The TOFF_FALL command sets the time, in milliseconds, from the end of the turn-off delay time until the reference DAC is commanded to 0mV. This command is used to cause the output voltage to decrease at a controlled rate, which effectively sets the slew rate of the reference DAC during the soft-off period. In the implementation of TOFF_FALL, the VREF DAC slew rate is adjusted for each of the supported 32 VBOOT levels to obtain a slew rate to have a soft-stop time close to (but not always exactly equal to) the target value. The selected slew rate for the 0.5ms TOFF_FALL is the same as shown in TON_RISE but with a negative slope. TOFF_FALL is scaled in the same manner as TON_RISE with the different settings.

The VOUT fall time is actually not equal to TOFF_FALL value since the device stops SW switching once the output voltage is discharged to 200mV, and the fall time is more for setting the reference DAC slew rate. See Shutdown for more details.

Return to Supported PMBus Commands.

Data Validity

Every mantissa binary value in the writable bits is writeable and readable. However, the actual divider is set to the nearest supported value. Additionally, that mantissa value restored from EEPROM is fixed for each setting supported in hardware.

Attempts to change the read-only bits (TOFF_FALL[15:4]) will be considered invalid/unsupported data. The device will NACK the unsupported data and the received value will be ignored. The ’cml’ bit in the STATUS_BYTE and the ‘ivd’ bit in the STATUS_CML registers will be set.