External Overtemperature And Undertemperature Fault Response; Responses To Input Overcurrent And Output Undercurrent Faults; Responses To External Faults; Fault Logging - Analog Devices Linear LTM 4700 User Manual

LTM4700
OPERATION
be ignored. Internal temperature limits cannot be adjusted
by the user. See Table 15.
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 overtem-
perature and under temperature condition, respectively. If
no external sense elements are used (not recommended)
set the UT_FAULT_ RESPONSE to ignore—and set the
UT_FAULT_LIMIT to –275°C. The fault responses are:
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the Time
n
Interval Specified in MFR_RETRY_DELAY. See Table 16.
RESPONSES TO INPUT OVERCURRENT AND OUTPUT
UNDERCURRENT FAULTS
Input overcurrent and output undercurrent are measured
with the ADC. The fault responses are:
Ignore
n
Shut Down Immediately—Latch Off
n
Shut Down Immediately—Retry Indefinitely at the
n
Time Interval Specified in MFR_RETRY_DELAY. See
Table 16.

RESPONSES TO EXTERNAL FAULTS

When either FAULTn 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 FAULTn 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.
38

FAULT LOGGING

The LTM4700 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 LTM4700 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 LTM4700 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
FAULTn being externally pulled low will not trigger a fault
logging event.

BUS TIMEOUT PROTECTION

The LTM4700 implements a timeout feature to avoid per-
sistent 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 LTM4700 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 LTM4700 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 applies
For more information www.analog.com
Rev. B