AD7675 Analog Devices, AD7675 Datasheet - Page 11

• Manufacturer Part Number: AD7675
• Manufacturer: Analog Devices

Specifications of AD7675

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 100kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: QFP

REV. A
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.
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
ANALOG INPUT+
ANALOG INPUT–
2.5V REF
ADR421
NOTE 1
IN+
IN–
Figure 6. Simplified Analog Input
ANALOG
SUPPLY
NOTE 4
NOTE 4
100nF
(5V)
1M
NOTES
1. SEE VOLTAGE REFERENCE INPUT SECTION.
2. WITH THE RECOMMENDED VOLTAGE REFERENCES, C
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.
AD8021
AD8021
NOTE 3
–
+
AGND
+
–
U1
U2
50
50
50k
C
AVDD
C
C
C
+
15
15
+
Figure 5. Typical Connection Diagram. ( ± 2.5 V Range Shown)
C
NOTE 2
REF
10 F
NOTE 5
2.7nF
NOTE 5
2.7nF
1 F
100nF
R+ = 684
R– = 684
REF
REFGND
IN+
IN–
AVDD
C
C
S
S
NOTE 6
100
AGND
+
REF
10 F
IS 47 F. SEE CHAPTER VOLTAGE REFERENCE INPUT SECTION
–11–
AD7675
DGND
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.
100nF
DVDD
DVDD
Figure 7. Analog Input CMRR vs. Frequency
85
80
75
70
65
60
55
50
45
40
1k
OVDD
BYTESWAP
SER/PAR
SDOUT
CNVST
RESET
OGND
OB/2C
SCLK
BUSY
10k
CS
RD
PD
100nF
FREQUENCY – Hz
+
NOTE 7
50
100k
DVDD
10 F
SERIAL PORT
DIGITAL SUPPLY
(3.3V OR 5V)
D
CLOCK
1M
AD7675
C/ P/DSP
10M