SLVUCU5 December 2025 UCD91160 , UCD91320
For systems where only power-on sequencing is a concern, the general approach is to:
Configure an LGPO to output a device's POWER_GOOD.
Connect the LGPO POWER_GOOD signal to another device.
This allows the rails of a device to have a dependency on the power-good output of the previous device in the chain, and imposes a controller-target relationship between multiple devices.
Optionally, connect the LGPO POWER_GOOD signal of the last device back to the MONx or GPIx pin of the first device.
There are two different approaches for how to connect a device's POWER_GOOD signal to another device.
Connect the LGPO POWER_GOOD signal to the PMBUS_CNTRL pin of another device.
Connect the LGPO POWER_GOOD signal to a MONx or GPIx pin of another device.
At startup, once the controller has completed its start sequence, and all of the controller's rails have reached regulation voltages, the target devices can initiate their own start sequences.
During shutdown, as soon as the controller starts to sequence-off, the controller's POWER_GOOD signal will de-assert, which initiates the shutdown of the target devices.
Since POWER_GOOD is a signal that depends on all configured rails reaching regulation voltages, a shutdown on one or more of the controller's rails can initiate the shutdown of the target devices.
The controller's shutdown can be initiated intentionally or by a fault condition.
If a fault condition occurs on a target device, the target device's rails will shutdown (if shutdown fault response is enabled), and the target's POWER_GOOD signal is also de-asserted.
If a fault condition occurs on the last device in the chain, the last device will de-assert its POWER_GOOD signal. The first device in the chain (the controller) will treat this in one of two ways, depending on whether the POWER_GOOD signal is connected to MON or GPI pin.
If connected to a MON pin, the controller will treat the de-assertion as an UV fault.
If connected to a GPI pin, the controller will treat the de-assertion as a GPI fault. GPIs can be used if not enough MON pins are available.