Ultralow Power, 1.8 V, 3 mm × 3 mm,
2-Channel Capacitance Converter
AD7156
FEATURES
GENERAL DESCRIPTION
Ultralow power
The AD7156 delivers a complete signal processing solution for
capacitive sensors, featuring an ultralow power converter with
fast response time.
Power supply voltage: 1.8 V to 3.6 V
Operation power supply current: 70 μA typical
Power-down current: 2 μA typical
Fast response time
Conversion time: 10 ms per channel
Wake-up time from serial interface: 300 μs
Adaptive environmental compensation
2 capacitance input channels
Sensor capacitance (CSENS): 0 pF up to 13 pF
Sensitivity up to 3 fF
The AD7156 uses an Analog Devices, Inc., capacitance-to-
digital converter (CDC) technology, which combines features
important for interfacing to real sensors, such as high input
sensitivity and high tolerance of both input parasitic ground
capacitance and leakage current.
The integrated adaptive threshold algorithm compensates for
any variations in the sensor capacitance due to environmental
factors like humidity and temperature or due to changes in the
dielectric material over time.
2 modes of operation
Standalone with fixed settings
Interfaced to a microcontroller for user-defined settings
2 detection output flags
2-wire serial interface (I2C-compatible)
Operating temperature: −40°C to +85°C
10-lead LFCSP package (3 mm × 3 mm × 0.8 mm)
By default, the AD7156 operates in standalone mode using the
fixed power-up settings and indicates detection on two digital
outputs. Alternatively, the AD7156 can be interfaced to a micro-
controller via the serial interface, the internal registers can be
programmed with user-defined settings, and the data and status
can be read from the part.
APPLICATIONS
The AD7156 operates with a 1.8 V to 3.6 V power supply. It is
specified over the temperature range of −40°C to +85°C.
Buttons and switches
Proximity sensing
Contactless switching
Position detection
Level detection
Portable products
FUNCTIONAL BLOCK DIAGRAM
VDD
CIN1
SCL
SDA
DIGITAL
FILTER
SERIAL
INTERFACE
C
C
SENS1
Σ-Δ CDC
AD7156
EXC1
CIN2
MUX
THRESHOLD
OUT1
OUT2
SENS2
EXCITATION
EXC2
THRESHOLD
GND
Figure 1.
Rev. 0
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