BQ2004ESLASHH datasheet(3/23 Pages) TI2

3 / 23 page

Functional Description

Figure 2 shows a block diagram and Figure 3 shows a

state diagram of the bq2004E/H.

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

two-cell potential for the battery under charge.

resistor-divider ratio of:

RB1

RB2

- 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 ther-

mistor placed in proximity to the battery may be used as a

low-cost temperature-to-voltage transducer. The tempera-

ture sense voltage input at TS is developed using a

resistor-thermistor network between VCC and VSS. See

Figure 1. Both the BAT and TS inputs are referenced to

SNS, so the signals used inside the IC are:

VBAT -VSNS =VCELL

and

VTS -VSNS =VTEMP

Discharge-Before-Charge

The DCMD input is used to command discharge-before-

charge via the DIS output. Once activated, DIS becomes

active (high) until VCELL falls below VEDV, at which time

DIS goes low and a new fast charge cycle begins.

The DCMD input is internally pulled up to VCC (its inac-

tive state). Leaving the input unconnected, therefore,

results in disabling discharge-before-charge. A negative

going pulse on DCMD initiates discharge-before-charge

at any time regardless of the current state of the

bq2004. If DCMD is tied to VSS, discharge-before-charge

will be the first step in all newly started charge cycles.

Starting A Charge Cycle

A new charge cycle is started by:

Application of VCC power.

VCELL falling through the maximum cell voltage,

VMCV where:

VMCV = 0.8

∗ VCC ± 30mV

A transition on the INH input from low to high.

If DCMD is tied low, a discharge-before-charge will be

executed as the first step of the new charge cycle. Oth-

erwise, pre-charge qualification testing will be the first

step.

The battery must be within the configured temperature

and voltage limits before fast charging begins.

The valid battery voltage range is VEDV <VBAT <VMCV

where:

VEDV = 0.4

∗ VCC ± 30mV

bq2004E/H

Fg2004a.eps

bq2004E/H

VCC

PACK +

PACK -

SNS

RT1

RT2

RB2

RB1

bq2004E/H

Negative Temperature

Coefficient Thermister

PACK+

PACK-

BAT

SNS

Figure 1. Voltage and Temperature Monitoring

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