Auto Enable means the UCD90xxx device automatically sequences on rails once the device is powered up. It is not controlled by the CONTROL pin or OPERATION command, so you cannot use the CONTROL pin or OPERATION command to sequence off rails. When ON_OFF_CONFIG is set to AUTO mode, the only source that can initiate a power-down sequence is by fault response.
To initiate a "normal" power down sequence (as opposed to a fault shutdown, which can trigger fault logging and the ALERT line), one way is to select the CONTROL Pin or OPERATION command in the On/Off Config setting instead of using Auto Enable (or None). Then you need to assert the CONTROL pin or send an OPERATION command to sequence on the rails, and likewise, de-assert the CONTROL pin or send an OPERATION command to sequence off the rails. The CONTROL Pin is a special logic IO pin as part of PMBus port. The OPERATION command is a PMBus command. In the Fusion Digital Power Designer GUI, you can toggle a CONTROL pin state or send an OPERATION command inside the Monitor page.
Another way to sequence off rails is through the Pin Selected States feature. You can define up to three GPI pins to toggle among up to eight rail states. In each state, you can program certain rails to be on and certain rails to be off. For the simplest case, you can have two states, toggled by one GPI pin. In State 0, all rails are off; in State 1, all rails are on. During the transition of two states, the rails that are going to change turnon and turnoff states follow their respective delay and dependency settings in sequenced manner. The Pin Selected states can be configured through the Fusion GUI. Note that to use the Pin Selected States feature, the On/Off Config setting must be in OPERATION Only or Both CONTROL Pin and OPERATION.
For more FAQ please check the following document.
UCD90xxx Family Frequently Asked Questions and Answers
UCD9090 UCD9090A UCD90120 UCD90120A UCD90124 UCD90124A UCD90160 UCD90160A UCD90320 UCD90320U