SLVUCU5 December 2025 UCD91160 , UCD91320
The UCD91x devices implement optional closed-loop margining for up to 32 voltage rails. During four-corner testing, a system operates at the minimum and maximum expected ambient temperature and with each power supply set to the minimum and maximum output voltage, commonly referred to as margining. Margining can be activated, and switched from low to high level margining via the PMBus interface using the OPERATION command, or by configuring two GPI pins as MARGIN-EN and MARGIN-LOW_nHIGH inputs with GPI_CONFIG.
The MARGIN_CONFIG command allows for the setting of several margining options, including ignoring faults while margining, and using closed-loop pwm feedback to trim the rail output voltage when not margining. In order to accommodate positive and negative feedback relationships, the command also allows the user to invert the relationship between the PWM Duty cycle. The specific PWM pin for a given page, and its behavior when margining is not active, is also configured with this command.
The UCD91x devices also allow for the PWM duty cycle when margining to operate in a nominal duty cycle mode, wherein the PWM duty cycle will always start from the nominal duty cycle set in the PWM_CONFIG command for the given PWM Output. When margining is stopped or disabled on a rail with nominal duty cycle mode enabled, the PWM will also return to the PWM_CONFIG command duty cycle before fully stopping. When not in nominal duty cycle mode, margining and active trimming, the PWM duty cycle will start from 0% and slowly ramp up, and disable immediately. Using nominal duty cycle mode can help prevent glitches on the power supply outputs as margining is enabled/disabled.
When set to ignore faults while margining, no over or undervoltage faults will be triggered or handled while a margining state is active. Both the OPERATION command and MARGIN_CONFIG commands can be used to dictate the UCD91xx fault status update behavior when margining. The most recently written command will determine if faults are ignored or not.