Datasheet

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AUTONOMOUS POWER SOURCE SELECTION
UDG−02187
USB MODE
AC MODE
AC > BATTERY
AC < BATTERY
USB > BATTERY
TEMPERATURE QUALIFICATION (bq24020, bq24024, bq24025, and bq24026 only)
BATTERY PRE-CONDITIONING
I
O (PRECHG)
V
(PRECGH)
K
(SET)
R
SET
(1)
V
LTF
V
HTF
I
TS
9
TS
bqTINYII
LTF
HTF
+
BATTERY
PACK
PACK+
PACK−
NTC
RT1
RT2
TEMP
UDG−02188
9
TS
bqTINYII
LTF
HTF
+
BATTERY
PACK
PACK+
PACK−
NTC
V
LTF
V
HTF
I
TS
TEMP
UDG−02186
bq24020 , , bq24022 , , bq24023
bq24024 , bq24025 , bq24026
bq24027
SLUS549E – DECEMBER 2002 – REVISED NOVEMBER 2007
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.
Figure 5. Typical Charging Profile
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-k Ω 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 .
If the battery voltage falls below the V
(LOWV)
threshold during a charge cycle, the bqTINY-II applies a precharge
current, I
O(PRECHG)
, to the battery. This feature revives deeply discharged cells. The resistor connected between
the ISET1 and V
SS
, R
SET
, 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.
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.
Figure 6. Temperature Sensing Configuration Figure 7. Temperature Sensing Thresholds
12 Submit Documentation Feedback Copyright © 2002 – 2007, Texas Instruments Incorporated
Product Folder Link(s): bq24020 bq24022 bq24023 bq24024 bq24025 bq24026 bq24027