LTM4677 datasheet(29/116 Pages) AD

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LTC3883/LTC3883-1

Rev. F

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OPERATION

The fault responses are:

Ignore

Shut Down Immediately—Latch Off

ShutDownImmediately—RetryIndefinitelyattheTime

Interval Specified in MFR_RETRY_DELAY

See Table 9.

RESPONSES TO INPUT OVERCURRENT AND OUTPUT

UNDERCURRENT FAULTS

Input overcurrent and output undercurrent are measured

with the MUX’d ADC. Both of these measurements are

naturally deglitched by the 80ms typical response time

of the ADC. The fault responses are:

Ignore

Shut Down Immediately—Latch Off

ShutDownImmediately—RetryIndefinitelyattheTime

Interval Specified in MFR_RETRY_DELAY

See Table 9.

RESPONSES TO EXTERNAL FAULTS

When the GPIO pin is pulled low, the OTHER bit is set in

the STATUS_WORD command, the appropriate bit is set

in the STATUS_MFR_SPECIFC command, and the ALERT

pin is pulled low. Responses are not deglitched. The

LTC3883 can be configured to ignore or shut down then

retry in response to its GPIO pin going low by modifying

theMFR_GPIO_RESPONSEcommand.ToavoidtheALERT

pin asserting low when GPIO is pulled low, assert bit 1 of

MFR_CHAN_CONFIG_LTC3883.

FAULT LOGGING

The LTC3883 has fault logging capability. Data is logged

into memory in the order shown in Table 11. 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 tempera-

tures 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 120°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 LTC3883 powers-up, 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 LTC3883 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. The GPIO pin being

externally pulled low will not trigger a fault logging event.

BUS TIMEOUT FAILURE

The LTC3883 implements a timeout feature to avoid hang-

ing the serial interface. The data packet timer begins at the

first START event before the device address write byte.

Datapacketinformationmustbecompletedwithin20msor

the LTC3883 will three-state the bus and ignore the given

data packet. 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 LTC3883 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

possible to maintain efficient data packet transfer between

all devices sharing the serial bus interface. The LTC3883

supports the full PMBus frequency range from 10kHz to

400kHz.

SIMILARITY BETWEEN PMBUS, SMBUS AND I2C

2-WIRE INTERFACE

The PMBus 2-wire interface is an incremental extension

of the SMBus. SMBus is built upon I2C with some minor

differences in timing, DC parameters and protocol. The

PMBus/SMBus protocols are more robust than simple

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