STw4102

Battery charger

19/34

6.4

Charging from a USB port

The MAIN or USBPWR input can be used to charge from a USB 2.0 port. When using the

MAIN input, bit SEL_DC_USB (bit 5 of register REG_CHG0) must be set to 1. Charging

from a USB port is similar to charging from a wall adapter, except the fast charge current

6.5

Charging using external power devices

To support charge currents higher than 1 A from the main supply adapter, the STw4102

provides the option to use an external power device and sense resistor. This OTP option is

factory set.

The STw4102 driver is able to drive an external PNP (STT818B or equivalent) or a PMOS

plus Schottky diode (STS2DPFS20V or equivalent). The driver maximum sink current is

60 mA.

The external current sensing device is usually a 200 m

Ω shunt resistor. With this resistor

value, the trickle and USB charge currents are close to the nominal values.

6.6

Charge mode summary

Table 13 summarizes the different charge modes.

Table 12.

USB charge current

REG_CHG0[7]

REG_CHG0[6]

0

0

60mA (100 mA max)

0

1

200mA

1

0

400mA (500 mA max)

11

off

Table 13.

Charge modes

MAIN

detected

USBPWR

detected

CHG_ENA

bit

SEL_DC_USB

bit

Charge

-

x

x

0

x

Charge disabled

0

0

1

x

No charge

under

1x

1x

Trickle charge from MAIN

0

1

Trickle charge from USBPWR

above

1x

10

Fast charge from MAIN input,

current set by Rset

11

Fast charge from MAIN input,

current set by USB_ICHG bits

0

1

1

x

Fast charge from USBPWR input,

current set by USB_ICHG bits