bq24020, bq24022, bq24023
bq24024, bq24025, bq24026
bq24027
www.ti.com
SLUS549D–DECEMBER 2002–REVISED MARCH 2006
FUNCTIONAL DESCRIPTION (continued)
Figure 4. Operational Flow Chart
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 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 common 10-kΩ negative-temperature coefficient
thermistors (NTC) (see Figure 6). The device compares the voltage on the TS pin with the internal V(LTF) and
V(HTF) thresholds to determine if charging is allowed. If a temperature outside the V(LTF) and V(HTF) thresholds is
detected, the device immediately suspends the 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 within the normal range.
The allowed temperature range for a 103AT-type thermistor is 0°C to 45°C. However the user may modify these
thresholds by adding two external resistors. See Figure 7.
BATTERY PRE-CONDITIONING
If the battery voltage falls below the V(LOWV) threshold during a charge cycle, the bqTINY-II applies a precharge
current, IO(PRECHG), to the battery. This feature revives deeply discharged cells. The resistor connected between
the ISET1 and VSS, RSET, determines the precharge rate. The V(PRECHG) and K(SET) parameters are specified in
the specifications table. Note that this applies to both AC and USB charging.
V
(PRECGH)
I
+
O (PRECHG)
R
SET
(1)
The bqTINY-II activates a safety timer, t(PRECHG), during the conditioning phase. If V(LOWV) threshold is not
reached within the timer period, the bqTINY-II turns off the charger and asserts a FAULT code on the STATx
pins. Please refer to the TIMER FAULT RECOVERY section for additional details.
PACK+
PACK+
bqTINYII
bqTINYII
+
+
I
PACK−
RT1
TS
PACK−
TS
I
TS
TS
NTC
NTC
TEMP
TEMP
9
9
LTF
HTF
LTF
HTF
V
BATTERY
PACK
LTF
BATTERY
PACK
V
LTF
RT2
V
HTF
V
HTF
UDG−02188
UDG−02186
Figure 6. Temperature Sensing Configuration
Figure 7. Temperature Sensing Thresholds
12
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