PM6644 datasheet(19/35 Pages) STMICROELECTRONICS

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PM6644

Device description

Doc ID 023203 Rev 1

19/35

2.1.6

Soft-start and soft-end

The switching section has an EN pin. A non-programmable soft-start procedure takes place

when the EN pin rises above 2.1 V.

To prevent high input inrush currents, the current limit is increased from 25% to 100% of the

current limit threshold with steps of 25%.

The procedure is not programmable and ends typically in 2.8 ms. The overvoltage protection

is always active while the undervoltage protection is enabled at the end of the 2.8 ms.

Driving one EN pin below 1.8 V makes the section perform a soft-end: gate driving signals

are pulled low and the output is discharged through an internal MOSFET with RDS(on) of

Ω typ.

2.1.7

Monitoring

The PM6644 controls its switching output to prevent any damage or uncontrolled working

condition.

2.1.8

Overvoltage protection

The PM6644 provides a latched overvoltage protection (OVP). If the output voltage rises

above 120% of the nominal value, a latched OVP protection is activated. The controller turns

on the low-side MOSFET keeping the output voltage at 0 V.

The protection is latched and this fault is cleared by cycling VCC < 2.1 V and then > 3 V.

2.1.9

Undervoltage protection

If, during regulation, the output voltage drops under 62% of the nominal value, an

undervoltage latched fault is detected. The controller performs a soft-end procedure (see

Section 2.1.6 ). The undervoltage fault is reset by toggling the EN pin or by cycling VCC <

2.1 V and then > 3 V.

2.1.10

VCC undervoltage

The device monitors the voltage at the VCC pin. The switching section can start operating

only if the voltage at the PVCC pin is above 3 V. If PVCC falls below 2.1 V, the switching

section is turned off until PVCC voltage goes over 3 V.

Table 8.

Fault management summary

Fault

Condition

Device behavior

Overvoltage

VOUT > +120%

The low-side MOSFET is turned on keeping the

output voltage at 0 V. Latched fault, cleared

toggling EN or cycling VCC < 2.1 V and then > 3

Undervoltage

VOUT < 62%

The controller performs a soft-end. Latched fault

cleared toggling EN or cycling VCC < 2.1 V and

then > 3 V.

VCC undervoltage

VCC < 2.1 V

The controller turns off the switching section until

PVCC voltage goes over 3 V. Not latched fault.

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