STW4102_08 datasheet(18/34 Pages) STMICROELECTRONICS

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Battery charger

STw4102

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6.2

Trickle charge

The trickle charge mode is enabled when the battery voltage Vbatt is lower than the trickle

voltage threshold Vtrickle. An internal current source charges the battery. When Vbatt is

above Vtrickle, the trickle current generator is off and the battery is charged using the

constant current method.

The trickle voltage threshold and trickle current are defined by OTP configuration bits and

are factory set to 2.9 V and 60 mA by default. Other values are possible, see Section 9:

Factory OTP options on page 24.

6.3

Charging from a wall adapter

The MAIN input is used for charging from a wall adapter or a dedicated USB charger. The

SEL_DC_USB bit (bit 5 of register REG_CHG0) must be set to 0. The fast charge current is

defined by the external resistor Rset connected to the ISET pin, and can be set up to 1 A.

The value of the fast charge current is given by the following formula:

Icharge = 12000 / Rset

In the constant voltage mode, the charger output voltage is regulated with 1% accuracy. The

charger output voltage is programmable using the REG_CHG0 register, bits 3 and 4 (see

Table 11).

Figure 20.

Main charge mode

Table 11.

Charger output voltage

REG_CHG0[4]

REG_CHG0[3]

Vcharge

4.10V +/-1%

4.20V +/-1%

4.30V +/-1%

4.35V +/-1%

Vcharge

Vtrickle (2.9v)

Trickle

Constant current

Constant voltage

charge

Itrickle (60mA)

(defined by Rset)

Icharge

Flag end of

charge (10% Icharge)

Ibatt

Vbatt

Battery Voltage

Charge current

Fast charge

Maintenance

charge

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