I'm thinking of using the National Semiconductor LM2639 Multiphase PWM Controller to design a high voltage Buck Converter. The chip is designed to provide outputs from 1.3 to 3.5V, depending on the programming code. I have two questions:
1) In order to provide higher voltages Im thinking of providing a separate 5V Vcc supply, and connecting the switching MOSFETs to a high voltage unregulated supply. I would also insert a voltage divider in the feedback path to "fool" the controller into providing a higher output voltage. Has anyone tried this? 2) The LM2639 is listed by National as "Not recommended for new design". Does anyone know why, and know of a suitable replacement. Basically, I need a multi-phase PWM buck converter controller capable of providing around 70VDC.- posted
16 years ago