Datasheet

CHARGESUSPENDED CHARGESUSPENDED
TEMPERATURERANGE
TOINITIATECHARGE
TEMPERATURERANGE
DURING A CHARGE
CYCLE
VLTF
VHTF
GND
VTCO
VLTF
GND
VLTFH
VLTFH
VREF
VREF
CHARGESUSPENDED CHARGESUSPENDED
VREF COLD HOT
LTF TCO
VREF VREF
HOT COLD
TCO LTF
1 1
V RTH RTH
V V
RT2 =
V V
RTH 1 RTH 1
V V
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SLUSA75 –JULY 2010 www.ti.com
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.
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:
(7)
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