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MAX4218EEE+T

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
MAX4212/MAX4213/MAX4216/MAX4218/MAX4220
_______________Detailed Description
The MAX4212/MAX4213/MAX4216/MAX4218/MAX4220
are single-supply, rail-to-rail, voltage-feedback ampli-
fiers that employ current-feedback techniques to
achieve 600V/µs slew rates and 300MHz bandwidths.
Excellent harmonic distortion and differential gain/
phase performance make these amplifiers an ideal
choice for a wide variety of video and RF signal-
processing applications.
The output voltage swing comes to within 50mV of each
supply rail. Local feedback around the output stage
assures low open-loop output impedance to reduce
gain sensitivity to load variations. This feedback also
produces demand-driven current bias to the output
transistors for ±100mA drive capability, while constrain-
ing total supply current to less than 7mA. The input
stage permits common-mode voltages beyond the nega-
tive supply and to within 2.25V of the positive supply rail.
__________Applications Information
Choosing Resistor Values
Unity-Gain Configuration
The MAX4212/MAX4213/MAX4216/MAX4218/MAX4220
are internally compensated for unity gain. When config-
ured for unity gain, the devices require a 24Ω resistor
(R
F
) in series with the feedback path. This resistor
improves AC response by reducing the Q of the parallel
LC circuit formed by the parasitic feedback capaci-
tance and inductance.
Inverting and Noninverting Configurations
Select the gain-setting feedback (R
F
) and input (R
G
)
resistor values to fit your application. Large resistor val-
ues increase voltage noise and interact with the amplifi-
er’s input and PC board capacitance. This can
generate undesirable poles and zeros and decrease
bandwidth or cause oscillations. For example, a nonin-
verting gain-of-two configuration (R
F
= R
G
) using 1kΩ
resistors, combined with 1pF of amplifier input capaci-
tance and 1pF of PC board capacitance, causes a pole
at 159MHz. Since this pole is within the amplifier band-
width, it jeopardizes stability. Reducing the 1kΩ resis-
tors to 100Ω extends the pole frequency to 1.59GHz,
but could limit output swing by adding 200Ω in parallel
with the amplifier’s load resistor. Table 1 shows sug-
gested feedback, gain resistors, and bandwidth for
several gain values in the configurations shown in
Figures 1a and 1b.
Layout and Power-Supply Bypassing
These amplifiers operate from a single 3.3V to 11V power
supply or from dual supplies to ±5.5V. For single-supply
operation, bypass V
CC
to ground with a 0.1µF capacitor
as close to the pin as possible. If operating with dual sup-
plies, bypass each supply with a 0.1µF capacitor.
Miniature, 300MHz, Single-Supply,
Rail-to-Rail Op Amps with Enable
10 ______________________________________________________________________________________
IN
R
G
V
OUT
= [1+ (R
F
/ R
G
)] V
IN
R
F
R
TO
R
TIN
R
O
V
OUT
IN
R
G
V
OUT
= -(R
F
/ R
G
) V
IN
R
F
R
TO
R
S
R
TIN
R
O
V
OUT
Figure 1a. Noninverting Gain Configuration Figure 1b. Inverting Gain Configuration
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.
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 50mV of either power-
supply rail with a 10kΩ 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.
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 MAX4213/MAX4218 are disabled, the amplifi-
er’s output impedance is 35kΩ. This high resistance
and the low 2pF output capacitance make these parts
ideal in RF/video multiplexer or switch applications. For
larger arrays, pay careful attention to capacitive load-
ing. See the Output Capacitive Loading and Stability
section for more information.
MAX4212/MAX4213/MAX4216/MAX4218/MAX4220
Miniature, 300MHz, Single-Supply,
Rail-to-Rail Op Amps with Enable
______________________________________________________________________________________ 11
Table 1. Recommended Component Values
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 =
75
1-
75
R
TIN
G
Ω
-25
+25-10+10-5+5-2+2-1
+1
49.9
10
∞
0
50
1200
GAIN (V/V)
49.9
6
49.9
—
20
500
49.9
25
∞
0
50
500
49.9
11
49.9
—
56
500
49.9
33
100
0
100
500
49.9
25
49.9
—
124
500
49.9
60
62
0
250
500
49.9
105
49.9
—
500
500
49.949.9
R
TO
(Ω)
90300Small-Signal -3dB Bandwidth (MHz)
5649.9
R
TIN
(Ω)
0—
R
S
(Ω)
COMPONENT
500
∞
R
G
(Ω)
50024
R
F
(Ω)
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
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

MAX4218EEE+T

Mfr. #:
Buy MAX4218EEE+T
Manufacturer:
Maxim Integrated
Description:
High Speed Operational Amplifiers Miniature 300MHz Single-Supply R-R
Lifecycle:
New from this manufacturer.
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