Ultra-Small, Low-Cost, 210MHz, Single-Supply
Op Amps with Rail-to-Rail Outputs
Pin Description
PIN
MAX4450
1
2
3
4
5
—
—
—
—
—
—
MAX4451
—
4
—
—
8
1
2
3
7
6
5
NAME
OUT
V
EE
IN+
IN-
V
CC
OUTA
INA-
INA+
OUTB
INB-
INB+
FUNCTION
Amplifier Output
Negative Power Supply
or Ground (in single-
supply operation)
Noninverting Input
Inverting Input
Positive Power Supply
Amplifier A Output
Amplifier A Inverting
Input
Amplifier A Noninverting
Input
Amplifier B Output
Amplifier B Inverting
Input
Amplifier B Noninverting
Input
R
G
R
F
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 lists suggest-
ed feedback and gain resistors, and bandwidths for
several gain values in the configurations shown in
Figures 1a and 1b.
MAX4450/MAX4451
Layout and Power-Supply Bypassing
These amplifiers operate from a single +4.5V to +11V
power supply or from dual ±2.25V to ±5.5V supplies. For
single-supply operation, bypass V
CC
to ground with a
Detailed Description
The MAX4450/MAX4451 are single-supply, rail-to-rail,
voltage-feedback amplifiers that employ current-feed-
back techniques to achieve 485V/µs slew rates and
210MHz bandwidths. Excellent harmonic distortion and
differential gain/phase performance make these ampli-
fiers an ideal choice for a wide variety of video and RF
signal-processing applications.
The output voltage swings to within 55mV of each sup-
ply rail. Local feedback around the output stage
ensures low open-loop output impedance to reduce
gain sensitivity to load variations. The input stage per-
mits common-mode voltages beyond the negative sup-
ply and to within 2.25V of the positive supply rail.
R
TO
MAX445 _
V
OUT
IN
R
TIN
V
OUT
= [1+ (R
F
/ R
G
)] V
IN
R
O
Figure 1a. Noninverting Gain Configuration
R
G
IN
R
TIN
R
F
Applications Information
Choosing Resistor Values
Unity-Gain Configuration
The MAX4450/MAX4451 are internally compensated for
unity gain. When configured 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 capacitance and inductance.
R
TO
MAX445 _
V
OUT
V
OUT
= -(R
F
/ R
G
) V
IN
R
S
R
O
Figure 1b. Inverting Gain Configuration
7
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