AAT3156

AAT3156 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications General Description The AAT3156 is a low noise, constant frequency charge pump DC/DC converter that uses a trimode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency for white LED applications. The AAT3156 is capable of driving six LED channels at a total of 180mA from a 2.7V to 5.5V input. The current sinks may be operated individually or in parallel for driving higher-current LEDs. A low external parts count (two 1µF flying capacitors and two small 1µF capacitors at VIN and VOUT) make this part ideally suited for small, battery-powered applications. 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 low-current settings down to 50µA for optimized efficiency, with a low housekeeping current of only 50µA. Each output of the AAT3156 is equipped with built-in protection for VOUT short circuit and auto-disable for LED failure conditions. Built-in soft-start circuitry prevents excessive inrush current during start-up. A lowcurrent shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1µA. The AAT3156 is available in a Pb-free, space-saving, thermally-enhanced 16-pin 4x4mm QFN package. Features • • ChargePump™ • • • • • • • • • • • VIN Range: 2.7V to 5.5V Fully Programmable Current with Single Wire — 16-Step Logarithmic Scale — 15/20/30mA Max Current — Four Low Current Settings Down to 50µA — Low IQ (50µA) for Low Current Mode Tri-Mode 1X, 1.5X, and 2X Charge Pump for Maximum Efficiency and VF Coverage Drives Six Channels of LEDs Individual Main/Sub-Group Control No Inductors, Low Noise Operation 1MHz Constant Switching Frequency Small Application Circuit Built-In Thermal Protection Built-In Auto-Disable For Open Circuit Automatic Soft Start IQ 1MHz data rate), the LED current drive of the AAT3156 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. For each Max current scale, there are 16 current level settings separated from one another by approximately 1dB (see Current Settings table). Code 1 is full-scale current and Code 15 is full-scale attenuated roughly 14dB. Code 16 is reserved as a "no current" setting. 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 AAT3156 main and sub-channels 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. AS2Cwire 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 AAT3156 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 AAT3156 has been disabled. Whenever shutdown mode is entered, all registers are reset to 1. Constant Current Programming Levels (mA)1 Data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 20mA Max2 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 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 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 1. There is an additional Low Current mode with currents down to 50µA. See the Low Current Register Settings section. 2. The device defaults to the 20mA Max scale. Use the Max Current Register to change the Max Scale. 3156.2005.09.1.2 9 AAT3156 High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications AS2Cwire Serial Interface Timing Address T HI T LO TLAT TLAT Data EN/SET 1 2 17 18 1 2... n