Other Parts Discussed in Thread: TPS55340, TLV431
Hi--
We have a new prototype design with a PoE front end essentially copied from the TPS23753AEVM-004. When powered from a RTN referenced supply at 36V (this is all we have tried so far), the converter output rises immediately to >6V. If we clamp the output at 3.6V, over 10W is delivered to the load. We can power the downstream load (~3W, 3.3V) with the actual eval board itself with no issues. The primary differences between the eval system and our design are:
- Layout
- Optocoupler is Broadcom ACPL-217-50AE
- Shunt Reference is TLV431AFTA (3-pin, Diodes, Inc.)
- MURA120 diodes replaced by other GP diode types
I've attached a schematic page if anyone is interested in looking. The TPS55340 boost regulator shown has been isolated by removing D5 and LB1. For test purposes, the 36V supply is connected at the cathode pad of D5. It looks a lot like we are not regulating at all. I'll try to capture some 'scope traces at key points and attach tomorrow. Anyway, if anyone has any suggestions about where to start looking for issues, we'd be very appreciative.
--Matt
