bq2002C
NiCd/NiMH Fast-Charge Management IC
Features
General Description
➤
The bq2002C Fast-Charge IC is a lowcost CMOS battery-charge controller
providing reliable charge termination
for both NiCd and NiMH battery applications. Controlling a current-limited
or constant-current supply allows the
bq2002C to be the basis for a costeffective stand-alone or system-integrated charger. The bq2002C integrates fast charge with pulsed-trickle
control in a single IC for charging one
or more NiCd or NiMH battery cells.
➤
➤
Fast charge of nickel cadmium
or nickel-metal hydride batteries
Direct LED output displays
charge status
Fast-charge termination by -∆V,
maximum voltage, maximum
temperature, and maximum
time
➤
Internal band-gap voltage reference
➤
Selectable pulse-trickle charge
rates
➤
Low-power mode
➤
8-pin 300-mil DIP or 150-mil
SOIC
Pin Connections
Fast charge is initiated on application
of the charging supply or battery
replacement. 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
Peak voltage detection (PVD)
n
Negative delta voltage (-∆V)
n
Maximum voltage
n
Maximum temperature
n
Maximum time
After fast charge, the bq2002C pulsetrickles the battery per the preconfigured limits. Fast charge may be
inhibited using the INH pin. The
bq2002C may also be placed in lowstandby-power mode to reduce
system power consumption.
Pin Names
TM
1
8
CC
LED
2
7
INH
BAT
3
6
VCC
VSS
4
5
TS
TM
Timer mode select input
TS
Temperature sense input
LED
Charging status output
VCC
Supply voltage input
BAT
Battery voltage input
INH
Charge inhibit input
VSS
System ground
CC
Charge control output
8-Pin DIP or
Narrow SOIC
PN-200201.eps
SLUS136 - AUGUST 2011
1
bq2002C
TM
Charge control output
CC
Pin Descriptions
An open-drain output used to control the
charging current to the battery. CC switching to high impedance (Z) enables charging
current to flow, and low to inhibit charging
current. CC is modulated to provide pulse
trickle.
Timer mode input
A three-level input that controls the settings
for the fast charge safety timer, voltage termination mode, pulse-trickle, and voltage
hold-off time.
LED
Functional Description
Charging output status
Open-drain output that indicates the charging
status.
BAT
Figure 2 shows a state diagram and Figure 3 shows a
block diagram of the bq2002C.
Battery input voltage
Battery Voltage and Temperature
Measurements
The battery voltage sense input. The input to
this pin is created by a high-impedance resistor divider network connected between
the positive and negative terminals of the
battery.
VSS
System ground
TS
Temperature sense input
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
Input for an external battery temperature
monitoring thermistor.
VCC
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
battery terminal. See Figure 1.
Supply voltage input
5.0V ± 20% power input.
INH
Charge inhibit input
Note: This resistor-divider network input impedance to
end-to-end should be at least 200kΩ and less than 1 MΩ.
When high, INH suspends the fast charge in
progress. When returned low, the IC resumes operation at the point where initially
suspended.
A ground-referenced negative temperature coefficient
thermistor placed near the battery may be used as a lowcost temperature-to-voltage transducer. The temperature
sense voltage input at TS is developed using a resistorthermistor network between VCC and VSS. See Figure 1.
VCC
PACK +
RT
RB1
VCC
R3
BAT
bq2002C
TM
RB2
TS
N
T
C
bq2002C
R4
VSS
VSS
BAT pin connection
Mid-level
setting for TM
Thermistor connection
NTC = negative temperature coefficient thermistor.
Fg2002/C.eps
Figure 1. Voltage and Temperature Monitoring and TM Pin Configuration
2
bq2002C
Battery Voltage
too High?
Chip on
4.0V
VCC
VBAT > 2V
VBAT < 2V
Battery Voltage
too Low?
VBAT < 0.84V
0.84V < VBAT
VTS > VCC/2
VTS < VCC/2
Battery
Temperature?
Charge
Pending
Fast
LED =
Low
VBAT > 0.84V and
VBAT < 2V and
VTS > VCC/2
VBAT > 2V or
VTS < VCC/2 or
PVD or - V or
Maximum Time Out
Trickle
LED =
Flash
VBAT > 2V
VBAT
2V
Trickle
LED = Z
SD2002C.eps
Figure 2. State Diagram
Clock
Phase
Generator
OSC
TM
Timing
Control
Sample
History
Voltage
Reference
PVD, - V
ALU
A to D
Converter
INH
Charge-Control
State Machine
LBAT
Check
HTF TCO
Check Check
Power-On
Reset
CC
LED
TS
Power
Down
VCC
MCV
Check
BAT
VSS
Bd2002CEG.eps
Figure 3. Block Diagram
3
bq2002C
VCC = 0
Fast Charging
Pulse-Trickle
Fast Charging
1s
CC Output
See
Table 1
Charge initiated by application of power
Charge initiated by battery replacement
LED
TD2002C1.eps
Figure 4. Charge Cycle Phases
pending state. In this state pulse trickle charge is
applied to the battery and the LED flashes until the
voltage and temperature come into the allowed fast
charge range or VBAT rises above VMCV. Anytime VBAT
≥ VMCV, the IC enters the Charge Complete/Battery
Absent state. In this state the LED is off and trickle
charge is applied to the battery until the next new
charge cycle begins.
Starting A Charge Cycle
Either of two events starts a charge cycle (see Figure 4):
1. Application of power to VCC or
2. Voltage at the BAT pin falling through the maximum
cell voltage VMCV where
Fast charge continues until termination by one or more of
the five possible termination conditions:
VMCV = 2V ±5%.
If the battery is within the configured temperature and
voltage limits, the IC begins fast charge. The valid
battery voltage range is VLBAT < VBAT < VMCV, where
VLBAT = 0.175 ∗ VCC ±20%
The valid temperature range is VTS > VHTF where
VHTF = 0.6 ∗ VCC ±5%.
n
Peak voltage detection (PVD)
n
Negative delta voltage (-∆V)
n
Maximum voltage
n
Maximum temperature
n
Maximum time
If VBAT ≤ VLBAT or VTS ≤ VHTF, the IC enters the charge-
Table 1. Fast-Charge Safety Time/Hold-Off Table
Corresponding
Fast-Charge
Rate
TM
Termination
Typical
FastCharge
Time Limits
(minutes)
C/2
Mid
PVD
160
300
C/32
73
18.7
1C
Low
PVD
80
150
C/32
37
18.7
2C
High
-∆V
40
75
C/32
18
9.4
Notes:
Typical PVD
and -∆V
Hold-Off
Time (seconds)
Typical conditions = 25°C, VCC = 5.0V
Mid = 0.5 * VCC ±0.5V
Tolerance on all timing is ±12%.
4
PulseTrickle
Rate
PulseTrickle
Pulse Width
(ms)
Maximum
Synchronized
Sampling
Period
(seconds)
bq2002C
_______________________________________________________________________
PVD and -∆V Termination
There are two modes for voltage termination, depending on
the state of TM. For -∆V (TM = high), if VBAT is lower than any
previously measured value by 12mV ±3mV, fast charge is
terminated. For PVD (TM = low or mid), a decrease of 2.5mV
±2.5mV terminates fast charge. The PVD and -∆V tests are
valid in the range 1V
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