Multiple Channel Capacitive Touch Sensor and LED Driver
Datasheet
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 CAP1014 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 off 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.
Table 5.56, "LED Polarity Behavior" shows the interaction between the polarity controls,
output controls and relative brightness.
Table 5.56 LED Polarity Behavior
LED
OUTPUT
CONTROL
REGISTER
LED
BEHAVIORS
LED
APPEARANCE
POLARITY
MAX DUTY
MIN DUTY
BRIGHTNESS
maximum % of
time that the LED
is on (logic 0)
minimum % of
time that the LED
is on (logic 0)
maximum brightness at
minimum duty cycle
on at minimum
duty cycle
0
1
0
1
inverted
off
on
off
on
maximum % of
time that the LED
is on (logic 0)
minimum % of
time that the LED
is on (logic 0)
maximum brightness at
max duty cycle. Brightness
ramps from min to max
according to
LED behavior
inverted
maximum % of
time that the LED
is off (logic 1)
minimum % of
time that the LED
is off (logic 1)
on at 100 - min
duty cycle
non-
inverted
maximum brightness at 100
- min duty cycle
(Note 5.4)
maximum % of
time that the LED
is off (logic 1)
minimum % of
time that the LED
is off (logic 1)
maximum brightness at 100
- min duty cycle. Brightness
ramps from max to min
non-
inverted
according to
LED behavior
Note 5.4 For example when polarity is non-inverted, if min duty cycle is 0, then the LED would be
at logic 1 (off) 0% of the time. It will be at logic 0 (on), 100% of the time (100 - min duty
cycle).
5.38.1
LED Polarity 1
Bit 7 - LED8_POL - Determines the polarity of the LED8 output.
‘0’ - The LED8 output is inverted. A setting of ‘1’ in the LED 8 Output 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 1, Pulse 2, and Breathe operations will indicate the amount of time that the
LED is driven to a logic ‘0’ state (corresponding to “active”).
SMSC CAP1014
Revision 1.65 (08-11-09)
DATA6S5HEET
SMSC [ SMSC CORPORATION ]
