MAX4012 datasheet(12/18 Pages) AD

12 / 18 page

To implement the mux function, the outputs of multiple

amplifiers can be tied together, and only the amplifier with

the selected input will be enabled. All of the other ampli-

fiers will be placed in the low-power shutdown mode, with

their high output impedance presenting very little load to

the active amplifier output. For gains of +2 or greater, the

feedback network impedance of all the amplifiers used in

a mux application must be considered when calculating

the total load on the active amplifier output

Output Capacitive Loading and Stability

The MAX4012/MAX4016/MAX4018/MAX4020 are opti-

mized for AC performance. They are not designed to drive

highly reactive loads, which decreases phase margin and

may produce excessive ringing and oscillation. Figure 5

shows a circuit that eliminates this problem. Figure 6 is

a graph of the optimal isolation resistor (RS) vs. capaci-

tive load. Figure 7 shows how a capacitive load causes

excessive peaking of the amplifier’s frequency response if

the capacitor is not isolated from the amplifier by a resis-

tor. A small isolation resistor (usually 20Ω to 30Ω) placed

before the reactive load prevents ringing and oscillation.

At higher capacitive loads, AC performance is controlled

by the interaction of the load capacitance and the isola-

tion resistor. Figure 8 shows the effect of a 27Ω isolation

resistor on closed-loop response.

Coaxial cable and other transmission lines are easily

driven when properly terminated at both ends with their

characteristic impedance. Driving back-terminated trans-

mission lines essentially eliminates the line’s capacitance.

Figure 2. Enable Logic-Low Input Current vs. VIL

Figure 3. Circuit to Reduce Enable Logic-Low Input Current

Figure 4. Enable Logic-Low Input Current vs. VIL with 10kΩ

Series Resistor

www.analog.com

Analog Devices │ 12

MAX4012/MAX4016/

MAX4018/MAX4020

Low-Cost, High-Speed, Single-Supply

Op Amps with Rail-to-Rail Outputs

-160

0 50 100 150

300 350

500

-100

-120

mV ABOVE VEE

200 250

400 450

-60

-140

-20

-40

-80

OUT

IN-

EN_

IN+

10kΩ

ENABLE

MAX40_ _

-160

0 50 100 150

300 350

500

-100

-120

mV ABOVE VEE

200 250

400 450

-60

-140

-20

-40

-80

MAX4012 Datasheet(PDF) 12 Page - Analog Devices

MAX4012 Datasheet(HTML) 12 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL