BQ2004E_07 Datasheet, PDF (3/19 Pages) Texas Instruments – Fast-Charge ICs

bq2004E/H
Functional Description
Figure 2 shows a block diagram and Figure 3 shows a
state diagram of the bq2004E/H.
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 VCC and VSS. See
Figure 1. Both the BAT and TS inputs are referenced to
SNS, so the signals used inside the IC are:
VBAT - VSNS = VCELL
and
VTS - VSNS = VTEMP
Discharge-Before-Charge
The DCMD input is used to command discharge-before-
charge via the DIS output. Once activated, DIS becomes
active (high) until VCELL falls below VEDV, at which time
DIS goes low and a new fast charge cycle begins.
The DCMD input is internally pulled up to VCC (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 VSS, discharge-before-charge
will be the first step in all newly started charge cycles.
Starting A Charge Cycle
A new charge cycle is started by:
1. Application of VCC power.
2. VCELL falling through the maximum cell voltage,
VMCV where:
VMCV = 0.8 ∗ VCC ± 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 VEDV < VBAT < VMCV
where:
VEDV = 0.4 ∗ VCC ± 30mV
bq2004E/H
RB1
BAT
RB2
SNS
PACK+
PACK-
Negative Temperature
Coefficient Thermister
VCC
RT1
TS
bq2004E/H
RT2
N
T
C
SNS
PACK +
PACK -
Figure 1. Voltage and Temperature Monitoring
Fg2004a.eps
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