For Li-Ion battery packs, the resistor values RB1 and
RB2are calculated by the following equation:
R
R
N
V
V
1
B1
B2
CELL
MCV
=∗
−
where N is the number of cells in series and VCELL is
the manufacturer-specified charging voltage. The
end-to-end input impedance of this resistive divider
network should be at least 200kΩ and no more than
1MΩ.
A NiCd or NiMH battery pack consisting of N se-
ries-cells may benefit by the selection of the RB1
value to be N-1 times larger than the RB2 value.
In a mixed-chemistry design, a common volt-
age-divider is used as long as the maximum charge
voltage of the nickel-based pack is below that of the
Li-Ion pack. Otherwise, different scaling is required.
Temperature Monitoring
The bq2000T measures the temperature by the
voltage at the TS pin. This voltage is typically
generated by a negative-temperature-coefficient
thermistor. The bq2000T compares this voltage
against its internal threshold voltages to determine if
charging is safe.
9
bq2000T
Parameter
Value
Maximum cell voltage (VMCV)2V
Minimum pre-charge qualification voltage (VLBAT)
950mV
High-temperature cutoff voltage (VTCO)
0.225 ∗ VCC
High-temperature fault voltage (VHTF)
0.25 ∗ VCC
Low-temperature fault voltage (VLTF)
0.5 ∗ VCC
bq2000T fast-charge maximum time out (MTO)
RMTO ∗ CMTO ∗ 35,988
Fast-charge charging current (IMAX)
0.05/RSNS
Hold-off period
MTO/32
Top-off charging current (optional)
IMAX/16
Top-off period (optional)
MTO
Trickle-charge frequency
1Hz
Trickle-charge pulse-width
See Figure 7
Table 2. Summary of NiCd or NiMH Charging Characteristics
Parameter
Value
Maximum cell voltage (VMCV)2V
Minimum pre-charge qualification voltage (VLBAT)
950mV
High-temperature cutoff voltage (VTCO)
0.225 ∗ VCC
High-temperature fault voltage (VHTF)
0.25 ∗ VCC
Low-temperature fault voltage (VLTF)
0.5 ∗ VCC
bq2000T fast-charge maximum time-out (MTO)
2 ∗ RMTO ∗ CMTO ∗ 35,988
Fast-charge charging current (IMAX)
0.05/RSNS
Hold-off period
MTO/32
Minimum current (for fast-charge termination)
IMAX/14
Trickle-charge frequency (before fast charge only)
1Hz
Trickle-charge pulse-width (before fast charge only)
See Figure 7
Table 3. Summary of Li-Ion Charging Characteristics
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