) for the AAT2847 in 2X mode is as follows: η= PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4 = PIN VIN · IIN 4 · VLEDX · ILEDX ; x = 1, 2, 3 or 4 and IIN = 2(4 · ILEDX) VIN · IIN Device Power Efficiency The AAT2847’s charge pump conversion efficiency is defined as the power delivered to the white LED load divided by the input power: η= η= PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4 = PIN VIN · IIN VLEDX η = 2V IN VLEDx = White LED Forward Voltage (VF) ILEDx = White LED Bias Current (ID) The expression to define the estimated ideal efficiency (η) for the AAT2847 in 1X mode is as follows: Capacitor Selection Careful selection of the six external capacitors CIN, C1, C2, CLDOA, CLDOB, and COUT are important because they will affect turn on time, output ripple and transient performance. Optimum performance will be obtained when low ESR (