TEXAS INSTRUMENTS bq2031 Technical data

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bq2031

Lead-Acid Fast-Charge IC

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, 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

V, mini-

∆

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, constantcurrent, or pulsed-current charging. The regulator frequency is set by an external capacitor for design flexibility. 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 until the battery voltage is within configured 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 temperaturecompensated.

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 provides temperature-compensated maintenance (float) charging to maintain battery capacity.

Pin Connections

TMTO

FLOAT

BAT

VCOMP

ICOMP

IGSEL

SNS

SLUS156–JUNE 1999 E

16-Pin Narrow

DIP or SOIC

PN203101.eps

LED2/DSEL

LED1/TSEL

MOD

COM

LED3/QSEL

TPWM

Pin Names

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

LED3/ Charge status output 3/ QSEL Charge algorithm select

input 1

COM Common LED output

System ground

5.0V±10% power

MOD Modulation control

output

/ Charge status output 1/

LED

TSEL Charge algorithm select

input 2

LED

/ Charge status output 2/

DSEL Display select input

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 charge regulation. See Figure 1.

BAT Battery voltage input

BAT is the battery voltage sense input. This po tential is generally developed using a highimpedance 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 network for voltage loop stability.

IGSEL Current gain select input

This three-state input is used to set I fast charge termination in the Two-Step Voltage algorithm and for maintenance current regulation in the Two-Step Current algorithm. 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

, connected in series with the low

SNS

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.

) for the float

FLT

MIN

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

. This output is

1–3

in a high-impedance state during initiali zat ion to read program inputs on TSEL,

QSEL Charge regulation select input

QSEL, and DSEL.

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

Charger display status 1–3 outputs

1–3

These charger status output drivers are for the direct drive of the LED display. Display modes are shown in Table 2. These outputs are

for

tri-stated during initialization so that QSEL, TSEL, and DSEL can be read.

DSEL Display select input

This three-level input controls the LED charge display modes. See Table 2.

TSEL Termination select input

With QSEL, selects the charge algorithm.

See Table 1.

Functional Description

VCCsupply

5.0V, ± 10% power

Ground

The bq2031 functional operation is described in terms of:

Charge algorithms

Charge qualification

Charge status display

Voltage and current monitoring

Temperature monitoring

1–3

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 qualification and temperature monitoring. The bq2031 first checks that the battery temperature is within the allowed, 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 battery temperature is within the allowed range. Charge Pending is annunciated by LED

flashing.

bq2031

Chip On

VCC 4.5V

Temperature

Checks On

Temperature

COND

MIN

< V

COND

HCO

Voltage Regulation @ V

0.25V

Current Regulation @I

MIN

Charge

COND

Bulk

in Range

Battery

Status?

Fail: t = t

QT1

> V

CELL

FLT

Termination

Present

< V

LCO

CELL

Test 1

< I

SNS

PASS: I

SNS

Test 2

< V

PASS: V

CELL

Figure 1. Cycle Start/Battery

Qualification State Diagram

Temperature Out

of Range or

Thermistor Absent

Absent

< V

CELL

LCO

> V

CELL

HCO

Fault LED3 = 1 MOD = 0

CELL

LCO or

CELL

HCO

Fail: t = t

QT2

< V

CELL

LCO or

> V

CELL

HCO

< V

CELL

LCO

> V

CELL

HCO

CELL

Charge Pending

LED3 Flash

MOD = 0

Temperature Out

of Range or

< V

MIN

Fast

Charge

FG203101.eps

Thermistor Absent

Temperature In Range, Return

to Original State

Table 1. bq2031 Charging Algorithms

Algorithm/State QSEL TSEL Conditions MOD Output

Two-Step Voltage

L H/L Fast charge, phase 1 while V Fast charge, phase 2 while I Primary termination I Maintenance V

Two-Step Current

HL - Fast charge while V Primary termination V Maintenance I

Pulsed Current

HH - Fast charge while V Primary termination V

Maintenance

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

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

Note 1

BAT<VBLK,ISNS=IMAX

SNS>IMIN,VBAT=VBLK

SNS=IMIN

BAT=VFLT

BAT<VBLK,ISNS=IMAX

BAT=VBLK

pulsed to average I

SNS

∆

BAT<VBLK,ISNS=IMAX

BAT=VBLK

SNS=IMAX

SNS

after V

= 0 after V

V < -8mV

BAT=VFLT

BAT=VBLK

Note 2

FLT

Current regulation

Voltage regulation

Current regulation

Fixed pulse current

Current regulation

;

Hysteretic pulsed

current

BAT

bq2031

Thermal monitoring continues throughout the charge cycle, and the bq2031 enters the Charge Pending state anytime the temperature is out of range. (There is one exception; if the bq2031 is in the Fault state—see be low—the out-of-range temperature is not recognized un til the bq2031 leaves the Fault state.) All timers are

test 2 before the bq2031 recognizes its “pass” criterion. If this second test passes, the bq2031 begins fast (bulk) charging.

Once in the Fault state, the bq2031 waits until V

cled or a battery insertion is detected. It then starts a new

charge cycle and begins the qualification process again.

suspended (but not reset) while the bq2031 is in Charge Pending. When the temperature comes back into range, the bq2031 returns to the point in the charge cycle where the out-of-range temperature was detected.

When the temperature is valid, the bq2031 performs two tests on the battery. In test 1, the bq2031 regulates a voltage of V

+ 0.25V across the battery and observes I

FLT

does not rise to at least I

within a time-out period (e.g.,

COND

SNS

.IfI

the cell has failed open), the bq2031 enters the Fault state. If test 1 passes, the bq2031 then regulates current to I I

/5) and watches V

MAX

not rise to at least V

(= V

CELL

within a time-out period (e.g., the cell

FLT

BAT-VSNS

). If V

COND

CELL

has failed short), again the bq2031 enters the Fault state. A

Charge Status Display

Charge status is annunciated by the LED driver outputs LED

–LED3. Three display modes are available in the bq2031;

the user selects a display mode by configuring pin DSEL. Table 2 shows the three modes and their programming pins.

SNS

The bq2031 does not distinguish between an over-voltage fault and a “battery absent” condition. The bq2031 enters the Fault state, annunciated by turning on LED

ever the battery is absent. The bq2031, therefore, gives an

does

indication that the charger is on even when no battery is in place to be charged.

hold-off period is enforced at the beginning of qualification

Table 2. bq2031 Display Output Summary

Mode Charge Action State LED

Battery absent or over-voltage fault Low Low High

Pre-charge qualification Flash Low Low

DSEL = 0

(Mode 1)

Charge pending (temperature out of range) X X Flash

Battery absent or over-voltage fault Low Low High

DSEL = 1

(Mode 2)

Charge pending (temperature out of range) X X Flash

Battery absent or over-voltage fault Low Low High

Fast charge: current regulation Low High Low

DSEL = Float

(Mode 3)

Fast charge: voltage regulation High High Low

Charge pending (temperature out of range) X X Flash

Notes: 1 = VCC; 0 = VSS; X = LED state when fault occurred; Flash =

In the Pulsed Current algorithm, the bq2031 annunciates maintenance when charging current is off and fast charge whenever charging current is on.

Fast charging High Low Low

Maintenance charging Low High Low

Charging fault X X High

Pre-charge qualification High High Low

Fast charge Low High Low

Maintenance charging High Low Low

Charging fault X X High

Pre-charge qualification Flash Flash Low

Maintenance charging High Low Low

Charging fault X X High

s low,

s high.

LED

is cy

, when

LED

MAX

COND

MIN

FLT

MAX

COND

Current

Voltage

Qualification

Phase 1

Fast Charge

Phase 2

Current

Time

Figure 2. Two-Step Voltage Algorithm

Current

Qualification

Fast Charge

Voltage

Maintenance

BLK

FLT

MIN

Voltage

BLK

FLT

MIN

Voltage

bq2031

MAX

COND

Current

Time

Figure 3. Two-Step Current Algorithm

Current

Qualification

Fast Charge

Voltage

Time

Figure 4. Pulsed Current Algorithm

Maintenance

BLK

FLT

MIN

Voltage

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