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TPS3306-Q1: WDI Input Levels for TPS3306-33QDRQ1

Varunesh Kumar
Intellectual 940 points
Part Number: TPS3306-Q1

Tool/software:

Hello 

I wanted to use the above for monitoring +5V and +3.3 V to my DSP.

Hence selected the --33 Version.

If I choose Vdd as 5V, Sense1 is connected to +5V and Sense2 to +3.3v

/RST pulled up to 3.3V & is going to my DSP. So far so good.

If I use the same DSP's O/P for driving the WDI, that would be 3.3V Levels.

While if I read the DS correctly, the WDI levels are 0.7Vdd and 0.3Vdd 

Does that mean I can't drive the WDI from my 3.3V DSP directly in this configuration?

Alternatively, if I choose Vdd as 3.3V, can I connect the Sense1 terminal directly to +5V,

( hoping the internal Res Divider shall keep the terminal below the 3.3V ) 

Thanks in advance

Varun

  • 0
    TI__Genius 9880 points

    Hi Varun,

    Thanks for your question! 

    If you look at the absolute maximum ratings all pins maximum can be connected to 7V. 

    Yes, you should be able to drive the WDI pin with  DSP.   

    Since you have TPS3306-33 variant, Sense 1 will casue the Reset pin to assert when Sense 1 voltage level goes below threshold (4.55 V), therefore, SENSE1 can be directly connected to 5V rail and Sense 2 will assert the reset when the voltage level at SENSE2 goes below 2.93V, there need to connect 3.3V rail. 

    I hope this helps! 

    Best Regards,

    Sila

  • 0 in reply to Sila Atalar
    Intellectual 940 points

    Thanks Sila 

    As an abundant clarification, 

    TPS... Powered by Vdd as 3.3 V,

    WDI driven by 3.3 signals from DSP, 

    Sense1 as +5V and Sense2 as 3.3 V. 

    directly from rails. 

    Hope that would be alright? 

    One final Q.. 

    Do I need to add a small capacitor say 1nF to 10nF at the sense terminals for deglitching? 

    Thanks n have a great day ahead

    Varun

  • +1 in reply to Varunesh Kumar
    TI__Genius 9880 points

    Hi Varun, 

    This is an old device and unfortunately I don't have any units currently in the lab to test and share the oscilloscope picture. It seems like everything is in the datasheet specs and I don't see any issue.

    Not sure how noisy your Sense signal is, but we recommend 0.1 to 1uF capacitor capacitor at VDD pin as a good design practice.  

    Is there any specific way you choosing TPS3306-Q1. I would like to suggest our newer devices. You can check TPS35-Q1 and/or TPS36-Q1. They have already 15 us glitch immunity at the sense pin. 

    Let me know if you have any further questions. And I hope you'll have nice day well!

    Best Regards,

    Sila 

  • 0 in reply to Sila Atalar
    Intellectual 940 points

    Hi Sila

    Thank you for your prompt replies.

    Answering you LIFO, there was no specific reason for selecting TP3306-33

    except that it monitors 5 & 3.3V directly and was available at TI Stores.

    Some other viable options were not.

    We shall incorporate deglitcher Caps as a prudent measure.

    I shall study the options you suggest for my future designs.

    Thanx again & have a grt weekend.

    Varun

  • 0 in reply to Varunesh Kumar
    TI__Genius 9880 points

    Hi Varun, 

    Happy to help!

    Best Regards,

    Sila