PSOC4 ADC in 3.3v mode

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Anonymous
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Can the psoc4 Adc be used to sense 0v-5v with single ended when jumper J9 is connected to 3.3v? I want to connected Vref (P1[7])  to 5v Is this th right way to go? I want to do eight channel Adc 0v to 5v.

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5 Replies
HeLi_263931
Level 8
Level 8
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No. The input voltage cannot be higher than the analog supply voltage. But you might use a voltage divider to reduce the range of your input voltage.

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Bob_Marlowe
Level 10
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... and of course the Vref may not exceed analog supply.

   

 

   

Bob

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ETRO_SSN583
Level 9
Level 9
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The consequences of using 3.3 V but desiring 5 V ADC range

   

in a multichannel design would require an (R) attenuator on

   

each input. Or use an external mux with 3.3 V control drive,

   

5V input range followed by a single attenuator. So you would

   

have to do an error budget to determine if design meets your

   

goals in any event.

   

 

   

If all you have as a power source, 3.3 V, as a source, consider a

   

boost converter, many offerings from various vendors, from sw cap

   

designs to L based boost converters. Note some PSOC's have

   

an internal boost converter, PSOC 1 & 3.

   

 

   

Also datasheet incomplete regarding relationship of Vssa, Vss and

   

Vdda, Vdd.    

   

 

   

          http://www.cypress.com/?app=forum&id=2492&rID=90735

   

 

   

Regards, Dana.

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ETRO_SSN583
Level 9
Level 9
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Here are simple charge pump converter examples, just an external C required

   

for many. ~ 50 to 80 cent kinds of parts.

   

 

   

    

   

          http://www.ti.com/lsds/ti/power-management/boost-charge-pump-products.page

   

 

   

Regards, Dana.

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ETRO_SSN583
Level 9
Level 9
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One other consideration to using R dividers, is impact on

   

signal loading of the measurement node you are examining,

   

and of course speed and settling time impact on SAR opera-

   

tion.

   

 

   

All this can be largely mitigated by operating part at 5V. Or

   

use PSOC 1 or 3 with internal boost converters.

   

 

   

Regards, Dana.

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