Datasheet

LTC2978A
37
2978afa
For more information www.linear.com/LTC2978A
FAULT RESPONSE FOR VALUES MEASURED BY THE ADC
OT_FAULT_RESPONSE, UT_FAULT_RESPONSE, VIN_OV_FAULT_RESPONSE and VIN_UV_FAULT_RESPONSE
The fault response documented here is for values that are measured by the ADC. These values are measured over a
longer period of time and are not deglitched. Note that in addition to the response described by these commands, the
LTC2978A will also:
• Set the appropriate bit(s) in the STATUS_BYTE
• Set the appropriate bit(s) in the STATUS_WORD
• Set the appropriate bit in the corresponding STATUS_VIN or STATUS_TEMPERATURE register, and
• Notify the host by pulling the ALERTB pin low.
Data Contents
BIT(S) SYMBOL OPERATION
b[7:6] Ot_fault_response_action,
Ut_fault_response_action,
Vin_ov_fault_response_action,
Vin_uv_fault_response_action
Response action:
00b: The unit continues operation without interruption.
01b to 11b: The device shuts down and responds according to the retry setting in bits [5:3].
b[5:3] Ot_fault_response_retry,
Ut_fault_response_retry,
Vin_ov_fault_response_retry,
Vin_uv_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 continuously, without limitation, using Mfr_retry_delay,
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.
Changing the value might not take effect until the next off-then-on sequence on that channel.
b[2:0]
Ot_fault_response_delay,
Ut_fault_response_delay,
Vin_ov_fault_response_delay,
Vin_uv_fault_response_delay
Hard coded to 000b. There is no additional deglitch delay applied to fault detection.
TIMED FAULT RESPONSE
TON_MAX_FAULT_RESPONSE
This command defines
the LTC2978A 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.
PMBus COMMAND DESCRIPTION