AAT3151B_08

PRODUCT DATASHEET AAT3151B ChargePump TM High Efficiency 1X/1.5X Charge Pump For White LED Applications Features • 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 • Dual Mode 1X and 1.5X Charge Pump for Maximum Efficiency and VF Coverage • Drives Four Channels of LEDs • No Inductors, Low Noise Operation • 1MHz Constant Switching Frequency • Small Application Circuit • Built-In Thermal Protection • Built-In Auto-Disable for Short-Circuit • Automatic Soft Start • IQ 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. For each Max Current scale, there are 16 current level settings separated from one another by approximately 1dB. Code 1 is full-scale current and Code 15 is full-scale current attenuated by roughly 14dB. Code 16 is reserved as a “no current” setting (see Table 1). The AAT3151B has an additional Low Current mode with reduced quiescent current. This mode is especially useful for low-current applications where a continuous, lowcurrent state is maintained. The reduction in quiescent current significantly reduces the impact due to maintaining a continuous backlighting state. Constant Current Output Level Settings The constant current level for the LED channels is set via the AS2Cwire serial interface according to a logarithmic scale. In this manner, LED brightness appears to change linearly when the settings in the scale are traversed. 8 www.analogictech.com 3151B.2008.02.1.1 PRODUCT DATASHEET AAT3151B ChargePump Data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 TM High Efficiency 1X/1.5X Charge Pump For White LED Applications 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 Max1 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 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 AAT3151B enters shutdown mode and draws less than 1μA from the supply. Address 1 is the default address on the first rising edge after the AAT3151B has been disabled. Whenever shutdown mode is entered, all registers are reset to 1. Table 1: Constant Current Programming Levels (mA)2. AS Cwire Serial Interface 2 AS2Cwire Addressing A number of addresses are available to control all of the part’s functionality. Use Address 1 to program all four LED channels to any one of 16 possible settings that depend on the Max Current scale setting. Use Address 4 to program the Max Current register, which sets the Max Current scale. Address 5 programs the Low Current register. The Low Current register controls the highly efficient Low Current mode. The AS Cwire single wire interface is used to set the possible combinations of current levels and LED channel states. 2 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 AS2Cwire Serial Interface Timing Address T HI T LO TLAT TLAT Data EN/SET 1 2 17 18 1 2... n