Measurement on Vbias0 and Vzero0 does not match what is expected on AD5940

Hi,

We will contact the product owner and get back to you.

Thanks,
Janine

Hi,

  Both VBias and Vzero must be 1.3V for this setting. They can be monitored on P7 through holes at CE0 and SE0.

VBIas = VCE0 - AGND

Vzero = VSE0 - AGND

Thanks Akila for your response!

I measured the CE0 on P7 with the TIA switches configured as what I mentioned preciously, and the CE0 is at 1.26V. Do you have some idea why I can not get 1.3V? BTW, I want to configure LPTIA switch SW6 from position 1 to position 2, and configure SW7 from position 1 to position 2 as well (as indicated in the attached figure). The reset values of the SW6 AND SW7 is 0, indicating they are open, If I set the corresponding register bits to 1, I assume they are going to be closed on position 1, right? If I want to configure them to close on position 2, how to do it?

Thanks,

Olive 

Hi,

  You may call LPDACCal() function to calibrate LPDAC to get exact expected voltage output. 

(Reference: (+) AD5940: Offset on the current measurement. - Q&A - Precision ADCs - EngineerZone (analog.com))

SW6, SW7 = 0 means they are in position 1.

                  = 1 means they are in position 2.

Hi Akila,

Just wondering how to configure the FORCE/SENSE switches shown in Figure 22 in the AD5940 datasheet?

Thanks,

Olive

Hi.

 May I know if you have referred to AD5940 example codes in github GitHub - analogdevicesinc/ad5940-examples: AD594x related application examples and block level examples. 

which shows how to configure the switches

Hi Akila,

Thanks for your reply!

Yes, I am using the Square wave voltammetry example from the examples github. The Force/Sense switches are shown in the Figure 22 in the datasheet, but it is no mentioning in any of the example code.

-Olive

Hi Akila,

There are a few more things that I'd like to get your help to clarify.

a). In addition to the reply I made above, the configuration that I would like to have with the Square wave voltammetry example is like what is shown in Figure 2 of the document AN-1563 (3/2019 version), where the FORCE/SENSE switches are closed. I don't know if there is any example code to show how to configure these switches to be closed?

b). Also I am trying the AMPEROMETRIC measurement example provided in the document AN-1563 (3/2019 version) on page 5.  I have two questions on this example. 1). the first paragraph in the THEORETICAL CALCULATION section, it says "the JP6 jumper (on position B) connects a resistor network to the SE0 pin and the CE0 pin, the network consists of two 10KΩ resistors in parallel". However, when I checked the EVAL-AD5940ELCZ schematic (https://wiki.analog.com/_media/resources/eval/user-guides/eval-ad5940/hardware/02_050193b.pdf), I did not see two 10KΩ resistors, but one for 3KΩ and one for 1KΩ. And the equation in the following paragraph "I = V(RE0 − SE0)/750 Ω" seems also support the resistors are 3KΩ and 1KΩ. Can you please confirm it? 2). In the second paragraph of this section, it says "if SensorBias is set to zero, there is no voltage between the reference electrode and sense electrode. Therefore, the current displayed is zero". However, when I run the example on the eval board, it shows non-zero current value from RealTerm. Just wondering why it happens?

c). in Figure 22 of the AD5940 datasheet, when set SW3 (LPTIASW0(3)), does it mean both switches at the SW3 will be closed?

Thanks,

Olive

Hi,

- This line below in example code AD5940_SquareWaveVoltammetry.c tells the switch configuration 

if(AppSWVCfg.LPTIARtiaSel == LPTIARTIA_OPEN) /* User want to use external RTIA */
lploop_cfg.LpAmpCfg.LpTiaSW = LPTIASW(13)|LPTIASW(2)|LPTIASW(4)|LPTIASW(5)|LPTIASW(9)/*|LPTIASW(10)*/; /* SW5/9 is closed to support external RTIA resistor */
else
lploop_cfg.LpAmpCfg.LpTiaSW = /*LPTIASW(13)|*/LPTIASW(2)|LPTIASW(4);

- The correct values present are 3k || 1k.

(10k || 10k was present in the older version of schematic).

- With SensorBias =0, typical current expected with Amperometric example is as shown below:

Hello AD5940-Build Time:10:04:43
Freq:32485.582031
index:0, Current:0.102128uA
index:1, Current:0.068085uA
index:2, Current:0.034043uA
index:3, Current:0.034043uA
index:0, Current:0.034043uA
index:1, Current:-0.000000uA
index:2, Current:-0.000000uA
index:3, Current:-0.000000uA
index:0, Current:-0.000000uA
index:1, Current:-0.034043uA
index:2, Current:-0.034043uA
index:3, Current:-0.000000uA
index:0, Current:-0.034043uA
index:1, Current:-0.034043uA
index:2, Current:-0.034043uA
index:3, Current:-0.068085uA

- Yes. If LPTIASW0(3) =0, both switches at SW3 will be closed.

Thanks Akila! it is very helpful!

One more thing I would like to confirm from you: Is it true when any of the TIA switch is closed, the FORCE/SENSE switch shown in Figure 22 will be closed automatically?

Thanks,

Olive