AN137 Datasheet, PDF(5/36 Page) Silicon Laboratories – LITHIUM ION BATTERY CHARGER USING C8051F300

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AN137 Datasheet, PDF (5/36 Pages) Silicon Laboratories – LITHIUM ION BATTERY CHARGER USING C8051F300

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AN137

toring. If a more accurate reference is required, an

external voltage reference can be used. Adjustment

to the divide resistors must be made accordingly.

Charging - Phase1

In phase 1, (for description purposes, we assume

the battery is initially discharged), the âF30x regu-

lates the batteryâs current to ILOWCURRENT (typi-

cally 1/50 C) until the batteryâs voltage reaches

VMINVOLTBULK. Note that the batteryâs charge cur-

rent is current limited to ILOWCURRENT to ensure

safe initial charge and to minimize battery self-

heating. If at any time the temperature increases out

of limit, charging is halted.

batteryâs current condition and starts charging from

that point.

Conclusion

The C8051F300âs high level of analog integration,

small form-factor, integrated FLASH memory, and

low power consumption makes it ideal for flexible

next generation battery charging applications. This

application note discussed how to use the

C8051F30x family in Lithium Ion battery charger

applications. Example code is provided as well.

References

Maxim Integrated Product, âDC-DC Converter

Tutorialâ.

Charging - Phase 2

Once the battery reaches VMINVOLTBULK the

charger enters phase 2, where the batteryâs algo-

rithm controls the PWM pass switch to ensure the

output voltage provides a constant charge-current

IBULK to the battery (rate or bulk current is usually

1C and is definable in the header file as is

ILOWCURRENT and VMINVOLTBULK).

Martinez, Carlos and Drori, Yossi and Ciancio,

Joe, âAN126 Smart Battery Primerâ, Xicor, Octo-

ber 1999.

Charging - Phase 3

After the battery reaches VTop (typically 4.2 V in

single cell charger), the charger algorithm enters

phase 3, where the PWM feeds back and regulates

the batteryâs voltage. In phase 3, the battery contin-

ues to charge until the batteryâs charge current

reaches IMINIBULKl, after which, the battery is

charged for an additional 30 minutes and then

charge terminates. Phase 3 typically takes the

majority of the charging time.

Note that in most practical applications, such as a

portable PC, the batteries may be in any of the three

phases when charging is activated. This doesnât

really affect the charger as it simply monitorâs the

Rev. 1.2

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