AD7676 Analog Devices, AD7676 Datasheet - Page 11

• Manufacturer Part Number: AD7676
• Manufacturer: Analog Devices

Specifications of AD7676

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 500kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7676.
Different circuitry shown on this diagram is optional and is
discussed below.
Analog Inputs
The AD7676 is specified to operate with a differential ± 2.5 V
range. The typical input impedance for each analog input range
is also shown. Figure 6 shows a simplified analog input section
of the AD7676.
The diodes shown in Figure 6 provide ESD protection for the
inputs. Care must be taken to ensure that the analog input signal
never exceeds the absolute ratings on these inputs. This will
cause these diodes to become forward-biased and start conducting
REV. B
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
AD8021
AD8021
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 INPUTS SECTION.
6. OPTION, SEE POWER SUPPLY SECTION.
7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
NOTE 3
AGND
–
+
–
+
U1
U2
50
50
50k
AVDD
C
C
C
C
+
15
15
+
Figure 5. Typical Connection Diagram ( ± 2.5 V Range Shown)
C
NOTE 2
REF
10 F
NOTE 5
NOTE 5
2.7nF
2.7nF
1 F
R+ = 684
R– = 684
100nF
REF
REFGND
IN+
IN–
AVDD
C
C
S
S
NOTE 6
100
AGND
+
REF
10 F
–11–
IS 47 F. SEE VOLTAGE REFERENCE INPUT SECTION.
AD7676
DGND
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.
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
AD7676
C/ P/DSP
10M