Application schematics

STw4102

16/34

5.3

Using LDO regulator to supply telephone from wall adapter

The regulator with external power PMOS (M1) supplies the telephone while the battery is

discharged or unplugged. When the charger is unplugged, the phone is supplied by the

battery through Power MOS M2. A Schottky diode (D1) avoids reverse current.

Figure 18.

Charge power path and regulator

Table 10.

Component list for LDO regulator

Name

Typ. value

Tolerance

Comments

M1 + D1

STS2DPFS20V

PMOS transistor with Schottky diode

M2

STT5PF20V

PMOS transistor

Co

10µF to 22µF

An output capacitor Co of at least 10µF is required.

C4

Co

An input capacitor C4 equal to or larger than Co is

required on MAIN input.

To phone

M2

M1

D1

Indicator LED

Battery voltage

32kHz

Rset

Rcg

C1

StandBy

C2

Reset

IO voltage

STw4102

VOUT

SENSE

BATT

BATTSENSE

ISET

CVIS

C32KHZ

STDBY

ICG+

ICG-

GND

RESETN

SDA

SCL

VIO

LDOFB

LDODRV

CVREF

EOCHG

PWRDETECTN

MAIN

USBPWR

DRIVER

C3

Co >= 15uF

to power

management

C4

TEST