# Why my operational amplifier TL3472IDR doesn't work properly with 1Mhz ?

#### Samaze123

Joined Sep 30, 2023
4
On a breadboard i'm using an Arduino Nano to produce a square signal of 1Mhz.
I pass it through a volage divider to keep 1V.
Until here all is working properly.
Then i use my op amp TL3472IDR to make a volage follower. The op amp can't produce a correct signal and using a scope i'm seeing that my square signal is almost flat.

This op amp is, according to its datasheet, functional up to 4Mhz and its slew rate is 13V/µs. ( I put the datasheet in the attachments)

In the image, the blue is the arduino output and the yellow is the op amp output.

#### Attachments

• 390.3 KB Views: 7

#### crutschow

Joined Mar 14, 2008
33,355
What are the power supply voltages to the op amp?

#### ronsimpson

Joined Oct 7, 2019
2,796
Assuming D3 is the output, there is a cap to ground that shorts out high frequencies. Why?
Your amplifier is built to have an input of 0 to 2.8V assuming a 0 to 5V supply. Don't get outside this range.
It appears you wany a 0 to 3V signal out. Most op-amps are not happy with the output voltage close to the supply voltage. The output voltage should be 0.3V above the negative supply and 1.3V below the plus supply.
If you violate any of these voltage limits the amp will get slow.

#### ericgibbs

Joined Jan 29, 2010
18,232
hi Sam
A 1n0 at 1MHZ has an impedance of 159R
The Nano output is 5V, so that's 5v/159R = 31mA, IIRC the Nano is rated at 20mA max.?
E

On checking, it is claimed to be able of higher output current.

#### Attachments

• 72.6 KB Views: 3
Last edited:

#### Samaze123

Joined Sep 30, 2023
4
What are the power supply voltages to the op amp?
vcc- = 0 and vcc+ = 5V (it's connected to the ground and the 5V pin of the arduino)

#### ericgibbs

Joined Jan 29, 2010
18,232
Hi sam,
This sim shows what you would expect with 4MHz BW OPA
E

@Samaze123
Repositioned the resistors to give a more accurate sim

Last edited:

#### Samaze123

Joined Sep 30, 2023
4
Assuming D3 is the output, there is a cap to ground that shorts out high frequencies. Why?
Your amplifier is built to have an input of 0 to 2.8V assuming a 0 to 5V supply. Don't get outside this range.
It appears you wany a 0 to 3V signal out. Most op-amps are not happy with the output voltage close to the supply voltage. The output voltage should be 0.3V above the negative supply and 1.3V below the plus supply.
If you violate any of these voltage limits the amp will get slow.
i put the cap to avoid this :

#### Bordodynov

Joined May 20, 2015
3,116
See

#### crutschow

Joined Mar 14, 2008
33,355
put the cap to avoid this :
Were you using a 10:1 probe with a short ground clip to view those waveforms?

#### ericgibbs

Joined Jan 29, 2010
18,232
Hi Alex, @Bordodynov
Your simulation post #9., is using a 50kHz pulse frequency, the TS is using a 1MHz pulse frequency.
Also, an output pulse height of 2.5V, with a MCU Vsupply of 5V, will be 'marginal' for a Logic '1'

E

Description: Nano
As the input voltage increases from 0V, the input is read as 0 and switches to 1 at 2.60V.
As the input voltage decreases from 5V, the input is read as 1 and switches to 0 at 2.35V.
Hysteresis is 0.25V.

Last edited:

#### ericgibbs

Joined Jan 29, 2010
18,232
hi sam,
This sim is using the TL3472 model and the 1MHz square wave source.
The circuit and OPA give a very poor performance at 1MHz.
E

#### Attachments

• 52.1 KB Views: 8
• 51.2 KB Views: 8

#### Samaze123

Joined Sep 30, 2023
4
hi sam,
This sim is using the TL3472 model and the 1MHz square wave source.
The circuit and OPA give a very poor performance at 1MHz.
E
Okay thanks, do you know another OPA that could works with this circuit ?

And what if I add 1V at the end of the voltage divider ? The signal will be in the opa working range ?

#### ericgibbs

Joined Jan 29, 2010
18,232
hi sam,
Is this Vout shape and level acceptable?
E

#### Attachments

• 49.6 KB Views: 7

#### ericgibbs

Joined Jan 29, 2010
18,232
hi sam,
E

#### Attachments

• 50.9 KB Views: 9
• 315.1 KB Views: 0

#### ericgibbs

Joined Jan 29, 2010
18,232
Hi sam,
This is about as good as it gets for 1 MHz.
E

#### Attachments

• 46.2 KB Views: 10

#### Bordodynov

Joined May 20, 2015
3,116
ericgibbs,
I first made sure that the proposed circuit does not work at 1 MHz. I was lowering the frequency until it was functioning normally. Also I showed the levels of zero and one. This I did to show the unsuitability of the operational amplifier.
Here's a more suitable operational amplifier:

#### ericgibbs

Joined Jan 29, 2010
18,232
Hi Alex,
The latest circuit shows a Vout that is below the required logic level for the Nano MCU.

What do you think about posts #14 & #15?

Eric
Description: Nano
As the input voltage increases from 0V, the input is read as 0 and switches to 1 at 2.60V.
As the input voltage decreases from 5V, the input is read as 1 and switches to 0 at 2.35V.
Hysteresis is 0.25V.