AD7452 Analog Devices, AD7452 Datasheet - Page 14

• Manufacturer Part Number: AD7452
• Description: Differential Input, 555 kSPS, 12-Bit A/D Converter in 8-Lead SOT-23
• Manufacturer: Analog Devices

Specifications of AD7452

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 555kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: SOT

AD7452
TYPICAL CONNECTION DIAGRAM
Figure 21 shows a typical connection diagram for the AD7452
for both 5 V and 3 V supplies. In this setup, the GND pin is
connected to the analog ground plane of the system. The V
pin is connected to either a 2.5 V or a 2 V decoupled reference
source, depending on the power supply, to set up the analog
input range. The common-mode voltage has to be set up
externally and is the value on which the two inputs are centered.
The conversion result is output in a 16-bit word with four
leading zeros followed by the MSB of the 12-bit result. For more
details on driving the differential inputs and setting up the
common mode, refer to the Driving Differential Inputs section.
ANALOG INPUT
The analog input of the AD7452 is fully differential. Differential
signals have a number of benefits over single-ended signals,
including noise immunity based on the device’s common-mode
rejection, improvements in distortion performance, doubling of
the device’s available dynamic range, and flexibility in input
ranges and bias points. Figure 22 defines the fully differential
analog input of the AD7452.
The amplitude of the differential signal is the difference
between the signals applied to the V
(i.e., V
signals, each of amplitude V
amplitude of the differential signal is therefore –V
peak-to-peak (i.e., 2 ×V
common mode (CM).
V
V
*CM IS THE COMMON-MODE VOLTAGE.
REF
REF
p-p
p-p
IN+
– V
COMMON-
VOLTAGE
MODE
CM*
CM*
IN–
0.1µF
). V
Figure 21. Typical Connection Diagram
Figure 22. Differential Input Definition
V
V
V
V
DD
IN–
IN+
REF
IN+
0.1µF
and V
REF
2V/2.5V
V
AD7452
V
p-p
V
p-p
). This is true regardless of the
REF
REF
REF
IN–
REF
10µF
, that are 180° out of phase. The
are simultaneously driven by two
IN+
SDATA
V
3V/5V
SUPPLY
V
SCLK
IN–
IN+
and V
GND
CS
AD7452
IN–
INTERFACE
SERIAL
pins
REF
to +V
µC/µP
REF
REF
Rev. B | Page 14 of 28
The common mode is the average of the two signals, i.e.,
(V
inputs are centered. This results in the span of each input being
CM ± V
range varies with V
common-mode range decreases. When driving the inputs with
an amplifier, the actual common-mode range is determined by
the amplifier’s output voltage swing.
Figure 23 and Figure 24 show how the common-mode range
typically varies with V
The common mode must be in this range to guarantee the
functionality of the AD7452.
For ease of use, the common mode can be set up to equal V
resulting in the differential signal being ±V
When a conversion takes place, the common mode is rejected,
resulting in a virtually noise-free signal of amplitude, –V
+V
IN+
REF
+ V
, corresponding to the digital codes of 0 to 4096.
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
2.5
2.0
1.5
1.0
0.5
REF
0
0
IN–
0
0
/2. This voltage has to be set up externally, and its
)/2, and is therefore the voltage upon which the two
Figure 23. Input Common-Mode Range vs. V
Figure 24. Input Common-Mode Range vs. V
0.25
0.5
(V
(V
REF
DD
0.50
DD
. As the value of V
REF
= 5 V and V
1.0
= 3 V and V
COMMON-MODE RANGE
for both 5 V and 3 V power supplies.
COMMON-MODE RANGE
0.75
1.5
V
V
REF
REF
REF
REF
1.00
(Max) = 3.5 V)
(Max) = 2 V)
(V)
(V)
2.0
1.25
REF
increases, the
REF
2.5
1.50
centered on V
REF
REF
3.0
1.75
3.25V
1.75V
1V
2V
REF
2.00
3.5
REF
to
REF
,
.