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AAT3123A Datasheet(PDF) 7 Page - Advanced Analogic Technologies |
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AAT3123A Datasheet(HTML) 7 Page - Advanced Analogic Technologies |
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7 / 18 page  AAT3123/23A/24 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications 3123.2005.12.1.4 7 Functional Block Diagram 1x/1.5x Charge Pump Soft-Start Control 1MHz Oscillator Voltage Reference Quad Output DAC Dual Output DAC Current S2Cwire Interface 32 x 8 bit ROM Current Reference C1+ C1- C2+ C2- OUT D1 D2 D3 D4 D5* D6* GND EN/SET VIN *AAT3124 only Functional Description The AAT3123/23A/24 is a dual mode load switch (1X) and high efficiency (1.5X) fractional charge pump device intended for white LED backlight applications. The fractional charge pump consists of a low dropout linear voltage regulator followed by a 1.5X charge pump with multiple current- source outputs. To maximize power conversion efficiency, an internal feedback control sensing cir- cuit monitors the voltage required on the constant current source outputs. This control circuit then sets the load switch and charge pump functions based upon the input voltage level versus the out- put voltage level needed. This function significant- ly enhances overall device efficiency when the input voltage level is greater than the voltage required at the constant current source outputs. For the AAT3123/23A, the 1X load switch/1.5X charge pump mode is decided on the voltage sensed on the output D1. The AAT3124 bases the 1X load switch/1.5X charge pump mode decision on the voltage levels sensed on either the D1-D4 output group or the D5-D6 output group, whichev- er is greater. Switchover between the 1.5X (charge-pump) operating mode and the 1X (load switch) mode occurs automatically (as a function of input and output voltages) and does not require user intervention to maintain maximum efficiency. The AAT3123/23A/24 requires only four external components: two 1µF ceramic capacitors for the charge pump flying capacitors (C 1 and C2), one 1µF ceramic input capacitor (C IN), and one 0.33µF to 1µF ceramic output capacitor (C OUT). The LDO/1.5X charge pump output is converted into four (D1 to D4) or six (D1 to D4 and D5 to D6) con- stant current outputs to drive four or six individual LEDs with a maximum current of 20mA each. The current source output magnitude is controlled by the EN/SET serial data S 2Cwire interface. The inter- face records rising edges of the EN/SET pin and decodes them into 32 individual current level set- tings each 1dB apart (see Table 1, Current Level Settings). Code 32 is full scale, and Code 1 is full scale attenuated by 31dB. The modulo 32 interface wraps states back to State 1 after the 32nd clock. With each EN/SET pulse, the output current increas- es by 1dB. To decrease the output current by 1dB, 31 EN/SET clock pulses are required. The counter can be clocked at speeds up to 1MHz, so intermedi- ate states are not visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to -31dB, the lowest setting equal to 525µA. Once the final clock cycle is input for the desired brightness level, the EN/SET pin is held high to maintain the device output current at the pro- grammed level. The device is disabled 500µs after the EN/SET pin transitions to a logic low state. |
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