Datasheet

LTC2977

2977fa

For more information www.linear.com/LTC2977

TIMED FAULT RESPONSE

TON_MAX_FAULT_RESPONSE

This command defines the LTC2977 response to a TON_MAX_FAULT. It may be used to protect against a short-circuited

output at start-up. After start-up use VOUT_UV_FAULT_RESPONSE to protect against a short-circuited output.

The device also:

• Sets the HIGH_BYTE bit in the STATUS_BYTE,

• Sets the VOUT bit in the STATUS_WORD,

• Sets the TON_MAX_FAULT bit in the STATUS_VOUT register, and

• Notifies the host by asserting ALERTB.

TON_MAX_FAULT_RESPONSE Data Contents

BIT(S) SYMBOL OPERATION

b[7:6] Ton_max_fault_response_action Response action:

00b: The unit continues operation without interruption.

01b-11b: The unit shuts down immediately or sequences off after TOFF_DELAY (See Mfr_config_chan_

mode). After shutting down, the unit responds according to the retry settings in bits [5:3].

b[5:3] Ton_max_fault_response_retry Response retry behavior:

000b: A zero value for the Retry Setting means that the unit does not attempt to restart. The output remains

disabled until the fault is cleared.

001b-111b: The PMBus device attempts to restart the number of times specified by the global Mfr_retry_

count[2:0] until it is commanded OFF (by the CONTROLn pin or OPERATION command or both), bias power

is removed, or another fault condition causes the unit to shut down.

b[2:0] Ton_max_fault_response_delay Hard coded to 000b. There is no additional deglitch delay applied to fault detection.

Clearing Latched Faults

When a channel shuts down due to a fault, the off state is latched. This is referred to as a latched fault condition. Latched

faults are reset by toggling the CONTROL pin, using the OPERATION or ON_OFF_CONFIG command,

or removing and

reapplying

the bias voltage to the V

IN_SNS

pin. All fault and warning conditions result in the ALERTB pin being asserted

low and the corresponding bits being set in the status registers. The CLEAR_FAULTS command resets the contents

of the status registers and de-asserts the ALERTB output, but it does not clear a faulted off state nor allow a channel

to turn back on.

PMBus

COMMAND DESCRIPTION