LTC2977 datasheet(50/138 Pages) AD

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LTM4664A

Rev. 0

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Output Undervoltage Response

The response to an undervoltage 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 14.

Peak Output Overcurrent Fault Response

Due to the current mode control algorithm, peak out-

put current across the inductor is always limited on a

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

is specified in Electrical Characteristics table. The cur-

rent limit circuit operates by limiting the COMP_Cn max-

imum voltage. Since internal DCR sensing is used, the

COMP_Cn maximum voltage has a temperature depen-

dency directly proportional to the TC of the DCR of the

inductor. The LTM4664A PSM automatically monitors

the external temperature sensors and modifies the maxi-

mum allowed COMP_Cn to compensate for this term. The

IOUT_OC_FAULT_LIMIT section provides data points for

IOUT Limiting on page103.

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 15.

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 detection of 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 TON_MAX_FAULT_

LIMIT always be set to a non-zero value, otherwise the

output may never come up and no flag will be set to the

user. See Table 16.

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 are:

Ignore

Shut Down Immediately—Latch Off

Shut Down Immediately—Retry Indefinitely at the

Time Interval Specified in MFR_RETRY_DELAY. See

Table 16.

RESPONSES TO OT/UT FAULTS

Internal Overtemperature Fault Response

An internal temperature sensor protects against NVM

damage. Above 85°C, no writes to NVM are recom-

mended. Above 130°C, the internal overtemperature warn

threshold is exceeded and the part disables the NVM and

does not re-enable until the temperature has dropped

to 125°C. When the die temperature exceed 160°C the

internal temperature fault response is enabled and the

PWM is disabled until the die temperature drops below

150°C. Temperature is measured by the ADC. Internal

DUAL 25A/30A PSM OPERATION

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