I'm currently designing a full-bridge PWM controlled DC motor driver with a24V/10A supply voltage. For driving each MOSFET half-bridge, I selected the LM5106 driver IC.
As the '5106 is only available in a 20mil lead spacing MSOP, I can't do any bench tests without designing a PCB right away, so I'd like to check up on things to prevent costly mistakes (this is my first PWM motor driver). Also, the datasheetis rather concise.
Apparently, the high side driver derives its positive gate drive voltage via the bootstrap capacitor. This doesn't mean that the PWM signal *must* have a duty-cycle of less than 100% (full positive DC) for the driver to function properly, or does it? Or does the chip contain some sort of internal oscillator-plus-charge-pump, with the bootstrap capacitor only necessary for storing the energy?
This is important, because I'm using a rather simple way of generating a PWM signal with a triangle wave and an LM339 comparator(*). I don't need precise speed control; it's only important that the motors don't start or stop abruptly. This also means that for most of the time, the "PWM" signal is actually a logic-level DC voltage.
Any information on this (including examples) is very welcome.*: I'd rather use a microcrontroller-generated PWM signal -- but I'd need six PWM outputs at least, two (both directions) for each motor. The PIC16Fxx controllers I can program don't have this many PWM outputs, and I calculated that it's impossible to generate even a 4-bit resolution 20kHz PWM output in software: the program would have to check/change outputs at 20x16=320kHz; with a PIC running at 20MHz (5MHz internal clock), this would require an interrupt rate of once per 16 clock cycles, which is not possible. The PIC30F2010 does have enough PWM outputs -- but my development environmnent (both the assembler and programmer) can't handle this device.
Thanks in advance, best regards,