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Offset very high when EVAL-AD5755-1 SDZ is controlled by µC instead of SDP

Question asked by geurjas on Jun 29, 2018
Latest reply on Jul 6, 2018 by geurjas

Getting different precision with two setups. Setup1 SDP & EVAL-AD575xSDZ, setup2 µC & EVAL-AD5755-1 SDZ.

 

When setting 800mV:

With SDP setup I measure 798mV, so very good precision 2mV offset.

With my µC setup I measure 782mV, so not so good -18mV offset. (BTW this offset is different on the the whole  0-5V scale, -18mV is the biggest offset, it looks like a sines around the values which are expected)

 

Both use the same eval board and same powersupply on the J5 & J6.

J5 = +24 unipolar

J6 = +5V

 

All jumpers on default eval AD5755-1 position.

 

We use the same init calls for both setup after cold start up in the following order (copied from the evalutation software):

Hardware reset

configureMainControlReg       0x1C2200

writeDCDCconfig                    0x1C6007

writeDACControlReg              0x1C4110

writeDACControlRegEnable   0x1C4150

Then setting the output to 800mV (DAC value channel 0, 0x0028F6)

 

On the µC setup the inputs next to the SPI lines are connected to ground (/LDAC, CLEAR, POC). /RESET is controlled by the µC.

 

I see no difference in the setup, only that the SDP setup uses the J9 (SDP Board Connector) and the µC uses the J11. The DVdd is tested on 3.3V and on 2.8V (2 different µC boards) both gave exact the same results, also the values we get are always the same on the 0-5V range.

 

So my question is why is there a difference in the offset between those two setups. We like to have the same minimal offset of course

 

Thanks!

Jasper

 

 

 





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