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irmanao
Joined: 08 Apr 2015
Posts: 77
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| Max input V(peak) for ADC on dspic33e |
 Posted: Mon Jun 15, 2015 5:09 am |
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Hey,
I can't seem to find what the max input V(peak) for ADC on dspic33e is? I'm guessing it's 5volts(0-5). Can anybody help me with this?
Thanks |
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alan
Joined: 12 Nov 2012
Posts: 357
Location: South Africa
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| Posted: Mon Jun 15, 2015 7:29 am |
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Vpeak can not be higher than Vadc which must be <= Vdd whichever is lower but limited to 3.3V
Regards |
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irmanao
Joined: 08 Apr 2015
Posts: 77
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| Posted: Tue Jun 16, 2015 2:34 pm |
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| So the peak of my input cannot be higher than 3.3V? |
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temtronic
Joined: 01 Jul 2010
Posts: 9225
Location: Greensville,Ontario
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| Posted: Tue Jun 16, 2015 2:50 pm |
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Whenever I hear/see 'peak' I think of an AC waveform so please do NOT inject/sample an AC waveform to the PIC. It is one SURE way of destroying it !!!
Jay |
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newguy
Joined: 24 Jun 2004
Posts: 1907
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| Posted: Tue Jun 16, 2015 3:39 pm |
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| irmanao wrote: | | So the peak of my input cannot be higher than 3.3V? |
This is from the dsPIC33F family reference manual. I'll leave it up to you to find the equivalent information for your processor.
From the ADC chapter:
| Quote: | The voltage references for A/D conversions are selected using the VCFG<2:0> control bits
(ADxCON2<15:13>). The upper voltage reference (VREFH) and the lower voltage reference
(VREFL) can be the internal AVDD and AVSS voltage rails or the VREF+ and VREF- input pins.
The voltages applied to the external reference pins must meet certain specifications. Refer to the
Electrical Specifications section of the device data sheet for details. |
(emphasis mine)
From the dspic33FJ256GP710A's data sheet (electrical characteristics chapter):
| Quote: | Device Supply
AVDD Module VDD Supply (min) Greater of VDD - 0.3 or 3.0 (typ) - (max) Lesser of VDD + 0.3 or 3.6 V
AVSS Module VSS Supply (min) VSS - 0.3 (typ) - (max) VSS + 0.3 V
Reference Inputs
VREFH Reference Voltage High (min)AVSS + 2.7 (typ) - (max) AVDD V See Note 2
VREFL Reference Voltage Low (min) AVSS (typ) - (max) AVDD - 2.7 V See Note 2
VREF Absolute Reference Voltage (min) 3.0 (typ) - (max) 3.6 V VREF = VREFH - VREFL
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| Quote: | | Note 2: These parameters are not characterized or tested in manufacturing. |
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irmanao
Joined: 08 Apr 2015
Posts: 77
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| Posted: Wed Jun 17, 2015 2:47 am |
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Thanks
(It is superimposed on a DC offset) |
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temtronic
Joined: 01 Jul 2010
Posts: 9225
Location: Greensville,Ontario
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| Posted: Wed Jun 17, 2015 4:57 am |
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ah ha ! I knew it was an AC signal, well sort of...
Just be sure the signal NEVER goes below 0 (zero) volts or you'll be buying another PIC.
Or... if you don't destroy it, you'll wonder why are the ADC readings 'wrong, it worked before...'
Jay |
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irmanao
Joined: 08 Apr 2015
Posts: 77
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| Posted: Wed Jun 17, 2015 5:46 am |
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So the datasheet doesn't mention an internal connection of AVDD and VDD.
If i want to use those rails (Vdd-Vss) for adc should i just connect AVDD to Vdd and AVSS to Vss? And how about the multiple couples of Vdd/Vss provided? Do i leave them alone if i power the PIC by a usb connected to a computer?
I use the dsPIC33E USB Starter Kit.
Thanks and sorry.. |
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