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PSoC 5, 3 & 1

Anonymous
Not applicable

 What is the input imedance of the v2.0 comparator module? I've been seeing some errorenous readings when I am using a voltage divider into the comparator. The divider is on the order of 50kohms.

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6 Replies
ETRO_SSN583
Esteemed Contributor

I do not see in module datasheet or device datadsheet or TRM

   

any discussion. If you are using Hysterisis I suspect you may be

   

seeing +fdbk R's used to develop fdbk.

   

 

   

File a case at -

   

 

   

    

   

          

   

www.cypress.com

   

“Support”

   

“Technical Support”

   

“Create a Case”

   

   

 

   

Or use DelSig, and a sampling R to measure the current going into Comparator,

   

that might be instructive. Are you using Hysteresis ?

   

 

   

If you file a case let forum know what answer was.

   

 

   

Regards. Dana.

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HeLi_263931
Honored Contributor II

In the CY8C38 family data sheet, the (typical) input current is specified as 2 nA, or 14nA for SIO pins. It might be higher, but not _that_ much.

   

Are you sure you have the pins really configured as analog high-Z?

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ETRO_SSN583
Esteemed Contributor

I am not sure of what the applicability of the SIO pin input leakage is to this

   

issue ?

   

 

   

Pins being used are GPIO configed as analog, connected to a comparator,

   

unless I misunderstood something...which wouldn't be the first time.

   

 

   

Regards, Dana.

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ETRO_SSN583
Esteemed Contributor

My apologies, I see you might have been think SIO comparator functionality

   

was being used -

   

 

   

   

Regards, Dana.

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HeLi_263931
Honored Contributor II

No, I meant to calculate the input impedance from the current flowing in the pin (2 nA would, at 5 V, result in an input resistance of 2.5 GigaOhm). This is the only specification I can find for that value. The Comparator compoinent data sheet states that the comparator is implemented as trimmer differential amplifier, and hysteresis is not handled by a feedback resistor it seems.

   

So I guess the problem doesn't stem from the input impedance.

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ETRO_SSN583
Esteemed Contributor

Pretty much all comparators implemented by using high gain diff amp,

   

and trimmed as it states. It does say offsetting currents are added to

   

input stage to generate Hysteresis, that could be done with I source or

   

simple R's, either way that would affect Zin, or so I think. Thats why a

   

case needs to be filed, we are fishing with guesses at this point.

   

 

   

Regards, Dana.

   

 

   

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