MAX4012 Maxim, MAX4012 Datasheet - Page 10

• Manufacturer Part Number: MAX4012
• Description: The MAX4012 single, MAX4016 dual, MAX4018 triple, and MAX4020 quad op amps are unity-gain-stable devices that combine high-speed performance with Rail-to-Rail outputs
• Manufacturer: Maxim

The MAX4012/MAX4016/MAX4018/MAX4020 are sin-
gle-supply, rail-to-rail, voltage-feedback amplifiers that
employ current-feedback techniques to achieve
600V/µs slew rates and 200MHz bandwidths. Excellent
harmonic distortion and differential gain/phase perfor-
mance 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 ±120mA 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.
The MAX4012/MAX4016/MAX4018/MAX4020 are inter-
nally compensated for unity gain. When configured for
unity gain, the devices require a 24
series with the feedback path. This resistor improves
AC response by reducing the Q of the parallel LC cir-
Low-Cost, High-Speed, Single-Supply
Op Amps with Rail-to-Rail Outputs
Figure 1a. Noninverting Gain Configuration
10
______________________________________________________________________________________
R
G
IN
R
TIN
Applications Information
MAX40_ _
R
F
V
OUT
Choosing Resistor Values
Detailed Description
= [1+ (R
F
Unity-Gain Configuration
/ R
R
TO
G
)] V
IN
resistor (R
V
OUT
F
R
) in
O
cuit formed by the parasitic feedback capacitance and
inductance.
Select the gain-setting feedback (R
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
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
tors to 100
but could limit output swing by adding 200
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.
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
as close to the pin as possible. If operating with dual sup-
plies, bypass each supply with a 0.1µF capacitor.
Figure 1b. Inverting Gain Configuration
R
IN
TIN
Layout and Power-Supply Bypassing
R
G
Inverting and Noninverting Configurations
R
S
extends the pole frequency to 1.59GHz,
MAX40_ _
CC
V
R
OUT
F
to ground with a 0.1µF capacitor
= -(R
F
/ R
G
) V
IN
R
TO
F
F
= R
) and input (R
G
) using 1k
in parallel
V
resis-
OUT
R
G
O
)