BQ2005STR datasheet(3/22 Pages) TI2

3 / 22 page

Functional Description

Figure 3 shows a block diagram and Figure 4 shows a

state diagram of the bq2005.

Battery Voltage and Temperature

Measurements

Battery voltage and temperature are monitored for maxi-

mum allowable values. The voltage presented on the bat-

tery sense input, BATA,B, must be divided down to be-

tween 0.95

∗ VCC and 0.475 ∗ VCC for proper operation. A

resistor-divider ratio of:

RB1

RB2

2.375

=− 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 TSA,B is developed using a

resistor-thermistor network between VCC and VSS.

See

Figure 1.

Both the BATA,B and TSA,B inputs are refer-

enced to SNSA,B, so the signals used inside the IC are:

VBAT(A,B) -VSNS(A,B) =VCELL(A,B)

and

VTS(A,B) -VSNS(A,B) =VTEMP(A,B)

Discharge-Before-Charge

The DCMDA input is used to command discharge-

before-charge via the DISA output.

Once activated,

DISA becomes active (high) until VCELL falls below VEDV

where:

VEDV = 0.475

∗ VCC ± 30mV

at which time DISA goes low and a new fast charge cycle

begins.

The DCMDA input is internally pulled up to VCC (its in-

active state). Leaving the input unconnected, therefore,

results in disabling discharge-before-charge. A negative

going pulse on DCMDA initiates discharge-before-charge

a t any t ime r egardless of t he current state of the

bq2005.

If DCMDA is tied to VSS, discharge-before-

charge will be the first step in all newly started charge

cycles.

Starting A Charge Cycle

Anew charge cycle is started by (see Figure 2):

VCC rising above 4.5V

VCELL falling through the maximum cell voltage,

VMCV where:

VMCV = 0.95

∗ VCC ± 30mV

If DCMDA 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.

bq2005

Fg2005-1.eps

bq2005

VCC

PACK +

PACK -

TSA,B

SNSA,B

RT1

RT2

RB2

RB1

bq2005

Negative Temperature

Coefficient Thermister

PACK+

PACK-

BATA,B

SNSA,B

Figure 1. Voltage and Temperature Monitoring

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