LTC2977 datasheet(51/138 Pages) AD

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LTM4664A

Rev. 0

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temperature faults cannot be ignored. Internal tempera-

ture limits cannot be adjusted by the user. See Table 14.

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

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the Time

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

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the Time

Interval Specified in MFR_RETRY_DELAY. See Table 15.

RESPONSES TO EXTERNAL FAULTS

When either FAULT_Cn 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_Cn pin going low by

modifying the MFR_FAULT_RESPONSE command. To

avoid the ALERT pin asserting low when FAULT_Cn is

pulled low, assert bit 1 of MFR_CHAN_CONFIG, or mask

the ALERT using the SMBALERT_MASK command.

FAULT LOGGING

The LTM4664A PSM 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 temperatures

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_FAULTScommand has been issued.

When the LTM4664A PSM 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 LTM4664A PSM 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_Cn being externally pulled low will not trigger a

fault logging event.

BUS TIMEOUT PROTECTION

The LTM4664A PSM 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 LTM4664A PSM 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 oper-

ation), device address byte read (if a read operation), all data

bytes and the PEC byte if applicable.

The LTM4664A PSM 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 primarily to the MFR_FAULT_LOG com-

mand. The timeout period defaults to 32ms.

DUAL 25A/30A PSM OPERATION

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