PM6686 datasheet(32/50 Pages) STMICROELECTRONICS

32 / 50 page

Device description

PM6686

32/50

Doc ID 15281 Rev 4

Figure 52.

Current limit circuit block diagram

A negative current control is also implemented: the low-side MOSFET is forced off when the

current exceeds the negative limit. This function prevents the excessive negative inductor

current during the PWM operating mode. The threshold is set approximately at the 120% of

the positive current limit.

8.1.8

Soft-start and soft-end

The two sections have independent enable pins, EN1 and EN2. A not programmable soft-

start procedure takes place when EN pin rises above 2.4 V typ.

To prevent high input inrush currents, the current limit is increased from 25% to 100% 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 typically 20 ms after the

beginning of the soft-start procedure.

Driving one EN pin below 0.8 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.

A power up sequence for the switching sections can be selected connecting one EN pin to

VREF2.

Table 10.

Current limit configuration

Control pin

Control pin voltage

Threshold SET

ILIM1

ILIM2

VILIM = VCC-1 V

100 mV

0.2 V = VILIM = 2 V

VILIM = 5µA * RILIM

VILIM/10

PHASE

ILIM

Ton

Generator

LGATE

HGATE

5uA

RILIM

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