LTM4675 datasheet(39/136 Pages) LINER

39 / 136 page

LTM4676A

4676afa

For more information www.linear.com/LTM4676A

operaTion

internal volatile memory. When a fault event occurs, the

recording into internal volatile memory is halted, the fault

log information is available from the MFR_FAULT_LOG

command, and the contents of the internal memory

are copied into EEPROM. Fault logging is allowed at

temperaturesabove85°C;however,retentionof10yearsis

not guaranteed. When the die temperature exceeds 130°C

the fault logging is delayed until the die temperature drops

below 125°C. After the fault condition that created the fault

log event has been removed, clear the fault before the fault

log data is erased, or else the part will immediately issue

another fault log.

When the LTM4676A powers-up, it checks the EEPROM

for a valid fault log. If a valid fault log exists in EEPROM,

the “Valid Fault Log” bit in the STATUS_MFR_SPECIFIC

commandwillbesetandanALERTeventwillbegenerated.

Also,faultloggingwillbeblockeduntiltheLTM4676Ahas

received a MFR_FAULT_LOG_CLEAR command before

fault logging will be re-enabled.

TheinformationisstoredinEEPROMintheeventofanyfault

that disables the controller on either channel. An external

GPIOn pulling low will not trigger a fault logging event.

BUS TIMEOUT PROTECTION

The LTM4676A implements a timeout feature to avoid

hanging 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

25ms or the LTM4676A 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 LTM4676A 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 command. In

no circumstances will the timeout period be less than the

tTIMEOUT_SMB specification of 32ms (typical).

The user is encouraged to use as high a clock rate as pos-

sible to maintain efficient data packet transfer between all

devices sharing the serial bus interface. The LTM4676A

supports the full PMBus frequency range from 10kHz to

400kHz.

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