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:
0.1µF capacitor as close to the pin as possible. If operat-
ing with dual supplies, bypass each supply with a 0.1µF
capacitor.
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 design guide-
lines:
• Don’t use wire-wrap boards; they are too inductive.
• Don’t use IC sockets; they increase parasitic capaci-
tance 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.
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.
The output swings to within 55mV 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 2.95V
P-P
and the out-
put can swing 4.9V
P-P
with minimal distortion.
Output Capacitive Loading and Stability
The MAX4450/MAX4451 are optimized for AC perfor-
mance. They are not designed to drive highly reactive
loads, which decrease phase margin and may produce
excessive ringing and oscillation. Figure 2 shows a cir-
cuit that eliminates this problem. Figure 3 is a graph of
the optimal isolation resistor (R
S
) vs. capacitive load.
Figure 4 shows how a capacitive load causes exces-
sive peaking of the amplifier’s frequency response if
the capacitor 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
oscillation. At higher capacitive loads, AC performance
is controlled by the interaction of the load capacitance
and the isolation resistor. Figure 5 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.
Table 1. Recommended Component Values
MAX4450/MAX4451
Ultra-Small, Low-Cost, 210MHz, Single-Supply
Op Amps with Rail-to-Rail Outputs
8 _______________________________________________________________________________________
-25
+25-10+10-5+5-2+2-1
+1
49.9
10
∞
0
50
1200
GAIN (V/V)
49.9
5
49.9
—
20
500
49.9
15
∞
0
50
500
49.9
11
49.9
—
56
500
49.9
25
100
0
100
500
49.9
25
49.9
—
124
500
49.9
50
62
0
250
500
49.9
95
49.9
—
500
500
49.949.9R
TO
(Ω)
100210Small-Signal -3dB Bandwidth (MHz)
5649.9R
TIN
(Ω)
0—R
S
(Ω)
COMPONENT
500
∞
R
G
(Ω)
50024R
F
(Ω)
