EVAL-AD7156EBZ Analog Devices Inc, EVAL-AD7156EBZ Datasheet - Page 25

• Manufacturer Part Number: EVAL-AD7156EBZ
• Description: Evaluation Board I.c.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7156EBZ

• Sensor Type: Touch, Capacitive
• Interface: I²C
• Voltage - Supply: 1.8 V ~ 3.6 V
• Embedded: No
• Utilized Ic / Part: AD7156
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -
• Sensing Range: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed

PARASITIC SERIAL RESISTANCE
The AD7156 CDC result is affected by a resistance in series
with the measured capacitance.
The total serial resistance (R
the order of hundreds of Ω (see Figure 14).
INPUT OVERVOLTAGE PROTECTION
The AD7156 capacitive input has an internal ESD protection.
However, some applications may require an additional over-
voltage protection, depending on the application-specific
requirements. Any additional circuit in the capacitive front
end must be carefully designed, especially with respect to the
limits recommended for maximum capacitance to ground,
maximum serial resistance, maximum leakage, and so on.
C
X
R
R
S1
S2
Figure 46. AD7156 CIN Overvoltage Protection
C
X
Figure 45. Parasitic Serial Resistance
EXC
CIN
R
R
S1
S2
S1
+ R
EXC
CIN
S2
in Figure 45) should be in
CDC
CDC
GND
DATA
Rev. 0 | Page 25 of 28
INPUT EMC PROTECTION
Some applications may require an additional input filter for
improving EMC. Any input filter must be carefully designed,
considering the balance between the system capacitance
performance and system electromagnetic immunity.
Figure 47 shows one of the possible input circuit configurations
for significantly improving the system immunity against high
frequency noise while only slightly affecting the AD7156
performance in terms of additional gain and offset error.
POWER SUPPLY DECOUPLING AND FILTERING
The AD7156 has good dc and low frequency power supply
rejection but may be sensitive to higher frequency ripple and
noise, specifically around the excitation frequency and its
harmonics. Figure 48 shows a possible circuit configuration
for improving the system immunity against ripple and noise
coupled to the AD7156 via the power supply.
If the serial interface is connected to the other circuits in the
system, it is better to connect the pull-up resistors on the other
side of the V
AD7156 is used in standalone mode and the serial interface
is not used, it is better to connect the pull-up resistors directly
to the AD7156 V
Figure 48. AD7156 V
DD
GND
C
X
filter than to connect to the AD7156. If the
Figure 47. AD7156 CIN EMC Protection
CDC
DD
39kΩ
.
0.1µF
SDA
SCL
68pF
82kΩ
10kΩ
DD
10µF
Decoupling and Filtering
22pF
47pF
1kΩ
EXC
CIN
1kΩ
GND
CDC
1kΩ
V
DD
AD7156