PM6652 datasheet(35/53 Pages) STMICROELECTRONICS

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PM6652

Device description

Doc ID 16867 Rev 5

35/53

8.9

Internal MOS drivers

The integrated high-current gate drivers allow different Power MOSFETs to be used.

The high-side driver, which is supplied by the +5 V rail, uses a bootstrap circuit with

integrated boot diode. Only one external ceramic capacitor (100 nF or bigger) is required.

The BOOT and PHASE pins work respectively as supply and return path for the high-side

driver, while the low-side driver is directly fed through the PVCC and PGND pins.

An important feature of the PM6652 gate drivers is the adaptive anti-cross-conduction

circuitry, which prevents high-side and low-side MOSFETs from being turned on at the same

time. When the high-side MOSFET is turned off, the voltage at the PHASE node begins to

fall. The low-side MOSFET is turned on only when the voltage at the PHASE node reaches

an internal threshold in the range of 2.5 V to 1 V. Similarly, when the low-side MOSFET is

turned off, the high-side one remains off until the LGATE pin voltage is above 0.8 V (typical

value).

8.10

Monitoring and protection

8.10.1

Power good

The power good signal is an open drain output which requires an external pull-up resistor.

When VOUT is lower than 300 mV or higher than 200 mV with respect to VDAC, or when the

COREON pin is de-asserted, the PWRGD pin is immediately forced low.

At startup, the PWRGD pin is allowed to rise only 4 ms after the VDAC programmed value is

reached, as shown in

Figure 6, Figure 34 and Figure 35.

8.10.2

Current monitor (IMON)

The voltage sensed between the CSNS and VOUT pins is mirrored across the RG external

resistor (between IMONFB and VOUT pins) and the resulting current is multiplied by the

current monitor block gain.

The typical gain value is:

Equation 14

The current monitor gain can be adjusted by choosing RIMON, as shown in Figure 39, in

order to program the required VIMON at maximum load. The total IMON gain becomes:

Equation 15

GIMON,INT=3 is a fixed internal parameter. The minimum suggested value for RG is equal to

400

Ω with maximum allowable IMONFB current lower than about IMAX = 40 µA (typ.).

A good range for RG choice is [0.68 k

Ω; 7 kΩ] with a maximum CSNS-VOUT voltage up to

60 mV.

INT

IMON

INT

IMON

VOUT

CSNS

⋅

−

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