ad8426 Analog Devices, Inc., ad8426 Datasheet - Page 15

• Manufacturer Part Number: ad8426
• Description: Wide Supply Range, Rail-to-rail Output Instrumentation Amplifier
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
APPLICATIONS INFORMATION
DIFFERENTIAL DRIVE
Figure 14 shows how to configure the
output.
The differential output is set by the following equation:
The common-mode output is set by the following equation:
The advantage of this circuit is that the dc differential accuracy
depends on the
This circuit takes advantage of the precise control that the
has of its output voltage relative to the reference voltage. Op amp
dc performance and resistor matching do affect the dc common-
mode output accuracy. However, because common-mode errors
are likely to be rejected by the next device in the signal chain,
these errors typically have little effect on overall system accuracy.
V
V
DIFF_OUT
CM_OUT
+IN
–IN
RECOMMENDED OP AMPS: AD8515, AD8641, AD820.
RECOMMENDED R VALUES: 5kΩ to 20kΩ.
Figure 14. Differential Output Using an Op Amp
= (V
= V
AD8426
OUT+
OUT+
AD8426
REF
− V
− V
and not on the op amp or the resistors.
OUT−
OUT−
R
R
)/2 = V
= Gain × (V
–
BIAS
OP AMP
AD8426
V
IN+
BIAS
+
− V
for differential
+OUT
–OUT
IN−
)
AD8426
Rev. PrD | Page 15 of 20
Tips for Best Differential Output Performance
For best ac performance, an op amp with at least 2 MHz gain
bandwidth and 1 V/μs slew rate is recommended. Good choices
for op amps are the AD8641, AD8515, or AD820.
Keep trace lengths from resistors to the inverting terminal of
the op amp as short as possible. Excessive capacitance at this
node can cause the circuit to be unstable. If capacitance cannot
be avoided, use lower value resistors.
For best linearity and ac performance, a minimum positive
supply voltage (+V
supply voltage required for optimum performance where
V
expected at the input of the AD8426.
Table 9. Minimum Positive Supply Voltage
Temperature
Less than −10°C
−10°C to +25°C
More than +25°C
CM_MAX
indicates the maximum common-mode voltage
S
) is required. Table 9 shows the minimum
Equation
+V
+V
+V
S
S
S
> (V
> (V
> (V
CM_MAX
CM_MAX
CM_MAX
+ V
+ V
+ V
BIAS
BIAS
BIAS
)/2 + 1.4 V
)/2 + 1.25 V
)/2 + 1.1 V
AD8426