thermal issue with ad7626 single-ended circuit

Hi ILKANG ,

I have some comments and questions regarding this issue.

Just for clarification, you encounter 50 degrees heat both in using 590 ohms and 100 ohms, is that right? One factor to look at is the exposed pad connection to the ground plane. This helps improve heat transfer to the ground plane. Can you verify that the exposed pad is properly connected to the ground plane? I'm also attaching the PCB layout section below.

- Why is Datasheet telling me to use 590 ohms and Precision ADC Driver Tool not to use 590 ohms?  - the warning shown is for gain of 2V/V while your configuration is only at gain = 1V/V. This should work, although from the tool we can see that the plots are not displayed if we change the Rf above 120 ohms. I will try to contact the Precision ADC Driver Tool Platform to confirm if this is a tool limitation, or an issue.

Best regards,

Gio

안녕,지오발게미노 ,

귀하의 질문에 답변해 드리겠습니다.

1. When using 590 ohms and 100 ohms, both ADA4899 generates 50 degrees of heat.

The exposed pad of ADA4899 is correctly connected to the GND.
I will attach the picture below. (Top Layer)

 Top Layer (Top silk)

U9 and U10 are ADA4899.

After looking at the ADA4899 PCB Layout you attached, I think there can be parallel capacitance in ADA4899.

 2 Layer (Top silk)

 3 Layer (Top silk)

 Bottom Layer (Top silk)

But I don't think 0.2pF parasitic capacitance generates heat of 50 degrees.
Wouldn't there be a problem in other parts?

2. If you get an answer from Precision ADC Driver Tool Platform, please reply to me.

Thank you for your kindness.

Best guard,

IL

Hi ILKANG ,

Can you share the ambient temperature you are operating at, what is the power dissipation and what is your expected temperature on the ADA4899-1? Can you also share how are you measuring the temperature?

"6. Is there a problem with the ada4899-1 having a heat of about 50 degrees in the ad7626 single-ended circuit?" - are you asking if it will damage the part? the junction temperature is rated at 150°C max.

Best regards,

Gio

Hi, GioBalgemino 

1. I use a thermal imaging camera called Seek Thermal.

So I'm looking at the approximate temperature.

I didn't set the emissivity and reflection temperature values of the thermal imaging camera accurately.
However, there is no difference of more than 3 degrees when measuring the temperature of human skin temperature, etc.

2. This is a picture of the PCB with a thermal imaging camera.

The white part has the highest temperature, and the device is ADA4899.

If you zoom in on the picture, the white part on the top left is about 68 degrees.

I thought ADA4899 is over 50 degrees with this.

3. In addition, the PCB has various devices, making it difficult to measure only one power consumption of ADA4899.

Can you measure the amount of power due to heat generation?

4. A 50-degree heat does not damage ADA4899.
However, ADA4899 has more heat than other devices.

So I want to know the exact cause of that part.

Moving this thread to the Precision Converters Community for better assistance.

Hi andreialejandro NathanT , can you help?

Thanks,

Mae