I have an application where the LM22676 output drives the VIn and Ven of a TPS62291. The LM22676 has VIN = 12V and is setup for Vout = 5V. The TPS62291 has Vin = 5V, Ven = 5V, and Vout = 3.3V.
The LM22676 is enabled by VBus from a PC in the system. When Vbus is removed, the LM22676 is disabled. The LM22676 output goes down, but only to about 0.3V - 0.4V. This sends 0.3V-0.4V into the TPS62291 VIN and VEN from the LM22676. This finally results in about 1V out of the TPS62291 which is set for 3.3V.
This somehow affects the concerto reset circuitry. Once 5V is applied again to the LM22676 VEN, the concerto does not run.
Also, while the LM22676 disabled I can short the output to ground. Since this is connected to the TPS62291 VIN and VEN, the TPS62291 output drops, but only to about 0.7V. It appears this is enough to reset the concerto.
What should be expected of the regulators output voltages if the input is disabled?
What should be the required /XRST low value for the concerto to safely and reliably reset?
thanks, jeff