LTC3883 datasheet(36/136 Pages) LINER

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LTM4676A

4676afa

For more information www.linear.com/LTM4676A

operaTion

Inaddition,theLTM4676Acanmapanycombinationoffault

indicatorstotheirrespectiveGPIOn pinusingthepropagate

GPIOn response commands, MFR_GPIO_PROPAGATEn.

Typical usage of a GPIO pin is as a driver for an external

crowbardevice,overtemperaturealert,overvoltagealertor

as an interrupt to cause a microcontroller to poll the fault

commands. Alternatively, the GPIOn pins can be used as

inputs to detect external faults downstream of the control-

ler that require an immediate response. The GPIO0 and/or

GPIO1pinscanalsobeconfiguredaspowergoodoutputs.

Power good indicates the controller output is within the

OV/UV fault thresholds. At power-up the pin will initially

be three-state. If it is necessary to have the desired polar-

ity on the pin at power-up in this configuration, attach a

Schottky diode between the RUN pin of the propagated

power good signal and the GPIO pin. The Cathode must

be attached to RUN and the Anode to the GPIO pin (see

Figure 2). If the GPIO pin is set to a power good status,

the MFR_GPIO_RESPONSE must be ignore otherwise a

latched off condition exists.

As described in the Soft-Start section, it is possible to

control start-up through concatenated events. If GPIOn

is used to drive the RUN pin of another controller, the

unfiltered VOUT_UV fault limit should be mapped to the

GPIO pin.

Any fault or warning event will cause the ALERT pin to as-

sert low unless the ALERT is masked by the SMBALERT_

MASK command. The pin will remain asserted low until

the CLEAR_FAULTS command is issued, the fault bit is

written to a 1, the PMBus master successfully reads the

device ARA register, bias power is cycled or a MFR_RESET

or RESTORE_USER_ALL command is issued. Channel

specific faults are cleared if the RUN pins are toggled OFF/

ON or the part is commanded OFF/ON via PMBus. If bit

0 of MFR_CONFIG_ALL is set to a 1, toggling the RUN

pins OFF/ON or commanding the part OFF/ON via PMBus

clears all faults. The MFR_GPIO_PROPAGATEn command

determines if the GPIO pins are pulled low when a fault is

detected; however, the ALERT pin is always pulled low if a

fault or warning is detected and the status bits are updated

unlesstheALERTpinismaskedusingtheSMBALERT_MASK

command.

Output and input fault event handling is controlled by the

corresponding fault response byte as specified in Table 24

to Table 28. Shutdown recovery from these types of faults

can either be autonomous or latched. For autonomous

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

is 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 components by repetitive power cycling. The

MFR_RETRY_DELAY must be greater than 120ms. It can

not exceed 83.88 seconds.

Channel-to-channel fault dependencies can be created

by connecting GPIOn pins together. In the event of an

internal fault, one or more of the channels is configured

to pull the bussed GPIOn pins low. The other channels

are then configured to shut down when the GPIOn pins

are pulled low. For autonomous group retry, the faulted

channel is configured to release the GPIOn pin(s) after a

retry interval, assuming the original fault has cleared. All

the channels in the group then begin a soft-start sequence.

If the fault response is LATCH_OFF, the GPIO pin remains

asserted low until either the RUN pin is toggled OFF/ON

or the part is commanded OFF/ON. The toggling of the

RUN either by the pin or OFF/ON command will clear

faults associated with the channel. If it is desired to have

all faults cleared when either RUN pin is toggled, set bit 0

of MFR_CONFIG_ALL to a 1.

The status of all faults and warnings is summarized in the

STATUS_WORD and STATUS_BYTE commands.

RESPONSES TO VOUT AND IOUT FAULTS

VOUTOVandUVconditionsaremonitoredbycomparators.

The OV and UV limits are set in three ways.

As a Percentage of the VOUT if Using the Resistor Con-

figuration Pins

In EEPROM if Either Programmed at the Factory or

Through the GUI

By PMBus Command

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