BQ2018TS datasheet(6/21 Pages) TI

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Table 3. WOE Thresholds

WOE3–1 (hex)

VWOE (mV)

n/a

3.840

1.920

1.280

0.960

0.768

0.640

7h*

0.549

* Default value after POR.

Temperature

The bq2018 has an internal temperature sensor which is

used to set the value in the temperature register

(TMP/CLR) and set the self-discharge count rate value.

The register reports the temperature in 8 steps of 10°C

from <0°C to >60°C as Table 4 specifies. The bq2018 tem-

perature sensor has typical accuracy of

±2°Cat 25°C.

See the TMP/CLR register description for more details.

Clear Register

The host system is responsible for register maintenance.

To facilitate this maintenance, the bq2018 has a Clear

ter or register pair to zero. The host system clears a reg-

ister by writing the corresponding register bit to 1. When

the bq2018 completes the reset, the corresponding bit in

the TMP/CLR register is automatically reset to 0, which

saves the host an extra write/read cycle. Clearing the

DTC register clears the STD bit and sets the DTC count

rate to the default value of 1 count per 0.8789s. Clearing

the CTC register clears the STC bit and sets the CTC

count rate to the default value of 1 count per 0.8789s.

Calibration Mode

The system can enable bq2018 VOS calibration by setting

the calibration bit in the MODE/WOE register (Bit 6) to

1. The bq2018 then enters calibration mode when the

HDQ line is low for greater than 10 seconds and when

the signal between SR1 and SR2 is below VWOE. Cau-

tion: Take care to ensure that no low-level exter-

nal signal is present between SR1 and SR2 because

this affects the calibration value that the bq2018

calculates.

If HDQ remains low for one hour and |VSR|<VWOE for

the entire time, the measured VOS is latched into the

OFR register, and the calibration bit is reset to zero, indi-

cating to the system that the calibration cycle is com-

plete. Once calibration is complete, the bq2018 enters a

bq2018

TD201801.eps

Break

Written by Host to bq2018

LSB

MSB

1110

CMDR = 73h

73h = 0 1 1 1 0 0 1 1

MSB

LSB

Received by Host from bq2018

LSB

Data (OFR) = 65h

MSB

011

65h = 0 1 1 0 0 1 0 1

MSB

LSB

Figure 4. Typical Communication with the bq2018

Temp

Value (hex)

SDR Count Rate

<0°

× 1/8

0–10°

× 1/4

10–20°

× 1/2

20–30°

1 count/hr.

30–40°

× 2

40–50°

× 4

50–60°

× 8

>60°

× 16

Table 4. Temperature Steps

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