8 Channel Capacitive Touch Sensor with 8 LED Drivers
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.
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
Table 5.39 LED Polarity Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
LED8_
POL
LED7_
POL
LED6_
POL
LED5_
POL
LED4_
POL
LED3_
POL
LED2_
POL
LED1_
POL
73h
R/W
LED Polarity
00h
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 CAP1088 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 7 - LED8_POL - Determines the polarity of the LED8 output.
‘0’ (default) - The LED8 output is inverted. A setting of ‘1’ in the LED Output Control register will
cause the output to be driven to a logic ‘0’ as determined by the LED behavior. Similarly, the duty
cycles corresponding to Pulse and Breathe operations will indicate the amount of time that the LED
is driven to a logic ‘0’ state (corresponding to “active”).
‘1’ - The LED8 output is non-inverted. A setting of ‘1’ in the LED Output Control register will cause
the output to be driven to a logic ‘1’ or left in the high-z state as determined by its output type and
LED behavior. Similarly, the duty cycles corresponding to Pulse and Breathe operations will indicate
to the amount of time that the LED is driven to a logic ‘1’ state (corresponding to “inactive”).
SMSC CAP1088
Revision 1.1 (08-05-09)
DATA5S5HEET
SMSC [ SMSC CORPORATION ]
