AD7142 Analog Devices, AD7142 Datasheet - Page 30

• Manufacturer Part Number: AD7142
• Description: Programmable Controller for Capacitance Touch Sensors
• Manufacturer: Analog Devices

Specifications of AD7142

• Resolution (bits): 16bit
• # Chan: 14
• Sample Rate: 250kSPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: ± 2 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

AD7142
OUTPUTS
EXCITATION SOURCE
The excitation source onboard the AD7142 is a square wave
source with a frequency of 250 kHz. This excitation source
forms the electric field between the transmitter and receiver in
the external capacitance sensor PCB. The source is output from
the AD7142 on two pins, the SRC pin and the SRC pin (outputs
an inverted version of the source square wave). The SRC signal
offsets large external sensor capacitances. SRC is not used in the
majority of applications.
The source output can be disabled from both output pins
separately by writing to the control register bits (Address
0x000[13:12]). Setting Bit 12 in this register to 1 disables the
source output on the SRC pin. Setting Bit 13 in this register to 1
disables the inverted source output on the SRC pin.
C
To prevent leakage from the external capacitance sensors, the
sensor traces can be shielded. The AD7142 has a voltage output
that can be used as the potential for any shield traces, C
The C
The C
internal amplifier, and is of equal potential to the CIN input
lines. Because the shield is at the same potential as the sensor
traces, no leakage to ground occurs. To eliminate any ringing on
the C
C
C
For most applications, C
used instead around the sensors.
SHIELD
SHIELD
SHIELD
SHIELD
SHIELD
SHIELD
is used in the application or not
pin and ground. This capacitor is required, whether
OUTPUT
output, connect a 10 nF capacitor between the
voltage is equal to AV
potential is derived from the output of the AD7142
SHIELD
is not used, and a ground plane is
DD
/2.
.
SHIELD
.
Rev. A | Page 30 of 72
GPIO
The AD7142 has one GPIO pin located at Pin 26. It can be
configured as an input or an output. The GPIO_SETUP
Bits[13:12] in the interrupt enable register determine how the
GPIO pin is configured.
Table 15. GPIO_SETUP Bits
GPIO_SETUP
00
01
10
11
When the GPIO is configured as an output, the voltage level on
the pin is set to either a low level or a high level, as defined by
the GPIO_SETUP bits shown in Table 15.
When the GPIO is configured as an input, the
GPIO_INPUT_CONFIG bits in the interrupt enable register
determine the response of the AD7142 to a signal on the GPIO
pin. The GPIO can be configured as either active high or active
low, as well as either edge-triggered or level-triggered, as listed
in Table 16.
Table 16. GPIO_INPUT_CONFIG Bits
GPIO_INPUT_CONFIG
00
01
10
11
When GPIO is configured as an input, it triggers the interrupt
output on the AD7142. Table 14 lists the interrupt output
behavior for each of the GPIO configuration setups.
USING THE GPIO TO TURN ON/OFF AN LED
The GPIO on the AD7142 can be used to turn on and off LEDs
by setting the GPIO as either output high or low. Setting the
GPIO output high turns on the LED; setting the GPIO output
low turns off the LED. The GPIO pin connects to a transistor
that provides the drive current for the LED. Suitable transistors
include the KTC3875.
Figure 45. Controlling LEDs Using the GPIO
AD7142
GPIO
GPIO Configuration
Triggered on negative level (active low)
Triggered on positive edge (active high)
Triggered on negative edge (active low)
Triggered on positive level (active high)
GPIO Configuration
GPIO disabled
Input
Output low
Output high
OR SIMILAR
KTC3875
V
CC