PM6680ATR datasheet(27/48 Pages) STMICROELECTRONICS

27 / 48 page

PM6680A

Device description

27/48

7.9

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.

7.10

Internal linear regulator

The PM6680A has an internal linear regulator providing 5 V (LDO5) at ± 2 % accuracy. High

side drivers, low side drivers and most 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 100

mA. Bypass LDO5 output with a minimum 1µF 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-switchover 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

Table 7.

V5SW multifunction pin

V5SW

Description

GND

The 5 V linear regulator is always turned on and supplies LDO5 output.

Switching 5 V

output

The 5 V linear regulator is turned off when the voltage on V5SW is above 4.8 V and

the LDO5 output is supplied by the switching 5 V output.

External 5 V

supply

The 5 V linear regulator is turned off when the voltage on V5SW is above 4.8 V and

LDO5 output is supplied by the external 5 V.

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