Maxim Integrated MAX15303 PMBus Command Set - Manual (Page 18)

MAX15303 PMBus Command Set User’s Guide
Page 18 of 52
TOFF_FALL
Reference: Standard Command Lockable: Yes
Command Code: 0x65 Format: Linear
Data Bytes: 2 Units: ms
Transfer: Read/Write Word Factory Value: 0xCA80 (5ms)
Description/Notes: See Section 16.6 of the PMBus Specification Part II.
The TOFF_FALL command sets the ramp-down time from regulation at VOUT_COMMAND to 0V. The
nominal factory value is 5ms.
The MAX15303 achieves shutdown dV
OUT
/dt control by decrementing the loop setpoint by one 12-bit
step every time a certain number of ramp-controller clock cycles have elapsed in an 8-bit counter.
This results in a setpoint that decreases at a controlled rate, in turn creating a constant dV
OUT
/dt
during shutdown.
Because the MAX15303 must calculate the ramp control timer setting based upon the value of
VOUT_COMMAND, the possible range and resolution of TOFF_FALL will vary significantly.
The desired value of TOFF_FALL is retained in memory, regardless of ramp-timer limitations, but the
read-back value is based on actual hardware register settings.