Maxim Integrated MAX15301 PMBus Command Set - Manual (Page 7)

MAX15301 PMBus Command Set User’s Guide
Rev 1 Page 7 of 53
On, Off, and Margin Testing Related Commands
OPERATION
Reference: Standard Command Lockable: Yes
Command Code: 0x01 Format: Bit field
Data Bytes: 1 Units: N/A
Transfer: Read/Write Byte Factory Value: 0x40 (see Description table)
Description/Notes: See Section 12.1 of the PMBus Specification Part II.
If the values of VOUT_OV_FAULT_LIMIT or VOUT_UV_FAULT_LIMIT are set between the values of
VOUT_MARGIN_HIGH and VOUT_MARGIN_LOW , it is possible that a fault will be detected when
exiting the “Margin High/Low (Ignore Fault)” command states. This occurs when fault detection is re-
enabled before the output has had time to return to the
VOUT_COMMAND value. This condition can
be avoided in most cases by increasing the value of VOUT_TRANSITION_RATE , thereby decreasing the
amount of time required for the output to return to normal VOUT_COMMAND setpoint.
The value of the OPERATION command is maintained in volatile memory, and cannot be stored in the
Default Store or User Store nonvolatile memory. This prevents inadvertent preservation of a
margin-high or margin-low state. If it is desired to keep the output always enabled or always disabled
upon power-up, this can be achieved by storing the appropriate value of the
ON_OFF_CONFIG
command.
Useful values for the OPERATION command:
0x00
Immediate-off, no sequencing: both DH and DL outputs low a (note: same as 0x01-0x3F)
0x40 Soft-off, with sequencing (factory setting) b (note: same as 0x41-0x7F)
0x80 Output enabled, if allowed by ON_OFF_CONFIG setting (note: same as 0x81-0x8F)
0x94 Margin low, ignore faults (note: same as 0x95-0x97)
0x98 Margin low, act on faults (note: same as 0x99-0x9B)
0xA4 Margin high, ignore faults (note: same as 0xA5-0xA7)
0xA8 Margin high, act on faults (note: same as 0xA9-0xAB)
Invalid values for the OPERATION command:
0x90-0x93
0x9C-0x9F
0xA0-0xA3
0xAC-0xFF
These invalid data bytes will trigger an “Invalid Or Unsupported Data” response per section 10.9.3 of
the PMBus specification.
After writing the OPERATION command to enable the output, the PMBus master must either wait for
a time equal to (TON_DELAY + TON_RISE + 50ms), or wait for PG to assert, before sending additional
PMBus commands.
ON_OFF_CONFIG
a An “immediate-off,” “hard-stop,” or “tri-state” shutdown means the MAX15301 will stop switching and keep both DH and
DL outputs low, allowing the output voltage to decay naturally according to load and output capacitance.
b In this application note (and other InTune documents) a “soft-off,” “soft-stop,” or “ramp-down” shutdown means the
MAX15301 actively controls the output voltage along a linear ramp to zero Volts, per the TOFF_DELAY and TOFF_FALL
values.