DUAL_OUTPUT_VOLTAGE_REGULATOR

Published:2009/7/16 22:13:00 Author:Jessie | From:SeekIC

The LTC1266-3.3 and the LTC1263 are perfect complements for one another. The combination of the two parts provides two regulated outputs of 3.3 V/5 A and 12 V/60 mA from an input range of 4.75 to 5.5 V. The LTC1263, using only four external components (two 0.47-μF charge capacitors, one 10-μF bypass capacitor, and one 10-μF output capacitor), generates the regulated 12-V/60-mA output from a 5-V input using a charge-pump tripler. During every period of the 300-kHz oscillator, the two charge capacitors are first charged to VCC and then stacked in series, with the bottom plate of the bottom capacitor shorted to VCC and the top plate of the top capacitor connected to the output capacitor. As a result, the output capacitor is slowly charged up from 5 to 12 V. The 12-V output is regulated by a gated oscillator scheme that turns the charge pump on when Vout is below 12 V and turns it off when it exceeds 12 V. The LTC1266-3.3 then uses the 5-V input, along with the 12-V output from the LTC1263 and various external components, including bypass capacitors, sense resistors, and Schottky diodes, to switch two external N-channel MOSFETs and a 5-μH inductor to charge and regulate the 3.3-V/5-A output. The charging scheme for this part, however is very different from that of the LTC1263. The LTC1266-3.3 first charges the output capacitor by turning on the top N-channel MOSFET, allowing current to flow from the 5-V input supply through the inductor. The amount of current flow in the inductor is monitored with a sense resistor, and the 3.3-V output is regulated by turning on and off the top and bottom N-channel MOSFETs to charge and discharge the output capacitor.



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