Cypress CY8C24794, AN2309, CY8C29x66 Two-Cell Battery Charger with Cell-Balancing Support

AN2309

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

Q1 D1

POWER+

C1 R1

R4

Q2

C4 R5

SERIAL_TX

R7

C5 R6 R8

RS_TX	PWM			Vbias	R9	Q4
(For Debug					bal2	Q3
Only)
	CPU	bal2				R10
		bal1				R11
	VREF	Vref		R13
	TIMERs		C6	R12		R14
				Vbias		Q5
					bal1
	AMUX
Incremental	INAMP
ADC						R17
	AMUX			R18
	PSoC internals		C7	R19
		Vref		Vbias
		R15	R16
		C8
		R20	R21
		R23
POWER-
		Current Sense

Li-Ion

Battery

Pack

Cell2

Cell1

T

Vbias

R24

Vref

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.

November 25, 2007 Document No. 001-17394 Rev. *B - 5 -

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