BQ26231 Datasheet, PDF (6/18 Pages) Texas Instruments – LOW COST BATTERY COULOMB COUNTER FOR EMBEDDED PORTABLE APPLICATIONS

bq26231
SLUS491 – JULY 2001
VCC
BAT+
HDQ
R5
100 Ω
R6
100 Ω
D2
5.6 V
APPLICATION INFORMATION
C3
0.1 µF
U1
1 _NC
2 _VCC
3 _VSS
4
HDQ
NC ⁸
SR1 ⁷
SR2 ⁶
5
RBI
bq26231
C2
0.01 µF
R2
100 kΩ
C1
0.01 µF
R3
100 kΩ
BAT–
R1
0.02 Ω
PACK–
C4
0.1 µF
RBI
D1
1N914
R4
1 MΩ
Figure 2. Typical Application
functional description
The bq26231 measures the voltage drop across a low-value series current sense resistor between the SR1 and
SR2 pins using a voltage-to-frequency converter. This information is placed into various internal counter and
timer registers. Using information from the bq26231, the system host can determine the battery state-of-charge,
estimate self-discharge, and calculate the average charge and discharge currents. During pack storage
periods, the use of an internal temperature sensor doubles the self-discharge count rate every 10° above 25°C.
A register is available to store the calculated offset, allowing current calibration. The offset cancellation register
is written by the bq26231 during pack assembly and is available to the host system to adjust the current
measurements. By adding or subtracting the offset value stored in the OFR, the true charge and discharge
counts can be calculated to a high degree of certainty.
A typical application diagram is shown in Figure 2 and operation states are shown in Table 1.
Table 1. bq26231 Operational States
RBI input
HDQ PIN DCR/CCR/SCR
WOE
OPERATING STATE
HDQ high
Yes
V(SRO) > V(WOE)
Normal
HDQ high
Yes
V(SRO) < V(WOE)
Normal
HDQ low
No
V(SRO) < V(WOE)
Sleep
NOTE: V(SRO) is the voltage difference between SR1 and SR2 plus the offset voltage,
V(OS).
The RBI input pin is used with a storage capacitor or external supply to provide backup potential to the internal
registers when V_CC drops below 2.4 V. The maximum discharge current is 100 nA in this mode. The bq26231
outputs V_CC on RBI when the supply is above 2.4 V; therefore, a diode is required to isolate an external supply.
(See the application diagram.)
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