BQ2018TS datasheet(4/21 Pages) TI

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RBI Input

The RBI input pin is used with a storage capacitor or ex-

ternal supply to provide back-up potential to the internal

RAM when VCC drops below 2.4V. The maximum dis-

charge current is 100nA in this mode. The bq2018 out-

puts VCC on RBI when the supply is above 2.4V, so a di-

ode is required to isolate an external supply.

Charge/Discharge Count Operation

Table 2 shows the main counters and registers of the

bq2018. The bq2018 accumulates charge and discharge

counts into two main count registers, the Discharge

Count Register (DCR) and the Charge Count Register

(CCR).

The bq2018 produces charge and discharge

counts by sensing the voltage difference across a low-

value resistor between the negative terminal of the bat-

tery pack and the negative terminal of the battery. The

DCR or CCR counts depending on the signal between

SR1 and SR2.

During discharge, the DCR and the Discharge Time

Counter (DTC) are active. If VSR1 is less than VSR2, indi-

cating a discharge, the DCR counts at a rate equivalent to

12.5

µV every hour, and the DTC counts at a rate of 1

count/0.8789 seconds (4096 counts per 1 hour). For exam-

ple, a -100mV signal produces 8000 DCR counts and 4096

DTC counts each hour.

The amount of charge removed

from the battery can easily be calculated.

bq2018

Table 2. bq2018 Counters

Name

Description

Range

RAM Size

DCR

Discharge count register

VSR1 < VSR2 (Max. =-200mV) 12.5µVh increments

16-bit

CCR

Charge count register

VSR1 >VSR2 (Max. = +200mV) 12.5µVh increments

16-bit

SCR

Self-discharge count register

1 count/hour @ 25°C

16-bit

DTC

Discharge time counter

1 count/0.8789s default

1 count/225s if STD is set

16-bit

CTC

Charge time counter

1 count/0.8789s default

1 count/225s if STC is set

16-bit

MODE/

WOE

MODE/

Wake output enable

—

8-bit

RBI

SR2

SR1

WAKE

HDQ

VSS

VCC

REG

BQ2018

VCC

SST113

BAT+

BZX84C5V6

HDQ

BZX84C5V6

100

BAV99

RBI

PACK-

BAT-

0.05

100K

WAKE

VCC

0.01

µF

0.1

µF

0.1

µF

0.1

µF

0.1

µF

2018typAp.eps

Figure 2. Typical Application

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