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AM3352 - Clarification regarding latest Errata

Harsha Lalwani
Intellectual 315 points
Other Parts Discussed in Thread: AM3352

Hi all,

We are using AM3352 in one of our designs. 

We need some clarification regarding the ADC input pins connection.

As per the requirement, we are using only one ADC input pin (AIN0), which is connected to the resistor voltage divider. We are using VDDA _ADC as the reference, by writing "000" to SEL_RFP_SWC_2_0 bits of IDLECONFIG Register.

And the remaining input pins ( AIN[1:7], VREFP and VREFN) are not  being used.

As per the latest Errata ( Advisory 1.0.32), it states that :-

1) When the ADC input pins are not in use, then either connect it to VSSA_ADC through 500E or leave the unused pins open circuited. Since, we are not using ADC input pins ( AIN[1:7]), we can make all the pins as NC ( not connect).

Is our understanding correct ?

2) Also, we would like to know the VREFP and VREFN connections in the above condition, where these pins are not used.

Can we make VREFP and VREFN  as NC (not connect) ?

Thanks,

Harsha

  • 0
    TI__Guru**** 393215 points

    Hi Harsha,

    Harsha Lalwani said:
    1) When the ADC input pins are not in use, then either connect it to VSSA_ADC through 500E or leave the unused pins open circuited. Since, we are not using ADC input pins ( AIN[1:7]), we can make all the pins as NC ( not connect). Is our understanding correct ?

    Yes.

    Harsha Lalwani said:
    2) Also, we would like to know the VREFP and VREFN connections in the above condition, where these pins are not used. Can we make VREFP and VREFN  as NC (not connect) ?

    Per Note 1 below Table 5-16 from the AM335X Datasheet Rev. H:

    "(1) VREFP and VREFN must be tied to ground if the internal voltage reference is used."

  • 0 in reply to Biser Gatchev-XID
    Intellectual 315 points

    Hi Biser,

    Thanks for your response.

    We understand the point that as per datasheet VREFP and VREFN should be connected to ground when internal reference is selected. 

    But according to the latest Errata ( Advisory 1.0.32), any of the TSC_ADC terminals  (AIN[7:0], VDDA_ADC, VREFP, VSSA_ADC, and VREFN) may be connected together during the power up sequence.

    And, if we are connecting VREFP and VREFN to ground, then as per above case there are chances of power to ground connection,  since VREFP and VREFN may get connected to VDDA_ADC during power up sequence.

    Please clarify.

    Thanks,

    Harsha

  • 0 in reply to Harsha Lalwani
    TI__Guru 62835 points
    You are correct, it may be possible for VDDA_ADC to get connected to VREFP and VREFN during power-up sequence. Advisory 1.0.32 does not address the case where a product does not use VREFP and VREFN. However, it does address a common use case where VREFN is connected directly to VSSA_ADC. When evaluating this common use case of VREFN being connected to VSSA_ADC, we determined the internal resistance of the analog multiplexers will limit current through these pins to a level that will not harm the AM335x device. This would also be the case for connecting VREFP to VSSA_ADC. Therefore, you do not need to worry about connecting the VREFP and VREFN directly to VSSA_ADC.

    FYI, we are going to change the note Biser referenced in the data sheet. The new note will be:

    The VREFP and VREFN terminals should not be allowed to float to prevent noise from coupling into the ADC. If VREFN is not used to connect an external negative voltage reference to the ADC, connect it to VSSA_ADC. If VREFP is not used to connect an external positive voltage reference to the ADC, connect it to VSSA_ADC or VDDA_ADC. Connecting VREFP to VSSA_ADC in this use case is the preferred option because VDDA_ADC may couple more noise into the ADC than VSSA_ADC.

    Regards,
    Paul