8 Channel Capacitive Touch Sensor with 2 LED Drivers
Datasheet
4.1
Power States
The CAP1128 has three operating states depending on the status of the STBY and DSLEEP bits.
When the device transitions between power states, previously detected touches (for inactive channels)
are cleared and the status bits reset.
1. Fully Active - The device is fully active. It is monitoring all active capacitive sensor inputs and
driving all LED channels as defined.
2. Standby - The device is in a lower power state. It will measure a programmable number of channels
using the Standby Configuration controls (see Section 5.20 through Section 5.22). Interrupts will still
be generated based on the active channels. The device will still respond to communications
normally and can be returned to the Fully Active state of operation by clearing the STBY bit.
3. Deep Sleep - The device is in its lowest power state. It is not monitoring any capacitive sensor
inputs and not driving any LEDs. All LEDs will be driven to their programmed non-actuated state
and no PWM operations will be done. While in Deep Sleep, the device can be awakened by SMBus
or SPI communications targeting the device. This will not cause the DSLEEP to be cleared so the
device will return to Deep Sleep once all communications have stopped.
If the device is not communicating via the 4-wire SPI bus, then during this state of operation, if the
WAKE/SPI_MOSI pin is driven high by an external source, the device will clear the DSLEEP bit
and return to Fully Active.
APPLICATION NOTE: In the Deep Sleep state, the LED output will be either high or low and will not be PWM’d at
the min or max duty cycle.
APPLICATION NOTE: If the CAP1128 is configured to communicate using the BC-Link protocol, the device does
not support Deep Sleep.
4.2
4.3
RESET Pin
The RESET pin is an active high reset that is driven from an external source. While it is asserted high,
all the internal blocks will be held in reset including the communications protocol used. No capacitive
touch sensor inputs will be sampled and the LEDs will not be driven. All configuration settings will be
reset to default states and all readings will be cleared.
The device will be held in Deep Sleep that can only be removed by driving the RESET pin low. This
will cause the RESET status bit to be set to a logic ‘1’ and generate an interrupt.
WAKE/SPI_MOSI Pin Operation
The WAKE / SPI_MOSI pin is a multi-function pin depending on device operation. When the device is
configured to communicate using the 4-wire SPI bus, this pin is an input.
However, when the CAP1128 is placed in Standby and is not communicating using the 4-wire SPI
protocol, the WAKE pin is an active high output. In this condition, the device will assert the
WAKE/SPI_MOSI pin when a touch is detected on one of its sampled sensor inputs. The pin will
remain asserted until the INT bit has been cleared and then it will be de-asserted.
When the CAP1128 is placed in Deep Sleep and it is not communicating using the 4-wire SPI protocol,
the WAKE/SPI_MOSI pin is monitored by the device as an input. If the WAKE/SPI_MOSI pin is driven
high by an external source, the CAP1128 will clear the DSLEEP bit causing the device to return to
Fully Active.
When the device is placed in Deep Sleep, this pin is a High-Z input and must have a pull-down resistor
to GND for proper operation.
Revision 1.32 (01-05-12)
SMSC CAP1128
DATA3S2HEET
SMSC [ SMSC CORPORATION ]
