PM6670AS datasheet(35/54 Pages) STMICROELECTRONICS

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PM6670AS

Device description

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7.1.9

Gate drivers

The integrated high-current gate drivers allow using different power MOSFETs. The high-

side driver uses a bootstrap circuit which is supplied by the +5 V rail. 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 VCC and PGND pins.

An important feature of the PM6670AS 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 (2.5 V typ.). Similarly, when the low-side MOSFET is turned off, the

high-side one remains off until the LGATE pin voltage is above 1 V.

The power dissipation of the drivers is a function of the total gate charge of the external

power MOSFETs and the switching frequency, as shown in the following equation:

Equation 23

The low-side driver has been designed to have a low-resistance pull-down transistor

(0.6

Ω typ.) in order to prevent undesired ignition of the low-side MOSFET due to the Miller

effect.

7.1.10

Reference voltage and bandgap

The 1.237 V internal bandgap reference has a granted accuracy of ±1 % over the

0 °C to 85 °C temperature range. The VREF pin is a buffered replica of the bandgap voltage.

It can supply up to ±100

µA and is suitable to set the intermediate level of MODE, DDRSEL

and DSCG multifunction pins. A 100 nF (min.) bypass capacitor toward SGND is required to

enhance noise rejection. If VREF falls below 0.87 V (typ.), the system detects a fault

condition and all the circuitry is turned OFF.

An internal divider derives a 0.9 V±1 % voltage (Vr) from the bandgap. This voltage is used

as a reference by the switching regulator output. The Over-Voltage Protection, the Under-

Voltage Protection and the Power-Good signal are also referred to Vr.

DRV

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driver

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⋅

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