AS3715 datasheet(47/159 Pages) AMSOSRAM

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[v1-03] 2015-Aug-10

AS3715 − Detailed Description – Power Management Functions

Battery Presence Indication

After EOC state is reached a timer for NOBAT detection is

started. If there is no battery present, the VBAT voltage will drop

to VRESUME. Depending on the load on VBAT and the capacitor

on VBAT this might take some milliseconds to 1 second. If the

RESUME mode is enabled (bit auto_resume=1), the charger will

restart charging (ConstantCurrent charging) after 100msec

delay.

The 100msec dead time is necessary to get a battery oscillation

frequency below 10Hz, if there is no battery present.

If the NOBAT detection timer is below 2 seconds after reaching

EOC state, and this happens 2 times in serial, the Nobat bit in

ChargerStatus register is set. If a battery is inserted the bit will

be reset after the timer exceeds the 2 seconds.

Charger Overvoltage Protection

This blocks checks if the charger voltage VUSB is above

VCHOVH. If the VUSB voltage is above VCHOVH , the pin XOFF

is pulled to GND immediately, to protect the pin VCHG_IN, and

the charger is set into OFF state. If the VUSB voltage is below

VCHOVH the XOFF pin is charged up to VXOFF_REG with an

integrated charge pump. If the pin exceeds VXOFF_MIN the bit

is set and the charger is started.

NTC Supervision

This charger block also features a supply for an external NTC

resistor to measure the battery temperature while charging. If

the temperature is too high the charger will stop operation. If

needed an interrupt can be generated based on this event.

When the battery temperature drops the voltage on BATTEMP

pin will rise above VBATTEMP_OFF and the charger will start

charging again. This is forming a temperature hysteresis of

about 3 to 5°C to avoid an oscillation of the charger.

The type of NTC (ntc_10k:10k or 100k) can be selected via

NTC can be switched OFF (ntc_on= 0).

The supply for the NTC will be on when the ntc_on bit is set, no

matter if a charger is detected or not.

NTC ß-Correction

To keep the voltage drop over the whole temperature range

inside of the ADC input range a parallel resistor to the NTC is

needed.

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