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UDG−03041

+

SCL

PACK−

PACK+

ESD Protection

D1

5.6 V

SDA

ESD Protection

D2

5.6 V

R7

100

Ω

R8

100

Ω

R1

1 k

Ω

C1

0.1

µF

R2

1 k

Ω

0.02

Ω

R4

10 k

Ω

C2

0.1

µF

C3

0.1

µF

C4

0.1

µF

C3

0.1

µF

R3

1 k

Ω

R5

100

Ω

R6

100

Ω

Li-Ion Protector

Li-Ion

or

Li-Pol

PGM TP

1

2

3

4

9

8

7

6

GPIO

SRP

SRN

BAT

RBI

VCC

VSS

SCL

bq27200DRK

5

SDA

10

PGM

11

Measurements

Charge and Discharge Coulometric and Current Measurements

bq27000, bq27200

SLUS556D – SEPTEMBER 2004 – REVISED MARCH 2006

FUNCTIONAL DESCRIPTION (continued)

Figure 3 shows a typical application circuit. Differential sense of the voltage across the current sense resistor,

R

µA pull-down on the HDQ or SDA and SCL lines ensures that the device detects a logic 0 on the communication

lines and allows the device to automatically enter the low-power sleep mode when the system power is switched

off or the pack is removed. A 100 k

Ω pullup to V

to be disabled. The bqJUNIOR can operate directly from a single Li-Ion or Li-Pol cell.

Figure 3. Typical Application Circuit (bq27200)

As shown in the functional block diagram, the bqJUNIOR uses a dedicated fully differential Delta-Sigma Coulomb

Counter (DSCC) for charge and discharge current and coulometric measurements and an analog-to-digital

converter (ADC) for battery voltage and temperature measurements. Both DSCC and ADC are automatically

compensated for offset. No user calibration or compensation is required. An EEPROM offset value can be

programmed to compensate for contributions to the DSCC offset due to the PCB layout.

The bqJUNIOR uses a DSCC to perform a continuous integration of the voltage waveform across a small value

sense resistor in the negative lead of the battery, as shown in Figure 3. The integration of the voltage across the

sense resistor is the charge added or removed from the battery. Because the DSCC does a direct integration of

the waveform, the shape of the current waveform through the sense resistor does not have any effect on the

coulometric measurement accuracy. The low-pass filter that feeds the sense resistor voltage to the bqJUNIOR

SRP and SRN inputs filters out system noise and does not affect the coulometric measurement accuracy,

because the low-pass filter does not change the integrated value of the waveform. The bqJUNIOR also uses the

DSCC to measure current. The reported current is determined by the average voltage across the sense resistor

over a 5.12 second interval.

8

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