LTM4680 datasheet(39/132 Pages) AD

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LTM4681

Rev. 0

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microcontroller to poll the fault commands. Alternatively,

the FAULTn pins can be used as inputs to detect external

faults downstream of the controller that require an imme-

diate response.

Any fault or warning event will always cause the ALERT_nn

pin to assert low unless the fault or warning is masked by

the SMBALERT_MASK. The pin will remain asserted low

until the CLEAR_FAULTS command is issued, the fault bit

is written to a 1 or bias power is cycled or a MFR_RESET

command is issued, or the RUNn pins are toggled OFF/

ON or the part is commanded OFF/ON via PMBus or an

ARA command operation is performed. The MFR_FAULT_

PROPAGATE command determines if the FAULTn pins are

pulled low when a fault is detected.

Output and input fault event handling is controlled by the

corresponding fault response byte as specified in Table 14

thru Table 18. Shutdown recovery from these types of

faults can either be autonomous or latched. For autono-

mous recovery, the faults are not latched, so if the fault

conditions not present after the retry interval has elapsed,

a new soft-start is attempted.

If the fault persists, the controller will continue to retry.

The retry interval is specified by the MFR_RETRY_DELAY

command and prevents damage to the regulator com-

ponents by repetitive power cycling, assuming the fault

condition itself is not immediately destructive. The MFR_

RETRY_DELAY must be greater than 120ms. It can not

exceed 83.88 seconds.

Status Registers and ALERT Masking

Figure 5 summarizes the internal LTM4681 status regis-

ters accessible by PMBus command. These contain indi-

cation of various faults, warnings and other important

operating conditions. As shown, the STATUS_BYTE and

STATUS_WORD commands also summarize contents of

other status registers. Refer to PMBus Command Details

for specific information.

NONE OF THE ABOVE in the STATUS_BYTE indicates that

one or more of the bits in the most-significant nibble of

STATUS_WORD are also set.

OPERATION

In general, any asserted bit in a STATUS_x register also

pulls the ALERT_nn pin low. Once set, ALERT_nn will

remain low until one of the following occurs.

A CLEAR_FAULTS or MFR_RESET Command Is

Issued

The Related Status Bit Is Written to a One

The Faulted Channel Is Properly Commanded Off and

Back On

The LTM4681 Successfully Transmits Its Address

During a PMBus ARA

Bias Power Is Cycled

With some exceptions, the SMBALERT_MASK command

can be used to prevent the LTM4681 from asserting

ALERT_nn for bits in these registers on a bit-by-bit basis.

These mask settings are promoted to STATUS_WORD

and STATUS_BYTE in the same fashion as the status bits

themselves. For example, if ALERT_nn is masked for all

bits in channel n STATUS_VOUT, then ALERT_nn is effec-

tively masked for the VOUT bit in STATUS_WORD for PAGE

n. The BUSY bit in STATUS_BYTE also asserts ALERT_nn

low and cannot be masked. This bit can be set as a result

of various internal interactions with PMBus communi-

cation. This fault occurs when a command is received

that cannot be safely executed with one or both channels

enabled. As discussed in the Application Information,

BUSY faults can be avoided by polling MFR_COMMON

before executing some commands.

If masked faults occur immediately after power up,

ALERT_nn may still be pulled low because there has not

been time to retrieve all of the programmed masking

information from EEPROM.

Status information contained in MFR_COMMON and

MFR_PADS can be used to further debug or clarify the

contents of STATUS_BYTE or STATUS_WORD as shown,

but the contents of these registers do not affect the state

of the ALERT_nn pin and may not directly influence bits

in STATUS_BYTE or STATUS_WORD.

LTM4680 Datasheet(PDF) 39 Page - Analog Devices

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