AAT2803

Six-Channel White LED Backlight Charge Pump with Flash General Description The AAT2803 is a dual charge pump designed to support both white LED backlight and flash applications for systems operating with lithium-ion/polymer batteries. The backlight charge pump is capable of driving up to six LEDs at a total of 180mA. The current sinks may be operated in group or in parallel for driving higher current LEDs. To maximize power efficiency, the charge pump operates in 1X, 1.5X, or 2X mode, where the mode of operation is automatically selected by comparing the forward voltage of each LED with the input voltage. AnalogicTech's AS2Cwire™ (Advanced Simple Serial Control™) serial digital input is used to enable, disable, and set current for each LED with a 16-level logarithmic scale plus four lowcurrent settings down to 50μA for optimized efficiency, with a low housekeeping current of only 50μA. The flash charge pump is a charge pump doubler with a regulated output voltage. It is designed to deliver 120mA of continuous current and up to 300mA of pulsed current. It has an independent enable pin for improved power savings. The AAT2803 is equipped with built-in protection, short-circuit, and auto-disable for load short-circuit condition. Built-in soft-start circuitry prevents excessive inrush current during start-up. A low-current shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1μA. The AAT2803 is available in a Pb-free, space-saving, thermally enhanced 24-pin 4x4mm QFN package and is rated over the -40°C to +85°C temperature range. AAT2803 Features • • • ChargePump™ • • • • • • • • VIN Range: 2.7V to 5.5V Dual Charge Pump: — Flash: Charge Pump Doubler — Backlight: Tri-Mode Charge Pump Backlight Charge Pump: — Programmable Current With Single GPIO — 16 Current Steps — 15/20/30mA Max Current — Four Low Current Settings — Individual Main/Sub-Group Control — Low IQ (50μA) for Low-Current Mode — Drives Six Channels of LEDs Flash Charge Pump: — Regulated VOUT_FL 4.5/5.0 Volts — Up to 300mA of Current for Flash 1MHz Constant Switching Frequency Independent Backlight/Flash Control Built-In Thermal Protection Built-In Auto-Disable for Open Circuit Automatic Soft Start IQ 4.0V 4.56 4.52 4.48 3.6V 3.0V 4.44 3.3V 2.7V 4.40 0.1 1.0 10.0 100.0 1000.0 Output Current (mA) Supply Voltage (V) Start-Up Time (50mA Load) Start-Up Time (100mA Load) EN_FLSH (1V/div) EN_FLSH (1V/div) VOUT_FL (1V/div) VOUT_FL (1V/div) 100μs/div 100μs/div Load Response vs. Time (50mA Load) VIN = 3.5V VOUT_FL (10mV/div) VOUT_FL (10mV/div) Load Response vs. Time (100mA Load) VIN = 3.5V IOUT (20mA/div) IOUT (50mA/div) 5ms/div 5ms/div 6 2803.2006.12.1.6 Six-Channel White LED Backlight Charge Pump with Flash Typical Characteristics–Flash Driver Charge Pump Section Output Ripple Voltage vs. Time (IOUT = 50mA @ VIN = 3.5V) VIN (10mV/div) VOUT (10mV/div) VIN (10mV/div) VOUT (20mV/div) AAT2803 Output Ripple Voltage vs. Time (IOUT = 100mA @ VIN = 3.5V) IIN (10mA/div) IIN (10mA/div) 500ns/div 500ns/div Supply Current vs. Supply Voltage IOUT = 0μA C3 = 1μF VEN_FL = VIN Oscillator Frequency vs. Supply Voltage Oscillator Frequency (MHz) 1.30 3.00 Supply Current (mA) 2.75 2.50 2.25 2.00 1.75 1.50 1.25 1.00 2.5 1.25 +25°C 1.20 +85°C -40°C 1.15 1.10 2.7 3.2 3.7 4.2 4.7 3.0 3.5 4.0 4.5 5.0 Supply Voltage (V) Supply Voltage (V) 2803.2006.12.1.6 7 Six-Channel White LED Backlight Charge Pump with Flash Typical Characteristics–White LED Backlight Driver Section Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = 25°C. AAT2803 Efficiency vs. Supply Voltage 100 90 4.1mA VF = 2.9V 10.2mA VF = 3.1V 20mA VF = 3.4V Turn-On to 1X Mode (VIN = 4.2V; 20mA Load) Efficiency (%) EN (2V/div) CP (2V/div) VSINK (500mV/div) IIN (200mA/div) 80 70 60 50 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 Supply Voltage (V) 100μs/div Turn-On to 1.5X Mode (VIN = 3.8V; 20mA Load) Turn-On to 2X Mode (VIN = 2.8V; 20mA Load) EN (2V/div) CP (2V/div) VSINK (500mV/div) IIN (200mA/div) 100μs/div EN (2V/div) CP (2V/div) VSINK (500mV/div) IIN (200mA/div) 100μs/div Turn-Off from 1.5X Mode (VIN = 3.5V; 20mA Load) 20.2 Current Matching vs. Temperature Channel 2 20.0 Channel 1 EN (2V/div) Current (mA) VF (1V/div) IIN (100mA/div) 19.8 19.6 Channel 3 19.4 19.2 -40 -20 0 20 40 60 Channel 5 Channel 4 Channel 6 80 100μs/div Temperature (°C) 8 2803.2006.12.1.6 Six-Channel White LED Backlight Charge Pump with Flash Typical Characteristics–White LED Backlight Driver Section Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = 25°C. Load Characteristics (VIN = 3.8V; 1.5X Mode; 15mA Load) VIN (40mV/div) CP (40mV/div) VIN (40mV/div) CP (40mV/div) AAT2803 Load Characteristics (VIN = 2.9V; 2X Mode; 15mA Load) VSINK (40mV/div) VSINK (40mV/div) 500ns/div 500ns/div Load Characteristics (VIN = 4.0V; 1.5X Mode; 20mA Load) VIN (40mV/div) CP (40mV/div) VIN (40mV/div) CP (40mV/div) Load Characteristics (VIN = 3.1V; 2X Mode; 20mA Load) VSINK (40mV/div) VSINK (40mV/div) 500ns/div 500ns/div Load Characteristics (VIN = 4.3V; 1.5X Mode; 30mA Load) VIN (40mV/div) CP (40mV/div) VIN (40mV/div) CP (40mV/div) Load Characteristics (VIN = 3.6V; 2X Mode; 30mA Load) VSINK (40mV/div) VSINK (40mV/div) 500ns/div 500ns/div 2803.2006.12.1.6 9 Six-Channel White LED Backlight Charge Pump with Flash Typical Characteristics–White LED Backlight Driver Section Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = 25°C. AAT2803 TLAT vs. VIN 350 300 250 400 350 TOFF vs. VIN -40°C 300 -40°C 200 150 100 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 TOFF (μs) TLAT (μs) 250 200 150 100 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 25°C 85°C 25°C 85°C VIN (V) VIN (V) Input Ripple vs. VIN 25 20 15 10 5 0 2.50 2.67 2.84 3.01 3.18 3.35 3.52 3.69 3.86 4.03 4.20 1.2 1.1 VIH vs. VIN Amplitude (mV) 30mA 1 0.9 -40°C VIH (V) 0.8 0.7 0.6 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 20mA 10.2mA 25°C 85°C VIN (V) VIN (V) VIL vs. VIN 1.2 1.1 1 0.9 -40°C VIL (V) 0.8 0.7 0.6 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 25°C 85°C VIN (V) 10 2803.2006.12.1.6 Six-Channel White LED Backlight Charge Pump with Flash Functional Block Diagram C1+ C1- AAT2803 Soft-Start EN_FL 1MHz Oscillator 2X Charge Pump VOUT_FL VIN VREF Soft-Start Control 1MHz Oscillator Voltage Reference D/A 6 x 16 bit ROM D/A D/A D/A 6 x 16 bit ROM D/A D/A 1X 1.5X 2X Charge Pump C2 + C2 C3 + C3 VOUT_BL D1 D2 D3 D4 D5 D6 GND EN/SET AS 2Cwire Interface Functional Description The AAT2803 is a dual charge pump targeted for backlight and flash applications. The charge pump for white LED applications 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 backlight charge pump is enabled when any of the six current sink inputs near dropout. The charge pump initially starts in 1.5X mode. If the charge pump output drops enough for any current source output to become close to dropout, the charge pump will automatically transition to 2X mode. For flash applications, charge pump doubler architecture is used to support the high current demand required by the application. Charge pump regulation is achieved by sensing the output voltage through an internal resistor divider network. A switch doubling circuit is enabled when the divided output drops below a preset trip point controlled by an internal comparator. The free-running charge pump switching frequency is approximately 1MHz. The charge pump is designed to deliver 120mA of continuous current and 300mA of pulsed current. The AAT2803 requires only six external components: three 1μF ceramic capacitors for the charge pump flying capacitors (C1, C2, and C3), one 1μF ceramic input capacitor (CIN), one 0.33μF to 1μF ceramic capacitor for the backlight charge pump output, and one 1μF for the flash charge pump output. The six constant current sink inputs (D1 to D6) can drive six individual LEDs with a maximum current of 30mA each. The unused sink inputs must be connected to VOUT_BL, otherwise the part will operate only in 2X charge pump mode. The AS2Cwire serial interface enables the backlight charge pump and sets the current sink magnitudes. AS2Cwire addressing allows independent control of two groups of current sink input: D1 to D4 and D5 to D6. 2803.2006.12.1.6 11 Six-Channel White LED Backlight Charge Pump with Flash Constant Current Output Level Settings The constant current sink levels for the white LED backlight (D1 to D6) are set via the serial interface according to a logarithmic scale where each code is 1dB lower than the previous code. In this manner, LED brightness appears linear with each increasing code count. Because the inputs D1 to D6 are true independent constant current sinks, the voltage observed on any single given input will be determined by the actual forward voltage (VF) for the LED being driven. Since the input current sinks are 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 highspeed serial interface (1MHz data rate), the input sink current 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. The 16 individual current level settings are each approximately 1dB apart (see Current Level Settings table). Code 1 is full scale, Code 15 is full scale attenuated by 14dB, and Code 16 is reserved as a "no current" setting. Data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 AAT2803 AS2Cwire Serial Interface The Advanced Simple Serial Control (AS2Cwire) single wire interface is used to set the possible combinations of current levels and LED channel states. AS2Cwire has addressing capability for multiple data registers. With multiple data registers, the backlight charge pump main and subchannels can be programmed together or independently from one another. AS2Cwire relies on the number of rising edges of the EN/SET pin to address and load the registers. AS 2Cwire latches data or address after the EN/SET pin has been held high for time TLAT. Address or data is 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 1 is signified by 17 rising edges, Address 2 by 18 rising edges, and so forth. Data is set to any number of rising edges between 1 and including 16. A typical write protocol is a burst of EN/SET rising edges, signifying a particular Address, followed by a pause with EN/SET held high for the TLAT timeout period, a burst of rising edges signifying Data, and a TLAT timeout for the data registers. Once an address is set, then multiple writes to the corresponding data register are allowed. When EN/SET is held low for an amount of time greater than TOFF, the backlight charge pump enters into shutdown mode and draws less than 1μA from the supply. Address 1 is the default address on the first rising edge after the backlight charge pump has been disabled. Whenever shutdown mode is entered, all registers are reset to 1. 30mA Max IOUT (mA) 30.0 26.7 23.8 21.4 19.0 16.7 15.2 13.3 11.9 10.5 9.5 8.6 7.6 6.7 6.2 0.0 20mA Max IOUT (mA) 20.0 17.8 15.9 14.3 12.7 11.1 10.2 8.9 7.9 7.0 6.3 5.7 5.1 4.4 4.1 0.0 15mA Max IOUT (mA) 15.0 13.3 11.9 10.7 9.5 8.3 7.6 6.7 6.0 5.2 4.8 4.3 3.8 3.3 3.1 0.0 Table 1: Current Level Settings. 12 2803.2006.12.1.6 Six-Channel White LED Backlight Charge Pump with Flash AS2Cwire Serial Interface Timing Address T HI T LO TLAT TLAT AAT2803 Data EN/SET 1 2 17 18 1 2... n