AD7147A Analog Devices, AD7147A Datasheet - Page 27

• Manufacturer Part Number: AD7147A
• Manufacturer: Analog Devices

Specifications of AD7147A

• Resolution (bits): 16bit
• # Chan: 13
• Sample Rate: 111SPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: Capacitive
• Ain Range: ± 8 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

INTERRUPT OUTPUT
The AD7147A has an interrupt output that triggers an interrupt
service routine on the host processor. The INT signal is on Pin A1
and is an open-drain output. There are three types of interrupt
events on the AD7147A: a CDC conversion-complete interrupt,
a sensor-touch interrupt, and a GPIO interrupt. Each interrupt
has enable and status registers. The conversion-complete and
sensor-touch (sensor-activation) interrupts can be enabled on
a per-conversion-stage basis. The status registers indicate what
type of interrupt triggered the INT pin. Status registers are cleared,
and the INT signal is reset high during a read operation. The
signal returns high as soon as the read address has been set up.
CDC CONVERSION-COMPLETE INTERRUPT
The AD7147A interrupt signal asserts low to indicate the comple-
tion of a conversion stage and that new conversion result data is
available in the registers.
The interrupt can be independently enabled for each conversion
stage. Each conversion-stage-complete interrupt can be enabled via
the STAGE_COMPLETE_INT_ENABLE register (Address 0x007).
This register has a bit that corresponds to each conversion stage.
Setting this bit to 1 enables the interrupt for that stage. Clearing this
bit to 0 disables the conversion-complete interrupt for that stage.
The AD7147A interrupt should be enabled only for the last
stage in a conversion sequence. For example, if there are five
conversion stages, only the conversion-complete interrupt for
STAGE4 is enabled. Therefore, INT asserts only when all five
conversion stages are complete and the host can read new data
from all five result registers. The interrupt is cleared by reading
the STAGE_COMPLETE_INT_STATUS register located at
Address 0x00A.
Register 0x00A is the conversion-complete interrupt status
register. Each bit in this register corresponds to a conversion
stage. If a bit is set, it means that the conversion-complete
interrupt for the corresponding stage was triggered. This
register is cleared upon a read if the underlying condition
that triggered the interrupt is not present.
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SENSOR-TOUCH INTERRUPT
The sensor-touch interrupt mode is implemented when the host
processor requires an interrupt only when a sensor is contacted.
Configuring the AD7147A into this mode results in the interrupt
being asserted when the user makes contact with the sensor and
again when the user stops touching the sensor. The second
interrupt is required to alert the host processor that the user is
no longer contacting the sensor.
The registers located at Address 0x005 and Address 0x006 are
used to enable the interrupt output for each stage. The registers
located at Address 0x008 and Address 0x009 are used to read
back the interrupt status for each stage.
Figure 39 shows the interrupt output timing during contact with
one of the sensors connected to STAGE0 while operating in the
sensor-touch interrupt mode. For a low limit configuration, the
interrupt output is asserted as soon as the sensor is contacted and
again after the user has stopped touching the sensor. (Note that
the interrupt output remains low until the host processor reads
back the interrupt status registers located at Address 0x008 and
Address 0x009.)
The interrupt output is asserted when there is a change in the
interrupt status bits. This can indicate that a user is touching the
sensor(s) for the first time, the number of sensors being touched
has changed, or the user is no longer touching the sensor(s).
Reading the status bits in the interrupt status register shows the
current sensor activations.
FINGER OFF SENSOR
FINGER ON SENSOR
CONVERSION
INT OUTPUT
READBACK
SERIAL
STAGE
Figure 39. Example of Sensor-Touch Interrupt
1
2
3
4
USER TOUCHING SENSOR.
ADDRESS 0x008 IS READ BACK TO CLEAR INTERRUPT.
USER STOPS TOUCHING SENSOR.
ADDRESS 0x008 IS READ BACK TO CLEAR INTERRUPT.
1
2
STAGE0
4
3
AD7147A
STAGE1