BQ24650 Datasheet, PDF (16/33 Pages) Texas Instruments – Synchronous Switch-Mode Battery Charge Controller for Solar Power With Maximum Power Point Tracking

bq24650
SLUSA75 – JULY 2010
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BATTERY OVER-VOLTAGE PROTECTION
The converter does not allow the high-side FET to turn on until the BAT voltage goes below 102% of the
regulation voltage. This allows one-cycle response to an over-voltage condition – such as occurs when the load
is removed or the battery is disconnected. A current sink from SRP to GND is on to discharge the stored energy
on the output capacitors.
CYCLE-BY-CYCLE CHARGE OVER-CURRENT PROTECTION
The charger has a secondary cycle-to-cycle over-current protection. It monitors the charge current and prevents
the current from exceeding 200% of the programmed charge current. The high-side gate drive turns off when
over-current is detected and automatically resumes when the current falls below the over-current threshold.
THERMAL SHUTDOWN PROTECTION
The QFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junction temperatures low. As an added level of protection, the charger converter turns off and
self-protects whenever the junction temperature exceeds the TSHUT threshold of 145°C. The charger stays off
until the junction temperature falls below 130°C.
TEMPERATURE QUALIFICATION
The controller continuously monitors battery temperature by measuring the voltage between the TS pin and
GND. A negative temperature coefficient thermistor (NTC) and an external voltage divider typically develop this
voltage. The controller 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 controller suspends charge and waits until the battery temperature is
within the V_LTF to V_HTF range. During the charge cycle the battery temperature must be within the V_LTF to V_TCO
thresholds. If battery temperature is outside of this range, the controller suspends charge and waits until the
battery temperature is within the V_LTF to V_HTF range. The controller suspends charge by turning off the PWM
charge FETs. Figure 17 summarizes the operation.
VREF
VREF
CHARGE SUSPENDED
VLTF
VLTFH
TEMPERATURE RANGE
TO INITIATE CHARGE
CHARGE SUSPENDED
VLTF
VLTFH
TEMPERATURE RANGE
DURING A CHARGE
CYCLE
VHTF
CHARGE SUSPENDED
VTCO
CHARGE SUSPENDED
GND
GND
Figure 17. TS Pin, Thermistor Sense Thresholds
Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 1, the values of RT1 and RT2 can be
determined by using Equation 7 and Equation 8:
RT2 =
V_VREF
´ RTH_COLD ´ RTH_HOT
´
æ
ç
1
-
1
ö
÷
è ^VLTF ^VTCO ø
RTH_HOT
´
æ
ç
è
V_VREF
V_TCO
ö
-1_÷ - RTH_COLD
ø
´
æ
ç
V_VREF
- 1^ö÷
è ^VLTF ø
(7)
16
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