Funny VDAC output signal, slow voltage settle

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Anonymous
Not applicable

Hi

   

I am using the PSOC kit with the CY8C3866 (ES2 silicon)

   

I have to use the DAC, but the output signal is strange (see attachment). When I set the DAC to a new value, it does not settle like it should in less than 5us

   

The DAC output is directly into a 1M scope input, DC coupled.

   

The code, somewhat snipped: (also attached)

   

// Enable DACs

   

VDAC8_1_Start();

   

 

   

while (1) {

   

VDAC8_1_SetValue(100);

   

 

   

for (i=1;i<100;i++) {

   

value1 = 100;

   

}

   

VDAC8_1_SetValue(0);

   

 

   

for (i=1;i<100;i++) {

   

value1 = 100;

   

}

   

}

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1 Solution
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

Keep in mind the VDAC output is NOT a voltage source. For the 1V range

   

its output Z is 4K , 4V range 16K, typical values. So if you have any signif-

   

icant C on pin that will show up as RC charging waveshape.

   

 

   

Your waveshape looks like C ramping from a current source. Or RC over a short

   

span.

   

 

   

I noticed you are using an ES version of PSOC 3, and old Creator. There have

   

been many bug fixes and components fixes/upgrades since then. Creator is now

   

3.2 SP1. You should, if you can, upgrade.

   

 

   

Regards, Dana.

View solution in original post

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5 Replies
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

Keep in mind the VDAC output is NOT a voltage source. For the 1V range

   

its output Z is 4K , 4V range 16K, typical values. So if you have any signif-

   

icant C on pin that will show up as RC charging waveshape.

   

 

   

Your waveshape looks like C ramping from a current source. Or RC over a short

   

span.

   

 

   

I noticed you are using an ES version of PSOC 3, and old Creator. There have

   

been many bug fixes and components fixes/upgrades since then. Creator is now

   

3.2 SP1. You should, if you can, upgrade.

   

 

   

Regards, Dana.

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ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

If you want a true V source out of the VDAC pass it thru OpAmp configed as

   

buffer, high power setting.

   

 

   

Regards, Dana.

odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted
        Also make sure that scope probe is balanced. There is a connector on front face of scope with 1kHz output and there is adjustment capacitor on the probe. Hook it up and tune capacitor to make square wave.   
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Anonymous
Not applicable

Thank you for the comments. It is really embarrasing, it was the probe compensation 😉

Anonymous
Not applicable

Thank you for the comments. It is really embarrasing, it was the probe compensation 😉

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