BQ24171 Datasheet, PDF (23/35 Pages) Texas Instruments – JEITA Compliant Stand-Alone Switch-Mode Li-Ion and Li-Polymer Battery Charger with Integrated MOSFETs and Power Path Selector

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VREF
bq24171
TS
bq24171
SLUSAF2A – FEBRUARY 2011 – REVISED MAY 2011
RT1
RT2
RTH
103AT
Figure 21. TS Resistor Network
For example, 103AT NTC thermistors are used to monitor the battery pack temperature. Select T1 = 0ºC for
COLD and T5 = 60ºC for HOT, then we get R_T2 = 6.8kΩ and R_T1 = 2.2kΩ as in the design tool. A small RC filter
is suggested to use for system-level ESD protection.
MOSFET SHORT CIRCUIT AND INDUCTOR SHORT CIRCUIT PROTECTION
The IC has a short circuit protection feature. Its cycle-by-cycle current monitoring feature is achieved through
monitoring the voltage drop across Rdson of the MOSFETs. The charger will be latched off, but the ACFET keep
on to power the system. The only way to reset the charger from latch-off status is remove adapter then plug
adapter in again. Meanwhile, STAT is blinking to report the fault condition.
THERMAL REGULATION AND SHUTDOWN PROTECTION
The QFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junctions temperatures low. The internal thermal regulation loop will fold back the charge
current to keep the junction temperature from exceeding 120°C. As added level of protection, the charger
converter turns off and self-protects whenever the junction temperature exceeds the TSHUT threshold of 150°C.
The charger stays off until the junction temperature falls below 130°C.
TIMER FAULT RECOVERY
The IC provides a recovery method to deal with timer fault conditions. The following summarizes this method:
Condition 1: The battery voltage is above the recharge threshold and a timeout fault occurs.
Recovery Method: The timer fault will clear when the battery voltage falls below the recharge threshold, and
battery detection will begin. A POR or taking ISET below 40mV will also clear the fault.
Condition 2: The battery voltage is below the recharge threshold and a timeout fault occurs.
Recovery Method: Under this scenario, the IC applies the fault current to the battery. This small current is used
to detect a battery removal condition and remains on as long as the battery voltage stays below the recharge
threshold. If the battery voltage goes above the recharge threshold, the IC disabled the fault current and
executes the recovery method described in Condition 1. A POR or taking ISET below 40mV will also clear the
fault.
INDUCTOR, CAPACITOR, AND SENSE RESISTOR SELECTION GUIDELINES
The IC provides internal loop compensation. With this scheme, the best stability occurs when the LC resonant
frequency, f_o, is approximately 15kHz – 25kHz for the IC.
1
f_o = _{2p LC}
(11)
Copyright © 2011, Texas Instruments Incorporated
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