BQ2018TS datasheet(2/21 Pages) TI

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Pin Descriptions

REG

Regulator output

REG is the output of the operational trans-

conductance amplifier (OTA) that drives an

external pass n-channel JFET to provide an

optional regulated supply. The supply is

regulated at 3.7V nominal.

VCC

Supply voltage input

When regulated by the REG output, VCC is

3.7V

±200mV. When the REG output is not

used, the valid operating range is 2.8V to

5.5V.

VSS

Ground

SR1–

SR2

Current sense inputs

The bq2018 interprets charge and discharge

activity by monitoring and integrating the

voltage drop (VSR) across pins SR1 and SR2.

The SR1 input connects to the sense resistor

and the negative terminal of the battery.

The SR2 input connects to the sense resistor

and the negative terminal of the pack. VSR1

<VSR2 indicates discharge, and VSR1 >VSR2

indicates charge. The effective voltage drop,

VSRO, as seen by the bq2018, is VSR +VOS.

Valid input range is

± 200mV.

HDQ

Data input/output

This bi-directional input/output communi-

cates the register information to the host

system. HDQ is open drain and requires a

pullup/down resistor in the battery pack to

disable/enable sleep mode if the pack is re-

moved from the system.

RBI

This input maintains the internal register

states during periods when VCC is below the

minimum operating voltage.

WAKE

Wake-up output

When asserted, this output is used to indi-

cate that the charge or discharge activity is

above a programmed minimal level.

Functional Description

General Operation

A host can use the bq2018 internal counters and timers

to measure battery state-of-charge, estimate self-

discharge, and calculate the average charge and dis-

charge current into and out of a rechargeable battery.

The bq2018 needs an external host system to perform all

Using information from the

bq2018, 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 sen-

sor doubles the self-discharge count rate every 10° above

25°C.

To reduce cost, power to the bq2018 may be derived using

a low-cost external FET in conjunction with the REG pin.

The bq2018 operating current is less than 80

µA. When

the HDQ line remains low for greater than ten seconds

and VSRO (VSR +VOS where VSR is the voltage drop be-

tween SR1 and SR2 and VOS is the offset voltage) is below

the programmed minimal level (WAKE is in High Z), the

bq2018 enters a sleep mode of <10

µA where all opera-

tions are suspended. HDQ transitioning high reinitiates

the bq2018.

A register is available to store the calculated offset, allow-

ing current calibration. The offset cancellation register is

written by the bq2018 during pack assembly and is avail-

able to the host system to adjust the current measure-

ments. 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.

Figure 1 shows a block diagram of the bq2018, and Table

1 outlines the bq2018 operational states.

REG Output

The bq2018 can operate directly from three or four

nickel-chemistry cells or a single Li-Ion cell as long as

VCC is limited to 2.8 to 5.5V. To facilitate the power sup-

ply requirements of the bq2018, a REG output is present

to regulate an external low-threshold n-JFET. A micro-

power VCC source for the bq2018 can inexpensively be

built using this FET.

bq2018

BQ2018TS Datasheet(PDF) 2 Page - Texas Instruments

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