Datasheet

REV. 0
–11–
AD7650
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.
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE – Straight Binary
ANALOG INPUT
V
REF
– 1.5 LSB
V
REF
– 1 LSB
1 LSB0V
0.5 LSB
1 LSB = V
REF
/65536
Figure 4. ADC Ideal Transfer Function
Table I. Output Codes and Ideal Input Voltages
Digital Output Code (Hex)
Analog Straight Two’s
Description Input Binary Complement
FSR – 1 LSB 2.499962 V FFFF
1
7FFF
1
FSR – 2 LSB 2.499923 V FFFE 7FFE
Midscale + 1 LSB 1.250038 V 8001 0001
Midscale 1.25 V 8000 0000
Midscale – 1 LSB 1.249962 V 7FFF FFFF
–FSR + 1 LSB 38 µV 0001 8001
–FSR 0 V 0000
2
8000
2
NOTES
1
This is also the code for overrange analog input (V
IN+
– V
IN–
above V
REF
– V
REFGND
).
2
This is also the code for underrange analog input (V
IN+
below V
IN–
).
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.
AD7650
2.5V REF
NOTE 1
NOTE 2 U1
D
NOTE 3
CLOCK
␮C/␮P/DSP
SERIAL
PORT
DIGITAL SUPPLY
(3.3V OR 5V)
DVDD
100nF
+
10␮F
100nF
+
10␮F
100⍀
100nF
+
10␮F
ANALOG
SUPPLY
(5V)
+
C
REF
1
1␮F
4.7nF
C
C
15⍀
ANALOG INPUT
(0V TO 2.5V)
PD RESET
CS
RD
IMPULSE
WARP
SER/PAR
OB/2C
CNVST
BUSY
SDOUT
SCLK
IN–
IN+
REFGND
REF
AGNDAVDD DGND DVDD OVDD OGND
Figure 5. Typical Connection Diagram
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7650.