until now I'm not able to use the AD7091R-5 with internal reference of 2,5V.I'm sending this bytes to the AD7091-R to configure it :\x02\x06\xC1\x01\x0F\x00meaning config reg 0x02 is set to 0x06C1 -> CMD Mode = 1, -> Software Reset = 1, -> Cycletimer to default, -> P_DOWN = 1, which should enable the internal reference.config reg 0x01 is set to 0x0F -> All 4 channels onthen set config Reg 0x00
After this I do 8 byte reads where I can see that the conversion results are comming, the channel index in each word counts also up, but the read values are wrong because the internal reference is not 2,5 V (I measured around 3,2V at the REFIN/OUT pin)Related to this "reference" the values are correct, so the AD Converter itself is ok,
But what's going wrong setting the INTERNAL REFERENCE ?
AD7091R uses internal reference as default unless external voltage is applied on the REFin/REFout. For me to help you, can I have your schematic?
Apologize, I was referring on the wrong device (AD7091R). From the Table 3 of the AD7091R-5, Analog input voltage should be from -0.3V to Vref + 0.3 V only with respect to ground. Having input voltage greater than the maximum voltage will cause the diode (D3 from Figure 36) to conduct affecting the operation of the reference voltage.
I think the internal reference is default OFF, this is also what the datasheet says:
Datasheet Page 15 : of AD7091R-5
"When the P_DOWN LSB bit is set to 0, supply an external reference in the range of 2.5 V to VDD through the REFIN/ REFOUT pin. At power-up, the internal reference disables by default."
The schematic I can post later. Is it possible that this behavour can be caused by overvoltageat the one of the analog Input pins? (3,5V) This is more than 2,5V+0,3...
No problem, but your idea with the diode is also my thinking. yesterday I saw later that one of the channelswas always in overdrive. I'll correct that and then the 2,5V internal ref. hopefully works :-)
Thank you !
Everything is running fine now, the overload at the analog input made the 2,5V internal reference to rise to Uin-0,3V !