AD7650_15 Datasheet, PDF (11/20 Pages) Analog Devices – 16-Bit, 570 kSPS Low Cost CMOS ADC

Transfer Functions
Using the OB/2C digital input, the AD7650 offers two output
codings: straight binary and two’s complement. The LSB size is
V_REF /65536, which is about 38.15 µV. The ideal transfer char-
acteristic for the AD7650 is shown in Figure 4 and Table I.
111...111
111...110
111...101
1 LSB = V _REF/65536
000...010
000...001
000...000
0V
1 LSB
0.5 LSB
V_REF – 1 LSB
V_REF – 1.5 LSB
ANALOG INPUT
Figure 4. ADC Ideal Transfer Function
AD7650
Table I. Output Codes and Ideal Input Voltages
Digital Output Code (Hex)
Description
Analog
Input
Straight
Binary
Two’s
Complement
FSR – 1 LSB
FSR – 2 LSB
Midscale + 1 LSB
Midscale
Midscale – 1 LSB
–FSR + 1 LSB
–FSR
2.499962 V
2.499923 V
1.250038 V
1.25 V
1.249962 V
38 µV
0V
FFFF¹
FFFE
8001
8000
7FFF
0001
0000²
7FFF¹
7FFE
0001
0000
FFFF
8001
8000²
NOTES
1_{This is also the code for overrange analog input (VIN+ – VIN– above VREF – VREFGND).}
2_{This is also the code for underrange analog input (VIN+ below VIN–).}
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7650.
ANALOG
SUPPLY
(5V)
+
10␮F
100nF
100⍀
+
10␮F
100nF
+
100nF
10␮F
DIGITAL SUPPLY
(3.3V OR 5V)
AVDD AGND
DGND DVDD OVDD OGND
2.5V REF
NOTE 1
+
C_REF1
REF
1␮F
REFGND
SCLK
SDOUT
BUSY
NOTE 2 U1
ANALOG INPUT
(0V TO 2.5V)
15⍀
C_C
IN+
4.7nF
IN–
PD
AD7650
RESET
CS
CNVST
OB/2C
SER/PAR
WARP
IMPULSE
RD
SERIAL
PORT
D
NOTE 3
DVDD
␮C/␮P/DSP
CLOCK
NOTES
1. THE ADR421 IS RECOMMENDED WITH C_REF = 47␮F.
2. THE AD8021 IS RECOMMENDED WITH A COMPENSATION CAPACITOR C_C = 10pF, TYPE CERAMIC NPO.
3. OPTIONAL LOW JITTER CNVST.
Figure 5. Typical Connection Diagram
REV. 0
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