Datasheet

REV. E
–12–
AD7664
The Normal Mode is the fastest mode (500 kSPS) without any
limitation on the time between conversions. This mode makes the
AD7664 ideal for asynchronous applications such as data
acquisition systems, where both high accuracy and fast sample
rate are required.
The Impulse Mode, the lowest power dissipation mode, allows
power saving between conversions. When operating at 100 SPS,
for example, it typically consumes only 21 µW. This feature
makes the AD7664 ideal for battery-powered applications.
Transfer Functions
Using the OB/2C digital input, the AD7664 offers two output
codings: straight binary and twos complement. The LSB size is
V
REF
/65536, which is about 38.15 µV. The ideal transfer charac-
teristics for the AD7664 are 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
Hexa
Analog Straight Twos
D escription 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 µV0001 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 AD7664.
100nF
10F
100nF
10F
AVDD
10F
100nF
AGND DGND DVDD OVDD OGND
WARP
IMPULSE
SER/PAR
CNVST
BUSY
SDOUT
SCLK
RDCSRESETPD
IN
INGND
REFGND
1F
C
REF
1
2.5V REF
1
REF
100
D
3
CLOCK
AD7664
ANALOG INPUT
(0V TO 2.5V)
C/P/DSP
SERIAL
PORT
DIGITAL SUPPLY
(3.3V OR 5V)
ANALOG
SUPPLY
(5V)
DVDD
C
C
OB/2C
4.7nF
U1
2
15
NOTES
1
THE ADR421 IS RECOMMENDED WITH C
REF
= 47F.
2
THE AD8021 IS RECOMMENDED WITH A COMPENSATION CAPACITOR C
C
= 10 pF, TYPE CERAMIC NPO.
3
OPTIONAL LOW JITTER CNVST.
Figure 5. Typical Connection Diagram