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bq2002/F
NiCd/NiMH Fast-Charge Management ICs
Features
➤
Fast charge of nickel cadmium
or nickel-metal hydride batter-
ies
Direct LED output displays
charge status
Fast-charge termination by -∆V,
maximum voltage, maximum
temperature, and maximum
time
Internal band-gap voltage ref-
erence
Optional top-off charge
Selectable pulse trickle charge
rates
Low-power mode
8-pin 300-mil DIP or 150-mil
SOIC
General Description
The bq2002 and bq2002/F Fast-Charge
ICs are low-cost CMOS battery-charge
controllers providing reliable charge
termination for both NiCd and NiMH
battery applications. Controlling a
current-limited or constant-current
supply allows the bq2002/F to be the
basis for a cost-effective stand-alone or
system-integrated charger. The
bq2002/F integrates fast charge with
optional top-off and pulsed-trickle con-
trol in a single IC for charging one or
more NiCd or NiMH battery cells.
Fast charge is initiated on application
of the charging supply or battery re-
placement. For safety, fast charge is
inhibited if the battery temperature
and voltage are outside configured
limits.
Fast charge is terminated by any of
the following:
n
n
n
n
n
Peak voltage detection (PVD)
Negative delta voltage (-∆V)
Maximum voltage
Maximum temperature
Maximum time
➤
➤
➤
➤
➤
➤
➤
After fast charge, the bq2002/F op-
tionally tops-off and pulse-trickles the
battery per the pre-configured limits.
Fast charge may be inhibited using
the INH pin. The bq2002/F may also
be placed in low-standby-power mode
to reduce system power consumption.
T h e bq 20 02 F d if f e rs f r om t h e
bq2002 only in that a slightly differ-
ent set of fast-charge and top-off
time limits is available. All differ-
ences between the two ICs are illus-
trated in Table 1.
Pin Connections
TM
LED
BAT
VSS
1
2
3
4
8
7
6
5
CC
Pin Names
TM
LED
INH
VCC
TS
Timer mode select input
Charging status output
Battery voltage input
System ground
TS
V
CC
INH
CC
Temperature sense input
Supply voltage input
Charge inhibit input
Charge control output
BAT
V
SS
8-Pin DIP or
Narrow SOIC
PN-200201.eps
bq2002/F Selection Guide
Part No.
bq2002
TCO
0.5
∗
V
CC
HTF
None
LTF
None
-∆V PVD
✔
✔
✔
✔
✔
✔
Fast Charge
C/2
1C
2C
C/2
1C
2C
t
MTO
160
80
40
160
100
55
Top-Off
C/32
C/16
None
C/32
C/16
None
Maintenance
C/64
C/64
C/32
C/64
C/64
C/32
bq2002F 0.5
∗
V
CC
None
None
SLUS131–JANUARY 1999 D
1
bq2002/F
Pin Descriptions
TM
Timer mode input
A three-level input that controls the settings
for the fast charge safety timer, voltage ter-
mination mode, top-off, pulse-trickle, and
voltage hold-off time.
LED
Charging output status
Open-drain output that indicates the charging
status.
BAT
Battery input voltage
The battery voltage sense input. The input to
this pin is created by a high-impedance re-
sistor divider network connected between
the positive and negative terminals of the
battery.
V
SS
TS
System ground
Temperature sense input
Input for an external battery temperature
monitoring thermistor.
V
CC
Supply voltage input
5.0V
±
20% power input.
INH
Charge inhibit input
When high, INH suspends the fast charge in
progress. When returned low, the IC re-
sumes operation at the point where initially
suspended.
CC
Charge control output
An open-drain output used to control the
charging current to the battery. CC switch-
ing to high impedance (Z) enables charging
current to flow, and low to inhibit charging
current. CC is modulated to provide top-off,
if enabled, and pulse trickle.
Functional Description
Figure 2 shows a state diagram and Figure 3 shows a
block diagram of the bq2002/F.
Battery Voltage and Temperature
Measurements
Battery voltage and temperature are monitored for
maximum allowable values. The voltage presented on
the battery sense input, BAT, should represent a
single-cell potential for the battery under charge. A
resistor-divider ratio of
RB1
=N-1
RB2
is recommended to maintain the battery voltage within
the valid range, where N is the number of cells, RB1 is
the resistor connected to the positive battery terminal,
and RB2 is the resistor connected to the negative bat-
tery terminal. See Figure 1.
Note:
This resistor-divider network input impedance to
end-to-end should be at least 200kΩ and less than 1 MΩ.
A ground-referenced negative temperature coefficient
thermistor placed near the battery may be used as a low-
cost temperature-to-voltage transducer. The temperature
sense voltage input at TS is developed using a resistor-
thermistor network between V
CC
and V
SS
. See Figure 1.
VCC
RT
PACK +
RB1
BAT
R3
TM
VCC
TS
N
T
C
bq2002/F
VSS
RB2
R4
bq2002/F
VSS
BAT pin connection
Mid-level
setting for TM
Thermistor connection
NTC = negative temperature coefficient thermistor.
Fg2002/F01.eps
Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration
2
bq2002/F
Chip on
4.0V
VCC
Battery
Voltage?
VBAT < 2V
VTS > VCC/2
Battery
Temperature?
VTS < VCC/2
VBAT > 2V
Fast
LED = Low
VBAT > 2V
VTS < VCC/2
((PVD or - V or
Maximum Time-Out)
and TM = high)
VCC
2V
Trickle
LED = Z
(PVD or - V or
Maximum Time-Out)
and TM = high
Top-off
LED = Z
Maximum Time-Out
or VBAT > 2V
or VTS < VCC/2
SD2002/F01
Figure 2. State Diagram
OSC
Clock
Phase
Generator
Timing
Control
Sample
History
Voltage
Reference
TM
INH
Charge-Control
State Machine
PVD, -∆V
ALU
A to D
Converter
MCV
Check
BAT
Power-On
Reset
CC
LED
TCO
Check
TS
Power
Down
VCC
VSS
Bd2002f.eps
Figure 3. Block Diagram
3
bq2002/F
VCC = 0
Fast Charging
Top-Off
(optional)
Pulse-Trickle
Fast Charging
CC Output
286 s
286 s
4576 s
See
Table 1
Charge initiated by application of power
Charge initiated by battery replacement
LED
TD2002F1.eps
Figure 4. Charge Cycle Phases
Starting A Charge Cycle
Either of two events starts a charge cycle (see Figure 4):
1. Application of power to V
CC
or
2. Voltage at the BAT pin falling through the maximum
cell voltage V
MCV
where
V
MCV
= 2V
±5%.
If the battery is within the configured temperature and
voltage limits, the IC begins fast charge. The valid bat-
tery voltage range is V
BAT
< V
MCV
. The valid tempera-
ture range is V
TS
> V
TCO
where
V
TCO
= 0.5
∗
V
CC
±5%.
If the battery voltage or temperature is outside of these
limits, the IC pulse-trickle charges until the next new
charge cycle begins.
Fast charge continues until termination by one or more of
the five possible termination conditions:
n
n
n
n
n
Peak voltage detection (PVD)
Negative delta voltage (-∆V)
Maximum voltage
Maximum temperature
Maximum time
Table 1. Fast-Charge Safety Time/Hold-Off Table
Typical Fast-Charge
and Top-Off
Time Limits
(minutes)
TM
Mid
Low
High
Termination
PVD
PVD
-∆V
bq2002
160
80
40
bq2002F
160
100
40
Corresponding
Fast-Charge
Rate
C/2
1C
2C
Notes:
Typical PVD
and -∆V Hold-Off Top-Off
Time (seconds)
Rate
600
300
150
C/32
C/16
Disabled
Pulse-
Trickle
Rate
C/64
C/64
C/32
Pulse-
Trickle
Period
(ms)
9.15
18.3
18.3
Typical conditions = 25°C, V
CC
= 5.0V.
Mid = 0.5 * V
CC
±
5V
Tolerance on all timing is
±
20%.
4
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