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My circuit has a 12V input and uses a PTR08060W to provide a 3.3V rail and a PTR08100W to provide a 5V rail.
The 5V and 3.3V rails are powering a bunch of circuitry including processor, USB controller, Ethernet PHY, DRAM etc. but not heavy inductive loads like motors or solenoids.
Both modules have the recommended capacitors on inputs and outputs.
The 5V rail seems to be fine, but the 3.3V rail is failing after several hours of operation.
So far I have made two boards of this new design. One board failed with a serious over-voltage (the 3.3V rail went up to 12V). Examining the PTR08060W showed that the high-side MOSFET was a direct short circuit (when unpowered).
The other board has failed with under-voltage (3.3V rail has gone down to about 1V). Examining the PTR08060W showed that the high-side MOSFET has a resistance of 11 Ohms (even when the module has no power and is removed from the board). On a good module this is open circuit (when unpowered).
On both boards, the low-side MOSFET is open circuit (when unpowered), as you would expect.
Has anyone encountered this failure mode before?
I'm assuming that the input is OK (i.e. no excessive transients) because the PTR08100W is fine on both boards. Also, my 12V input rail has a 15V zener clamp to limit transients.
Anyway, I'm looking for ideas and hints about what might be causing the problem.
All comments / suggestions gratefully received.
I reviewed your comments and the PTR08060 .
I have a number of questions on this application.
1. A schematic of the power section would assist in this analysis.
How the inhibit pin used in this application?
What is the quantity of ceramic capacitors on teh output bus?
What is the polarized capacitor type and ESR for both 5Vout and 3.3Vout?
2. If you send me your e-mail address, I can contact you to discuss this application.
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