AD7740 Output Frequency Stabilization

Hi,

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

Regards,

JC

Hi hbsts 

Good day.
Would it be possible for you to share a link or reference in your circuit design? This is for further details, and we could deduce your queries.
Thank you.

Kind Regards,

Red

Hi  

Thanks for your answer. We want to convert a voltage to the frequency by using AD7740. We designed the circuit according to related datasheet. In our application, CLK is good and stable. We also try applying voltage to Pin-CLKIN using voltage follower but result did not change.

Reference link/datasheet:

https://www.analog.com/media/en/technical-documentation/data-sheets/ad7740.pdf

Regards.

Hi hbsts ,

Let me share with you these links, could probably help you to understand the problem you are facing. This is to troubleshoot your setup.

Please check these links:

(+) troubleshooting help - AD7740 - Q&A - Precision ADCs - EngineerZone (analog.com)

(+) AD7740 AD7740: maximum input frequency - Documents - Precision ADCs - EngineerZone (analog.com)

Let me know this helps, or if you still need further assistance let me know.

Many thanks.

Kind regards,

Red

Hi  ,

I checked these links but i still need further assistance.

I also contacted  engineer working in your company and he gave me advice to place 0.1uF on the REFIN/OUT (pin-4) pin. This helped a little but it was not a complete solution. The IC breaks down after about 16kHz.

Best regards.

Hi hbsts 

The part has a maximum input frequency of 1 MHz.

For an analog input signal that goes from 0 V to VREF, the output frequency goes from 10% to 90% of fCLKIN.  Can you please share your data with us, epecially the fCLKIN,CLKOUT, VIN and the corresponding Fout.

Thank you.

Kind regards,

Red

Hi  

Our design is for 32KHz frequency with external clock at CLKIN pin. We are using CD40106B Schmitt-trigger inverter (You can see our schematics above).

We also know that the output frequency goes from 10% to 90% of CLKIN and it correctly works at 10% frequency (3277Hz) in VIN=0V.  

Here are datas you want;

fCLKIN = 32768kHz

CLKOUT = 32768kHz

VIN = 1.8V 

FOUT = Distorted signal (You can see it above)

According to this formula in datasheet, for instance, we must measure Fout=(0.1 * 32768) + ( 0.8 * (1.8 / 2.5) *32768) = 22kHz

Thank you 

Best regards.

Hi hbsts 

Let me first review this and will get back to you ASAP.

Thank you.

Kind regards,

Red