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BQ24105-Q1 Datasheet, PDF (16/35 Pages) Texas Instruments – SYNCHRONOUS SWITCHMODE, LI-ION AND LI-POLYMER CHARGE-MANAGEMENT IC WITH INTEGRATED POWER FETs ( bqSWITCHER™)
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bq24105-Q1
SLUS953 – AUGUST 2009................................................................................................................................................................................................. www.ti.com
Timer Fault Recovery
As shown in Figure 6, bqSWITCHER provides a recovery method to deal with timer fault conditions. The
following summarizes this method.
Condition 1 VI(BAT) above recharge threshold (VOREG - VRCH) and timeout fault occurs.
Recovery method: bqSWITCHER waits for the battery voltage to fall below the recharge threshold. This could
happen as a result of a load on the battery, self-discharge or battery removal. Once the battery falls below the
recharge threshold, the bqSWITCHER clears the fault and enters the battery absent detection routine. A POR or
CE toggle also clears the fault.
Condition 2 Charge voltage below recharge threshold (VOREG – VRCH) and timeout fault occurs
Recovery method: Under this scenario, the bqSWITCHER applies the IDETECT current. 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, then the bqSWITCHER disables the IDETECT
current and executes the recovery method described in Condition 1. Once the battery falls below the recharge
threshold, the bqSWITCHER clears the fault and enters the battery absent detection routine. A POR or CE toggle
also clears the fault.
Output Overvoltage Protection
The bqSWITCHER provides a built-in overvoltage protection to protect the device and other components against
damages if the battery voltage gets too high, as when the battery is suddenly removed. When an overvoltage
condition is detected, this feature turns off the PWM and STATx pins. The fault is cleared once VIBAT drops to the
recharge threshold (VOREG – VRCH).
Inductor, Capacitor, and Sense Resistor Selection Guidelines
The bqSWITCHER provides internal loop compensation. With this scheme, best stability occurs when LC
resonant frequency, fo is approximately 16 kHz (8 kHz to 32 kHz). Equation 9 can be used to calculate the value
of the output inductor and capacitor. Table 3 provides a summary of typical component values for various charge
rates.
Ǹ f0 + 2p
1
LOUT
COUT
(9)
CHARGE CURRENT
Output inductor, LOUT
Output capacitor, COUT
Sense resistor, R(SNS)
Table 3. Output Components Summary
0.5 A
22 µH
4.7 µF
0.2 Ω
1A
10 µH
10 µF
0.1 Ω
2A
4.7 µH
22 µF (or 2 × 10 µF) ceramic
0.05 Ω
16
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