BQ2012 datasheet(8/20 Pages) TI

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Self-Discharge Estimation

The bq2012 continuously decrements NAC and increments

DCR for self-discharge based on time and temperature.

The self-discharge count rate is programmed to be a nomi-

nal 1

* NAC or

* NAC per day or disabled as selected

by PROG5. This is the rate for a battery whose tempera-

ture is between 20°–30°C. The NAC register cannot be

decremented below 0.

Count Compensations

The bq2012 determines fast charge when the NAC up-

dates at a rate of

≥2 counts/sec. Charge and discharge are

compensated for temperature and charge/discharge

rate before updating the NAC and/or DCR. Self-dis-

charge estimation is compensated for temperature be-

fore updating the NAC or DCR.

Charge Compensation

Two charge efficiency compensation factors are used for

trickle charge and fast charge. Fast charge is defined as

a rate of charge resulting in

≥ 2 NAC counts/sec (≥ 0.15C

to 0.32C depending on PFC selections; see Table 2). The

compensation defaults to the fast charge factor until the

actual charge rate is determined.

Temperature adapts the charge rate compensation factors

over three ranges between nominal, warm, and hot tem-

peratures. The compensation factors are shown below.

Discharge Compensation

Corrections for the rate of discharge are made by adjusting

an internal discharge compensation factor. The discharge

factor is based on the dynamically measured VSR. The

compensation factors during discharge are:

Temperature compensation during discharge also takes place.

At lower temperatures, the compensation factor increases by

0.05 for each 10°C temperature range below 10°C.

Compensation factor = 1.0 + (0.05 * N)

Where N = Number of 10°C steps below 10°C and

-150mV < VSR <0.

For example:

T > 10°C : Nominal compensation, N = 0

0°C<T< 10°C: N = 1 (i.e., 1.0 becomes 1.05)

-10°C<T<0°C: N=2 (i.e., 1.0 becomes 1.10)

-20°C<T< -10°C: N = 3 (i.e., 1.0 becomes 1.15)

-20°C<T< -30°C: N = 4 (i.e., 1.0 becomes 1.20)

Self-Discharge Compensation

The self-discharge compensation is programmed for a

nominal rate of 1

* NAC or

* NAC per day. This is

the rate for a battery within the 20–30°C temperature

range (TMPGG = 6x). This rate varies across 8 ranges

from <10°C to >70°C, doubling with each higher tem-

perature step (10°C). See Table 3.

Digital Magnitude Filter

The bq2012 has a programmable digital filter to eliminate

charge and discharge counting below a set threshold. The de-

fault setting is -0.30mV for VSRD and +0.38mV for VSRQ. The

proper digital filter setting can be calculated using the following

equation. Table 4 shows typical digital filter settings.

VSRD (mV) = -45 / DMF

VSRQ (mV) = -1.25 * VSRD

bq2012

Temperature

Step

Typical Rate

PROG5 = Z

PROG5 = L

< 10°C

NAC

256

NAC

188

10–20°C

NAC

128

NAC

20–30°C

NAC

30–40°C

NAC

23 5

40–50°C

NAC

11 8

50–60°C

NAC

588

Table 3. Self-Discharge Compensation

Charge

Temperature

Trickle Charge

Compensation

Fast Charge

Compensation

<30°C

0.80

0.95

30–40°C

0.75

0.90

> 40°C

0.65

0.80

Approximate

VSR Threshold

Discharge

Compensation

Factor

Efficiency

VSR > -150 mV

1.00

100%

VSR < -150 mV

1.05

95%

DMF

Hex.

VSRD

(mV)

VSRQ

(mV)

-0.60

0.75

100

-0.45

0.56

150 (default)

-0.30

0.38

175

-0.26

0.32

200

-0.23

0.28

Table 4. Typical Digital Filter Settings

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