BQ26220 Datasheet, PDF (10/19 Pages) Texas Instruments – HIGH PERFORMANCE BATTERY MONITOR IC WITH COULOMB COUNTER, VOLTAGE AND TEMPERATURE MEASUREMENT

bq26220
SLUS521B − AUGUST 2002 − REVISED FEBRUARY 2004
APPLICATION INFORMATION
battery voltage measurement
The bq26220 senses the battery voltage on the BAT pin and reports it through register pair BATH−BATL. The
BATH (address = 0x72 – bits 0 through 2) and the BATL low-byte register (address = 0x71) contain the result
of ADC conversion on the battery voltage. The voltage is expressed in an 11-bit binary format with an LSB step
size of 2.44 mV. Bit 2 of BATH register represents the MSB and bit 0 of the BATL represent the LSB. The
full-scale voltage for this measurement is 5 V and is optimized for direct sensing in single-cell Li-Ion or Li-pol
applications (see Figure 3).
Note that Bits 3 through 7 of the BATH register store the offset information for the voltage ADC. The most
significant bit is the sign-bit followed by 4 bits of offset data.
Also note that LSB gain correction factor, in µV, is stored in address 0x79 (byte 1 of the ID ROM) in 2’s
complement. The host is responsible for applying the LSB gain correction factor and offset to the ADC
measurements.
Correct V_BAT = V_BAT × (2.44 + LSB correction factor) − offset
example 1: (If real LSB = + 2.45mV and offset = +80 mV)
in address 0x79 ⇒ 0000 1010 (in binary) 2’s complement
in BATH (0x72) ⇒ 0101 0XXX (in binary) signed magnitude
To calculate the correct V_BAT:
LSB correction factor = +10 µV = +0.01 mV
offset = +10 × 8 mV = 80 mV
Correct V_BAT (in mV) = V_BAT × (2.44 + 0.01) − 80
example 2: (If real LSB = +2.43 mV and offset = −80 mV
in address 0x79 ⇒ 1111 0110 (in binary), 2’s complement
in BATH (0x72) ⇒ 1101 0XXX (in binary), signed magnitude
To calculate the correct V_BAT:
LSB correction factor = −10 µV= −0.01 mV
offset = −10 × 8 mV = −80 mV
Correct V_BAT (in mV) = V_BAT × (2.44 − 0.01) − (−80)
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