Data Sheet

LT7170/LT7170-1

THEORY OF OPERATION

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Rev. 0 | 19 of 36

for a fault condition are restarted only when the fault condition is no

longer present and the following occurs:

►

The output is commanded to turn off and then to turn back on via

the RUN pin and/or OPERATION command.

►

A MFR_RESET command is issued.

►

VIN and EXTVCC bias power are removed and reapplied to the

LT7170/LT7170-1.

An LT7170/LT7170-1 retry following a fault does not clear the status

command bits. Therefore, when the output powers on after a fault,

the status bits can be read to determine the cause of the fault.

When a warning occurs related to the output voltage, output cur-

rent, or temperature, the LT7170/LT7170-1 pull the ALERT pin low,

the corresponding bit is set in the appropriate status commands,

and the regulators continue to operate.

If the output voltage falls to less than VOUT_UV_FAULT_LIMIT, the

LT7170/LT7170-1 respond as follows:

►

The PGOOD pin pulls low.

►

The ALERT pin pulls low.

►

The VOUT_UV fault bit is set in the STATUS_VOUT, STA-

TUS_BYTE, and STATUS_WORD commands.

►

The regulators continue to operate while limiting the maximum

valley current.

If a fault occurs due to output overvoltage or input overvoltage, the

LT7170/LT7170-1 respond as follows:

►

The output shuts down immediately.

►

The PGOOD pin pulls low.

►

The ALERT pin pulls low.

►

The corresponding indicator bits are set in the appropriate status

commands.

►

After 10 ms MFR_RETRY_DELAY time, the LT7170/LT7170-1

attempt to restart when the fault condition is no longer present.

Table 6. Factory Default Warnings and Faults Behavior

Warning or Fault Type

Detection

Method

Default Threshold

Default Regulator Response

PGOOD

ALERT

VOUT UV Warning

Comparator

VOUT_COMMAND: −6.5%

Continues operation

High-Z

Pull low

VOUT OV Warning

Comparator

VOUT_COMMAND: 7.5%

Continues operation

High-Z

Pull low

VOUT UV Fault

Comparator

VOUT_COMMAND: −7%

Continues operation

Pull low

Pull low

VOUT OV Fault

Comparator

VOUT_COMMAND: 10%

Shuts down and retries

Pull low

Pull low

VIN OV Fault

Comparator

17.6 V

Shuts down and retries

Pull low

Pull low

VIN UV Warning

ADC

−1.0 V (disabled)

Continues operation

High-Z

Pull low

Overtemperature Warning

ADC

140°C

Continues operation

High-Z

Pull low

Overtemperature Fault

ADC

160°C

Shuts down and retries

Pull low

Pull low

IOUT Overcurrent (IOUT_OC) Warning ADC

Average current (IAVG) > 20 A

Continues operation

High-Z

Pull low

IOUT Overcurrent Fault

Valley

comparator

IVALLEY > 6.5 A1

Continues operation

High-Z

High-Z

Turn-On Time (TON_MAX) Fault

Comparator and

timer

5 ms without exceeding

VOUT_UV_FAULT_LIMIT

Continues operation

Pull low

Pull low

Turn-Off Time (TOFF_MAX) Warning ADC and timer

0 (disabled)

Not applicable

High-Z

High-Z

SYNC Input Clock Error2

Input and output Not applicable

Locks off until next reset

Pull low

Pull low

NVM Error

CRC, ECC

Not applicable

Locks off until next reset

Pull low

Pull low

PMBus/I2C Communication Error

(CML)

Logic

Not applicable

Not applicable

High-Z

Pull low

1 The IOUT_OC_FAULT valley current threshold is controlled by MFR_PWM_MODE_LT7170, Bits[10:9].

2 When a SYNC input clock error is detected during initialization, the output of the devices is disabled.