Datasheet

8 Channel Capacitive Touch Sensor with 8 LED Drivers
Datasheet
SMSC CAP1188 67 Revision 1.32 (01-05-12)
DATASHEET
Bit 2 - CS3_LED3 - Links the LED3 output to a detected touch on the CS3 sensor input. When a touch
is detected, the LED is actuated and will behave as determined by the LED Behavior controls.
Bit 1 - CS2_LED2 - Links the LED2 output to a detected touch on the CS2 sensor input. When a touch
is detected, the LED is actuated and will behave as determined by the LED Behavior controls.
Bit 0 - CS1_LED1 - Links the LED1 output to a detected touch on the CS1 sensor input. When a touch
is detected, the LED is actuated and will behave as determined by the LED Behavior controls.
5.27 LED Polarity Register
The LED Polarity register controls the logical polarity of the LED outputs. When these bits are set or
cleared, the corresponding LED Mirror controls are also set or cleared (unless the BLK_POL_MIR bit
is set - see Section 5.6, "Configuration Registers"). Table 5.48, "LED Polarity Behavior" shows the
interaction between the polarity controls, output controls, and relative brightness.
APPLICATION NOTE: The polarity controls determine the final LED pin drive. A touch on a linked capacitive touch
sensor input is treated in the same way as the LED Output Control bit being set to a logic ‘1’.
APPLICATION NOTE: 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 CAP1188 LED pin is sinking the LED current.
Conversely, if the LED pin is driven to a logic ‘1’, the LED will be off and there is no current
flow. See Figure 4.1, "System Diagram for CAP1188".
APPLICATION NOTE: This application note applies when the LED polarity is inverted (LEDx_POL = ‘0’). For LED
operation, the duty cycle settings determine the % of time that the LED pin will be driven to
a logic ‘0’ state in. The Max Duty Cycle settings define the maximum % of time that the LED
pin will be driven low (i.e. maximum % of time that the LED is on) while the Min Duty Cycle
settings determine the minimum % of time that the LED pin will be driven low (i.e. minimum
% of time that the LED is on). When there is no touch detected or the LED Output Control
register bit is at a logic ‘0’, the LED output will be driven at the minimum duty cycle setting.
Breathe operations will ramp the duty cycle from the minimum duty cycle to the maximum
duty cycle.
APPLICATION NOTE: This application note applies when the LED polarity is non-inverted (LEDx_POL = ‘1’). For
LED operation, the duty cycle settings determine the % of time that the LED pin will be driven
to a logic ‘1’ state. The Max Duty Cycle settings define the maximum % of time that the LED
pin will be driven high (i.e. maximum % of time that the LED is off) while the Min Duty Cycle
settings determine the minimum % of time that the LED pin will be driven high (i.e. minimum
% of time that the LED is off). When there is no touch detected or the LED Output Control
register bit is at a logic ‘0’, the LED output will be driven at 100 minus the minimum duty
cycle setting. Breathe operations will ramp the duty cycle from 100 minus the minimum duty
cycle to 100 minus the maximum duty cycle.
APPLICATION NOTE: The LED Mirror controls (see Section 5.30, "LED Mirror Control Register") work with the
polarity controls with respect to LED brightness but will not have a direct effect on the output
pin drive.
Bit 7 - LED8_POL - Determines the polarity of the LED8 output.
Table 5.46 LED Polarity Register
ADDR R/W REGISTER B7 B6 B5 B4 B3 B2 B1 B0 DEFAULT
73h R/W LED Polarity
LED8_
POL
LED7_
POL
LED6_
POL
LED5_
POL
LED4_
POL
LED3_
POL
LED2_
POL
LED1_
POL
00h