Datasheet

REV. D
AD7660
–11–
100nF
10F
100nF
10F
AVDD
10F
100nF
AGND DGND DVDD OVDD OGND
CS
RD
SER/PAR
CNVST
BUSY
SDOUT
SCLK
RESETPD
IN
INGND
NOTE 2 U1
REFGND
C
REF
NOTE 1
2.5V REF
NOTE 1
REF
100
D
NOTE 3
CLOCK
AD7660
ANALOG INPUT
(0V TO 2.5V)
C/P/DSP
SERIAL
PORT
DIGITAL SUPPLY
(3.3V OR 5V)
ANALOG
SUPPLY
(5V)
DVDD
OB/2C
NOTES
1. WITH THE AD780 OR THE ADR291 VOLTAGE REFERENCE, C
REF
IS 47F,
SEE VOLTAGE REFERENCE INPUT SECTION.
2. THE OP184 IS RECOMMENDED.
3. OPTIONAL LOW JITTER CNVST.
Figure 5. Typical Connection Diagram
Transfer Functions
Using the OB/2C digital input, the AD7660 offers two output
codings: straight binary and twos complement. The LSB size is
V
REF
/65536, which is about 38.15 mV. The ideal transfer charac-
teristic for the AD7660 is shown in Figure 4 and Table II.
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 II. Output Codes and Ideal Input Voltages
Digital Output Code (Hex)
Analog Straight Twos
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 mV 0001 8001
–FSR 0 V 0000
2
8000
2
NOTES
1
This is also the code for overrange analog input (V
IN
– V
INGND
above
V
REF
– V
REFGND
).
2
This is also the code for underrange analog input (V
IN
below V
INGND
).
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7660.