BQ24742 Datasheet, PDF (21/35 Pages) Texas Instruments – Li-Ion or Li-Polymer Battery Charger with Low Iq and Accurate Trickle Charge

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bq24741, bq24742
SLUS875B – MARCH 2009 – REVISED OCTOBER 2009
Short-Circuit Protection
The charger has a secondary short-circuit protection. It monitors the voltage-drop (detect ACP-SW for protecting
high-side MOSFET and detect SW-AGND for protecting low-side MOSFET) to prevents the short-circuit current
from exceeding a certain value to damage the charger. It will be monitored after typical blanking time of 100ns.
The MOSFET gate driver signal turns off when the short-circuit current is detected in every switching cycle. The
charger will shut-down and latch off after this occurs 7 times. POR or toggling CE pin can resume normal charge
function.
Thermal 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. As 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, then the charger will soft-start again if all other enable charge
conditions are valid.
Input Low Power Detection
In order to optimize the system performance, the HOST keeps an eye on the adapter current. Once the adapter
current is above a threshold set via LPREF, the LPMOD pin sends a signal to the HOST. The signal alarms the
host that input power has exceeded the programmed limit. The LPMOD pin is an open-drain output. Connect a
pull-up resistor to LPMOD. The LPMOD output is logic LOW when the 20X current sense voltage (20 x
V_(ACP-ACN)) is higher than the LPREF input voltage. The LPREF threshold may be set by an external resistor
divider using VREF, or may be programmed from a resistor divider off of ACSET to maintain an LPREF voltage
proportional to the adapter current. The LPMOD comparator has an internal 6% hysteresis built in.
ACDET
ACP
ACN
+
2.4 V -
AC_VGOOD
ACVDET
Comparator
1 kΩ
20 kΩ
Adaptor
Current Sense
Amplifier
+
-
ACIDET
Comparator
250 mV
(1.25 A) ^-
AC_IGOOD
+
IADAPT Error
Amplifier
Disable
EXTPWR
-
+
IADAPT
OUTPUT
BUFFER
20 xV(ACP-ACN)
IADAPT
Disable
IADAPT
LPREF
LPMOD
Comparator
+
LOPWR_DET
- _{Hysteresis = 6%}
LPMOD
Figure 30. EXTPWR , LPREF, and LPMOD Logic
Copyright © 2009, Texas Instruments Incorporated
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