CRTOUCH datasheet(21/68 Pages) FREESCALE

21 / 68 page

Functional Description

CRTouch Data Sheet, Rev. 3

Freescale Semiconductor

Any of the capacitive electrodes may be enabled as a Low Power Electrode and can be configured for a scanning period and

sensitivity. To enable this electrode as a wakeup source from Shutdown, the CLPEN bit must be enabled in the Capacitive

System Configuration register. Enabling this bit inhibits normal functioning of all the electrodes, therefore it should only be

enabled prior to sending the device into Shutdown mode. Baseline tracking is not performed for the Low Power Electrode.

2.4

Internal voltage regulator

The voltage regulator module is a LDO linear voltage regulator to provide 3.3 V power from an input power supply varying

from 2.7 V to 5.5 V. It consists of one 3.3 V power channel. The internal voltage regulator can be used to be the main power

supply of the device. When the input power supply is below 3.6 V, the regulator goes to pass-through mode.

2.4.1

Internal voltage regulator features

•

Low drop-out linear voltage regulator with one power channel (3.3 V)

•

Low drop-out voltage— 300 mV.

•

Output current—120 mA.

•

Three different power modes— RUN, SLEEP, and SHUTDOWN.

•

Low quiescent current in RUN mode.

•

Typical value is around 120

A (one thousand times smaller than the maximum

•

load current).

•

Very low quiescent current in STANDBY mode.

•

Typical value is around 1

A.

•

Automatic current limiting if the load current is greater than 290 mA.

•

Automatic power-up once some voltage is applied to the regulator input.

•

Pass-through mode for regulator input voltages less than 3.6 V

•

Small output capacitor— 2.2

F

•

Stable with aluminum, tantalum, or ceramic capacitors.

2.4.2

Internal voltage regulator modes of operation

The regulator has these power modes:

•

RUN— The regulating loop of the RUN regulator and the SLEEP regulator are active, but the switch connecting the

SLEEP regulator output to the external pin is open.

•

SLEEP— The regulating loop of the RUN regulator is disabled and the standby regulator is active. The switch

connecting the SLEEP regulator output to the external pin is closed.

•

SHUTDOWN— The module is disabled.

This is the recommended connections to power CRTouch from internal voltage regulator:

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