Hello.
TPS2553 abnormal operation
We designed a complex card, which contains about 10 DC to DC and about 10 LDOs. On several DC to DC outputs there are current limiters, with TPS2553. Most of the current limiters are operating as expected. With two limiters, there are two kinds of abnormal operation.
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A current limit higher than the maximum which was calculated according the data sheet equations. For example, for a 39.2K resistor, the maximum calculated current is 732mA, while we measured 820mA.
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A more sever abnormal operation is described here:
When we operate the circuit by manually command the input voltage and the enable input- the operation is as expected: The fault output is High, and the value of the output is as expected: 3.6V.But, when we performed the same sequence automatically (FPGA commands) - the outputs behave as follows:
AT first, the input is 0 volts and the enable is also “Lo”. The fault is goes “HI”. Immediately after the input voltage starts ramping – the fault output falls to “Lo” state and the output remains 0 Volta even after the enable input goes “Hi”.
Attached scope picture. I added red and green signs to mark the Vin and the Fault signals.
According the TPS2553, there are three reasons to fault condition: Overcurrent, over temperature and reverse voltage. We check the output current during the event of fault, and also the reverse voltage. All was OK. The TPS2553 was not hot, so, none of those reasons was valid.
So, can you help to understand what the reason to the fault output fall was? Please notice the fault fell even when the enable was “Lo” (disable state).
