Functional Description

Figure 3 shows a state diagram and Figure 4 shows a

block diagram of the bq2003.

Battery Voltage and Temperature

Measurements

Battery voltage and temperature are monitored for

maximum allowable values. The voltage presented on

the battery sense input, BAT, should represent a

single-cell potential for the battery under charge.

A

resistor-divider ratio of:

RB1

RB2

= N - 1

is recommended to maintain the battery voltage within

the valid range, where N is the number of cells, RB1 is

the resistor connected to the positive battery terminal,

and RB2 is the resistor connected to the negative bat-

tery terminal. See Figure 1.

Note: This resistor-divider network input impedance to

end-to-end should be at least 200k

Ω and less than 1MΩ.

A ground-referenced negative temperature coefficient

thermistor placed in proximity to the battery may be used

as a low-cost temperature-to-voltage transducer. The tem-

perature sense voltage input at TS is developed using a re-

tive terminal See Figure 1. Both the BAT and TS inputs

are referenced to SNS, so the signals used inside the IC are:

and

3

Table 1. New Charge Cycle and Discharge Stimulus

CCMD

DCMD

New Charge Cycle

Started by:

Discharge-Before-Charge

Started by:

Pulled Up/Down to:

A rising edge on DCMD

Battery replacement

A rising edge on CCMD

A rising edge on DCMD

Battery replacement

A falling edge on CCMD or DCMD

A rising edge on CCMD

A rising edge on DCMD

A falling edge on CCMD

A rising edge on DCMD

bq2003

Fg2003a2.eps

N

T

C

bq2003

VCC

PACK +

PACK -

TS

SNS

RT1

RT2

RB2

RB1

bq2003

VDC

External Trickle Resistor

Negative Temperature

Coefficient Thermister

Pass Element

PACK+

PACK-

MOD

BAT

SNS

Figure 1. Voltage and Temperature Monitoring and Trickle Resistor