Datasheet

AD7625 Data Sheet
Rev. A | Page 16 of 24
DRIVING THE AD7625
Differential Analog Input Source
Figure 24 shows an ADA4899-1 driving each differential input
to the AD7625.
Single-Ended-to-Differential Driver
For applications using unipolar analog signals, a single-ended-
to-differential driver, as shown in Figure 23, allows for a differ-
ential input into the part. This configuration, when provided
with an input signal of 0 V to 4.096 V, pr o d u c e s a differential
±4.096 V with midscale at 2.048 V. T h e o n e -pole filter using
R = 33 Ω and C = 56 pF provides a corner frequency of 86 MHz.
The VCM output of the AD7625 can be buffered and then used
to provide the required 2.048 V common-mode voltage.
56pF
33Ω
33Ω
50Ω
IN+
IN–
AD7625
VCM
V–
V+
AD8031, AD8032
07652-033
U2
U1
ADA4899-1
ADA4899-1
56pF
100nF
100nF
590Ω
590Ω
ANALOG INPUT
(UNIPOLAR 0V TO 4.096V)
Figure 23. Single-Ended-to-Differential Driver Circuit
56pF
33Ω
–V
S
0V TO V
REF
+V
S
56pF
33Ω
–V
S
V
REF
TO 0V
+V
S
C
REF
10µF
2
REF
1
REF
GND
IN+
IN–
AD7625
ADA4899-1
1
SEE THE VOLTAGE REFERENCE OPTIONS SECTION. CONNECTION TO EXTERNAL REFERENCE SIGNALS
IS DEPENDENT ON THE EN1 AND EN0 SETTINGS.
2
C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESL AND ESR.
THE REF AND REFIN PINS ARE DECOUPLED REGARDLESS OF EN1 AND EN0 SETTINGS.
VCM
–V
S
+V
S
BUFFERED VCM PIN OUTPUT
GIVES THE REQUIRED 2.048V
COMMON-MODE SUPPLY FOR
ANALOG INPUTS.
VCM
2.048V
AD8031, AD8032
ADA4899-1
REFIN
REF
1
C
REF
10µF
2
07652-025
0.1µF
Figure 24. Driving the AD7625 from a Differential Analog Source