AD8426ACPZ-R7 datasheet(27/29 Pages) AD

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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 (+VS) is required. Table 13 shows the minimum supply

voltage required for optimum performance, where VCM_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

+VS > (VCM_MAX + VBIAS)/2 + 1.4 V

−10°C to +25°C

+VS > (VCM_MAX + VBIAS)/2 + 1.25 V

More than +25°C

+VS > (VCM_MAX + VBIAS)/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 Ω.

AD8426

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.

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