AD7450BRZ Analog Devices Inc, AD7450BRZ Datasheet - Page 11

• Manufacturer Part Number: AD7450BRZ
• Description: 3V/5V DIFFERENTIAL INPUT 12 BIT SAR IC
• Manufacturer: Analog Devices Inc

Specifications of AD7450BRZ

• Number Of Bits: 12
• Sampling Rate (per Second): 1M
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 9.25mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7450CBZ - BOARD EVALUATION FOR AD7450
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

THE ANALOG INPUT
The analog input of the AD7450 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 7 defines the fully differential analog input of the AD7450.
The amplitude of the differential signal is the difference between
the signals applied to the V
V
amplitude V
the differential signal is therefore –V
(i.e., 2
The common mode is the average of the two signals, i.e.,
(V
are centered on. This results in the span of each input being
CM ± V
range varies with V
mon-mode range decreases. When driving the inputs with an
amplifier, the actual common-mode range will be determined
by the amplifier’s output voltage swing.
REV. 0
V
V
IN+
REF
REF
IN+
and V
p-p
p-p
*CM = COMMON-MODE VOLTAGE
+ V
COMMON-MODE
REF
V
IN–
Figure 6. Typical Connection Diagram
IN–
REF
/2. This voltage has to be set up externally and its
Figure 7. Differential Input Definition
VOLTAGE
REF
)/2, and is therefore the voltage that the two inputs
are simultaneously driven by two signals each of
). This is regardless of the common mode (CM).
that are 180° out of phase. The amplitude of
CM*
CM*
REF
. As the value of V
V
V
V
V
REF
DD
IN+
IN–
0.1 F
IN+
V
V
0.1 F
REF
REF
AD7450
1.25V/2.5V
and V
V
p-p
p-p
REF
IN–
10 F
SDATA
REF
SCLK
pins (i.e., V
GND
REF
CS
3V/5V
SUPPLY
V
to +V
V
IN+
IN–
increases, the com-
SERIAL
INTERFACE
AD7450
REF
IN+
p-p
– V
C/ P
IN–
).
–11–
Figures 8 and 9 show how the common-mode range typically
varies with V
common mode must be in this range to guarantee the
functionality of the AD7450.
For ease of use, the common mode can be set up to be equal to
V
on V
rejected resulting in a virtually noise free signal of amplitude
–V
Figure 9. Input Common-Mode Range vs. V
and V
Figure 10 shows examples of the inputs to V
different values of V
mum and minimum common-mode voltages for each reference
value according to Figure 8.
REF
REF
, resulting in the differential signal being ± V
REF
Figure 8. Input Common-Mode Range vs. V
(V
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
REF
to +V
3.0
2.5
2.0
1.5
1.0
0.5
0
. When a conversion takes place, the common mode is
0.25
DD
0
0.25
(Max) = 2.2 V)
= 5 V and V
REF
REF
0.50
0.75
corresponding to the digital codes of 0 to 4095.
for both a 5 V and a 3 V power supply. The
0.75
REF
1.25
COMMON-MODE RANGE
COMMON-MODE RANGE
REF
for V
1.00
(Max) = 3.5 V)
1.75
DD
V
REF
V
1.25
= 5 V. It also gives the maxi-
REF
2.25
1.50
2.75
1.75
IN+
AD7450
and V
REF
REF
2.00
3.25 3.50
(V
centered
DD
IN–
REF
2.20
3.25V
1.75V
= 3 V
2V
1V
for