VBAT 2V/div

VACIN=5V,VBAT =3.4Vto5V

CHGIN2V/div

I

0.5 A/div

ACIN

Time:2mS/div

0.1

1

10

100

1000

10000

0

1000

2000

3000

4000

5000

Vgs-Vchgin-Vgatdrv-mV

Q2

VCHGIN=5V,

V

-V

=200mV

CHGIN

OUT

100

150

200

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400

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-50

0

50

100

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T -JunctionTemperature-°C

J

Q1+Q2

Q1

Q2

BACKGROUND

DETAILED FUNCTIONAL DESCRIPTION

bq24350

bq24352

TYPICAL PERFORMANCE CHARACTERISTICS (continued)

BATTERY OVP

Rdson vs Vgs

Figure 10.

Figure 11.

FET ON RESISTANCE vs TEMPERATURE

Figure 12.

During the charging process for portable devices, input voltage spikes usually happen when the AC/DC adaptor

is plugged in, or charge current is cut off quickly under fault conditions, such as input OVP, OCP or battery OVP

and so on. The over voltage stress may damage the analog baseband chip which has lower voltage rating due to

its increased complexity. Therefore, over voltage protection is needed for the safe operation of portable devices.

Another challenge arises from the charge circuit that uses external charging FET in series with a reverse

blocking diode as the charging device. The battery may not be fully charged when input voltage is low due to the

additional diode voltage drop. bq24350/2 will provide the solution for above problems since it has input OVP,

OCP, battery OVP function, together with integrated charging FET which will eliminate the reverse blocking diode

in the previously mentioned charge circuit, as shown in Figure 1.

The bq24350/2 is a highly integrated circuit designed to provide protection to Li-ion batteries from failures of the

charging circuit. The IC continuously monitors the input voltage and the battery voltage. In case of an input

over-voltage condition, the IC will turn off the internal power FET after a blanking time. If the battery voltage rises

to unsafe levels during charging process, power is removed from the system. If the input current exceeds the

over current threshold for a limited time, the IC will turn off the output power. The integrated charging FET can

regulate the charge voltage and current according to the control from the host. The device can also provide a

voltage source with over voltage and over current protection for host controller.

Copyright © 2009, Texas Instruments Incorporated

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Product Folder Link(s): bq24350 bq24352