x

ACSET

ADAPTER

REF

AC

V

0.10

I

=

V

R

(3)

ADAPTER DETECT AND POWER UP

ENABLE AND DISABLE CHARGING

AUTOMATIC INTERNAL SOFT-START CHARGER CURRENT

bq24705

The input voltage range of ACSET is between 0 and VREF, up to 3.3 V.

can also be used. A larger the sense resistor, gives a larger sense voltage, and a higher regulation accuracy;

but, at the expense of higher conduction loss.

An external resistor voltage divider attenuates the adapter voltage before it goes to ACDET. 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 ACDET divider should be placed before the ACFET in order to sense

the true adapter input voltage whether the ACFET is on or off.

If PVCC is below 4 V, the device is disabled.

If ACDET is below 0.6 V but PVCC is above 4 V, part of the bias is enabled, including a crude bandgap

reference. IADAPT is disabled and pulled down to GND. The total quiescent current is less than 10

µA.

Once ACDET rises above 0.6 V and PVCC is above 4 V, all the bias circuits are enabled. VREF goes to 3.3 V

and REGN output goes to 6 V. IADAPT becomes valid to proportionally reflect the adapter current.

When ACDET rises and passes 2.4 V, a valid AC adapter is present. Then the following occurs:

• ACGOOD becomes high through external pull-up resistor to the host digital voltage rail;

• Charger turns on if all the conditions are satisfied (see Enable and Disable Charging).

The following conditions must be valid before a charge is enabled:

• CHGEN is LOW;

• PVCC > UVLO;

• Adapter is detected;

• Adapter is higher than PVCC-BAT threshold;

• Adapter is not over voltage;

• 700 ms delay is complete after adapter detected;

• REGNGOOD and VREFGOOD are valid;

• Thermal Shut (TSHUT) is not valid;

One of the following conditions will stop on-going charging:

• CHGEN is HIGH;

• PVCC < UVLO;

• Adapter is removed;

• Adapter is less 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).

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 1.7ms, for a typical rise time of 13.6ms. No external components are needed for this function.

16

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