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Features

Fast charging and conditioning of

NiCd and NiMH batteries

Precise charging independent
of battery pack number of cells

Discharge-before-charge on
demand

Pulse trickle charge
conditioning

Battery undervoltage and
overvoltage protection

Built-in 10-step voltage-based

charge status monitoring

Charge status display options
include seven-segment
monotonic bargraph and fully
decoded BCD digit

Display interface options for
direct drive of LCD or LED
segments

Charger state status
indicators for pending,
discharge, charge, completion,
and fault

Audible alarm for charge
completion and fault
conditions

Charge control flexibility

Fast or Standard speed
charging

Top-off mode for NiMH

Charge rates from

to 2C

(30 minutes to 8 hours)

Charge termination by:

Negative delta voltage (-

Peak voltage detect (PVD)

Maximum voltage

Maximum time

Maximum temperature

High-efficiency switch-mode de-

sign

Ideal for small heat-sensitive
enclosures

24-pin, 300-mil SOIC or DIP

General Description

The bq2007 is a highly integrated
monolithic CMOS IC designed to pro-
vide intelligent battery charging and
charge status monitoring for stand-
alone charge systems.

The bq2007 provides a wide variety of
charge status display formats. The
bq2007 internal charge status moni-
tor supports up to a seven-segment
bargraph or a single BCD digit dis-
play. The bargraph display indicates
up to seven monotonic steps, whereas
the BCD digit counts in ten steps of
10% increments. The bq2007 output
drivers can direct-drive either an
LCD or LED display.

Charge action begins either by appli-
cation of the charging supply or by
replacement of the battery pack. For
safety, charging is inhibited until
battery temperature and voltage are
within configured limits.

PN200701.eps

24-Pin Narrow DIP

or SOIC

2
3

7
8

23
22

21
20
19

11
12

14
13

SEGC/MSEL

SEGB
SEGA

LED1
LED2

INH

COM

ALARM

VSEL

FAST

DCMD

SEGD/DSEL1
SEGE/DSEL2
SEGF/MULT
SEGG/QDSEL
MOD

VCC
VSS
DIS
TS

BAT
SNS
TCO

Fast-Charge IC

bq2007

Pin Connections

Pin Names

SEG

Display output segment C/

MSEL

driver mode select

SEG

Display output segment B

SEG

Display output segment A

LED

Charge status output 1

LED

Charge status output 2

INH

Charge inhibit input

COM

Common LED/LCD output

ALARM

Audio alarm output

Timer mode select

VSEL

Voltage termination select

FAST

Fast charge rate select

DCMD

Discharge command

TCO

Temperature cutoff

SNS

Sense resistor input

BAT

Battery voltage

Temperature sense

DIS

Discharge control

System ground

5.0V

±10% power

MOD

Modulation control

SEG

Display output segment G/

QDSEL

charge status display select

SEG

Display output segment F/

MULT

multi-cell pack select

SEG

Display output segment E/

DSEL

display select 2

SEG

Display output segment D/

DSEL

display select 1

9/96 B

The acceptable battery temperature range is set by an
internal low-temperature threshold and an external
high-temperature cutoff threshold. The absolute tem-
perature is monitored as a voltage on the TS pin with
the external thermistor network shown in Figure 2.

The bq2007 provides for undervoltage battery protection
from high-current charging if the battery voltage is less
than the normal end-of-discharge value. In the case of a
deeply discharged battery, the bq2007 enters the
charge-pending state and attempts trickle-current condi-
tioning of the battery until the voltage increases. Should
the battery voltage fail to increase above the discharge
value during the undervoltage time-out period, a fault
condition is indicated.

Discharge-before-charge may be selected to automatically
discharge the battery pack on battery insertion or with a
push-button switch. Discharge-before-charge on demand
provides conditioning services that are useful to correct or
prevent the NiCd voltage depression, or "memory" effect,
and also provide a zero capacity reference for accurate
capacity monitoring.

After prequalification and any required discharge-
before-charge operations, charge action begins until one of
the full-charge termination conditions is detected. The
bq2007 terminates charging by any of the following methods:

Negative delta voltage (-

Peak voltage detect (PVD)

Maximum absolute temperature

Maximum battery voltage

Maximum charge time-out

The bq2007 may be programmed for negative delta
voltage (-

V) or peak voltage detect (PVD) charge

termination algorithms. The VSEL input pin selects -

or PVD termination to match the charge rate and
battery characteristics.

To provide maximum safety for battery and system,
charging terminates based on maximum temperature
cutoff (TCO), maximum cutoff voltage (MCV), and
maximum time-out (MTO). The TCO threshold is the
maximum battery temperature limit for charging. TCO
terminates charge action when the temperature sense
input voltage on the TS pin drops below the TCO pin
voltage threshold. MCV provides battery overvoltage
protection by detecting when the battery cell voltage
(V

CELL

= V

BAT

- V

SNS

) exceeds the VMCV value and ter-

minates fast charge, standard charge, or top-off charge.
The maximum time-out (MTO) termination occurs when
the charger safety timer has completed during the active
charge state.

The bq2007 indicates charge state status with an audio
alarm output option and two dedicated output pins with pro-
grammable display options. The DSEL12 inputs can select
one of the three display modes for the LED12 outputs.

Charger status is indicated for:

Charge pending

Charge in progress

Charge complete

Fault condition

Pin Descriptions

SEG

AG

Display output segments AG

State-of-charge monitoring outputs. QDSEL
input selects the bargraph or BCD digit dis-
play mode. See Table 3.

MSEL

Display driver mode select

Soft-programmed input selects LED or LCD
driver configuration at initialization.

When

MSEL is pulled up to V

, outputs SEG

are

LED interface levels; when MSEL is pulled
down to V

, outputs SEG

are LCD levels.

DSEL

Display mode select 12

Soft-programmed inputs control the LED

1--2

charger status display modes at initialization.
See Table 2.

MULT

Fixed-cell pack select

Soft-programmed input is pulled up to V

when charging multi-cell packs and is pulled
down to V

for charging packs with a fixed

number of cells.

QDSEL

State-of-charge display select

The QDSEL input controls the SEG

state-of-charge display modes. See Table 3.

LED

Charger status outputs 12

Charger status output drivers for direct
drive of LED displays.

Display modes are

selected by the DSEL input. See Table 2.

INH

Charge inhibit input

When low, the bq2007 suspends all charge ac-
tions, drives all outputs to high impedance, and
assumes a low-power operational state. When
transitioning from low to high, a charge
cycle is initiated. See page 10 for details.

bq2007

COM

Common LCD/LED output

Common

output

for

LCD/LED

display

SEG

A--G

. Output is high-impedance during

initialization

allow

reading

soft-programmed

inputs

DSEL

MSEL, MULT, and QDSEL.

ALARM

Audio output

Audio alarm output.

Timer mode select

TM is a three-level input that controls the set-
tings for charge control functions. See Table 5.

VSEL

Voltage termination select

This

input

switches

the

voltage

detect

sensitivity. See Table 5.

FAST

Fast charge rate select

The FAST input switches between Fast and
Standard charge rates. See Table 4.

DCMD

Discharge command

The DCMD input controls the discharge-
before-charge function. A negative-going
pulse initiates a discharge action. If DCMD
is connected to V

, automatic discharge-

before-charge is enabled. See Figure 3.

TCO

Temperature cut-off threshold input

Minimum allowable battery temperature-
sensor voltage. If the potential between TS
and SNS is less than the voltage at the TCO
input, then any fast charging or top-off
charging is terminated.

SNS

Sense resistor input

SNS controls the switching of MOD output based
on an external sense resistor. This provides the
lower reference potential for the BAT pin and the
TS pin.

BAT

Battery voltage input

Battery voltage sense input referenced to SNS
for the battery pack being charged. This resis-
tor divider network is connected between the
positive and the negative terminals of the
battery. See Figure 1.

Temperature sense input

Input referenced to SNS for battery tem-
perature monitoring negative temperature
coefficient (NTC) thermistor.

DIS

Discharge control

DIS is a push-pull output that controls an
external transistor to discharge the battery
before charging.

Ground

supply input

MOD

Current-switching control output

Push/pull output that controls the charging
current to the battery. MOD switches high to
enable current flow and low to inhibit current
flow.

Functional Description

Figure 1 illustrates charge control and display status
during a bq2007 charge cycle. Table 1 summarizes the
bq2007 operational features. The charge action states
and control outputs are given for possible input
conditions.

Charge Action Control

The bq2007 charge action is controlled by input pins
DCMD, VSEL, FAST, and TM. When charge action is
initiated, the bq2007 enters the charge-pending state,
checks for acceptable battery voltage and temperature,
and performs any required discharge-before-charge
operations. DCMD controls the discharge-before-charge
function, and VSEL, FAST, and TM select the charger
configuration. See Tables 4 and 5.

During charging, the bq2007 continuously tests for
charge termination conditions: negative delta voltage,
peak voltage detection, maximum time-out, battery
over-voltage, and high-temperature cutoff. When the
charge state is terminated, a trickle charge continues to
compensate for self-discharge and maintain the fully
charged condition.

Charge Status Indication

Table 2 summarizes the bq2007 charge status display
indications. The charge status indicators include the
DIS output, which can be used to indicate the discharge
state, the audio ALARM output, which indicates charge
completion and fault conditions, and the dedicated
status outputs, LED

and LED

bq2007

Outputs LED

have three display modes that are

selected at initialization by the input pins DSEL

and

DSEL

. The DSEL

and DSEL

input pins, when pulled

down to V

, are intended for implementation of a

simple two-LED system. LED

indicates the precharge

status (i.e., charge pending and discharge) and LED

indi-

cates the charge status (i.e., charging and completion).
DSEL

pulled up to V

and DSEL

pulled down to V

mode is for implementation of a single tri-color LED such
that discharge, charging, and completion each have a unique
color. DSEL

pulled down to V

and DSEL

pulled up to

allows for fault status information to be displayed.

Audio Output Alarm

The bq2007 audio alarm output generates an audio tone
to indicate a charge completion or fault condition. The
audio alarm output is a symmetrical duty-cycle AC sig-
nal that is compatible with standard piezoelectric alarm
elements. A valid battery insertion is indicated by a sin-
gle high-tone beep of

-second typical duration.

The

charge completion and fault conditions are indicated by
a 9.5- to 15-second high-tone sequence of

-second typi-

cal duration at a 2-second typical repetition rate.

Charge Status Monitoring

The bq2007 charge status monitor may display the bat-
tery voltage or charge safety timer as a percentage of
the full-charged condition. These options are selected
with the MULT soft-programmed input pin.

When MULT is pulled down to V

, the battery charge

status is displayed as a percentage of the battery
voltage, and the single-cell battery voltage at the BAT
pin is compared with internal charge voltage reference
thresholds.

When V

BAT

is greater than the internal

thresholds of V

, V

, or V

, the respective 20%,

40%, 60%, or 80% display outputs are activated. The
b a t t e r y v o l t a g e d i r e c t l y i n d i c a t e s 2 0 % ch a r g e
increments, while the 10% charge increments use a
timer that is a function of the charge safety timer.

When MULT is pulled down to V

and when V

BAT

exceeds V

during charging, the 20% charge indication

is activated and the timer begins counting for a period
equal to

of the charge safety time-out period.

When the timer count is completed, the 30% charge
indication is activated. Should V

BAT

exceed V

prior to

the timer count completion, the charge status monitor
activates the 30% and 40% indications. This technique

bq2007

Charge Action

State

Conditions

MOD Output

DIS Output

Battery absent

applied and V

CELL

MCV

Trickle charge per Table 4

Low

Charge initiation

applied or V

CELL

drops

from

MCV

to < V

MCV

Low

Discharge-before-
charge

DCMD high-to-low transition or to V

on charge

initiation and V

EDV

< V

CELL

< V

MCV

Low

High

Charge pending

Charge initiation occurred and V

TEMP

LTF

TEMP

TCO

or V

CELL

< V

EDV

Trickle charge per Table 4

Low

Fast charging

Charge pending complete and FAST = V

Low if V

SNS

> 250mV;

high if V

SNS

< 200mV

Low

Standard charging

Charge pending complete and FAST = V

Low if V

SNS

> 250mV;

high if V

SNS

< 200mV

Low

Charge complete

V termination or V

TEMP

< V

TCO

or PVD

0 to

-3mV/cell or maximum time-out or V

CELL

> V

MCV

Top-off pending

VSEL = V

, charge complete and V

TEMP

LTF

or V

TEMP

TCO

or V

CELL

< V

EDV

Trickle charge per Table 4

Low

Top-off charging

VSEL = V

and charge complete and

time-out not exceeded and V

TEMP

> V

TCO

and

CELL

< V

MCV

Activated per V

SNS

for

73ms of every 585ms

Low

Trickle charging

Charge complete and top-off disabled or

top-off complete or pending

Trickle charge per Table 4

Low

Fault

Charge pending state and charge pending

time-out (t

PEND

) complete

Trickle charge per Table 4

Low

Definitions:

CELL

= V

BAT

- V

SNS

; V

MCV

= 0.8 * V

; V

EDV

= 0.262 * V

or 0.4 * V

; V

TEMP

= V

- V

SNS

;

LTF

= 0.5 * V

Table 1. bq2007 Operational Summary

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