Datasheet

MAX4212/MAX4213/MAX4216/MAX4218/MAX4220
Output Capacitive Loading and Stability
The MAX4212/MAX4213/MAX4216/MAX4218/MAX4220
are optimized for AC performance. They are not
designed to drive highly reactive loads, which de-
creases 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 opti-
mal isolation resistor (R
S
) vs. capacitive load. Figure 7
shows how a capacitive load causes excessive peak-
ing of the amplifier’s frequency response if the capaci-
tor is not isolated from the amplifier by a resistor. A
small isolation resistor (usually 20Ω to 30Ω) placed
before the reactive load prevents ringing and oscilla-
tion. At higher capacitive loads, AC performance is
controlled by the interaction of the load capacitance
and the isolation 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
transmission lines essentially eliminates the line’s
capacitance.
Miniature, 300MHz, Single-Supply,
Rail-to-Rail Op Amps with Enable
12 ______________________________________________________________________________________
OUT
IN-
EN_
IN+
10kΩ
ENABLE
MAX42_ _
20
-160
0 50 100 150 300 350 500
-100
-120
0
mV ABOVE V
EE
INPUT CURRENT (µA)
200 250 400 450
-60
-140
-20
-40
-80
0
-10
0 50 100 150 300 350 500
-7
-8
-1
mV ABOVE V
EE
INPUT CURRENT (µA)
200 250 400 450
-3
-5
-9
-2
-4
-6
Figure 2. Enable Logic-Low Input Current vs. V
IL
Figure 4. Enable Logic-Low Input Current vs. V
IL
with 10kΩ
Series Resistor
Figure 3. Circuit to Reduce Enable Logic-Low Input Current