AnsweredAssumed Answered

AD7858LARS, erroneous converted result after high impedance on some input pins

Question asked by usaghi on Apr 5, 2013
Latest reply on Apr 19, 2013 by KarenNE

Hi,

 

Our customer said he is connecting SYNC、DIN、SCLK、CLKIN、CONVST pins of AD7858LARS part, directly to MCU, without pulling-up or down.

When MCU is reset, these pins become into high impedance state, and this state can be continued for seconds or more than a minute in some cases.

During above reset, 5V power is still continue to supply to AVDD and DVDD, despite above pins are high impedance.

Then after ending reset status in above, it starts data converting but results FFFh seems erroneous.

This erroneous result is observed under the condition of, 0.1V for AIN1~8, VREF=4.5V, against they can have 05Ah as normally converted reselt when not using above reset function.

 

Questions are:

1) Is it available that SYNC、DIN、SCLK、CLKIN、CONVST pins of AD7858LARS are become to be high-impedance, while 5V is applying to AVDD and DVDD ?

2) Even it is available, it is still good to continue the state for one minute at most ?

3) Converted result, FFFh, is erroneous they are thinking, what are real causes can you assume ?

 

Thank you very much for your considerations and helps.

Best Regards,

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