PM6685 datasheet(32/52 Pages) STMICROELECTRONICS

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Monitoring and protections

PM6685

32/52

Monitoring and protections

8.1

Power good signals

The PM6685 provides three independent power good signals: one for each switching

section(PGOOD5/PGOOD3) and the other for the internal linear regulator

LDO3(PGOOD_LDO3).

PGOOD5/PGOOD3 signals are low if the output voltage is out of ±10% of the designed set

point or during the soft-start, the soft end and when the device works in standby and

shutdown mode.

PGOOD_LDO3 signal is low when the output voltage of LDO3 output is lower than its falling

voltage threshold(2.6V typ.). Each power good pin is an open-drain output and can sink

current up to 4mA.

8.2

Thermal protection

The PM6685 has a thermal protection to preserve the device from overheating. The thermal

shutdown occurs when the die temperature goes above +150°C. In this case all internal

circuitry is turned off and the power sections are turned off after the discharge mode.

A power on reset or a toggle on the SHDN pin is necessary to restart the device.

8.3

Overvoltage protection

When the switching output voltage is about 115% of its nominal value, a latched

overvoltage protection occurs. In this case, the synchronous rectifier immediately turns on

while the high-side MOSFET turns off. The output capacitor is rapidly discharged and the

load is preserved from being damaged. The overvoltge protection is also active during the

soft start. Once an overvoltage protection has been detected, a toggle on SHDN, EN3/EN5

pins or a power on reset is necessary to exit from the latched state.

8.4

Undervoltage protection

When the switching output voltage is below 70% of its nominal value, a latched undervoltage

protection occurs. In this case the switching section is immediately disabled and both

switches are open. The controller enters in soft end mode and the output is eventually kept

to ground, turning low side MOSFET on. The undervoltage circuit protection is enabled only

at the end of the soft-start. Once an overvoltage protection has been detected, a toggle on

SHDN, EN5/EN3 pin or a power on reset is necessary to clear the undervoltage fault and

starts with a new soft-start phase.

PM6685 Datasheet(PDF) 32 Page - STMicroelectronics