LTM4673 datasheet(42/132 Pages) AD

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LTM4683

Rev. 0

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OPERATION

byte value. This hardware-level fault response delay is typ-

ically 2µs from the overvoltage condition to BG asserted

high. Using the VOUT_OV_FAULT_RESPONSE command,

the user can select any of the following behaviors:

OV Pull-Down Only (OV Cannot Be Ignored)

Shut Down (Stop Switching) Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY

Either the Latch Off or Retry fault responses can be de-

glitched in increments of (0–7) • 10µs. See Table 17.

Output Undervoltage Response

The response to an undervoltage (UV) comparator output

can be the following:

Ignore

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY.

The UV responses can be deglitched. See Table 18.

Peak Output Overcurrent Fault Response

Due to the current mode control algorithm, peak output

current across the inductor is always limited on a cycle-

by-cycle basis. The value of the peak current limit is speci-

fied in the Electrical Characteristics table. The current limit

circuit operates by limiting the COMPn maximum voltage.

Since internal DCR sensing is used, the COMPn maximum

voltage has a temperature dependency directly propor-

tional to the TC of the DCR of the inductor. The LTM4683

automatically monitors the external temperature sensors

and modifies the maximum allowed COMPn to compen-

sate for this term. See the IOUT_OC_FAULT_LIMIT in the

PMBus Command Details section for IOUT limiting details.

The overcurrent fault processing circuitry can execute the

following behaviors.

Current Limit Indefinitely

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY.

The overcurrent responses can be deglitched in incre-

ments of (0–7) • 16ms. See Table 19.

RESPONSES TO TIMING FAULTS

TON_MAX_FAULT_LIMIT is the time allowed for VOUT to

rise and settle at start-up. The TON_MAX_FAULT_LIMIT

condition is predicated upon detecting the VOUT_UV_

FAULT_LIMIT as the output is undergoing a SOFT_START

sequence. The TON_MAX_FAULT_LIMIT time is started

after TON_DELAY has been reached, and a SOFT_START

sequence is started. The resolution of the TON_MAX_

FAULT_LIMIT is 10µs. If the VOUT_UV_FAULT_LIMIT is

not reached within the TON_MAX_FAULT_LIMIT time,

the response of this fault is determined by the value of

the TON_MAX_FAULT_RESPONSE command value. This

response may be one of the following.

Ignore

Shut Down (Stop Switching) Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY.

This fault response is not deglitched. A value of 0 in

TON_MAX_FAULT_LIMIT means the fault is ignored.

The TON_MAX_FAULT_LIMIT should be set longer than

the TON_RISE time. It is recommended that TON_MAX_

FAULT_LIMIT always be set to a non-zero value; other-

wise, the output may never come up, and no flag will be

set for the user. See Table 21.

RESPONSES TO VIN OV FAULTS

VIN overvoltage is measured with the ADC. The response

is naturally deglitched by the 100ms typical response time

of the ADC. The fault responses:

Ignore

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY. See

Table 21.

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