Carbon composition resistors with leads are manufac-

tured by pouring the resistor material into a mold. This

process yields a relatively low-inductance resistor that

is very useful in high-frequency applications, although

they tend to cost more and have more thermal noise

than other types. The ability of carbon composition

resistors to self-heal after a large current overload

makes them useful in high-power RF applications.

For general-purpose use, surface-mount metal-film

resistors seem to have the best overall performance for

low cost, low inductance, and low noise.

Driving Capacitive Loads

When driving 50

Ω or 75Ω back-terminated transmission

lines, capacitive loading is not an issue; therefore an iso-

lation resistor is not required. For other applications

where the ability to drive capacitive loads is required, the

MAX4100/MAX4101 can typically drive 5pF and 20pF,

respectively. Figure 4a illustrates how a capacitive load

influences the amplifier’s peaking without an isolation

decreases the amplifier’s peaking.

The MAX4100/MAX4101 can drive capacitive loads up to

5pF. By using a small isolation resistor between the

amplifier output and the load, large capacitance values

may be driven without oscillation (Figure 5a). In most

cases, less than 50

Ω is sufficient. Use Figure 5b to deter-

mine the value needed in your application. Determine the

worst-case maximum capacitive load you may encounter

and select the appropriate resistor from the graph.

500MHz, Low-Power Op Amps

______________________________________________________________________________________

11

MAX4100

24

Ω

Figure 5a. Using an Isolation Resistor for High Capacitive

Loads (MAX4100)

Figure 5b. Isolation vs. Capacitive Load

0

20

120

CAPACITIVE LOAD (pF)

60

25

20

5

15

10

0

40

80

100

MAX4100

MAX4101