8 Channel Capacitive Touch Sensor with 2 LED Drivers
Datasheet
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 1 - LED2_POL - Determines the polarity of the LED2 output.
‘0’ (default) - The LED2 output is inverted. For example, a setting of ‘1’ in the LED Output Control
register will cause the LED pin output to be driven to a logic ‘0’.
‘1’ - The LED2 output is non-inverted. For example, a setting of ‘1’ in the LED Output Control
register will cause the LED pin output to be driven to a logic ‘1’ or left in the high-z state as
determined by its output type.
Bit 0 - LED1_POL - Determines the polarity of the LED1 output.
5.28
LED Output Control Register
Table 5.47 LED Output Control Register
ADDR
R/W
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
LED Output
Control
LED2_
DR
LED1_
DR
74h
-
-
-
-
-
-
00h
The LED Output Control Register controls the output state of the LED pins that are not linked to sensor
inputs.
Note: If an LED is linked to a sensor input in the Sensor Input LED Linking Register (Section 5.26,
"Sensor Input LED Linking Register"), the corresponding bit in the LED Output Control Register
is ignored (i.e. a linked LED cannot be host controlled).
The LED Polarity Control Register will determine the non actuated state of the LED pins. The actuated
LED behavior is determined by the LED behavior controls (see Section 5.31, "LED Behavior Register").
Table 5.48 shows the interaction between the polarity controls, output controls, and relative brightness.
Bit 1 - LED2_DR - Determines whether LED2 output is driven high or low.
‘0’ (default) - The LED2 output is driven at the minimum duty cycle or not actuated.
Revision 1.32 (01-05-12)
SMSC CAP1128
DATA6S6HEET
SMSC [ SMSC CORPORATION ]
