A UT_FAULT was detected because the measured temperature was less than the UT_FAULT_LIMIT value. This fault applies to the die temperature on the 2977/2978 devices but is a paged fault on all other PSM devices. The OT/UT warning and fault limits and responses are global registers on the 2977/78 and are paged on all other PSM devices.
Possible Causes:
- If the device is a LTC2977/78, low temperature was detected on either the internal die
- Otherwise (all other PSM devices) this fault indicates low temperature was detected on an external temperature sensor on this PSM channel.
- UT_FAULT_LIMIT set too high
- A VSENSEP pin is floating
- External TSENSE pin is floating
Remedies and Workarounds
- If applicable, check for floating TSENSE pins and ground them
- If a VSENSE pin is floating, it is possible that the internal die temp measurement is grossly in error, causing an OT or UT fault or warning.
Other Debugging Tips
For 2977/78 devices, only an internal die temperature is available and therefore the OT/UT warn and fault limits are applied to the measured die temperature. For all other PSM devices, the OT/UT warn and fault limits are paged and applied to each channel’s TSENSE pin; there are no internal die temp limits for these devices.