EVAL-CONTROLBRD2 AD [Analog Devices], EVAL-CONTROLBRD2 Datasheet - Page 13

• Manufacturer Part Number: EVAL-CONTROLBRD2
• Description: Differential Input, 1MSPS, 12-Bit ADC in ?SO-8 and S0-8
• Manufacturer: AD [Analog Devices]

Figure 10 shows examples of the inputs to V
for different values of V
the maximum and minimum common mode voltages for
each reference value according to figure 8.
REV. PrJ
(Vdd = 5V and V
Figure 8. Input Common Mode Range (CM) versus V
-1
0
0
0
Figure 9. Input Common Mode Range versus V
5
4
3
2
1
0
0.75
0
with the AD8138 Differential Amplifier
(Vdd = 5V and V
1
0
REF
(max) = 2.5V) when Driving V
1.25
0
REF
1.5
TITLE
for V
PRELIMINARY TECHNICAL DATA
0
VREF
REF
(max) = 2.5V)
DD
1.75
= 5 V. It also gives
0
2
0
IN+
2.25
IN+
and V
and V
REF
0
2.5
REF
IN-
2.8
0.9
IN-
–13–
Analog Input Structure
Figure 11 shows the equivalent circuit of the analog input
structure of the AD7450. The four diodes provide ESD
protection for the analog inputs. Care must be taken to
ensure that the analog input signals never exceed the sup-
ply rails by more than 200mV. This will cause these
diodes to become forward biased and start conducting into
the substrate. These diodes can conduct up to 10mA with-
out causing irreversible damage to the part.
The capacitors C1, in figure 11 are typically 4pF and can
primarily be attributed to pin capacitance.
are lumped components made up of the on-resistance of
the switches. The value of these resistors is typically about
100 . The capacitors, C2, are the ADC’s sampling ca-
pacitors and have a capacitance of 16pF typically.
For ac applications, removing high frequency components
from the analog input signal is recommended by the use of
an RC low-pass filter on the relevant analog input pins.
In applications where harmonic distortion and signal to
noise ratio are critical, the analog input should be driven
from a low impedance source. Large source impedances
will significantly affect the ac performance of the ADC.
This may necessitate the use of an input buffer amplifier.
The choice of the opamp will be a function of the particu-
lar application.
Figure 10. Examples of the Analog Inputs to V
Common Mode (CM)
CM min = 0.275 V
CM max = 3.8 V
Common Mode (CM)
CM min = 0.85 V
CM max = 3.55 V
Common Mode (CM)
CM min = 2 V
CM max = 3 V
for Different Values of V
Reference = 1.25 V (V REF max/2)
Reference = 0.625 V (V REF max/4)
Reference = 2.5 V (V REF max)
REF
0.625 V peak to peak
1.25 V peak to peak
2.5 V peak to peak
for V
DD
= 5 V.
The resistors
AD7450
IN+
and V
IN-