AD698 LVDT excitation no signal &Signal distortion issue

Hi,

We will look into this, I'll contact the product owner and get back to you.

Hi, andreialejandro

I would like a quick answer.

thank you.

Hi, 

Apologies. We are reaching out to the product to better assist you on this. 

Thanks,

Jellenie

Hi, JellenieR 

If you need a schematic diagram of my application for quick cause analysis, you can share it.
However, since it is a confidential document, it can be delivered by personal e-mail.

Please confirm.

thank you

Hi, JellenieR 

Is there a problem with the operation of AD698AP 28-Pin PLCC TYPE when working with SMT?

Please confirm.

thank you

Hi, 

Apologies. This is an old part so I am not really quite familiar. But I've already contacted the product owner to get back to you on this.

However, looks like the excitation are controlled via R1 and C1 in shown in figure 7, 8 and 13 of the datasheet. Can you try using an R value specified in the datasheet? 

In terms of the distortion is it present with or without LVDT? Have you also consider the thermal shutdown and loading consideration as stated in the datasheet as well? 

And also have you consider this reference circuit in your schematic? 

CN-0301 (Rev. A) (analog.com)

Thanks,

Jellenie

Hi, JellenieR 

Answer your questions.

1.

However, looks like the excitation are controlled via R1 and C1 in shown in figure 7, 8 and 13 of the datasheet. Can you try using an R value specified in the datasheet? 

-> I tried changing R1 to the same as in the datasheet. However, the EXC signal is not output.

2.

In terms of the distortion is it present with or without LVDT? Have you also consider the thermal shutdown and loading consideration as stated in the datasheet as well?

->Even if the LVDT sensor is not connected, the EXC signal is not output.

   And, what are the considerations for thermal isolation and load?

   Is it the reflow temperature?

   Or what should be considered in the application circuit? My application is a half-bridge LVDT circuit.

Thanks,

Do yoon.

Doyoon,

Based on your connectivity I believe the values you have selected for the excitation frequency capacitor and the filter capacitors are correct for 13KHz excitation and for 250 Hz bandwidth.   

My question is do you really only want 3.3V RMS excitation output as you've set R304 to 27KOhms.   

Also I'm not sure what you are attempting to do with the output offset as to bias the SIGOUT you should only be populating one of R301 or R302 respectively.  If you desire a positive shift you should populate R302 and leave R301 open.   

Let me know if this helps

Sean

HI, Sean

I want to AD698 excitation pin sign wave. But I don't understand why there is no signal coming out.

The reason why I set R304 to 27Kohm is because of the spec. of my lvdt sensor.

thank you

Doyoon,

Schematically nothing stands out as to why the device doesn't start up and provide the excitation output.  Have you tested multiple boards and observed the same behavior?

Sean