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Detailed Description
The MAX4450/MAX4451 are single-supply, rail-to-rail,
voltage-feedback amplifiers that employ current-feed-
back techniques to achieve 485V/s 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.
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 24
Ω resistor (RF) 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.
Inverting and Noninverting Configurations
Select the gain-setting feedback (RF) and input (RG)
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 (RF = RG) using 1k
Ω
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 1k
Ω resis-
tors to 100
Ω extends the pole frequency to 1.59GHz,
but could limit output swing by adding 200
Ω 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.
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 VCC to ground with a
MAX4450/MAX4451
Ultra-Small, Low-Cost, 210MHz, Single-Supply
Op Amps with Rail-to-Rail Outputs
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7
Pin Description
PIN
OUT
VEE
IN+
INA-
OUTA
VCC
IN-
INB+
INB-
OUTB
INA+
—
4
—
2
1
8
—
5
6
7
3
1
Amplifier Output
2
Negative Power Supply
or Ground (in single-
supply operation)
3
Noninverting Input
—
Amplifier A Inverting
Input
—
Amplifier A Output
5
Positive Power Supply
4
Inverting Input
—
Amplifier B Noninverting
Input
—
Amplifier B Inverting
Input
—
Amplifier B Output
—
Amplifier A Noninverting
Input
IN
RG
VOUT = [1+ (RF / RG)] VIN
RF
RTO
RTIN
RO
VOUT
MAX445 _
Figure 1a. Noninverting Gain Configuration
IN
RG
VOUT = -(RF / RG) VIN
RF
RTO
RS
RTIN
RO
VOUT
MAX445 _
Figure 1b. Inverting Gain Configuration
FUNCTION
MAX4450
NAME
MAX4451