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ꢂꢃ ꢄꢂ ꢄ ꢅ
ꢂꢃ ꢄꢂ ꢆ ꢅ
ꢂ ꢃꢄ ꢂ ꢇꢅ
ꢀ ꢁ
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ꢂ
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SLUS549C − DECEMBER 2002 − REVISED AUGUST 2004
FUNCTIONAL DESCRIPTION
AUTONOMOUS POWER SOURCE SELECTION
As default the bqTINY-II attempts to charge from the AC input. If AC input is not present, the USB is selected. If both inputs
are available, the AC adapter has the priority. See Figure 5 for details.
AC > BATTERY
AC MODE
USB MODE
AC < BATTERY
USB > BATTERY
UDG−02187
Figure 5. Typical Charging Profile
TEMPERATURE QUALIFICATION (bq24020, bq24024, bq24025, and bq24026 only)
The bqTINY-II continuously monitors battery temperature by measuring the voltage between the TS and VSS pins.
An internal current source provides the bias for most common 10-kΩ negative-temperature coefficient thermistors
(NTC) (see Figure 6). The device compares the voltage on the TS pin against the internal V
and V
thresholds
(LTF)
(HTF)
to determine if charging is allowed. Once a temperature outside the V
and V
thresholds is detected the
(LTF)
(HTF)
device immediately suspend the charge. The device suspend charge by turning off the powerFET and holding the
timer value (i.e. timers are NOT reset). Charge is resumed when the temperature returns to the normal range.
The allowed temperature range for 103AT type thermistor is 0ꢂ C to 45ꢂ C. However the user may modify these
thresholds by adding two external resistors. See Figure 7.
BATTERY PRE-CONDITIONING
During a charge cycle if the battery voltage is below the V
threshold, the bqTINY-II applies a precharge current,
(LOWV)
I
, to the battery. This feature revives deeply discharged cells. The resistor connected between the ISET1
o(PRECHG)
and Vss, R
, determines the precharge rate. The V
and K
parameters are specified in the
SET
(PRECHG)
(SET)
specifications table. Note that this applies to both AC and USB charging.
V
K
(SET)
(PRECGH)
I
+
O (PRECHG)
R
SET
(1)
threshold is not reached
The bqTINY-II activates a safety timer, t
, during the conditioning phase. If V
(LOWV)
(PRECHG)
within the timer period, the bqTINY-II turns off the charger and enunciates FAULT on the STATx pins. Please refer
to the TIMER FAULT RECOVERY section for additional details.
PACK+
bqTINYII
PACK+
bqTINYII
+
+
PACK−
TS
I
I
PACK−
RT1
TS
TS
TS
NTC
NTC
TEMP
TEMP
9
9
LTF
HTF
LTF
HTF
BATTERY
PACK
V
V
BATTERY
PACK
LTF
LTF
RT2
V
V
HTF
HTF
UDG−02186
UDG−02188
Figure 7. Temperature Sensing Thresholds
Figure 6. Temperature Sensing Configuration
12
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