LTM4677 datasheet(31/110 Pages) AD

31 / 110 page

LTC3888-1

Rev. 0

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OPERATION

assuming the original fault has cleared. All the channels

in the group then begin a soft-start sequence.

As noted above, FAULT pins can also find use as inputs

to detect faults external to the controller that require an

immediate response. External faults propagated into the

chip using FAULT pins are not deglitched.

Refer to MFR_FAULT_PROPAGATE for additional details.

FAULT LOG OPERATION

The LTC3888-1 supports fault logging to provide telem-

etry recording capability. A conceptual diagram of the fault

log is shown in Figure 3. During normal operation the

contents of primary status registers and all ADC readings,

including peak voltage and current results, are stored in

a continuously updated RAM buffer if enabled by bit 7

of MFR_CONFIG_ALL. The operation is similar to a strip

recorder. When a fault occurs that disables either master

channel, recording to internal memory is halted (locked)

and the fault log information is made available from RAM

via the MFR_FAULT_LOG command. Some contents of

the locked RAM fault log are also copied into EEPROM for

nonvolatile storage. See Fault Log Details below.

A fault log write to EEPROM is allowed above a die tem-

perature of 85°C, but 10 years of retention is not guaran-

teed. When die temperature exceeds 130°C, any EEPROM

fault log storage is delayed until the temperature drops

below 125°C.

Once created, a fault log cannot be overwritten by sub-

sequent fault events, even if the log is only partial. An

MFR_FAULT_LOG_CLEAR command must be executed

to erase an existing log, leaving the IC free to generate a

new one.

Faults propagated into the IC through FAULT pins do not

trigger a fault logging event, regardless of their impact on

PWM operation. Faults that generate a fault log should be

fully cleared before the log is erased to prevent creation

of spurious fault logs.

When the LTC3888-1 powers up it checks the EEPROM

for a valid fault log. If one is found the Fault Log Present

bit in STATUS_MFR_SPECIFIC is set. If the Memory Fault

Detected bit is also set in STATUS_CML, then the stored

fault log is partial. Data in one or more event records may

be incomplete or incorrect.

Fault Log Details

The MFR_FAULT_LOG command uses a block read pro-

tocol with a fixed length of 147 bytes. The LTC3888-1

returns a block byte count of zero if a fault log is not

present.

Contents of a fault log are shown in Table 1 through

Table 4. Refer to Table 6 for an explanation of data for-

mats. Each event record represents one complete conver-

sion cycle through all multiplexed monitor ADC inputs

and related status. When a fault log is created the present

ADC input cycle is completed and the ADC input being

converted at the time of the fault is noted in the log header.

Referring to Figure 3, the six most recent event records

are maintained in internal RAM in reverse chronological

order. If input power is cycled or the part is reset after

a fault log is creatred, the RAM record is restored from

EEPROM where only the four most recent events are

retained due to available storage.

Figure 3. Fault Log Conceptual Diagram

388812 F03

LOCK RAM

AND TRANSFER

TO EEPROM

AT TIME OF FAULT

TRANSFER FROM

EEPROM AFTER

RESET

ADC READINGS

CONTINUOUSLY

FILL BUFFER

UNTIL FAULT

RAM BYTES

EEPROM BYTES

•

PMBus READ

OF FAULT

LOG

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RECORDS

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