PM6680ATR datasheet(29/48 Pages) STMICROELECTRONICS

29 / 48 page

PM6680A

Monitoring and protections

29/48

Monitoring and protections

Power good signals

The PM6680A provides two independent power good signals: one for each switching

section (PGOOD1/PGOOD2).

PGOOD1/PGOOD2 signals are low if the output voltage is out of ± 10 % of the designed set

point or during the soft-start, standby and shutdown mode.

Thermal protection

The PM6680A 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 circutry 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.

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, EN1/EN2

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

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, EN1/EN2 pin or a power on reset is necessary to clear the

undervoltage fault and starts with a new soft-start phase.

Table 9.

Protections and operatives modes

Mode

Conditions

Description

Overvoltage

protection

OUT1/OUT2 > 115% of the

nominal value

LGATE1/LGATE2 pin is forced high, LDO5 remains

active. Exit by a power on reset or toggling SHDN or

EN1/EN2

Undervoltage

protection

OUT1/OUT2 < 70 % of the

nominal value

LGATE1/LGATE2 is forced high after the soft end

mode, LDO5 remains active. Exit by a power on reset

or toggling SHDN or EN1/EN2

Thermal

shutdown

TJ> +150 °C

All circuitry off. Exit by a POR on VIN or toggling

SHDN.

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