A6986F datasheet(15/72 Pages) STMICROELECTRONICS

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A6986F

Functional description

Figure 3. Internal block diagram

5.1

Power supply and voltage reference

The internal regulator block consists of a start-up circuit, the voltage pre-regulator that

provides current to all the blocks and the bandgap voltage reference. The starter supplies

the startup current when the input voltage goes high and the device is enabled (SS/INH pin

over the inhibits threshold).

The pre-regulator block supplies the bandgap cell and the rest of the circuitry with

a regulated voltage that has a very low supply voltage noise sensitivity.

Switchover feature

The switchover scheme of the pre-regulator block features to derive the main contribution of

the supply current for the internal circuitry from an external voltage (3 V < VBIAS < 5.5 V is

typically connected to the regulated output voltage). This helps to decrease the equivalent

quiescent current seen at VIN. (Please refer to Section 5.6: Switchover feature on page 31).

5.2

Voltages monitor

An internal block continuously senses the VCC, VBIAS and VBG. If the monitored voltages are

good, the regulator starts operating. There is also a hysteresis on the VCC (UVLO).

RST

DRIVER

GND

PEAK

VALLEY

ZERO

CROSSING

LOOP

CONTROL

OSCILLATOR

L.N. / L.C.

RST TH.

VOUT

E/A

POWER

PMOS

POWER

NMOS

SENSE

PMOS

SENSE

NMOS

Vcc

SLOPE

VIN

SYNC

COMP

GND

DRIVER

GND

VALLEY

LOOP

CONTROL

E/A

POWER

PMOS

MOS

SLOPE

OVP

MLF

DELAY

SS/INH

VREF

TSS

FSW

GDIV INT

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