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AN2309
November 25, 2007 Document No. 001-17394 Rev. *B - 5 -
A two-cell battery charger structure with cell-balancing support is shown in Figure 3. Similar battery charger structures are
explained in detail in AN2258, AN2294, and AN2267. Note that the fuel gauge function can easily be added to this project
without changing any hardware: It is only necessary to switch from the CY8C24423A to a PSoC device with more program
memory. The main fuel gauge calculation parameters are described in AN2294, “The Li-Ion/Li-Pol Battery Charger with Fuel
Gauge Function.
Figure 3. Two-Cell Battery Charger with Cell-Balancing Support
PSoC internals
R23
R1
POWER+
INAMP
AMUX
Incremental
ADC
CPU
RS_TX
(For Debug
Only)
SERIAL_TX
R5
AMUX
Q1
PWM
Q2
T
Cell2
TIMERs
R11
Li-Ion
Battery
Pack
Cell1
Q5
R14
R17
R6
R7
C5
Vbias
R12
R13
C6
Vbias
R19
R18
C7
Vbias
R24
D1
R20 R21
R15 R16
POWER-
C8
bal2
bal1
bal2
bal1
VREF
Vref
Vref
Vref
Vbias
C1
Q4
C4
R4
R10
Q3
R8
R9
Current Sense
The following abbreviations are used in Figure 3:
RS_TX: RS232 transmitter for debug purposes (uses
external level translator). It monitors temperature, voltage,
current and cell-balancing statistics. RS_TX is used only in
the debug stage and may be removed in the released
product.
CPU: Central processor to implement charge and cell-
balancing algorithms, and perform charge control functions.
PWM: Pulse width modulator to regulate the charge current.
VREF: Reference voltage source.
TIMERs: Several timers are used by the CPU in charge and
cell-balancing algorithms.
Incremental ADC: Analog-to-digital converter to digitize the
analog signals.
INAMP: Instrumentation amplifier to measure charge
voltage, current, and temperature.
AMUX: Analog multiplexers.
Figure 3 also contains a two-cell Li-Ion battery pack, a linear
regulator (based on Q1, Q2), a cell-balancing circuit (based
on Q4, Q5), a current-sense resistor, and other elements
that allow the PSoC device to use and interpret battery
current, voltage, and temperature.
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