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STCC2540

Application information

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5.5

Charging detection

The STCC2540 device continuously monitors the current drawn by the portable device.

While programmed in CDP or DCP mode, the STCC2540 device sends a charging flag to

the system if the current through the USB power switch is above the charging threshold, set

at 20 mA typ.: open drain active low output CHARGING is asserted.

Note:

In CDP mode, the charging flag is asserted only if the CDP handshaking between the

portable device and the host is performed before the current is above the threshold.

If a device is charging (CDP mode) while the system is turned off and the battery supplied,

the risk is that the charging process stops before the end of charge due to the system

power-off. To avoid this, the flag CHARGING can be used by the host to prevent the

switching-off of the high power DC-DC converter when the host goes to S5 state, even if

battery supplied.

After the charging current drops below the threshold and the deglitch delay expires, the

CHARGING output is deasserted.

5.6

Power switch

Overcurrent conditions

When an overcurrent condition is detected, the device maintains a constant output current

and reduces the voltage accordingly. There are two overload conditions:

•

The first occurs when a short-circuit or a partial short-circuit is already present when

the device is being powered-up or enabled. The output voltage is held near zero

potential with respect to ground and the STCC2540 device ramps the output current to

•

The second condition is when a short-circuit, a partial short-circuit, or a transient

overload occurs while the device is already enabled and powered-on. The STCC2540

amplifier is overdriven during this time and momentarily disables the internal current

thermal cycle starts.

Thermal protection

The STCC2540 device has an internal thermal sensing circuit which monitors the operating

temperature of the circuit. It disables the power switch operation if the die temperature

has cooled down by 20 °C.

Undervoltage lockout

The UVLO circuit disables the circuit until the input voltage reaches the UVLO turn-on

threshold. Built-in hysteresis prevents unwanted on/off cycling due to input voltage drop

during turn-on.