BQ24070 Datasheet, PDF (17/26 Pages) Texas Instruments – SINGLE-CHIP CHARGE AND SYSTEM POWER-PATH MANAGEMENT IC

bq24070
www.ti.com
SLUS694A – MARCH 2006 – REVISED MARCH 2006
FUNCTIONAL DESCRIPTIONS (continued)
pins. An internal current source provides the bias for most-common 10 kΩ negative-temperature coefficient
thermistors (NTC) (see Figure 9). The device compares the voltage on the TS pin against the internal V_(LTF) and
V_(HTF) thresholds to determine if charging is allowed. Once a temperature outside the V_(LTF) and V_(HTF) thresholds
is detected, the device immediately suspends the charge. The device 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. The allowed temperature range for 103AT-type thermistor is 0°C to 45°C. However, the user
may increase the range by adding two external resistors. See Figure 10.
bq24070
LTF
HTF
V_LTF
V_HTF
PACK+
I_TS
PACK−
TS
12
+
NTC
BATTERY
PACK
Figure 9. TS Pin Configuration
UDG−04085
bq24070
LTF
HTF
V_LTF
V_HTF
PACK+
+
I_TS
PACK−
TS
12
RT1 _TEMP
NTC
BATTERY
RT2
PACK
UDG−04086
Figure 10. TS Pin Thresholds
Battery Pre-Conditioning
During a charge cycle, if the battery voltage is below the V_(LOWV) threshold, the bq24070 applies a precharge
current, I_O(PRECHG), to the battery. This feature revives deeply discharged cells. The resistor connected between
the ISET1 and VSS, 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-mode and USB-mode charging.
I_O
(PRECHG)
+
V_(PRECHG)
R_SET
K_(SET)
(3)
The bq24070 activates a safety timer, t_(PRECHG), during the conditioning phase. If V_(LOWV) threshold is not
reached within the timer period, the bq24070 turns off the charger and enunciates FAULT on the STAT1 and
STAT2 pins. The timeout is extended if the charge current is reduced by DPPM or thermal regulation. See the
Timer Fault Recovery section for additional details.
Battery Charge Current
The bq24070 offers on-chip current regulation with programmable set point. The resistor connected between the
ISET1 and VSS, R_SET, determines the charge level. The charge level may be reduced to give the system priority
on input current (see DPPM). The V_(SET) and K_(SET) parameters are specified in the specifications table.
I_O
(OUT)
+
V_(SET) K_(SET)
R_SET
(4)
When powered from a USB port, the input current available (0.1 A/0.5 A) is typically less than the programmed
(ISET1) charging current, and therefore, the DPPM feature attempts to keep the output from being pulled down
by reducing the charging current.
The charge level, during AC mode operation only (Mode = High), can be changed by a factor of 2 by setting the
ISET2 pin high (full charge) or low (half charge). The voltage on the ISET1 pin, VSET1, is divided by 2 when in
the half constant current charge mode. Note that with Mode low, the ISET2 pin controls only the 0.1 A/0.5 A
USB current level.
See the section titled Power-Path Management for additional details.
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