PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs General Description Features The AAT2845 is a highly integrated power solution for single-cell lithium-ion-based LCD display applications. It includes a four-channel LED backlight driver and two integrated 200mA LDOs as additional power supplies for display and camera-related chipsets. • Input Voltage Range: 2.7V to 5.5V • Four-Channel LED Driver: ▪ Tri-Mode Charge Pump ▪ Up to 20mA/Channel ▪ Easy Control with Single Wire Interface ▪ 16 Current Levels ▪ Four Low Current Settings Down to 50µA ▪ Low IQ (50µA) for Low Current Mode ▪ >90% Peak Efficiency • Dual, 200mA LDOs ▪ User-Programmable Outputs: AAT2845-EE ▪ Fixed Output Voltages • AAT2845-QG: 2.8V and 1.5V • AAT2845-QI: 2.8V and 1.8V • Automatic Soft-Start • Over-Temperature Protection • Available in 3x4mm TQFN34-20 Package • -40°C to +85°C Temperature Range The backlight driver is a low noise, constant frequency charge pump DC/DC converter that uses a tri-mode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency. Each of the four channels is capable of driving up to 20mA per channel. AnalogicTech’s S2Cwire™ (Simple Serial Control™) serial digital input is used to enable, disable, and set current for each LED with 16 available settings down to 50µA. The low current mode supply current can be as low as 50µA to save power and maintain high efficiency. Each LED output is equipped with built-in protection for short-circuit and auto-disable functions. Built-in softstart circuitry prevents excessive inrush current during start-up. A low current shutdown feature disconnects the load from the input and reduces quiescent current to less than 1µA. The AAT2845 is available in a Pb-free, thermallyenhanced 20-pin 3x4mm TQFN package. Applications • • • • Camera Function Power Supplies Camera Phone Displays LCD Modules White LED Backlighting Typical Application CF1 1µF C1- CF2 1µF C1+ C2- CF1 1µF C2+ C1- C1+ C2- OUT VBAT 3.6V CIN 2.2µF LDOA FBA S2Cwire Backlight Control EN/SET LDO Enable ENLDO LDOB CBYP 0.1µF 2845.2008.05.1.2 COUT 1µF WLEDs OSRAM LW M673 or equivalent D1 D2 D3 D4 IN CBP FBB GND/PGND C2+ OUT IN AAT2845-EE CF2 1µF IN VBAT 3.6V AAT2845-QI CIN 2.2µF 200mA COUTB 2.2µF WLEDs OSRAM LW M673 or equivalent D1 D2 D3 D4 IN VOUTA 2.8V, 200mA LDOA COUTA 2.2µF 200mA COUT 1µF COUTA 2.2µF S2Cwire Backlight Control EN/SET LDO Enable ENLDO CBYP 0.1µF www.analogictech.com VOUTB 1.8V, 200mA LDOB COUTB 2.2µF CBP GND/PGND 1 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Pin Descriptions Symbol Pin # AAT2845-EE AAT2845-QG/QI 1 2 3 D2 D1 LDOB D2 D1 LDOB 4 IN IN 5 PGND PGND 6 IN IN 7 FBA N/C 8 9 LDOA C2- LDOA C2- 10 C2+ C2+ 11 OUT OUT 12 C1- C1- 13 C1+ C1+ 14 15 16 17 18 EN/SET ENLDO D4 D3 GND EN/SET ENLDO D4 D3 GND 19 CBP CBP 20 FBB N/C Function Current sink input #2. Current sink input #1. Output of LDO B. Connect a 2.2µF or larger ceramic capacitor to GND. Input power supply for charge pump. Requires a 2.2µF or larger ceramic capacitor connected between IN and PGND. Power ground. Connect PGND to GND at a single point as close to the AAT2845 as possible. Input power pin for both LDOs. Connect Pin 6 to Pin 4 with as short a PCB trace as practical. AAT2845-EE: Feedback pin for LDOA. Internally regulated at 1.2V. AAT2845-QG/QI: No connection. Do not make any connection to this pin. Output of LDOA. Connect a 2.2µF or larger ceramic capacitor to GND. Negative terminal of Charge Pump Capacitor 2. Positive terminal of Charge Pump Capacitor 2. Connect a 1µF ceramic capacitor between C2+ and C2-. Charge pump output to drive load circuit. Connect a 1µF or larger ceramic capacitor between OUT and PGND. Negative terminal of Charge Pump Capacitor 1. Positive terminal of Charge Pump Capacitor 1. Connect a 1µF ceramic capacitor between C1+ and C1-. S2Cwire control pin for backlight LED current control. Enable input pin for LDOA and LDOB. Current sink input #4. Current sink input #3. Ground. Connect GND to PGND at a single point as close to the AAT2845 as possible. Bypass pin for the internal reference. Connect a 0.1µF ceramic capacitor from CBP to GND. AAT2845-EE: Feedback pin for LDOB. Internally regulated at 1.2V. AAT2845-QG/QI: No connection. Do not make any connection to this pin. Exposed paddle (bottom). Connect to PGND as close as possible to the device. EP Pin Configuration AAT2845-EE TQFN34-20 (Top View) AAT2845-QG/-QI TQFN34-20 (Top View) D3 GND CBP N/C D3 GND CBP FBB 15 3 14 4 13 5 12 6 11 D4 ENLDO EN/SET C1+ C1OUT D2 D1 LDOB IN PGND IN 1 16 2 15 3 14 4 13 5 12 6 11 D4 ENLDO EN/SET C1+ C1OUT 9 10 8 7 9 10 8 7 C2+ C2LDOA N/C C2+ C2LDOA FBA 2 17 16 2 18 1 19 20 17 18 19 20 D2 D1 LDOB IN PGND IN www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Absolute Maximum Ratings1 TA = 25°C, unless otherwise noted. Pin descriptions below apply to AAT2845-EE (AAT2845-QG/-QI). Symbol TJ TLEAD Description IN, OUT, D1, D2, D3, D4 Voltage to GND/PGND C1+, C1-, C2+, C2- Voltage to GND/PGND LDOA, LDOB, FBA (N/C), FBB (N/C), EN/SET, ENLDO, CBP Voltage to GND/PGND PGND Voltage to GND/PGND Operating Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units -0.3 to 6.0 -0.3 to VOUT +0.3 -0.3 to VIN +0.3 -0.3 to +0.3 -40 to 150 300 V V V V °C °C Value Units 50 2 °C/W W Thermal Information2, 3 Symbol θJA PD Description Thermal Resistance Maximum Power Dissipation 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 40°C ambient temperature. 3. Mounted on a FR4 circuit board. 2845.2008.05.1.2 www.analogictech.com 3 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Electrical Characteristics1 IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions Power Supply IN Input Voltage ISHDN Total Shutdown Current at VIN and LDOIN Charge Pump ICC IDX I(D-Match) Operating Current Average Current Accuracy Current Matching 1X to 1.5X or 1.5X to 2X Transition VTH Threshold at Any DX Pin TSS Soft-Start Time Clock Frequency FCLK 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 EN/SET Input Low Threshold Voltage VIL(EN/SET) VIH(EN/SET) EN/SET Input High Threshold Voltage IEN/SET EN/SET Input Leakage 2 Min Typ 2.7 EN/SET = ENLDO = GND 1X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load Current 1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load Current 2X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load Current 50µA Setting, 1X Mode 20mA Setting, TA = 25°C 1mA Setting, TA = 25°C VIN - VF = 1.5V Max Units 5.5 1.0 V µA 1.0 3.0 5.0 18 0.9 50 20 1.0 0.5 µA 22 1.1 1.0 % mV 100 1 140 15 µs MHz °C °C 75 50 75 500 500 0.4 1.4 -1 mA 150 0.3 VEN/SET = VIN = 5V mA 1 µs ns µs µs µs V V µA 1. The AAT2845 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. 4 www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Electrical Characteristics1 IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol Description LDOs: AAT2845-EE IIN IN Operating Current VFBA, VFBB Feedback Voltage VDO Dropout Voltage ∆VOUT/ Line Regulation VOUT*∆VIN PSRR Power Supply Rejection Ratio LDOs: AAT2845-QG IN Operating Current IIN LDOA LDOA Voltage Tolerance LDOB LDOB Voltage Tolerance VDO LDOA, LDOB Dropout Voltage2 ∆VLDOA/B/ LDOA, LDOB Line Regulation VLDOA/B*∆VIN PSRR LDOA, LDOB Power Supply Rejection Ratio LDOs: AAT2845-QI IIN IN Operating Current LDOA LDOA Voltage Tolerance LDOB LDOB Voltage Tolerance VDO LDOA, LDOB Dropout Voltage2 ∆VLDOA/B/ LDOA, LDOB Line Regulation VLDOA/B*∆VIN PSRR LDOA, LDOB Power Supply Rejection Ratio LDO Logic Control – All Options VIL(ENLDO) ENLDO Pins Logic Low Threshold ENLDO Pins Logic High Threshold VIH(ENLDO) IENLDO ENLDO Input Leakage Conditions Min Typ Max Units ENLDO = IN, EN/SET = AGND, No Load IOUT = 1mA to 200mA IOUT = 150mA 1.17 80 1.2 150 150 1.23 300 µA V mV VIN = (VOUT + 1V) to 5.0V IOUT =10mA, 1kHz ENLDO = IN, EN/SET = GND, No Load IOUTA = 1mA to 150mA IOUTB = 1mA to 150mA IOUTA/B = 150mA VIN = (LDOA + 1V) to 5.0V; VIN = (LDOB + 1.2V) to 5.0V ENLDO = IN, EN/SET = GND, No Load IOUTA = 1mA to 150mA IOUTB = 1mA to 150mA IOUTA/B = 150mA 2.716 1.455 %/V 50 dB 80 2.8 1.5 150 150 2.884 1.545 300 0.09 2.716 1.746 VIN = (LDOA/B + 1V) to 5.0V VENLDO = VIN = 5V 0.09 80 2.8 1.8 150 % 50 dB 150 2.884 1.854 300 µA V V mV 0.09 1.4 -1 µA V V mV % 50 dB 0.4 V V µA 1 1. The AAT2845 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 is defined as VIN - LDOA/B when LDOA/B is 98% of nominal. 2845.2008.05.1.2 www.analogictech.com 5 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Typical Characteristics IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. Backlight Efficiency vs. Supply Voltage Turn-On to 1X Mode (VIN = 4.2V; 20mA/ch Load) 100 EN/SET (2V/div) Efficiency (%) 90 20mA/ch 80 VOUT (2V/div) 70 60 1mA/ch 50 VSINK (1V/div) IIN (100mA/div) 14.7mA/ch 40 30 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 Time (100µs/div) Supply Voltage (V) Turn-On to 1.5X Mode Turn-On to 2X Mode (VIN = 3.5V; 20mA/ch Load) (VIN = 2.8V; 20mA/ch Load) EN/SET (2V/div) EN/SET (2V/div) VOUT (2V/div) VOUT (2V/div) VSINK (500mV/div) IIN (500mA/div) VSINK (1V/div) IIN (200mA/div) Time (100µs/div) Time (100µs/div) Turn-Off from 1.5X Mode Backlight (30mA/ch; Data 1) EN (2V/div) VDIODE (2V/div) IIN (200mA/div) Time (100µs/div) 6 www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Typical Characteristics IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. Backlight Operating Characteristic Backlight Operating Characteristic (VIN = 2.9V; 2X Mode; 14mA/ch Load) (VIN = 2.9V; 2X Mode; 20mA/ch Load) VIN (20mV/div) VIN (20mV/div) VCP (40mV/div) VCP (40mV/div) VSINK (40mV/div) VSINK (40mV/div) Time (500ns/div) Time (500ns/div) Backlight Operating Characteristic Backlight Operating Characteristic (VIN = 3.5V; 1.5X Mode; 14mA/ch Load) (VIN = 3.7V; 1.5X Mode; 20mA/ch Load) VIN (20mV/div) VIN (20mV/div) VCP (40mV/div) VCP (40mV/div) VSINK (20mV/div) VSINK (20mV/div) Time (500ns/div) Time (500ns/div) 500 400 350 300 -40°C 250 200 150 25°C 100 85°C 50 0 EN/SET Off Timeout vs. Supply Voltage EN/SET Off Timeout (µs) EN/SET Latch Timeout (µs) EN/SET Latch Timeout vs. Supply Voltage 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 5.5 450 400 350 250 200 150 100 25°C 85°C 50 0 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 Supply Voltage (V) 2845.2008.05.1.2 -40°C 300 Supply Voltage (V) www.analogictech.com 7 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Typical Characteristics EN/SET and ENLDO Low Threshold Voltage vs. Supply Voltage and Temperature 1 0.9 -40°C 0.8 0.7 0.6 0.5 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 EN/SET High Threshold Voltage (V) EN/SET Low Threshold Voltage (V) IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. EN/SET and ENLDO High Threshold Voltage vs. Supply Voltage and Temperature 1 -40°C 0.9 0.8 0.7 0.6 25°C 0.5 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 Supply Voltage (V) Supply Voltage (V) AAT2845-EE LDOA Turn-On Characteristic AAT2845-EE LDOB Turn-On Characteristic (VOUTA = VFBA) (VOUTB = VFBB) ENLDO (2V/div) ENLDO (2V/div) VOUT (500mV/div) VOUT (500mV/div) Time (50µs/div) Time (50µs/div) AAT2845-QG/QI LDOA Turn-On Characteristic AAT2845-QI LDOB Turn-On Characteristic (VOUTA = 2.8V) (VOUTB = 1.8V) ENLDO (2V/div) ENLDO (2V/div) VOUT (1V/div) VOUT (500mV/div) Time (50µs/div) 8 85°C Time (50µs/div) www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Typical Characteristics IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. AAT2845-QG LDOB Turn-On Characteristic LDOs A and B Line Regulation, All Options (VOUTB = 1.5V) (10mA Load) 0.4 0.3 ENLDO (2V/div) Error (%) 0.2 VOUT (500mV/div) 0.1 OUTA 0.0 -0.1 OUTB -0.2 -0.3 -0.4 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 Time (50µs/div) Supply Voltage (V) LDOs A and B Load Regulation, All Options LDOB Line Transient Response, All Options (10mA Load) 1.0 0.8 VIN (400mV/div) Error (%) 0.6 0.4 VIN = 4.2V 0.2 OUTA 0.0 VIN = 3.7V -0.2 -0.4 -0.6 VOUT (10mV/div) OUTB -0.8 -1.0 0.1 1 10 100 1000 Time (40µs/div) Load Current (mA) LDOB Line Transient Response, All Options (10mA Load) VIN (400mV/div) VIN = 4.2V VIN = 3.7V VOUT (10mV/div) Time (40µs/div) 2845.2008.05.1.2 www.analogictech.com 9 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Typical Characteristics IN = 3.6V; CIN = COUTA = COUTB = 2.2µF; COUT = 1µF; C1 = C2 = 1.0µF; CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C. LDOA Load Transient Response, All Options LDOB Load Transient Response, All Options IOUT (100mA/div) IOUT (100mA/div) VOUT (100mV/div) VOUT (100mV/div) Time (20µs/div) 10 Time (20µs/div) www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Functional Block Diagram C1+ C1- C2+ C2- Tri-Mode (1X, 1.5X and 2X) Charge Pump IN OUT Soft-Start Control 1MHz Oscillator Voltage Reference EN/SET S2Cwire Interface 6x16 Bit ROM IN D1 D/A D2 D/A D3 D/A D4 LDOA LDO A ENLDO CBP D/A FBA 1.2V Reference LDOB LDO B FBB GND Functional Description The AAT2845 is an integrated solution for LCD display applications with a built-in driver for white LED backlight and two LDO voltage regulators for logic power supplies. The backlight driver is a tri-mode load switch (1X) and high-efficiency (1.5X or 2X) charge pump device. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant current sink input and sets the load switch and charge pump modes based on the input battery voltage and the current sink input voltage. As the battery discharges over time, the charge pump is enabled when any of the four current sink inputs nears dropout. The charge pump initially starts in 1.5X mode. If the charge pump output droops enough for any current source output to become close to dropout, the charge pump will automatically transition to 2X mode. The charge pump requires only four external components: two 1µF ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1µF 2845.2008.05.1.2 ceramic input capacitor (CIN), and one 0.33µF to 1µF ceramic charge pump output capacitor (COUT). The four constant current sink inputs (D1 to D4) can drive four individual LEDs with a maximum current of 20mA each. The unused sink inputs must be connected to the OUT pin; otherwise the part will operate only in 2X charge pump mode. The S2Cwire serial interface enables the charge pump and sets the current sink magnitudes. Constant Current Output Level Settings The constant current sink levels for D1 to D4 are set via the S2Cwire serial interface according to a logarithmic scale for the first 12 codes, and a separate low-current scale for the last four codes. Because the inputs D1 to D4 are true independent constant current sinks, the voltage observed on any single given input will be determined by the difference between VOUT and the actual forward voltage (VF) of the LED being driven. www.analogictech.com 11 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Since the current level is programmable, no PWM (pulse width modulation) or additional control circuitry is needed to control LED brightness. This feature greatly reduces the burden on a microcontroller or system IC to manage LED or display brightness, allowing the user to “set it and forget it.” With its high-speed serial interface (>1MHz data rate), the LED current drive can be changed successively to brighten or dim LEDs in smooth transitions (e.g., to fade out) or in abrupt steps, giving the user complete programmability and real-time control of LED brightness. programming, the number of rising edges corresponding to the desired code must be applied on the EN/SET pin. When the EN/SET pin is held low for an amount of time longer than TOFF (500µs), the AAT2845 enters shutdown mode and draws less than 1µA from the input. An internal data register is reset to zero during shutdown. Auto-Disable Feature The last four codes of the current level scale engage a reduced quiescent current mode that enhances the lowcurrent setting efficiency. This mode is especially useful for low-current applications where a continuous, low-current state is maintained for a substantial length of time. The charge pump in the AAT2845 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 100µA (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular DX pin does not drop to a certain threshold. This feature is convenient for disabling an unused channel or during an LED fail-short event. S2Cwire Serial Interface Low Dropout Regulators The current sink magnitude is controlled by AnalogicTech’s S2Cwire serial digital input. The interface records rising edges of the EN/SET pin and decodes them into 16 different states. The 16 current level settings available are indicated in Table 1. The AAT2845 product family includes two LDO linear regulators. The regulators run from the same 2.7V to 5.5V input voltage as the charge pump and have a common ON/OFF control input, ENLDO. For the AAT2845-EE, the LDO output voltages are set through a resistive voltage divider from the output (OUTLDOA or OUTLDOB) to the feedback input (FBA or FBB). The ratio of resistor values determines the LDO output voltage. For the AAT2845-QG option, LDOA is internally set to 2.8V and LDOB is internally set to 1.5V. For the AAT2845-QI option, LDOA is also 2.8V and LDOB is internally set to 1.8V. Data Output (mA/Ch) Data Output (mA/Ch) 1 2 3 4 5 6 7 8 20 18.9 18.0 17.0 15.7 14.8 10.2 8.0 9 10 11 12 13 14 15 16 6.0 4.2 2.9 2.0 1.0 0.53 0.10 0.05 Table 1: Current Level Settings. The S2Cwire serial interface has flexible timing. Data can be clocked-in at speeds higher than 1MHz, or much slower, such as 15kHz. After data is applied, EN/SET is held high to latch the data. Once EN/SET has been held in the logic high state for time TLAT (500µs), the programmed current becomes active and the internal data register is reset to zero. For subsequent current level 12 The low 200mV dropout voltage at 200mA load current allows the regulator to maintain output voltage regulation. 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 LDOs. Thermal Protection The charge pump has a built-in thermal protection circuit that will shut down the charge pump and the LDOs if the die temperature rises above the thermal limit, as is the case during a short-circuit of the OUT pin. www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs T HI T LO TOFF TLAT EN/SET 1 2 n-1 n ≤ 16 0 Data Reg n-1 0 Figure 1: S2Cwire Serial Interface Timing. Applications Information Shutdown LED Selection The AAT2845 is specifically intended for driving white LEDs. However, the device design will allow the AAT2845 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 D4 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. The low dropout current sinks in the AAT2845 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. Since the sink switches are the only power returns for all loads, there is no leakage current when all of the sink switches are disabled. To activate the shutdown mode, hold the EN/SET input low for longer than TOFF (500µs). In this state, the AAT2845 typically draws less than 1µA from the input. Data and address registers are reset to 0 in shutdown. AAT2845-EE LDO Output Voltage Programming The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown below, 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 increase bias current and decrease efficiency. LDO(A/B) Device Switching Noise Performance The AAT2845 operates at a fixed frequency of approximately 1MHz to 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-to-peak, typically ten times less than inductor-based DC/DC boost converter white LED backlight solutions. The AAT2845 soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit. 2845.2008.05.1.2 VOUT(A/B) R2(A/B) FB(A/B) VREF = 1.2V R1(A/B) Figure 2: Selection of External Resistors. To select appropriate resistor values, first choose R1 such that the feedback network bias current is reasonable. Then, according to the desired VOUT, calculate R2 according to the equation below. An example calculation follows. www.analogictech.com 13 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs R1 is chosen to be 120K, resulting in a small feedback network bias current of 1.2V/120K = 10µA. The desired output voltage is 1.8V. From this information, R2 is calculated from the equation below. R2 = R1(VOUT - 1.2V) 1.2V The result is R2 = 60K. Since 60K is not a standard 1% value, 60.4K is selected. From this example calculation, for VOUT = 1.8V, use R1 = 120K and R2 = 60.4K. A table of example output voltages and corresponding resistor values is provided below. R2 Standard 1% Values (R1 = 120K) VOUT (V) R2 (Ω) 2.8 2.5 2.0 1.8 1.5 160K 130K 79.6K 60.4K 30.1K Table 2: Example Output Voltages and Corresponding Resistor Values Power Efficiency and Device Evaluation The charge pump efficiency discussion in the following sections accounts only for efficiency of the charge pump section itself. Due to the unique circuit architecture and design of the AAT2845, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT2845 outputs are pure constant current sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output (D1 to D4) 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. The AAT2845 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 D4 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 for each operational mode. 1X Mode Efficiency The AAT2845 1X mode is operational at all times and functions alone to enhance device power conversion efficiency when VIN is higher than the voltage across the load. When in 1X mode, voltage conversion efficiency is defined as output power divided by input power: η= POUT PIN The expression to define the ideal efficiency (η) can be rewritten as: η= POUT VOUT · IOUT VOUT = = PIN VIN · IOUT VIN -or- η(%) = 100 ⎛ VOUT ⎞ ⎝ VIN ⎠ 1.5X and 2X Charge Pump Mode Efficiency The AAT2845 contains a fractional charge pump which will boost the input supply voltage in the event where VIN is less than the voltage required to supply the output. The efficiency (η) can be simply defined as a linear voltage regulator with an effective output voltage that is equal to one and one half or two times the input voltage. Efficiency (η) for an ideal 1.5X charge pump can typically be expressed as the output power divided by the input power. η= POUT PIN In addition, with an ideal 1.5X charge pump, the output current may be expressed as 2/3 of the input current. 14 www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs The expression to define the ideal efficiency (η) can be rewritten as: η= POUT VOUT · IOUT VOUT = = PIN VIN · 1.5IOUT 1.5VIN 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 -or- 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 the voltage level at VIN approaches the voltage level at 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 equivalent series resistance (ESR) ceramic capacitors are used; in general, low ESR may be defined as less than 100mΩ. A value of 1µF for all four capacitors is a good starting point when choosing capacitors. If the constant current sinks are only programmed for light current levels, then the capacitor size may be decreased. Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2845. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Ceramic capacitors less than 0.1µF 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 2.2µF) are often available in low-cost Y5V and Z5U dielectrics, but capacitors larger than 1µF are not typically required for AAT2845 applications. 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. Evaluation Board User Interface The user interface for the AAT2845 evaluation board is provided by three buttons and two connection terminals. The board is operated by supplying external power and pressing individual buttons or button combinations. The table below indicates the function of each button or button combination. To power-on the evaluation board, connect a power supply or battery to the DC- and DC+ terminals. Close the board’s supply connection by positioning the J1 jumper to the ON position. A red LED indicates that power is applied. The evaluation board is made flexible so that the user can disconnect the enable lines from the microcontroller and apply external enable signals. By removing the jumpers from J2, and/or J3, external enable signals can be applied to the board. External enable signals must be applied to the ON pin of each J2, or J3 terminal. Equivalent Series Resistance When applying external enable signals, consideration must be given to the voltage levels. The externally applied voltages should not exceed the supply voltage that is applied to the IN pins of the device (DC+). 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 The LDO loads can be connected directly to the evaluation board. For adequate performance, be sure to connect the load between OUTA/OUTB and DC- as opposed to some other GND in the system. 2845.2008.05.1.2 www.analogictech.com 15 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Evaluation Board Layout Figure 3: AAT2845 Evaluation Board Top Layer. Button(s) Pushed1 DATA LIGHT LIGHT+DATA ENLDO DATA+LIGHT+ENLDO Figure 4: AAT2845 Evaluation Board Bottom Layer. Description Increment the backlight data setting. Hold down the button to auto-cycle through the brightness levels. Toggle ON/OFF the backlighting section. Set the brightness level using the DATA button. Decrement the backlight data setting. Hold down to auto-cycle. Toggle ON/OFF the LDOs. Reset. Clear data and bring all enable lines low. Table 3: Evaluation Board User Interface. 1. The “+” indicates that these buttons are pressed and released together. 16 www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs DC+ 1 2 VOUT 3 J1 C9 100µF D1 D2 D3 D4 Optional 100µF capacitor to bypass lab supply C7 0.1µF D3 D4 16 ENLDO 15 EN/SET 14 IN C1+ 13 5 PGND C1- 12 6 IN OUTCP 11 7 8 9 ENL EN/SET C1 1.0µF C3 1.0µF C2+ C4 2.2µF U1 AAT2845 4 C2- R11 120K C6 2.2µF LDOB 17 GND FBB R10 160K D1 3 LDOA Programmed for 2.8V output D2 2 18 FBA OUTB 1 19 CBYP 20 10 C2 1.0µF OUTA R8 60.4K C5 2.2µF Programmed for 1.8V output R9 120K Figure 5: AAT2845-EE Section Schematic. 2845.2008.05.1.2 www.analogictech.com 17 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs J2 R6 220 EN/SET 3 2 1 R7 100K VIN VIN R1 R2 R3 1K 1K 1K U2 1 2 3 4 DATA SW1 LIGHT VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 C8 1µF 8 7 6 5 R5 330 LED7 RED PIC12F675 SW2 ENLDO J3 SW3 ENL 3 2 1 R4 100K DC- Figure 6: MCU Section Schematic. Evaluation Board Component Listing 18 Component Part# Description Manufacturer U1 U2 D1 - D4 C1 - C3 C4 - C6 C7 C8 C9 R1 - R3 R4, R7 R5 R6 R8 R9, R11 R10 J1 - J3 LED7 SW1 - SW3 AAT2845IML-EE-T1 PIC12F675 LW M673 GRM18x GRM18x GRM18x GRM31x TAJBx Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 PTS645TL50 Four-Channel Backlight Driver with Dual LDOs 8-bit CMOS, FLASH MCU; 8-pin PDIP Mini TOPLED White LED; SMT 1.0µF, 10V, X5R, 0603, ceramic 2.2µF, 10V, X5R, 0603, ceramic 0.1µF, 16V, X7R, 0603, ceramic 1µF, 10V, X5R, 1206, ceramic 100µF, 10V, 10µA, tantalum 1K, 5%, 1/4W; 1206 100K, 5%, 1/4W; 1206 330, 5%, 1/4W; 1206 220, 5%, 1/4W; 1206 60.4K, 1%, 1/10W; 0603 120K, 1%, 1/10W; 0603 160K, 1%, 1/10W; 0603 Conn. Header, 2mm zip Red LED; 1206 Switch Tact, SPST, 5mm AnalogicTech Microchip OSRAM Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries www.analogictech.com 2845.2008.05.1.2 PRODUCT DATASHEET AAT2845 ChargePumpTM Four-Channel Backlight Driver with Dual LDOs Ordering Information Low Dropout Regulators Package LDOA LDOB Marking Part Number (Tape and Reel) TQFN34-20 TQFN34-20 TQFN34-20 Programmable 2.8V 2.8V Programmable 1.5V 1.8V UHXYY XEXYY XFXYY AAT2845IML-EE-T1 AAT2845IML-QG-T1 AAT2845IML-QI-T1 Package Information3 TQFN34-20 3.00 ± 0.05 0.40 ± 0.100 1.55 ± 0.05 2.55 ± 0.05 0.50 BSC 0.24 ± 0.060 4.00 ± 0.05 Detail "A" Top View Bottom View 0.75 ± 0.05 Detail "A" 0.025 ± 0.025 Side View 0.214 ± 0.036 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 2845.2008.05.1.2 www.analogictech.com 19