39
Rev. B
OPERATION
External Overtemperature and Undertemperature
Fault Response
Two internal temperature sensors are used to sense the
temperature of critical circuit elements like inductors
and power MOSFETs on each channel. The OT_FAULT_
RESPONSE and UT_FAULT_ RESPONSE commands are
used to determine the appropriate response to an over-
temperature and under temperature condition, respec-
tively. If no external sense elements are used (not recom-
mended) set the UT_FAULT_ RESPONSE to ignore—and
set the UT_FAULT_LIMIT to 275°C. The fault responses
are:
n
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY. See Table 19.
RESPONSES TO INPUT OVERCURRENT AND OUTPUT
UNDERCURRENT FAULTS
Input overcurrent and output undercurrent are measured
with the ADC. The fault responses are:
n
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
Time Interval Specified in MFR_RETRY_DELAY.
RESPONSES TO EXTERNAL FAULTS
When either
FAULT
n
pin is pulled low, the OTHER bit is
set in the STATUS_WORD command, the appropriate bit
is set in the STATUS_MFR_SPECIFIC command, and the
ALERT
pin is pulled low. Responses are not deglitched.
Each channel can be configured to ignore or shut down
then retry in response to its
FAULT
n
pin going low by
modifying the MFR_FAULT_RESPONSE command. To
avoid the
ALERT
pin asserting low when
FAULT
is pulled
low, assert bit 1 of MFR_CHAN_CONFIG, or mask the
ALERT using the SMBALERT_MASK command.
FAULT LOGGING
The LTM4680 has fault logging capability. Data is logged
into memory in the order shown in Table 19. The data is
stored in a continuously updated buffer in RAM. When a
fault event occurs, the fault log buffer is copied from the
RAM buffer into NVM. Fault logging is allowed at tem-
peratures above 85°C; however, retention of 10 years is
not guaranteed. When the die temperature exceeds 130°C
the fault logging is delayed until the die temperature drops
below 125°C. The fault log data remains in NVM until a
MFR_FAULT _LOG_CLEAR command is issued. Issuing
this command re-enables the fault log feature. Before re-
enabling fault log, be sure no faults are present and a
CLEAR_FAULTS command has been issued.
When the LTM4680 powers-up or exits its reset state, it
checks the NVM for a valid fault log. If a valid fault log
exists in NVM, the “Valid Fault Log” bit in the STATUS_
MFR_SPECIFIC command will be set and an
ALERT
event
will be generated. Also, fault logging will be blocked until
the LTM4680 has received a MFR_FAULT_LOG_CLEAR
command before fault logging will be re-enabled.
The information is stored in EEPROM in the event of
any fault that disables the controller on either channel. A
FAULT
n
being externally pulled low will not trigger a fault
logging event.
BUS TIMEOUT PROTECTION
The LTM4680 implements a timeout feature to avoid
persistent faults on the serial interface. The data packet
timer begins at the first START event before the device
address write byte. Data packet information must be
completed within 30ms or the LTM4680 will three-state
the bus and ignore the given data packet. If more time
is required, assert bit 3 of MFR_CONFIG_ALL to allow
typical bus timeouts of 255ms. Data packet information
includes the device address byte write, command byte,
repeat start event (if a read operation), device address
byte read (if a read operation), all data bytes and the PEC
byte if applicable.
The LTM4680 allows longer PMBus timeouts for block
read data packets. This timeout is proportional to the
length of the block read. The additional block read timeout
