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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