BQ24742 Datasheet, PDF (20/35 Pages) Texas Instruments – Li-Ion or Li-Polymer Battery Charger with Low Iq and Accurate Trickle Charge

bq24741, bq24742
SLUS875B – MARCH 2009 – REVISED OCTOBER 2009
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• Thermal Shut (TSHUT) is not active
• The PWM frequency is programmed inside the allowable range
There’s a 2ms charge enable delay from when adapter is detected to when the charger is allowed to turn on.
One of the following conditions will stop on-going charging:
• CE is LOW
• Adapter is removed
• Adapter Voltage is lower than PVCC-BAT threshold
• Adapter is over voltage
• Adapter is over current
• TSHUT IC temperature threshold is reached (155 °C on rising-edge with 20 °C hysteresis).
Automatic Internal Soft-Start Charger Current
The charger automatically soft-starts the charger regulation current every time the charger is enabled to ensure
there is no overshoot or stress on the output capacitors or the power converter. The soft-start consists of
stepping-up the charge regulation current into 8 evenly divided steps up to the programmed charge current. Each
step lasts around 1ms, for a typical rise time of 8ms. No external components are needed for this function.
High Accuracy IADAPT Using Current Sense Amplifier (CSA)
An industry standard, high accuracy current sense amplifier (CSA) is used to monitor the input current by the
host or some discrete logic through the analog voltage output of the IADAPT pin. The CSA amplifies the input
sensed voltage of ACP–ACN by 20x through the IADAPT pin. The IADAPT output is a voltage source 20 times
the input differential voltage. Once PVCC is above 8 V and ACDET is above 0.6 V, IADAPT no longer stays at
ground, but becomes active. If the user wants to lower the voltage, they could use a resistor divider from IOUT to
AGND, and still achieve accuracy over temperature as the resistors can be matched their thermal coefficients.
Input Overvoltage Protection (ACOV)
ACOV provides protection to prevent system damage due to high input voltage. Once the adapter voltage is 30%
above adapter detect voltage, (ACDET pin voltage is 30% above 2.4 V (2.4 V X 130% = 3.1 V), charge is
disabled. ACOV does not latch, and normal operation resumes when ACDET < 3.1 V.
Input Undervoltage Lock Out (UVLO)
The system must have a typical 8 V PVCC voltage to allow proper operation. This PVCC voltage could come
from an input adapter . When the PVCC voltage is below 8 V the bias circuits REGN and VREF stay inactive,
even with ACDET above 0.6 V.
Battery Overvoltage Protection
The converter will 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.
Charge Overcurrent Protection
The charger has a secondary over-current protection. It monitors the charge current, and prevents the current
from exceeding 6.25A peak value with a 20 mΩ sensing resistor. The high-side gate drive turns off when the
over-current is detected, and automatically resumes at the next switching cycle that occurs after the current falls
below the OCP threshold. When the BAT-GND short is detected, the charger will be automatically shut down
immediately and then restarts again 100 μs later.
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