Each rail has its own ON/OFF Config setting. In the setting, there are three sources that can control rail on and off:
1. OPERATION: the rail attempts to turn on and off when it receives an OPERATION command.
2. CONTROL pin: the rail attempts to turn on and off when the CONTROL pin state is toggled.
3. NONE (Auto Enable): the rail automatically attempts to turn on once the UCD90xxx device is out of reset.
Dependencies are only examined after the rail attempts to change the on and off state. Therefore, toggling the GPI sequence-off dependency alone does not turn off the rail. A rail must first receive instructions to change state and then checks dependency conditions to determine the actual timing to change its EN pin state.
Another mechanism to sequence down rails is fault response (overvoltage (OV), undervoltage (UV), overcurrent (OC), undercurrent (UC), over-temperature (OT), time on max, GPI fault, and so forth). A rail can turn off immediately according to its fault response setting. Each rail can include several other rails as fault shutdown slaves. The slave rails turn off according to their respective dependency and delay settings. There is one condition: a rail must shut down itself in fault response configuration in order to shut down its slaves. If a rail ignores the fault in its fault response configuration, it does not shut down its slaves.
The UCD9090A, UCD90160A, UCD90240, UCD90320, and UCD90320U devices support GPI faults to turn off rails. The UCD9090, UCD90160, UCD90120, UCD90120A, UCD90124, and UCD90160 devices do not support GPI faults to turn off rails.
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