Datasheet
REV. A
AD7675
–11–
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7675.
Different circuitry shown on this diagram is optional and is
discussed below.
Analog Inputs
Figure 6 shows a simplified analog input section of the AD7675.
IN+
IN–
AGND
AV DD
R+ = 684
C
S
C
S
R– = 684
Figure 6. Simplified Analog Input
The diodes shown in Figure 6 provide ESD protection for the
inputs. Care must be taken to ensure that the analog input sig-
nal never exceeds the absolute ratings on these inputs. This will
cause these diodes to become forward-biased and start conducting
current. These diodes can handle a forward-biased current of
120 mA maximum. This condition could eventually occur when
the input buffer’s (U1) or (U2) supplies are different from
AVDD. In such a case, an input buffer with a short-circuit
current limitation can be used to protect the part.
This analog input structure is a true differential structure. By
using these differential inputs, signals common to both inputs
are rejected, as shown in Figure 7, which represents the typical
CMRR over frequency.
FREQUENCY – Hz
CMRR – dB
45
75
10k 10M1k 1M
80
65
100k
55
85
70
60
50
40
Figure 7. Analog Input CMRR vs. Frequency
AV DD AGND DGND
DVDD
OVDD OGND
SER/PAR
CNVST
BUSY
SDOUT
SCLK
RD
CS
RESET
PD
REFGND
C
REF
2.5V REF
NOTE 1
REF
100
D
CLOCK
AD7675
C/P/DSP
SERIAL PORT
DIGITAL SUPPLY
(3.3V OR 5V)
ANALOG
SUPPLY
(5V)
DVDD
OB/2C
NOTE 7
BYTESWAP
DVDD
50k
100nF
1M
IN+
ANALOG INPUT+
C
C
2.7nF
U1
NOTE 4
NOTE 5
50
AD8021
–
+
15
NOTE 2
NOTE 3
NOTE 6
ADR421
10F
100nF
+
10F 100nF
+
100nF
+
10F
IN–
ANALOG INPUT–
C
C
2.7nF
U2
NOTE 4
NOTE 5
50
AD8021
–
+
15
50
+
1F
NOTES
1. SEE VOLTAGE REFERENCE INPUT SECTION.
2. WITH THE RECOMMENDED VOLTAGE REFERENCES, C
REF
IS 47F. SEE CHAPTER VOLTAGE REFERENCE INPUT SECTION
3. OPTIONAL CIRCUITRY FOR HARDWARE GAIN CALIBRATION.
4. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.
5. SEE ANALOG INPUT SECTION.
6. OPTION, SEE POWER SUPPLY SECTION
7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
Figure 5. Typical Connection Diagram. (
±
2.5 V Range Shown)