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PSoC Creator & Designer Software

Anonymous
Not applicable

Hello Every one,

   

I took one example code for PGA. I set 1 V from VDAC and measuring the output. The problem is, if i set gain of 8 or higher it is only showing me 3.284 V on Multimeter.

   

Can you tell me why this is happening and how i can get rid of this thing?

   

Looking forward for your suggestions.

   

Regards

   

Awais

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9 Replies
Anonymous
Not applicable

I am using PSOC 5LP.

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ETRO_SSN583
Esteemed Contributor

The input and output V limits of a psoc pin and analog

   

are basically Vdda >= Vanalog >= 0. So with a G = 8, and

   

input of 1 V, you are asking for 8V out, which exceeds your

   

Vdda.

   

 

   

Regards, Dana.

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Anonymous
Not applicable

Sorry,

   

I didnt get your point.

   

How i can set my Vdda Value in order to get accurate result?

   

Regards

   

Awais

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ETRO_SSN583
Esteemed Contributor

The CM range is limited by -

   

Vdda >= Vanalog >= 0 and Vdda is basically limited to 3.3 V or 5V, see spec sheet

   

for exact number.

   

 

   

You cannot get > Vdda out of the chip.

   

 

   

Regards, Dana.

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Anonymous
Not applicable

oh yes,

   

Now i know what do u mean 🙂

   

Thankyou for your replay.

   

Regards

   

Awais

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ETRO_SSN583
Esteemed Contributor

Glad I could help.

   

 

   

Regards, Dana.

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Anonymous
Not applicable

Hi One more time 🙂

   

So this means it applies to normal op amps also?

   

I cannot get more than 5 volts?

   

Am i right?

   

Regards

   

Awais

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ETRO_SSN583
Esteemed Contributor

Thats correct.

   

 

   

If you need to get higher voltage swings you can use external parts, split power

   

supplies to do that.

   

 

   

Regards, Dana.

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ETRO_SSN583
Esteemed Contributor

If you need to produce higher V swings that a PSOC Vdda allows you

   

can use external OpAmp running on higher voltages, and / or split supplies.

   

 

   

Some ways of generating simple negative supplies for a split supply application

   

here -

   

 

   

www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip

   

 

   

Note you can, in some applications, use an unregulated supply on external OpAmp

   

because its PSRR aids in reducing its supply sensitivity to changes in its supply.

   

 

   

Regards, Dana.

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