AN3064

Battery monitoring functions

Doc ID 16263 Rev 1

7/15

Figure 5.

Coulomb counter operation

2.2

Coulomb counter reading

The charge data as well as the conversion count can be read at any time by the system

controller. The recommended procedure is to read the locations REG_CHARGE (2 bytes)

and REG_COUNTER (2 bytes) in one go using a single I²C block read to ensure data

consistency between the accumulator and counter.

The charge code is a 16-bit binary number using the two’s complement binary format. Bit 15

is the sign bit and the LSB value is 6.70 µV.h. To convert the charge data into mA.h, the

external resistance Rsense must be taken into account:

charge data (mA.h) = 6.70 * charge_code / Rsense (m

Ω).

When the result of an accumulation exceeds the limits of a signed binary number (below

0x8000 or above 0x7FFFF), the carry bit is lost, no overflow is generated and the

accumulator continues to accumulate.

I

battery

current

(mA)

Idle

Fast charge

End of

charge

Idle

Medium

discharge rate

Fast

discharge rate

Coulomb counter detail:

current samples are

accumulated at each

end of conversion:

Acc =

Σ(Ι x Δt)

Δt

AM04581

Acc

Coulomb

counter

accumulator

(mA.h)

End of

discharge

Time

Discharge

current

Time

Charge

current

Table 1.

REG_CHARGE_LOW. address 2 (02h)

Name

Pos.

Type

Power-

up

Description

DATA[7..0]

[7..0]

R

00

Coulomb counter data

Table 2.

REG_CHARGE_HIGH. address 3 (03h)

Name

Pos.

Type

Power-

up

Description

DATA[15..8]

[7..0]

R

00

Coulomb counter data