Low-Cost, High-Speed, SOT23, Single-Supply
Op Amps with Rail-to-Rail Outputs
Maxim recommends using microstrip and stripline tech-
niques to obtain full bandwidth. To ensure that the PC
board does not degrade the amplifier’s performance,
design it for a frequency greater than 1GHz. Pay care-
ful attention to inputs and outputs to avoid large para-
sitic capacitance. Whether or not you use a constant-
impedance board, observe the following guidelines
when designing the board:
• Don’t use wire-wrap boards because they are too
inductive.
• Don’t use IC sockets because they increase parasitic
capacitance and inductance.
• Use surface-mount instead of through-hole compo-
nents for better high-frequency performance.
• Use a PC board with at least two layers; it should be
as free from voids as possible.
• Keep signal lines as short and as straight as possi-
ble. Do not make 90° turns; round all corners.
The output swings to within 60mV of either power-
supply rail with a 2kΩ load. The input ground-sensing
and the rail-to-rail output substantially increase the
dynamic range. With a symmetric input in a single +5V
application, the input can swing 2.95Vp-p, and the out-
put can swing 4.9Vp-p with minimal distortion.
MAX4012/MAX4016/MAX4018/MAX4020
Enable Input and Disabled Output
The enable feature (EN_) allows the amplifier to be
placed in a low-power, high-output-impedance state.
Typically, the EN_ logic low input current (I
IL
) is small.
However, as the EN voltage (V
IL
) approaches the nega-
tive supply rail, I
IL
increases (Figure 2). A single resis-
tor connected as shown in Figure 3 prevents the rise in
the logic-low input current. This resistor provides a
feedback mechanism that increases V
IL
as the logic
input is brought to V
EE
. Figure 4 shows the resulting
input current (I
IL
).
When the MAX4018 is disabled, the amplifier’s output
impedance is 35kΩ. This high resistance and the low
2pF output capacitance make this part ideal in
RF/video multiplexer or switch applications. For larger
arrays, pay careful attention to capacitive loading. See
the
Output Capacitive Loading and Stability
section for
more information.
Rail-to-Rail Outputs,
Ground-Sensing Input
The input common-mode range extends from
(V
EE
- 200mV) to (V
CC
- 2.25V) with excellent common-
mode rejection. Beyond this range, the amplifier output
is a nonlinear function of the input, but does not under-
go phase reversal or latchup.
Table 1. Recommended Component Values
GAIN (V/V)
COMPONENT
+1
R
F
(Ω)
R
G
(Ω)
R
S
(Ω)
R
TIN
(Ω)
R
TO
(Ω)
Small-Signal -3dB Bandwidth (MHz)
24
∞
—
49.9
49.9
200
-1
500
500
0
56
49.9
90
+2
500
500
—
49.9
49.9
105
-2
500
250
0
62
49.9
60
+5
500
124
—
49.9
49.9
25
-5
500
100
0
100
49.9
33
+10
500
56
—
49.9
49.9
11
-10
500
50
0
∞
49.9
25
+25
500
20
—
49.9
49.9
6
-25
1200
50
0
∞
49.9
10
Note:
R
L
= R
O
+ R
TO
; R
TIN
and R
TO
are calculated for 50Ω applications. For 75Ω systems, R
TO
= 75Ω; calculate R
TIN
from the
following equation:
R
TIN
=
75
Ω
75
1-
R
G
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