MAX44206AUA+

Lower resistor values are ideal for low-noise performance 

at the cost of increased distortion due to increased load-

ing of the feedback network on the output stage. Higher 

resistor values will yield better distortion performance 

due to less loading on the output stage but at the cost of 

increase in higher output noise.

Improving Stability Using 

Feedback Capacitors

When the MAX44206 is configured such that a combina-

tion of parasitic capacitances at the inverting input form 

a pole whose frequency lies within the closed-loop band-

width of the amplifier, a feedback capacitor across the 

feedback resistor is needed to form a zero at a frequency 

close to the frequency of the parasitic pole to recover the 

lost phase margin. 
Adding larger value feedback capacitors will reduce the 

peaking of the amplifier but decreases the closed-loop 

-3dB bandwidth.

Layout and Bypass Capacitors

For single-supply applications, it is recommended to place 

a 0.1µF NPO or C0G ceramic capacitor within 1/8

th

 of 

an inch from the V

S+

 pin to ground and to also connect 

a 10µF ceramic capacitor within 1 inch of the V

S+

 pin to 

GND. 
In dual-supply applications, it is recommended to install 

0.1µF NPO or C0G ceramic capacitor within 1/8

th

 of an 

inch from the V

S+

 and V

S-

 pins to GND and place 10µF 

ceramic capacitors within 1 inch of the V

S+

 and V

S-

 pins 

to GND. Low ESR\ESL NPO capacitors are recommend-

ed for 0.1µF or smaller decoupling capacitors. A 0.1µF or 

0.22µF capacitor is a good choice close to VOCM input 

pin to ground.
Signal routing into and out of the part should be direct 

and as short as possible into and out of the op amp 

inputs and outputs. The feedback path should be carefully 

routed with the shortest path possible without any para-

sitic capacitance forming between feedback trace and 

board power planes. Ground and power planes should be 

removed from directly under the amplifier input and output 

pins. Also, care should be taken such that there will be no 

parasitic capacitance formed around the summing nodes 

at the inputs that could affect the phase margin of the part.
Any load capacitance beyond a few picofarads needs to 

be isolated using series output resistors placed as close 

as possible to the output pins to avoid excessive peaking 

or instability.

Driving a Fully Differential ADC

The MAX44206 was designed to drive fully differential 

SAR ADCs such as the MAX11905. The MAX11905 is 

part of a family of 20-/18-/16-bit, 1.6Msps/1Msps ADCs 

that offer excellent AC and DC performance. 

Figure 8

 

details a fully differential input to the MAX44206, which 

then drives the fully differential MAX11905 ADC inputs 

through the ADC input filter shown in the dashed box.
The MAX6126 provides a 3V reference output voltage, 

which is fed to the ADC’s reference. The MAX44206’s 

common mode (VOCM) is created by dividing down the 

reference voltage by a factor of two. A pair of 1kΩ 0.1% 

resistors are used for this purpose. The VOCM input is 

bypassed to GND with a combination of 2.2µF (X7R) and 

0.1µF (NPO) capacitors.
The MAX44206 is connected in a unity-gain configuration. 

The  input  resistors  and  feedback  resistors  are  all  1kΩ 

0.1% resistors. The feedback resistors are bypassed by 

a pair of 4.7nF (C0G, 100V) capacitors. These feedback 

components roll the amplifier off to about 60MHz corner 

frequency.
The ADC  input  filter  uses  a  pair  of  10Ω  0.1%  resistors 

and a 2.2nF (C0G) capacitor. This input filter assists the 

MAX44206’s settling response with the MAX11905’s fast 

acquisition window.

Figure 8

 was used to test the AC performance in Figures 

9 and 10. Data were taken with the input frequencies 

at 10kHz on the MAX11905 Evaluation Kit. Figures 9 

to 13 detail the results of the MAX11905 Evaluation Kit 

(MAX11905DIFEVKIT#) GUI.

MAX44206

180MHz, Low-Noise, Low-Distortion, Fully 

Differential Op Amp/ADC Driver

www.maximintegrated.com

Maxim Integrated  │

  22

MAX44206AUA+ Information:
Part No.
MAX44206AUA+

RFQ

Description
IC OPERATIONAL AMP UMAX
File Size
1576689 bytes
Page Size
612 x 792 pts (letter)
All Pages
29
Manufacturer
Maxim Integrated
Homepage
http://www.maximintegrated.com/en.html
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