• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 1085 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS7823: ADS7823 ripple issue...

Peter Tseng
Genius 5770 points
Part Number: ADS7823

Dear Sir,

Please refer to attached pic.

ch1 is SDA and ch2 is Ain of ADS7823 (pin2)

My customer found:

1. while they tried to read the Ain signal, the Ain signal will have ripple about 600mV Vpp.

Meanwhile, the value that got from ADC(red block 1) will difference with the data read from meter(red block 2) around 200~300mV.

2. if customer add 10uF in schematics of R31 and test again, the difference of value will low to 20~30mV.

Is there anything need to pay attention about this issue?

How to correct it?

Thanks.

  • 0
    TI__Genius 16890 points

    Hi Peter,

    This is caused by current flows, both from the I2C communcation and also by the internal workings of the part itself. 

    The best way to minimize this is by a good layout and using correct components. 

    They have pins 5, 6, 7 connected to ground.  They should be connected together by a large traces.  Even better is to have a solid ground plane layer that they connect to.  C23 should be as close to pin 1 as possible.  A big trace should be between pin 1 and C23 and the ground side of C23 should be connected either by a big trace to pins 3, 4 and 5 or to the ground plane.  C24 should be as close to pin 8 as possible.  A big trace should be between pin 8 and C24 and the ground side of C24 should be connected either by a big trace to pin 3, 4 and 5 or to the ground plane.

    A cap on the input is also a good idea.  The same placement should be used for this cap, it should be as close as possible to pin 2 and connected to ground with a good low impedance connection.

    Mike

  • 0 in reply to Michael Stout
    Genius 5770 points

    Dear Mike,

    Thanks your reply.