LTM4680 datasheet(44/132 Pages) AD

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LTM4681

Rev. 0

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OPERATION

Overtemperature and Undertemperature

Fault Response

Four 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:

Ignore

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the Time

Interval Specified in MFR_RETRY_DELAY. See Table 18.

RESPONSES TO INPUT OVERCURRENT AND OUTPUT

UNDERCURRENT FAULTS

Input overcurrent and output undercurrent are measured

with the ADC. The fault responses are:

Ignore

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY.

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_nn 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_nn pin asserting low when FAULTn is

pulled low, assert bit 1 of MFR_CHAN_CONFIG, or mask

the ALERT using the SMBALERT_MASK command.

FAULT LOGGING

The LTM4681 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 LTM4681 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 LTM4681 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 LTM4681 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 LTM4681 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 LTM4681 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

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