AD7151BRMZ Analog Devices Inc, AD7151BRMZ Datasheet - Page 10

• Manufacturer Part Number: AD7151BRMZ
• Description: IC CAP CONV 1CH ULT LP 10MSOP
• Manufacturer: Analog Devices Inc
• Type: Capacitance-to-Digital Converterr

Specifications of AD7151BRMZ

• Input Type: Voltage
• Output Type: Digital
• Interface: 2-Wire Serial
• Current - Supply: 120µA
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Resolution (bits): 12bit
• Sampling Rate: 100SPS
• Input Channel Type: Single Ended
• Data Interface: 2-Wire, I2C, Serial
• Supply Voltage Range - Analog: 2.7V To 3.6V
• Supply Current: 70µA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7151
ARCHITECTURE AND MAIN FEATURES
The AD7151 core is a high performance capacitance-to-digital
converter (CDC) that allows the part to be interfaced directly to
a capacitive sensor.
The comparator compares the CDC result with thresholds, either
fixed or dynamically adjusted by the on-chip adaptive threshold
algorithm engine. Thus, the output indicates a defined change in
the input sensor capacitance.
The AD7151 also integrates an excitation source and CAPDAC
for the capacitive inputs, an input multiplexer, a complete clock
generator, a power-down timer, a power supply monitor, control
logic, and an I
part and accessing the internal CDC data and status, if required
in the system (see Figure 20).
CAPACITANCE-TO-DIGITAL CONVERTER
Figure 21 shows the CDC simplified functional diagram. The
converter consists of a second-order sigma delta (Σ-Δ), charge
balancing modulator and a third-order digital filter. The
measured capacitance C
source and the Σ-Δ modulator input. The excitation signal is
applied on the C
continuously samples the charge going through the C
digital filter processes the modulator output, which is a stream
of 0s and 1s containing the information in 0 and 1 density. The
data is processed by the adaptive threshold engine and output
comparators; the data can be also read through the serial interface.
The AD7151 is designed for floating capacitive sensors.
Therefore, both C
any other fixed potential node in the system.
The AD7151 features slew rate limiting on the excitation voltage
output, which decreases the energy of higher harmonics on the
excitation signal and dramatically improves the system
electromagnetic compatibility (EMC).
2
C®-compatible serial interface for configuring the
X
X
during the conversion, and the modulator
plates have to be isolated from ground or
X
is connected between an excitation
C
X
EXC
CIN
GENERATOR
EXCITATION
CAPDAC
CLOCK
Σ-Δ CDC
X
. The
Figure 20. AD7151 Block Diagram
POWER-DOWN
THRESHOLD
3.3V
DIGITAL
FILTER
TIMER
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VDD
GND
POWER SUPPLY
CAPDAC
The AD7151 CDC core maximum full-scale input range is 4 pF.
However, the part can accept a higher capacitance on the input,
and the offset (nonchanging component) capacitance of up to 10
pF can be balanced by a programmable on-chip CAPDAC.
The CAPDAC can be understood as a negative capacitance
connected internally to the CIN pin. The CAPDAC has a 6-bit
resolution and a monotonic transfer function. Figure 22 shows
how to use the CAPDAC to shift the CDC 4 pF input range to
measure capacitance between 10 pF and 14 pF.
INTERFACE
MONITOR
SERIAL
AD7151
C
0pF TO 4pF
X
C
10pF TO 14pF
SENS
EXC
CIN
EXC
Figure 21. CDC Simplified Block Diagram
CIN
SDA
OUT
SCL
GENERATOR
CAPDAC
MODULATOR
EXCITATION
Figure 22. Using CAPDAC
CAPACITANCE TO DIGITAL CONVERTER
10pF
PROGRAMMING
INTERFACE
DIGITAL
OUTPUT
CLOCK
Σ-Δ
(CDC)
0pF TO 4pF
DIGITAL
FILTER
CDC
0x000 TO 0xFFF
0x000 TO 0xFFF
DATA
DATA