PM6681ATR datasheet(26/47 Pages) STMICROELECTRONICS

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Device description

PM6681A

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high side MOSFET is turned off the voltage at the phase node begins to fall. The low side

MOSFET is turned on when the voltage at the phase node reaches an internal threshold.

When the low side MOSFET is turned off, the high side remains off until the LGATE pin

voltage goes approximately under 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 11

Where Vdriver is the 5 V driver supply.

Reference voltage and bandgap

The 1.237 V (typ.) internal bandgap voltage is accurate to 1 % over the temperature range.

It is externally available (VREF pin) and can supply up to 100

µA and can be used as a

voltage threshold for the multifunction pins FSEL and SKIP to select the appropriate working

mode. Bypass VREF to ground with a 100 nF minimum capacitor.

If VREF goes below 0.87 V (typ.), the system detects a fault condition and all the circuitry is

turned off. A toggle on the input voltage (power on reset) or a toggle on SHDN pin is

necessary to restart the device.

An internal divider of the bandgap provides a voltage reference Vr of 0.9 V. This voltage is

used as reference for the linear and the switching regulators outputs. The overvoltage

protection, the undervoltage protection and the Power Good signals are referred to Vr.

7.9

Internal linear regulators

The PM6681A has two linear regulators providing respectively 5 V (LDO5) and an

adjustable voltage (LDO) at ± 2 % accuracy. High side drivers, low side drivers and

MOSFETs of internal circuitry are supplied by LDO5 output through VCC pin (an external

RC filter may be applied between LDO5 and VCC). The linear regulator can provide an

average output current of 50 mA and a peak output current of 100mA. Bypass LDO5 output

with a minimum 1

µF ceramic capacitor and a 4,7 µF tantalum capacitor (ESR ≥ 2 Ω). If the

5 V output goes below 4 V, the system detects a fault condition and all the circuitry is turned

off. A power on reset or a toggle on SHDN pin is necessary to restart the device.

V5SW pin allows to keep the 5 V linear regulator always active or to enable the internal

bootstrap-switch over function: if the 5 V switching output is connected to V5SW, when the

voltage on V5SW pin is above 4.8 V, an internal 3.0

Ω max P-channel MOSFET switch

connects V5SW pin to LDO5 pin and simultaneously LDO5 shuts down. This configuration

allows to achieve higher efficiency. V5SW can be connected also to an external 5 V supply.

LDO5 regulator turns off and LDO5 is supplied externally. If V5SW is connected to ground,

the internal 5 V regulator is always on and supplies LDO5 output.

driver

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