BQ24747 Datasheet, PDF (21/36 Pages) Texas Instruments – SMBus-Controlled Level 2 Multi-Chemistry Battery Charger With Input Current Detect Comparator and Charge Enable Pin

bq24747
www.ti.com ............................................................................................................................................................................................. SLUS988 – OCTOBER 2009
INPUT CURRENT COMPARATOR TRIP DETECTION
To optimize system performance, the host monitors the adapter current. When the adapter current is above a
threshold set via ICREF, the ICOUT pin asserts low to act as an alarm signal to the host, indicating that input
power has exceeded the programmed limit, allowing the host to throttle back system power by reducing clock
frequency, lowering rail voltages, or disabling parts of the system. The ICOUT pin is an open-drain output, and
must have a pull-up resistor connected. The output is logic HI when the VICM output voltage [VICM = 20 ×
V(CSSP-CSSN)] is lower than the ICREF input voltage. The ICREF threshold is set by an external resistor
divider using VREF. A hysteresis can be programmed by connecting a positive feedback resistor from the ICOUT
pin to the ICREF pin.
ACIN
ACOK
Comparator
ENABLE VICM
Comparator
-
2.4V ⁺
ACOK
+
0.6V -
ENA_BIAS & ENA_VICM
t_dg
rising
100us
ACOK_DG
CHARGE_DISABLE
ACOK
CSSP
CSSN
VICM
Current Sense
1k
Amplifier
+
-
VICM
Error
20k
Amplifier
Disable
-
+
Program Hysteresis of
comparator
by putting a resistor in feedback
from ICOUT pin to ICREF pin.
VICM
Disable
Input Current
Comparator
+
-
VICM
ICOUT
Figure 33. ACOK, ICREF, and ICOUT Logic
CHARGE OVERCURRENT PROTECTION
The charger has a secondary overcurrent monitor that prevents the charge current from exceeding 145% of the
programmed charge current. The high-side gate drive turns off when the overcurrent is detected, and
automatically resumes when the current falls below the overcurrent threshold.
THERMAL SHUTDOWN PROTECTION
The QFN package has low thermal impedance, providing good thermal conduction from the silicon to the
ambient air, 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 155°C. The charger stays
off until the junction temperature falls below 135°C.
Copyright © 2009, Texas Instruments Incorporated
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