Hi All:
Have a look at ths schematic:
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After about 600 hours of operation (1Khz signal pulses at <10% DC) the MCP1407 starts to 'miss' and 'skip' pulses and then dies. Replacing with a new one restores correct ops. This has happened several times.
I am currently using a 500mA, 1K imp. @ 100Mhz ferrite bead in the MCP output drive splitting into 4, 5 ohm resistor gate drives for the IRFP 3306 NFETS. An 18V zener clamp on the MCP1407 output as well in case of ringing spikes. The 4 Power FETS switch a peak of 700A @ 1Khz,3% DC. The 4n25 optoisolator is fed by a TL494PWM logic signal. The MCP1407 has a 12V supply. The NFETS switch the negative rail of a 0-36V supply. Ths negative rail is the common ground.A 4n25 opto isolates the MCP1407.
My current action plan is to bump the gate drive resistors to 10 ohm metal film rather than 5 ohm. Scoping the MCP1407 output drive reveals minimal ringing due to the ferrite bead. The bead does heat up by about 25C during ops. I can only assume some type of stress on the MCP1407 is eventually killing it. Perhaps adding a bead for each gate maybe useful as well, rather than a single common bead.
I'm looking for any advice here, thanks.
Sorry for the small Pic schematic...yahoo shrunk it.
