PM6670AS datasheet(36/54 Pages) STMICROELECTRONICS

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Device description

PM6670AS

36/54

7.1.11

Over voltage and under voltage protections

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

Voltage Protection (OVP) 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 OVP is also active during the soft-start. Once

an OVP has occured, a toggle on S5 pin or a Power-On-Reset is necessary to exit from the

latched state.

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

Voltage Protection occurs. This event causes the switching section to be immediately

disabled and both switches to be opened. The controller enters in soft-end mode and the

output is eventually kept to ground, turning the low side MOSFET on when the voltage is

lower than 400 mV. If S3 and S5 are forced low, the low-side MOSFET is released and only

the 22

Ω switch is active.

The Under-Voltage Protection circuit is enabled only at the end of the soft-start. Once an

UVP has toccured, a toggle on S5 pin or a Power-On-Reset is necessary to clear the fault

state and restart the device.

7.1.12

Device thermal protection

The internal control circuitry of the PM6670AS self-monitors the junction temperature and

turns all outputs off when the 150 °C limit has been overrun. This event causes the switching

section to be immediately disabled and both switches to be opened. The controller enters in

soft-end Mode and the output is eventually kept to ground, turning the low side MOSFET on

when the voltage is lower than 400 mV. If S3 and S5 are forced low, the low-side switch is

released and only the 22

Ω discharge MOSFET is active.

The thermal fault is a latched protection and normal operating condition is restored by a

Power-On Reset or toggling S5.

Table 3. OV, UV and OT faults management

Fault

Conditions

Action

VDDQ over voltage

VDDQ > 115 % of the

nominal value

LGATE pin is forced high and the device latches off.

Exit by a Power-On Reset or toggling S5

VDDQ under voltage

VDDQ < 70 % of the

nominal value

LGATE pin is forced high after the soft-end, then the

device latches off. Exit by a Power-On Reset or

toggling S5.

Junction over

temperature

TJ > +150 °C

LGATE pin is forced high after the soft-end, then the

device latches off. Exit by a Power-On Reset or

toggling S5 after 15°C temperature drop.

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