1940 hot problem

Hello,

The AD1940 is tested at 125degC for Tc, and guaranteed for proper operation up to and including that temperature ceiling. Can you give me an idea about the temperature rating of the passive components around the AD1940? What grade capacitors are you using for the Loop Filter and PS decoupling? What type resistors are you using, 1% metal film? Have you looked at the power supply rail as the temperature goes up? Do you have this problem on more than one board? Have you swapped out the AD1940 for a new piece of silicon?

Can you please include the schematic for your board? Maybe we can spot a problem in your design.

Best regards,
Coleman

Hello,

I'd just like to add to what Coleman wrote, just to provide some peace of mind for you. The AD1940 has shipped millions of units over the past 10 years in automotive applications, where our customers routinely do high temperature testing. We are confident that there are no problems with the AD1940 at high temperatures since we have never received a field return of an AD1940 due to temperature concerns.

I expect that this is an applications level issue. Are you using a 4-layer PCB with appropriate design for thermal dissipation? Is there a solid ground plane? Are you following the best practice guidelines? (for reference, see here: https://ez.analog.com/docs/DOC-1889 )

Hello ,

thanks for your reply.The schematic is included.

On my borad,the resistors are all 1% metal film. I testing 3 boards, the 3 boards are the same hot problem.

I use a finger at the top of the chip, About 15 minutes,I can feel the IC becomes more and more hot.In the end, the fingers will feel hard to bear(But if insist on not let go, the human body is also acceptable),The voice of the output in addition to the normal testing sound, there are a lot of the "PUM". the 2.5V AND 3.3v are always been normal. After the test, except the 1940, the other IC no fever phenomenon(including the power ic 1117-3.3 and 1117-2.5).

There is another phenomenon.In my project,I use the the filters(second order, double precision), if i set that (b0=1.0), (b1,b2,a1,a2=0), or I set up for the other parameters but with the cold wind continues to blow, the strange noises will not appear.

and this is the my first project using the ad1940 runing the fs at 96k,is something that i didn't notice that?

thanks a lot

hello ,

thanks for your reply. I have several successful experience to use 1940,but all the sample rate is 48k but this.

my pcb is 2-layer,you can see the photo. thanks

Can you please post your schematic as a PDF? Thanks, Coleman

PDF schematic

With 750 instructions you are running close to the limit, especially if there are slew hardware controls in the project. Could you try decreasing the size of the program slightly?

(More details about sample rate vs. instruction count here: https://ez.analog.com/docs/DOC-2734 )

Can you please look at the master clock signal as the temperature increases? Is it holding steady at 12.288 MHz?

Are you following the steps to change the sample rate of the project?

(More details about setting the sample rate here: https://ez.analog.com/docs/DOC-1431 )

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EZ Admin