AD8270 Analog Devices, AD8270 Datasheet - Page 18

• Manufacturer Part Number: AD8270
• Description: Precision Dual-Channel, Difference Amplifier
• Manufacturer: Analog Devices

AD8270
DRIVING AN ADC
The AD270 high slew rate and drive capability, combined with
its dc accuracy, make it a good ADC driver. The AD8270 can
drive both single-ended and differential input ADCs. Many
converters require the output to be buffered with a small value
resistor combined with a high quality ceramic capacitor. See the
converter data sheet for more details. Figure 51 shows the AD8270
in differential configuration, driving the
AD8270 divides down the 5 V reference voltage from the ADR435,
so that the common-mode output voltage is 2.5 V, which is
precisely where the AD7688 needs it.
DRIVING CABLING
All cables have a certain capacitance per unit length, which varies
widely with cable type. The capacitive load from the cable may
cause peaking or instability in output response, especially when the
AD8270 is operating in a gain of 0.5.
5V_REF
0.1µF
–IN
+IN
–IN
+IN
AD7688
10
11
2
3
4
5
6
7
8
9
+12V –12V
16
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
20kΩ
20kΩ
10kΩ
10kΩ
10kΩ
ADC. The
13
10kΩ
10kΩ
10kΩ
10kΩ
Figure 51. Driving an ADC
AD8270
Rev. 0 | Page 18 of 20
15
14
12
1
To reduce the peaking, use a resistor between the AD8270 and the
cable. Because cable capacitance and desired output response vary
widely, this resistor is best determined empirically. A good starting
point is 20 Ω.
33Ω
33Ω
NOTE:
POWER SUPPLY DECOUPLING
NOT SHOWN.
2.7nF
COG
2.7nF
COG
ADR435
+12V
V
GND
2
IN
4
(SINGLE OUT)
AD8270
AD8270
(DIFF OUT)
V
OUT
3
4
+IN
–IN
5
AD7688
Figure 50. Driving Cabling
10µF
REF
1
0.1µF
5V_REF