BQ2003_12 Datasheet, PDF (3/18 Pages) Texas Instruments – Fast-Charge IC

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 _{= N - 1}
RB2
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
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 VCC 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:
VBAT - VSNS = VCELL
and
VTS - VSNS = VTEMP
Table 1. New Charge Cycle and Discharge Stimulus
CCMD
DCMD
Pulled Up/Down to:
VSS
VSS
VCC
VCC
VSS
VCC
VSS
VCC
New Charge Cycle
Started by:
VCC rising to valid level
Battery replacement
(VCELL falling through VMCV)
A rising edge on CCMD
VCC rising to valid level
Battery replacement
(VCELL falling through VMCV)
A falling edge on CCMD or DCMD
A rising edge on CCMD
A falling edge on CCMD
Discharge-Before-Charge
Started by:
A rising edge on DCMD
A rising edge on DCMD
A rising edge on DCMD
A rising edge on DCMD
External Trickle Resistor
VDC
Pass Element
MOD
bq2003
RB1
BAT
RB2
SNS
PACK+
PACK-
Negative Temperature
Coefficient Thermister
VCC
RT1
TS
bq2003
N
RT2
T
C
SNS
PACK +
PACK -
Fg2003a2.eps
Figure 1. Voltage and Temperature Monitoring and Trickle Resistor
3