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SLUS530H – SEPTEMBER 2002 – REVISED JUNE 2007
FUNCTIONAL DESCRIPTION (continued)
TEMPERATURE QUALIFICATION
NOTE
The temperature qualifications apply only to versions with temperature sense input
(TS) pin option (bq24020 and bq24014).
Versions of the bqTINY with the TS pin option, continuously monitor battery temperature by measuring the
voltage between the TS and VSS pins. A negative temperature coefficient thermistor (NTC) and an external
voltage divider typically develops this voltage (see
The bqTINY compare this voltage against the
internal V
(TS1)
and V
(TS2)
thresholds to determine if charging is allowed (see
The temperature sensing
circuit is immune to any fluctuation in V
CC
since both the external voltage divider and the internal thresholds are
ratiometric to V
CC
.
Once a temperature outside the V
(TS1)
and V
(TS2)
thresholds is detected the bqTINY immediately suspend the
charge. The bqTINY suspends charge by turning off the power FET and holding the timer value (i.e. timers are
NOT reset). Charge is resumed when the temperature returns to the normal range.
VCC
Charge Suspend
V(TS2)
Normal T
emperature Range
V(TS1)
Charge Suspend
VSS
Figure 6. TS Pin Thresholds
The resistor values of R
T1
and R
T2
are calculated by
and
(for NTC Thermistors).
(
5 x R
TH
x R
TC
)
R
T1
=
3 x
(
R
TC
- R
TH
)
(
)
(1)
R
T2
=
(
5 x R
TH
x R
TC
)
(
2 x R
TC
)
-
(
7 x R
TH
)
(2)
Where R
TC
is the cold temperature resistance and R
TH
is the hot temperature resistance of thermistor, as
specified by the thermistor manufacturer.
R
T1
or R
T2
can be omitted If only one temperature (hot or cold) setting is required. Applying a constant voltage
between the V
TS1
and V
TS2
thresholds to pin TS disables the temperature-sensing feature.
11
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