Multiphase Buck Converter Controller

Nov 19, 2007 1 Replies
J

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.
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L

So long as you provide housekeeping power and isolate the drive signal from switches operating on the HV bus, you are free to do whatever you want with LV controllers.

Synchronizing commodity controllers for interleaved operation is no great expense.

I suggest, however that a 2MHz conversion frequency is poorly suited to higher voltage applications, regardless of the control method used.

Originally aimed for local VRMM and point of load regulators for PII processors in Y2K, using the VRM 8X standard. The new standard is VRM10 for P4 or later.

RL

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