1
Features
Fast charge and conditioning of
nickel cadmium or nickel-metal
hydride batteries
Hysteretic PWM switch-mode
current regulation or gated con-
trol of an external regulator
Easily integrated into systems
or used as a stand-alone charger
Pre-charge qualification of tem-
perature and voltage
Direct LED outputs display
battery and charge status
Fast-charge termination by
temperature/ time, -V, maxi-
mum voltage, maximum tem-
perature, and maximum time
Optional top-off charge
General Description
The bq2003 Fast Charge IC provides
comprehensive fast charge control
functions together with high-speed
switching power control circuitry on a
monolithic CMOS device.
Integration of closed-loop current
control circuitry allows the bq2003
to be the basis of a cost-effective so-
lution for stand-alone and system-
integrated chargers for batteries of
one or more cells.
Switch-activated discharge-before-
charge allows bq2003-based chargers
to support battery conditioning and
capacity determination.
High-efficiency power conversion is
accomplished using the bq2003 as a
hysteretic PWM controller for
switch-mode regulation of the charg-
ing current. The bq2003 may alterna-
tively be used to gate an externally
regulated charging current.
Fast charge may begin on applica-
tion of the charging supply, replace-
ment of the battery, or switch de-
pression. For safety, fast charge is
inhibited unless/until the battery
temperature and voltage are within
configured limits.
Temperature, voltage, and time are
monitored throughout fast charge.
Fast charge is terminated by any of
the following:
n
Rate of temperature rise
(
T/t)
n
Negative delta voltage (-
V)
n
Maximum voltage
n
Maximum temperature
n
Maximum time
After fast charge, an optional top-off
phase is available.
Constant-cur-
rent maintenence charge is provided
by an external trickle resistor.
Fast-Charge IC
bq2003
CCMD
Charge command/select
DCMD
Discharge command
DVEN
-
V enable/disable
TM
1
Timer mode select 1
TM
2
Timer mode select 2
TS
Temperature sense
BAT
Battery voltage
V
SS
System ground
1
PN200301.eps
16-Pin DIP or SOIC
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VCC
DIS
MOD
CHG
TEMP
MCV
TCO
SNS
CCMD
DCMD
DVEN
TM1
TM2
TS
BAT
VSS
SNS
Sense resistor input
TCO
Temperature cutoff
MCV
Maximum voltage
TEMP
Temperature status
output
CHG
Charging status output
MOD
Charge current control
DIS
Discharge control
V
CC
5.0V
10% power
Pin Connections
Pin Names
SLUS095A - OCTOBER 1999 I
Pin Descriptions
CCMD,
DCMD
Charge initiation and discharge-before-
charge control inputs
These two inputs control the conditions that
b e g i n a n e w ch a r g e c y cl e a n d e n a b l e
discharge-before-charge. See Table 1.
DVEN
-
V enable input
This input enales/disables -
V charge termina-
tion. If DVEN is high, the -
V test is enabled.
If DVEN is low, -
V test is disabled. The state
of DVEN may be changed at any time.
TM
1
TM
2
Timer mode inputs
TM
1
and TM
2
are three-state inputs that con-
figure the fast charge safety timer, -
V hold-
off time, and that enhance/disable top-off.
See Table 2.
TS
Temperature sense input
Input, referenced to SNS, for an external
thermistor monitoring battery temperature.
BAT
Single-cell voltage input
The battery voltage sense input, referenced
to SNS. This is created by a high-impedance
resistor divider network connected between
the positive and the negative terminals of
the battery.
Vss
Ground
SNS
Charging current sense input
SNS controls the switching of MOD based on
the voltage across an external sense resistor
in the current path of the battery. SNS is the
reference potential for the TS and BAT pins.
If SNS is connected to V
SS
, MOD switches
high at the beginning of charge and low at
the end of charge.
TCO
Temperature cutoff threshold input
Input to set maximum allowable battery
temperature.
If the potential between TS
and SNS is less than the voltage at the TCO
input, then fast charge or top-off charge is
terminated.
MCV
Maximum-Cell-Voltage threshold input
Input to set maximum single-cell equivalent
voltage. If the voltage between BAT and SNS
is greater than or equal to the voltage at the
MCV input, then fast charge or top-off charge
is inhibited.
Note: For valid device operation, the
voltage level on MCV must not exceed
0.6
V
CC
.
TEMP
Temperature status output
Push-pull output indicating temperature
status. TEMP is low if the voltage at the TS
pin is not within the allowed range to start
fast charge.
CHG
Charging status output
Push-pull output indicating charging status.
See Figure 1.
MOD
Current-switching control output
MOD is a push/pull output that is used to
control the charging current to the battery.
MOD switches high to enable charging cur-
rent flow and low to inhibit charging current
flow.
DIS
Discharge FET control output
Push-pull output used to control an external
transistor to discharge the battery before
charging.
V
CC
V
CC
supply input
5.0 V, 10% power input.
2
bq2003
Functional Description
Figure 3 shows a state diagram and Figure 4 shows a
block diagram of the bq2003.
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
RB2
= N - 1
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 200k
and less than 1M.
A ground-referenced negative temperature coefficient
thermistor placed in proximity to the battery may be used
as a low-cost temperature-to-voltage transducer. The tem-
perature sense voltage input at TS is developed using a re-
sistor-thermistor network between V
CC
and battery's nega-
tive terminal See Figure 1. Both the BAT and TS inputs
are referenced to SNS, so the signals used inside the IC are:
V
BAT
- V
SNS
= V
CELL
and
V
TS
- V
SNS
= V
TEMP
3
Table 1. New Charge Cycle and Discharge Stimulus
CCMD
DCMD
New Charge Cycle
Started by:
Discharge-Before-Charge
Started by:
Pulled Up/Down to:
V
SS
V
SS
V
CC
rising to valid level
A rising edge on DCMD
Battery replacement
(V
CELL
falling through V
MCV
)
A rising edge on CCMD
V
CC
V
CC
V
CC
rising to valid level
A rising edge on DCMD
Battery replacement
(V
CELL
falling through V
MCV
)
A falling edge on CCMD or DCMD
V
CC
V
SS
A rising edge on CCMD
A rising edge on DCMD
V
SS
V
CC
A falling edge on CCMD
A rising edge on DCMD
bq2003
Fg2003a2.eps
N
T
C
bq2003
VCC
PACK +
PACK -
TS
SNS
RT1
RT2
RB2
RB1
bq2003
VDC
External Trickle Resistor
Negative Temperature
Coefficient Thermister
Pass Element
PACK+
PACK-
MOD
BAT
SNS
Figure 1. Voltage and Temperature Monitoring and Trickle Resistor
Discharge-Before-Charge
The DCMD input is used to command discharge-before-
charge via the DIS output. Once activated, DIS becomes
active (high) until V
CELL
falls below V
EDV,
at which time
DIS goes low and a new fast charge cycle begins. See
Table 1 for the conditions that initiate discharge-before-
charge.
Discharge-before-charge is qualified by the
same voltage and temperature conditions that qualify a
new charge cycle start (see below). If a discharge is ini-
tiated but the pack voltage or temperature is out of
range, the chip enters the charge pending mode and
trickle charges the battery until the voltage and tem-
perature qualification conditions are met, and then
starts to discharge.
Starting A Charge Cycle
The stimulus required to start a new charge cycle is de-
termined by the configuration of the CCMD and DCMD
inputs.
If CCMD and DCMD are both pulled up or
pulled down, then a new charge cycle is started by (see
Figure 2):
1.
V
CC
rising above 4.5V
2.
V
CELL
falling through the maximum cell voltage,
V
MCV
. V
MCV
is the voltage presented at the MCV
input pin, and is configured by the user with a re-
sistor divider between V
CC
and ground.
The al-
lowed range is 0.2 to 0.4
V
CC
.
3.
A rising edge on CCMD if it is pulled down, or a fal-
ling edge on CCMD if it is pulled up.
Starting a new charge cycle may be limited to a push-
button or logical pulse input only by pulling one member
of the DCMD and CCMD pair up while pulling the other
input down. In this configuration a new charge cycle
will be started only by a falling edge on CCMD if it is
pulled up, and by a falling edge on CCMD if it is pulled
down. See Table 1.
If the battery is within the configured temperature and
voltage limits, the IC begins fast charge. The valid bat-
tery voltage range is V
EDV
< V
BAT
< V
MCV
where:
V
EDV
= 0.2
V
CC
30mV
The valid temperature range is V
HTF
< V
TEMP
< V
LTF
,
where:
V
LTF
= 0.4
V
CC
30mV
V
HTF
= [(1/8
V
LTF
) + (7/8
V
TCO
)]
30mV
V
TCO
is the voltage presented at the TCO input pin, and is
configured by the user with a resistor divider between V
CC
and ground. The allowed range is 0.2 to 0.4
V
CC
.
If the temperature of the battery is out of range, or the
voltage is too low, the chip enters the charge pending
state and waits for both conditions to fall within their
allowed limits.
There is no time limit on the charge
pending state; the charger remains in this state as long
as the voltage or temperature conditons are outside of
4
bq2003
Fast Charging
Top-Off
(Optional)
34 sec.
TD200301a.eps
Discharge
(Optional)
Charge
Pending
DIS
MOD Switch-Mode Configuration
MOD External Regulation
(SNS Grounded)
CHG Status Output
TEMP Status Output
Charge cycle start.
Battery outside temperature limits.
or
Battery within temperature limits.
Battery discharged to 0.2 VCC.
4
sec
.
Figure 2. Charge Cycle Phases
the allowed limits. If the voltage is too high, the chip
goes to the battery absent state and waits until a new
charge cycle is started.
Fast charge continues until termination by one or more
of the five possible termination conditions:
n
Delta temperature/delta time (
T/t)
n
Negative delta voltage (-
V)
n
Maximum voltage
n
Maximum temperature
n
Maximum time
-
V Termination
If the DVEN input is high, the bq2003 samples the volt-
age at the BAT pin once every 34s. If V
CELL
is lower
than any previously measured value by 12mV
4mV,
fast charge is terminated. The -
V test is valid in the
range V
MCV
- (0.2
V
CC
) < V
CELL
< V
MCV
.
Voltage Sampling
Each sample is an average of 16 voltage measurements
taken 57
s apart. The resulting sample period (18.18ms)
filters out harmonics around 55Hz. This technique mini-
mizes the effect of any AC line ripple that may feed
through the power supply from either 50Hz or 60Hz AC
sources. Tolerance on all timing is
16%.
Voltage Termination Hold-off
A hold-off period occurs at the start of fast charging.
During the hold-off period, -
V termination is disabled.
This avoids premature termination on the voltage spikes
sometimes produced by older batteries when fast-charge
current is first applied.
T/t, maximum voltage and
maximum temperature terminations are not affected by
the hold-off period.
T/t Termination
The bq2003 samples at the voltage at the TS pin every
34s, and compares it to the value measured two samples
earlier. If V
TEMP
has fallen 16mV
4mV or more, fast
charge is terminated.
The
T/t termination test is
valid only when V
TCO
< V
TEMP
< V
LTF
.
Temperature Sampling
Each sample is an average of 16 voltage measurements
taken 57
s apart. The resulting sample period
(18.18ms) filters out harmonics around 55Hz. This tech-
nique minimizes the effect of any AC line ripple that
may feed through the power supply from either 50Hz or
60Hz AC sources. Tolerance on all timing is
16%.
Maximum Voltage, Temperature, and Time
Anytime V
CELL
rises above V
MCV,
CHG goes high (the LED
goes off) immediately. If the bq2003 is not in the voltage
hold-off period, fast charging ceases if V
CELL
remains above
MCV for a minimum of t
MCV
. If V
CELL
then falls back be-
low V
MCV
before 1.5t
MCV
50ms, the chip transitions to the
Charge Complete state (maximum voltage termination). If
V
CELL
remains above V
MCV
beyond 1.5t
MCV
, the bq2003
transitions to the Battery Absent state (battery removal).
See Figure 3.
If the bq2003 is in the voltage hold-off period when
V
CELL
rises above V
MCV,
the LED goes out but fast
charging continues until the expiration of the hold-off
period. Temperature sampling continues during the
hold-off period as well. If a new battery is inserted be-
fore the hold-off period expires, it continues in the fast
charge cycle started by its predecessor. No precharge
qualification is performed, and a temperature sample
5
bq2003
Corresponding
Fast-Charge Rate
TM1
TM2
Typical Fast Charge
and Top-Off
Time Limits
Typical -
V/MCV
Hold-Off
Time (seconds)
Top-Off
Rate
C/4
Low
Low
360
137
Disabled
C/2
Float
Low
180
820
Disabled
1C
High
Low
90
410
Disabled
2C
Low
Float
45
200
Disabled
4C
Float
Float
23
100
Disabled
C/2
High
Float
180
820
C/16
1C
Low
High
90
410
C/8
2C
Float
High
45
200
C/4
4C
High
High
23
100
C/2
Note:
Typical conditions = 25C, V
CC
= 5.0V.
Table 2. Fast-Charge Safety Time/Hold-Off/Top-Off Table
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