CAP1028 datasheet(54/71 Pages) SMSC

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8 Channel Capacitive Touch Sensor with 2 LED Drivers

Datasheet

Revision 1.1 (08-05-09)

SMSC CAP1028

DATASHEET

Bit 1 - CS2_LED2 - Links the LED2 output to a detected touch on the CS2 sensor. When a touch is

detected, the LED is actuated and will behave as determined by the LED Behavior controls.

‘0’ (default) - The LED 2 output is not associated with a the CS2 input. If a touch is detected on

the CS2 input, then the LED will not automatically be actuated. The LED is enabled and controlled

via the LED Output Configuration register (see Section 5.24) and the LED Behavior registers (see

Section 5.27).

‘1’ - The LED 2 output is associated with the CS2 input. If a touch is detected on the CS2 input

then the LED will be actuated and behave as defined in Table 5.43.

Bit 0 - CS1_LED1 - Links the LED1 output to a detected touch on the CS1 sensor. When a touch is

detected, the LED is actuated and will behave as determined by the LED Behavior controls.

5.25

LED Polarity Register

The LED Polarity registers control the logical polarity of the LED outputs.

APPLICATION NOTE: The polarity controls determine the final LED pin drive. A touch on a linked Capacitive Touch

Sensor is treated in the same way as the LED Output Control bit being set to a logic ‘1’.

APPLICATION NOTE: For LED operation, the duty cycle settings determine the % of time that the LED pin will be

driven to a logic ‘1’ state in a non-inverted system or to a logic ‘0’ state in an inverted system.

The duty cycle settings operate independently of the polarity controls. Therefore, the Max

Duty Cycle settings define the maximum % of time that the LED pin will be driven high in a

non-inverted system while the Min Duty Cycle settings determine the minimum % of time that

the LED pin will be driven high in a non-inverted system.

The LED drive assumes that the LEDs are configured such that if the LED pin is driven to

a logic ‘0’ then the LED will be on and that the CAP1028 LED pin is sinking the LED current.

Conversely, if the LED pin is driven to a logic ‘1’ then the LED will be off and there is no

current flow.

Finally, the breathe operations will always ramp the duty cycle from the minimum duty cycle

to the maximum duty cycle and then back down to the minimum duty cycle.

The LED Polarity controls lead to two conditions that have the apparent effect of changing

the duty cycle settings. If an LED output is non-inverted then the Maximum Duty Cycle

settings will define the maximum % of time that the LED is off. Conversely the Minimum

Duty Cycle settings will define the minimum % of time that the LED is off. As well, when

there is no touch detected or the LED Output Control register bit is at a logic ‘0’ then the

LED output will be driven at the minimum duty cycle setting. The relative brightness will then

ramp from maximum to minimum and back.

If an LED output is inverted, then the Maximum Duty Cycle settings will define the maximum

% of time that the LED is on and the Minimum Duty Cycle settings will determine the

minimum % of time that the LED is on. As well, when there is no touch detected, or the LED

Output Control register bit is at a logic ‘0’, then the LED output will be driven at the minimum

duty cycle setting. The relative brightness will then ramp from minimum to maximum and

back.

Bit 1 - LED2_POL - Determines the polarity of the LED2 output.

Table 5.39 LED Polarity Register

ADDR

R/W

DEFAULT

73h

R/W

LED Polarity

LED2_

POL

LED1_

POL

00h

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