Datasheet

AD8426
Rev. 0 | Page 26 of 28
Tips for Best Differential Output Performance
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
S
) is required. Table 13 shows the minimum supply
voltage required for optimum performance, where V
CM_MAX
indicates the maximum common-mode voltage expected at the
input of the AD8426.
Table 13. Minimum Positive Supply Voltage
Temperature Equation
Less than −10°C +V
S
> (V
CM_MAX
+ V
BIAS
)/2 + 1.4 V
−10°C to +25°C +V
S
> (V
CM_MAX
+ V
BIAS
)/2 + 1.25 V
More than +25°C +V
S
> (V
CM_MAX
+ V
BIAS
)/2 + 1.1 V
DRIVING A CABLE
All cables have a certain capacitance per unit length, which varies
widely with cable type. The capacitive load from the cable may
cause peaking in the output response of the AD8426. To reduce
the peaking, use a resistor between the AD8426 outputs and the
cable (see Figure 71). Because cable capacitance and desired output
response vary widely, this resistor is best determined empirically.
A good starting point is 50 .
AD8426
AD8426
09490-165
DIFFERENTIAL OUTPUT
SINGLE OUTPUT
Figure 71. Driving a Cable
The AD8426 operates at such a relatively low frequency that
transmission line effects are rarely an issue; therefore, the resistor
need not match the characteristic impedance of the cable.