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Description:
BQ2004E Fast-Charge ICs
Prototype PCB
Part No.:   BQ2004E
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Description:   Fast-Charge ICs
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Page : 19 Pages
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bq2004E/H
Functional Description
Figure 2 shows a block diagram and Figure 3 shows a
state diagram of the bq2004E/H.
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.
The DCMD input is internally pulled up to V
CC
(its inac-
tive state). Leaving the input unconnected, therefore,
results in disabling discharge-before-charge. A negative
going pulse on DCMD initiates discharge-before-charge
at any time regardless of the current state of the
bq2004. If DCMD is tied to V
SS
, discharge-before-charge
will be the first step in all newly started charge cycles.
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
two-cell potential for the battery under charge. A
resistor-divider ratio of:
RB1 N
=
-1
RB2 2
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 1MΩ.
A ground-referenced negative temperature coefficient ther-
mistor placed in proximity to the battery may be used as a
low-cost temperature-to-voltage transducer. The tempera-
ture sense voltage input at TS is developed using a
resistor-thermistor network between V
CC
and V
SS
. 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
Starting A Charge Cycle
A new charge cycle is started by:
1.
2.
Application of V
CC
power.
V
CELL
falling through the maximum cell voltage,
V
MCV
where:
V
MCV
= 0.8
V
CC
±
30mV
3.
A transition on the INH input from low to high.
If DCMD is tied low, a discharge-before-charge will be
executed as the first step of the new charge cycle. Oth-
erwise, pre-charge qualification testing will be the first
step.
The battery must be within the configured temperature
and voltage limits before fast charging begins.
The valid battery voltage range is V
EDV
< V
BAT
< V
MCV
where:
V
EDV
= 0.4
V
CC
±
30mV
Negative Temperature
Coefficient Thermister
VCC
RT1
PACK +
PACK+
bq2004E/H
BAT
RB1
TS
bq2004E/H
SNS
PACK-
RT2
N
T
C
PACK -
RB2
SNS
Fg2004a.eps
Figure 1. Voltage and Temperature Monitoring
3
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