BQ24721 Datasheet, PDF (32/48 Pages) Texas Instruments – ADVANCED MULTI-CHEMISTRY AND MULTI-CELL SYNCHRONOUS SWITCH-MODE CHARGER AND SYSTEM POWER SELECTOR

bq24721
SLUS683 – NOVEMBER 2005
ISYNC FET -
Charger Undercurrent
Comparator
+
ISYNC_LOWD
−
−
+ ^t_bo
40ns
500W
1V
+
−
SYNP
SYNN
ISYNSET
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CHARGE_ENZ
R_ISYNSET
NOTE: Patent Pending
Figure 58. SRUC Block – Charger Under Current (ISYNC Block – Cycle-by-cycle, prevents negative
inductor current)
TEMPERATURE QUALIFICATION (TS pin)
The bq24721 continuously monitors battery temperature by measuring the voltage between the TS pin and
AGND. A negative temperature coefficient thermistor (NTC) and an external voltage divider typically develop this
voltage. The bq24721 compares this voltage against its internal thresholds to determine if charging is allowed. To
initiate a charge cycle, the battery temperature must be within the V_(LTF) to V_(HTF) thresholds. If battery
temperature is outside of this range, the bq24721 suspends charge and waits until the battery temperature is
within the V_(LTF) to V_(HTF) range. During the charge cycle (both precharge and fast charge) the battery
temperature must be within the V_(LTF) to V_(TCO) thresholds. If battery temperature is outside of this range, the
bq24721 suspends charge and waits until the battery temperature is within the V_(LTF) to V_(HTF) range. The
bq24721 suspends charge by turning off the PWM charge FETs. Figure 59 summarizes this operation.
Vcc
Vcc
VLTF
VHTF
Vss
Charge Suspend
Temperature
range to initiate
charge
Charge Suspend
Charge Suspend
Temperature
range during a
charge cycle
Charge Suspend
V _LTF
V _TCO
Vss
Figure 59.
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