Features

Safe charge of Li-Ion battery

packs

Pulse-width modulation control

for current and voltage reg-
ulation

Programmable high-side/low-side

current-sense

Fast charge terminated by se-

lectable minimum current; safety
backup termination at maximum
time

Pre-charge qualification detects

shorted or damaged cells and
conditions battery

Charging continuously qualified

by temperature and voltage limits

Direct LED control outputs to

display charge status and fault
conditions

General Description

The bq2954 Li-Ion Charge-Manage-
ment IC uses a flexible pulse-width
modulation regulator to control volt-
age and current during charging.
The regulator frequency is set by an
external capacitor for design flexi-
bility. The switch-mode design mini-
mizes power dissipation.

For safety, the bq2954 inhibits fast
charging until the battery voltage
and temperature are within config-
ured limits. If the battery voltage is
less than the low-voltage threshold,
the bq2954 provides low-current
conditioning of the battery.

For charge qualifiction, the bq2954
uses an external thermistor to mea-
sure battery temperature. Charging
begins when power is applied or the
battery is inserted

The bq2954 charges a battery in two
phases.

First a constant-current

phase replenishes approximately
70% of battery capacity. Then a volt-
age-regulation phase completes the
battery charge.

The bq2954 provides status indica-
tions of all charger states and faults
for accurate determination of the
battery and charge-system condi-
tions.

Time-out programming
input

CHG

Charge active output

BAT

Battery voltage input

VCOMP

Voltage loop comp input

ICOMP

Current loop comp input

TERM

Minimum current
termination select input

SNS

Sense resistor input

Temperature sense input

PN295401.eps

16-Pin Narrow

DIP or SOIC

LED2/DSEL

LED1/CSEL

MOD

VCC

VSS

LCOM

BTST

TPWM

CHG

BAT

VCOMP

ICOMP

ITERM

SNS

TPWM

Regulator timebase input

BTST

Battery test output

LCOM

Common LED output

System ground

5.0V

±10% power

MOD

Modulation control
output

LED

Charge status output 1/

CSEL

Charge sense select
input

LED

Charge status output 2/

DSEL

Display select input

Pin Connections

Pin Names

SLUS064OCTOBER 1998 B

Lithium Ion Charge Management IC

with Integrated Switching Controller

bq2954

Pin Descriptions

Time-out programming input

Sets the maximum charge time. The resistor
and capacitor values are determined using
Equation 5. Figure 10 shows the resistor/ca-
pacitor connection.

CHG

Charge active output

An open-drain output is driven low when the
battery is removed, during a temperature
pend, when a fault condition is present, or
when charge is done. CHG can be used to
disable a high-value load capacitor to detect
quickly any battery removal.

BAT

Battery voltage input

Sense input. This potential is generally de-
veloped using a high-impedance resistor di-
vider network connected between the posi-
tive and the negative terminals of the bat-
tery. See Figures 6 and 7 and Equation 1.

VCOMP

Voltage loop compensation input

Connects to an external R-C network to sta-
bilize the regulated voltage.

ICOMP

Current loop compensation input

Connects to an external R-C network to sta-
bilize the regulated current.

ITERM

Charge full and minimum current termi-
nation select

Three-state input is used to set I

FULL

and

MIN

for fast charge termination. See Table 4.

SNS

Charging current sense input

Battery current is sensed via the voltage devel-
oped on this pin by an external sense-resistor.

Temperature sense input

Used to monitor battery temperature. An exter-
nal resistor-divider network sets the lower and
upper temperature thresholds. (See Figures 8
and 9 and Equations 3 and 4.)

TPWM

Regulation timebase input

Uses an external timing capacitor to ground
to set the pulse-width modulation (PWM)
frequency. See Equation 7.

BTST

Battery test output

Driven high in the absence of a battery in or-
der to provide a potential at the battery ter-
minal when no battery is present.

LCOM

Common LED output

Common output for LED

1-2

. This output is

in a high-impedance state during initiali-
zation to read programming input on DSEL
and CSEL.

Ground

supply

5.0V,

±10%

MOD

Current-switching control output

Pulse-width modulated push/pull output used
to control the charging current to the battery.
MOD switches high to enable current flow and
low to inhibit current flow.

(The maximum

duty cycle is 80%.)

LED

Charger display status 12 outputs

Drivers for the direct drive of the LED dis-
play.

These outputs are tri-stated during

initialization so that DSEL and CSEL can be
read.

DSEL

Display select input (shared pin with
LED

)

Three-level input that controls the LED

charge display modes.

CSEL

Charge sense-select input (shared pin
with LED

)

Input that controls whether current is
sensed on low side of battery or high side of
battery.

A current mirror is required for

high-side sense.

bq2954

Functional Description

The bq2954 functional operation is described in terms of
the following (Figure 1):

Charge algorithm

Charge qualification

Charge status display

Configuring the display and termination

Voltage and current monitoring

Battery insertion and removal

Temperature monitoring

Maximum time--out

Charge regulation

Recharge after fast charge

Charge Algorithm

The bq2954 uses a two-phase fast-charge algorithm. In
phase 1, the bq2954 regulates constant current until the
voltage on the BAT pin, V

BAT

, rises to the internal

threshold, V

REG

. The bq2954 then transitions to phase 2

and regulates constant voltage (V

BAT

= V

REG

) until the

charging current falls below the programmed I

MIN

threshold. Fast charge then terminates, and the bq2954
enters the Charge Complete state. (See Figure 2.)

Charge Qualification

The bq2954 starts a charge cycle when power is applied
while a battery is present or when a battery is inserted.
Figure 2 shows the state diagram for the bq2954. The
bq2954 first checks that the battery temperature is
within the allowed, user-configurable range. If the tem-
perature is out of range, the bq2954 remains in the
QUALIFICATION state (S01) and waits until the battery
temperature and voltage are within the allowed range.

If during any state of charge, a temperature excursion
occurs HOT, the bq2954 proceeds to the DONE state
(S04) and indicates this state on the LED outputs and
provides no current. If this occurs, the bq2954 remains
in the DONE state unless the following two conditions
are met:

Temperature falls within valid charge range

BAT

falls below the internal threshold,V

RCHG

If these two conditions are met, a new charge cycle be-
gins. During any state of charge, if a temperature ex-
cursion occurs COLD, the bq2954 terminates charge and
returns to the QUALIFICATION state (S01). Charge re-
starts if V

BAT

and temperature are in valid range.

When the temperature and voltage are valid, the bq2954
enters the CONDITIONING state (S02) and regulates
current to I

COND

(=I

MAX

/10). After an initial holdoff pe-

riod t

(which prevents the IC from reacting to tran-

sient voltage spikes that may occur when charge current
is first applied), the IC begins monitoring V

BAT

. If V

BAT

does not rise to at least V

MIN

before the expiration of

bq2954

BD2954.eps

Voltage

Reference

Charge
Control

State

Machine

PWM

Regulator

Display
Control

Power-On

Reset

MTO

Timer

Oscillator

DSEL

CSEL

LED1
LED2
BTST
CHG

LCOM

MOD

ICOMP

VCC

TPWM

ITERM

VSS

VCOMP

BAT

SNS

Figure 1. Functional Block Diagram

bq2954

Power-On

Reset

Fault

CHG = 0

Mod = 0

No Action

Latch DSEL/CSEL Inputs

FGbg295401.eps

VCC "Up"

S01

S02

S03a

S03b

VOLTAGE

REGULATION

CURRENT

REGULATION

CONDITIONING

QUALIFICATION

DONE

Full Charge

Indication

ISNS = IMIN

Temp Not Hot andVBAT VRCHG

1s Hold Time after VBAT < VRCHG

VBAT VRCHG

VBAT > VHCO

Volt Fault

VBAT > VHCO

Volt Fault

VBAT > VHCO or T = MTO

Volt or Time Fault

T = MTO/25

Time Fault

Temp Not Valid

Temp Valid

Temp Not Valid

VBAT < 0.8V Reset Faults

0.8V > VBAT > VHCO
Hold Time
Hold-off Faults
CHG = 0
Battst = 1

ISNS = IMAX: VBAT VREG
T MTO
Hold Time
CHG = 1

VBAT < VMIN: ISNS = IMAX/10
Hold Time
CHG = 1

VBAT = VREG: IMAX > ISNS > ITRMN

T MTO
CHG = 1

VBAT > VRCHG
Hold-off MOD
VRCHG < VBAT < VHCO
CHG = 1

VHCO < VBAT >0.8V
Reset MTO

VBAT VMIN
Reset MTO

VBAT = VREG

T = MTO
ISNS = ITRM

Temp Hot

Battery Removal

Volt or
Time Fault

S04

VBAT Voltages:

VRCHG = 1.92V 0.5V
VMIN = 1.50V 0.5V

VREG = 2.05V
VHCO = 2.30V

Volt Fault: When VBAT > VHCO
Time Fault: When T = MTO/4 in State S02 or T = MTO in S03a
Hold Time: A VHCO Fault or State charge held off for 0.740s to 1.12s

Figure 2. bq2954 Charge Algorithm

bq2954

BAT+

R14

RB1

C11
10uF
20V
PCS4106

47uH

B130DI

10 uH

1uF

4.7K

10K

FMMT3906

FMMt3904

FZT789A

1N4148

VDC

1uF

25V

10K

C10

47uF

25V

OUT

G
N
D

U2
ZMR500

B130DI

8-24VDC ±10%

0.1 uF

R6
10K

220

R10

62K

FMMT451

R7
1K

BAT-

0.25 5%

0.5W

R15

RB2

TEM+

R12

8.45K

0.1uF

2954sch9/23/98

0.01uF

1000pF

R11

4.32K

CHG

BAT

VCOMP

ICOMP

ITERM

SNS

TPWM

BTST

LCOM

VSS

VCC

MOD

LED1/CSEL

LED2/DSEL

bq2954

0.1uF

470pF

10K

0.1 uF

FMMT3904

R13

GRREN

RED

3. TEMP = 0-45

4. Frequency = 200kHz

2. MTO = 3 HRS, I

FULL

= I

MAX

/5, I

TERM

= I

MAX

/10

1. I

MAX

= 1.0A, Vreg = 4.2V ± 1% PER CELL

Figure 3. High-Efficiency Li-Ion Charger for 14 Cells

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