Features

➤

Conforms to battery manufactur

ers' charge recommendations for

cyclic and float charge

➤

Pin-selectable charge algorithms

Two-Step Voltage with

temperature-compensated

constant-voltage maintenance

Two-Step Current with

constant-rate pulsed current

maintenance

Pulsed Current: hysteretic,

on-demand pulsed current

➤

Pin-selectable charge termination

by maximum voltage,

∆

V, mini-

mum current, and maximum

time

➤ Pre-charge qualification detects

shorted, opened, or damaged cells

and conditions battery

➤ Charging continuously qualified by

temperature and voltage limits

➤ Internal temperature-compen-

sated voltage reference

➤ Pulse-width modulation control

Ideal for high-efficiency

switch-mode power conversion

Configurable for linear or

gated current use

➤

Direct LED control outputs dis

play charge status and fault con

ditions

General Description

The bq2031 Lead-Acid Fast Charge

IC is designed to optimize charging

of lead-acid chemistry batteries. A

flexible pulse-width modulation

regulator allows the bq2031 to con

trol constant-voltage, constant-

current, or pulsed-current charging.

The regulator frequency is set by an

external capacitor for design flexi-

bility. The switch-mode design keeps

power dissipation to a minimum for

high charge current applications.

A charge cycle begins when power is

applied or the battery is replaced.

For safety, charging is inhibited un-

til the battery voltage is within con-

figured limits. If the battery voltage is

less than the low-voltage threshold,

the bq2031 provides trickle-current

charging until the voltage rises into

the allowed range or an internal

timer runs out and places the

bq2031 in a Fault condition. This

procedure prevents high-current

charging of cells that are possibly

damaged or reversed. Charging is

inhibited anytime the temperature

of the battery is outside the config

urable, allowed range. All voltage

thresholds are temperature-

compensated.

The bq2031 terminates fast (bulk)

charging based on the following:

■

Maximum voltage

■

Second difference of cell voltage

(

∆

■

Minimum current (in constant-

voltage charging)

■

Maximum time-out (MTO)

After bulk charging, the bq2031 pro-

vides temperature-compensated

maintenance (float) charging to

maintain battery capacity.

Lead-Acid Fast-Charge IC

TMTO Time-out timebase input

FLOAT State control output

BAT Battery voltage input

VCOMP Voltage loop comp input

ICOMP Current loop comp input

IGSEL Current gain select input

SNS Sense resistor input

TS Temperature sense input

TPWM Regulator timebase input

PN203101.eps

16-Pin Narrow

DIP or SOIC

LED

/DSEL

LED

/TSEL

MOD

COM

LED

/QSEL

TPWM

TMTO

FLOAT

BAT

VCOMP

ICOMP

IGSEL

SNS

LED

/ Charge status output 3/

QSEL Charge algorithm select

input 1

COM Common LED output

System ground

5.0V

10% power

MOD Modulation control

output

LED

/ Charge status output 1/

TSEL Charge algorithm select

input 2

LED

/ Charge status output 2/

DSEL Display select input

Pin Connections

Pin Names

SLUS156–JUNE 1999 E

bq2031

Pin Descriptions

TMTO Time-out timebase input

This input sets the maximum charge time.

The resistor and capacitor values are deter

mined using equation 6. Figure 9 shows the

resistor/capacitor connection.

FLOAT Float state control output

This open-drain output uses an external re

sistor divider network to control the BAT in

put voltage threshold (V

FLT

) for the float

charge regulation. See Figure 1.

BAT Battery voltage input

BAT is the battery voltage sense input. This po

tential is generally developed using a high-

impedance resistor divider network connected

between the positive and the negative terminals

of the battery. See Figure 6 and equation 2.

VCOMP Voltage loop compensation input

This input uses an external C or R-C net-

work for voltage loop stability.

IGSEL Current gain select input

This three-state input is used to set I

MIN

for

fast charge termination in the Two-Step

Voltage algorithm and for maintenance cur-

rent regulation in the Two-Step Current al-

gorithm. See Tables 3 and 4.

ICOMP Current loop compensation input

This input uses an external C or R-C net

work for current loop stability.

SNS Charging current sense input

Battery current is sensed via the voltage de

veloped on this pin by an external sense re

sistor, R

SNS

, connected in series with the low

side of the battery. See equation 8.

TS Temperature sense input

This input is for an external battery tem

perature monitoring thermistor or probe. An

external resistor divider network sets the

lower and upper temperature thresholds.

See Figures 7 and 8 and equations 4 and 5.

TPWM Regulation timebase input

This input uses an external timing capacitor

to ground the pulse-width modulation

(PWM) frequency. See equation 9.

COM Common LED output

Common output for LED

1–3

. This output is

in a high-impedance state during initiali

zation to read program inputs on TSEL,

QSEL, and DSEL.

QSEL Charge regulation select input

With TSEL, selects the charge algorithm.

See Table 1.

MOD Current-switching control output

MOD is a pulse-width modulated push/pull

output that is used to control the charging

current to the battery. MOD switches high

to enable current flow and low to inhibit cur

rent flow.

LED

1–3

Charger display status 1–3 outputs

These charger status output drivers are for

the direct drive of the LED display. Display

modes are shown in Table 2. These outputs are

tri-stated during initialization so that QSEL,

TSEL, and DSEL can be read.

DSEL Display select input

This three-level input controls the LED

1–3

charge display modes. See Table 2.

TSEL Termination select input

With QSEL, selects the charge algorithm.

See Table 1.

supply

5.0V, ± 10% power

Ground

Functional Description

The bq2031 functional operation is described in terms of:

Charge algorithms

Charge qualification

Charge status display

Voltage and current monitoring

Temperature monitoring

bq2031

Fast charge termination

Maintenance charging

Charge regulation

Charge Algorithms

Three charge algorithms are available in the bq2031:

Two-Step Voltage

Two-Step Current

Pulsed Current

The state transitions for these algorithms are described

in Table 1 and are shown graphically in Figures 2

through 4. The user selects a charge algorithm by con

figuring pins QSEL and TSEL.

Charge Qualification

The bq2031 starts a charge cycle when power is applied

while a battery is present or when a battery is inserted.

Figure 1 shows the state diagram for pre-charge qualifi-

cation and temperature monitoring. The bq2031 first

checks that the battery temperature is within the al-

lowed, user-configurable range. If the temperature is

out-of-range (or the thermistor is missing), the bq2031

enters the Charge Pending state and waits until the bat-

tery temperature is within the allowed range. Charge

Pending is annunciated by LED

flashing.

bq2031

Algorithm/State QSEL TSEL Conditions MOD Output

Two-Step Voltage

L H/L

Note 1

Fast charge, phase 1 while V

BAT

BLK

SNS

MAX

Current regulation

Fast charge, phase 2 while I

SNS

MIN

BAT

BLK

Voltage regulation

Primary termination I

SNS

MIN

Maintenance V

BAT

FLT

Voltage regulation

Two-Step Current

HL - -

Fast charge while V

BAT

BLK

SNS

MAX

Current regulation

Primary termination V

BAT

BLK

∆

V < -8mV

Note 2

Maintenance I

SNS

pulsed to average I

FLT

Fixed pulse current

Pulsed Current

HH - -

Fast charge while V

BAT

BLK

SNS

MAX

Current regulation

Primary termination V

BAT

BLK

Maintenance

SNS

MAX

after V

BAT

FLT

;

SNS

= 0 after V

BAT

BLK

Hysteretic pulsed

current

Notes: 1. May be high or low, but do not float.

2. A Unitrode proprietary algorithm for accumulating successive differences between samples of V

BAT

Table 1. bq2031 Charging Algorithms

Chip On

4.5V

Temperature

Checks On

Battery

Status?

Temperature

in Range

Temperature Out

of Range or

Thermistor Absent

Voltage

Regulation

@ V

FLT

0.25V

Bulk

Charge

Fault

LED3 = 1

MOD = 0

Charge

Pending

LED3 Flash

MOD = 0

Current

Regulation

COND

Temperature Out

of Range or

Thermistor Absent

Temperature In

Range, Return

to Original State

CELL

< V

LCO

CELL

> V

HCO

CELL

LCO or

Fail:

t = t

QT1

CELL

> V

HCO

Present

LCO

< V

CELL

< V

HCO

SNS

< I

COND

CELL

< V

MIN

FG203101.eps

Test 1

CELL

HCO

PASS: I

SNS

COND

Test 2

PASS: V

CELL

MIN

Fast

Charge

CELL

< V

MIN

Termination

Fail:

t = t

QT2

CELL

< V

LCO or

CELL

> V

HCO

Absent

CELL

< V

LCO

CELL

> V

HCO

Figure 1. Cycle Start/Battery

Qualification State Diagram

Part #	BQ2031SN-A5
Description	IC, LEAD ACID FAST CHARGE16-PIN SOIC
Category	IC
Availability	In Stock
Qty	56

Qty	Price
1 - 11	$5.80327
12 - 23	$4.61624
24 - 35	$4.35246
36 - 47	$4.04471
48 +	$3.60506

BQ2031SN-A5

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Technical Document