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SP6128AHY Datasheet(PDF) 4 Page - Exar Corporation |
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SP6128AHY Datasheet(HTML) 4 Page - Exar Corporation |
4 / 10 page 4 Rev. 08/19/05 SP6128A Low Voltage, Synchronous Step Down PWM Controller © Copyright 2005 Sipex Corporation General Overview The SP6128A is a constant frequency, voltage mode, synchronous PWM controller designed for low voltage, DC/DC step down converters. It is intended to provide complete control for a high power, high efficiency, precisely regulated output voltage from a highly integrated 14-pin solution. The internal free-running oscillator accurately sets the PWM frequency at 300kHz without requiring any external elements and allows the use of physically small, low value external com- ponents without compromising performance. A transconductance amplifier is used for the error amplifier, which compares an attenuated sample of the output voltage with a precision, 0.8V reference voltage. The output of the error ampli- fier (COMP), is compared to a 0.75V peak-to- peak ramp waveform to provide PWM control. The COMP pin provides access to the output of the error amplifier and allows the use of external components to stabilize the voltage loop. High efficiency is obtained through the use of synchronous rectification. Synchronous regula- tors replace the catch diode in the standard buck converter with a low RDS(ON) N-channel MOSFET switch allowing for significant ef- ficiency improvements. The SP6128A in- cludes two fast MOSFET drivers with inter- nal non-overlap circuitry and drives a pair of N-channel power transistors. The SP6128A includes an internal 0.27V/ms soft-start cir- cuit that provides controlled ramp up of the output voltage, preventing overshoot and in- rush current at power up. Current limiting is implemented by monitoring the voltage drop across the RDS(ON) of the high side N-channel MOSFET while it is conducting, thereby eliminating the need for an external sense resistor. The overcurrent threshold can be programmed by a single resistor. FUNCTIONAL DIAGRAM + - - + - + Synchronous Driver PWM Logic S Q R Reset Dominant R Q S VCC SWN Reference 6 10 0.8V UVLO FAULT SWN 12 1 GL 13 DRIVER ENABLE RESET Dominant PWM COMP FAULT GH GH 5µA 350mV SHUTDOWN GM ERROR AMP Over Current 2.8V ON 2.7V OFF COMP SHUTDOWN F = 300kHz 750mV RAMP 0.27V/ms SOFTSTART VFB COMP 3 - + - + 1V + - GND 5 14 BST ISET 15µA 2 PVCC 11 PGND 4 OPERATION |
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