LTC2972 datasheet(95/112 Pages) LINER

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LTC2972

2972fa

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APPLICATIONS INFORMATION

FAULT MANAGEMENT

Output Overvoltage and Undervoltage Faults

Thehigh-speedvoltagesupervisorOVandUVfaultthresh-

oldsareconfiguredusingtheVOUT_OV_FAULT_LIMITand

VOUT_UV_FAULT_LIMIT commands, respectively. The

VOUT_OV_FAULT_RESPONSE and VOUT_UV_FAULT_

RESPONSE commands determine the responses to OV/

UV faults. Fault responses can range from disabling the

DC/DC converter immediately, waiting to see if the fault

condition persists for some interval before disabling

the DC/DC converter, or allowing the DC/DC converter

to continue operating in spite of the fault. If a DC/DC

converter is disabled, the LTC2972 can be configured to

retry one to six times, retry continuously without limita-

tion, or latch-off. The retry interval is specified using the

MFR_RETRY_DELAY command. Latched faults are reset

bytogglingtheCONTROLpin,usingtheOPERATIONcom-

mand, or removing and reapplying the bias voltage to the

VIN_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.

Output Overvoltage, Undervoltage, and Overcurrent

Warnings

OV, UV, and OC warning thresholds are processed by

the LTC2972’s ADC. These thresholds are set by the

VOUT_OV_WARN_LIMIT, VOUT_UV_WARN_LIMIT, and

IOUT_OC_WARN_LIMIT commands, respectively. Note

that there is no IOUT UC warning threshold. If a warning

occurs, the corresponding bits are set in the status reg-

isters and the ALERTB output is asserted low. Note that a

warning will never cause a VOUT_EN output pin to disable

a DC/DC converter.

Configuring the AUXFAULTB Output

The AUXFAULTB output may be used to indicate an

output OV or UV fault. Use the MFR_CONFIG2_LTC2972

and MFR_CONFIG3_LTC2972 registers to configure the

AUXFAULTB pin to assert low in response to VOUT_OV

or VOUT_UV fault conditions. The AUXFAULTB output

will stop pulling low when the LTC2972 is commanded

to re-enter the ON state following a faulted-off condition.

Figure 30 shows an application circuit where the AUX-

FAULTB output is used to trigger an SCR crowbar on the

intermediate bus in order to protect the DC/DC converter’s

load from a catastrophic fault such as a stuck top gate. The

stuck top gate causes an OV fault, which in turn causes

the LTC2972 to pull AUXFAULTB low, thus de-asserting

the ON input to the LTC4210 hot swap controller, which

opens the switch Q1 that supplies the DC/DC converter

input. In addition, when AUXFAULTB goes low it forces the

S4010DS3 SCR device into the on-state via the 2N2907

PNP, thus quickly dropping the voltage on the VIN input to

the DC/DC converter, preventing the stuck top gate from

damaging components supplied by this converter. Note

that the VPWR input to the LTC2972 bypasses switch Q1,

keeping the LTC2972 fully powered throughout the above

sequence.

Multi-Channel Fault Management

Multi-channel fault management is handled using the

bidirectional FAULTB pins. Figure 31 illustrates the con-

nections between channels and the FAULTB pins.

• The MFR_FAULTBn_PROPAGATE command acts like

a programmable switch that allows faulted_off condi-

tions from a particular channel (PAGE) to propagate to

eitherFAULTBoutput.TheMFR_FAULTBn_RESPONSE

command controls similar switches on the inputs to

each channel that allow any channel to shut down

in response to any combination of the FAULTB pins.

Channels responding to a FAULTB pin pulling low will

attempt a new start sequence when the FAULTB pin in

question is released by the faulted channel.

• A FAULTB pin can also be asserted low by an external

driver in order to initiate an immediate off-sequence

after a 10μs deglitch delay.

LTC2972 Datasheet(PDF) 95 Page - Linear Technology

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