Other Parts Discussed in Thread: TPS23880EVM-008, USB2ANY, BOOST-PSEMTHR-007
I'm having a bit of an issue with the TPS2372 TPH and TPL outputs. Hopefully
you can tell me what I'm doing wrong.
We think that their output should be a direct function of the number
of class cycles produced by the PSE per table 2 in the datasheet.
Unfortunately, the observed outputs are different.
By changing the requested class, we can observe a change in number of
class cycles:
Requested Observed Expected Observed
Class Class TPH TPL TPH TPL
Cycles
3 1 1 1 1 1
4 3 1 0 0 0
5 4 0 1 0 0
6 4 0 1 0 0
As you can see, TPH and TPL are either both high or both low.
We never observe them having different values. This has been confirmed with
multiple boards. We also checked that they are not shorted together.
Attached is cut/paste of the relevant schematic sections as well as
a scope shot for the power on sequence when we request class 4 operation.
The scope is observing VDD relative to VSS as seen by the TPS2372-4.
Any ideas?