BQ2005_13 Datasheet, PDF (3/18 Pages) Texas Instruments – Fast- Charge IC for Dual-Bat tery Packs

bq2005
Functional Description
Figure 3 shows a block diagram and Figure 4 shows a
state diagram of the bq2005.
Battery Voltage and Temperature
Measurements
Battery voltage and temperature are monitored for maxi-
mum allowable values. The voltage presented on the bat-
tery sense input, BATA,B, must be divided down to be-
tween 0.95 ∗ VCC and 0.475 ∗ VCC for proper operation. A
resistor-divider ratio of:
RB1 N
RB2 ⁼ 2.375 ^{− 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 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 TSA,B is developed using a
resistor-thermistor network between VCC and VSS. See
Figure 1. Both the BATA,B and TSA,B inputs are refer-
enced to SNSA,B, so the signals used inside the IC are:
VBAT(A,B) - VSNS(A,B) = VCELL(A,B)
and
VTS(A,B) - VSNS(A,B) = VTEMP(A,B)
Discharge-Before-Charge
The DCMDA input is used to command discharge-
before-charge via the DISA output. Once activated,
DISA becomes active (high) until VCELL falls below VEDV
where:
VEDV = 0.475 ∗ VCC ± 30mV
at which time DISA goes low and a new fast charge cycle
begins.
The DCMDA input is internally pulled up to VCC (its in-
active state). Leaving the input unconnected, therefore,
results in disabling discharge-before-charge. A negative
going pulse on DCMDA initiates discharge-before-charge
a t any t ime r egardless of t he current state of the
bq2005. If DCMDA is tied to VSS, discharge-before-
charge will be the first step in all newly started charge
cycles.
Starting A Charge Cycle
Anew charge cycle is started by (see Figure 2):
1. VCC rising above 4.5V
2. VCELL falling through the maximum cell voltage,
VMCV where:
VMCV = 0.95 ∗ VCC ± 30mV
If DCMDA 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.
bq2005
BAT_A,B
SNS_A,B
RB1
RB2
PACK+
PACK-
Negative Temperature
Coefficient Thermister
V_CC
RT1
TS_A,B
bq2005
N
RT2
T
C
SNS_A,B
PACK +
PACK -
Fg2005-1.eps
Figure 1. Voltage and Temperature Monitoring
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