BQ24765_15 Datasheet, PDF (16/43 Pages) Texas Instruments – SMBus-Controlled Multi-Chemistry Battery Charger With Integrated Power MOSFETs

bq24765
SLUS999A – NOVEMBER 2009 – REVISED NOVEMBER 2015
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8.3 Feature Description
8.3.1 Adapter Detect and Power Up
An external resistor voltage divider attenuates the adapter voltage before it goes to ACIN. The adapter detect
threshold should typically be programmed to a value greater than the maximum battery voltage and lower than
the minimum allowed adapter voltage. The ACIN divider should be placed before the input power path selector in
order to sense the true adapter input voltage.
If DCINA is below 4 V, the device is disabled.
If ACIN is below 0.6 V but DCINA is above 4.5 V, ACOK and VICM are disabled and pulled down to GND. The
total quiescent current is less than 10 µA.
Once ACIN rises above 0.6 V and DCINA is above 4.5 V, VREF goes to 3.3 V and all the bias circuits are
enabled, ACOK low indicated ACIN is still below 2.4 V and the valid adaptor is not available. VICM becomes
valid to proportionally reflect the adapter current.
When ACIN keeps rising and passes 2.4 V, a valid AC adapter is present. 100 µs later, the following occurs:
• ACOK becomes high through external pull-up resistor to the VREF rail
• Charger turns on if all the conditions are satisfied (refer to )
8.3.2 Enable and Disable Charging
The following conditions must be valid before charging is enabled:
• Not in UVLO (DCINA > 4.5 V, and VDDSMB > 2.5 V)
• Adapter is detected (ACIN > 2.4 V)
• Adapter – Battery voltage is higher than V(DCINA-VFB) Comparator threshold
• SMBus ChargeVoltage(),ChargeCurrent(), and InputCurrent() DAC registers are inside the valid range
• CE is HIGH
• 2 ms delay is complete after adapter detected and CE goes high
• VDDP and VREF are valid
• Not in Thermal Shutdown (TSHUT)
One of the following conditions will stop the on-going charging:
• SMBus ChargeVoltage(),ChargeCurrent(), or InputCurrent() DAC registers are outside the valid range
• CE is LOW
• Adapter is removed; (DCINA < 4 V)
• VDDSMB supply is removed. (VDDSMB < 2.35 V)
• Adapter – Battery voltage is less than V(DCINA-VFB) Comparator threshold
• Battery is over voltage
• In Thermal Shutdown: TSHUT IC temperature threshold is above 155°C
8.3.3 Automatic Internal Soft-Start Charger Current
The charger automatically soft-starts the output 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 1.6 ms, for a typical rise time of 10ms. No external components are needed for this function.
The regulation limits can be changed in the middle of charging without soft start.
8.3.4 Switching Frequency
The bq24765 switching frequency is 700 kHz. A high switching frequency allows a smaller inductor to give the
same ripple current, or can be used to reduce the ripple current for the same inductor. A smaller inductor value
may allow using a smaller inductor physical size, for a smaller board footprint area.
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