AN137 Silicon_Laboratories, AN137 Datasheet - Page 5

• Manufacturer Part Number: AN137
• Description: Lithium ION Battery Charger Using C8051f300
• Manufacturer: Silicon_Laboratories

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 ‘F30x regu-
lates the battery’s current to I
cally 1/50 C) until the battery’s voltage reaches
V
rent is current limited to I
safe initial charge and to minimize battery self-
heating. If at any time the temperature increases out
of limit, charging is halted.
Charging - Phase 2
Once the battery reaches V
charger enters phase 2, where the battery’s algo-
rithm controls the PWM pass switch to ensure the
output voltage provides a constant charge-current
I
1C and is definable in the header file as is
I
Charging - Phase 3
After the battery reaches V
single cell charger), the charger algorithm enters
phase 3, where the PWM feeds back and regulates
the battery’s voltage. In phase 3, the battery contin-
ues to charge until the battery’s charge current
reaches I
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 doesn’t
really affect the charger as it simply monitor’s the
BULK
LOWCURRENT
MINVOLTBULK
to the battery (rate or bulk current is usually
MINIBULKl
and V
. Note that the battery’s charge cur-
, after which, the battery is
MINVOLTBULK
LOWCURRENT
Top
LOWCURRENT
MINVOLTBULK
(typically 4.2 V in
).
to ensure
(typi-
the
Rev. 1.2
battery’s current condition and starts charging from
that point.
Conclusion
The C8051F300’s 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, “DC-DC Converter
Tutorial”.
Martinez, Carlos and Drori, Yossi and Ciancio,
Joe, “AN126 Smart Battery Primer”, Xicor, Octo-
ber 1999.
AN137
5