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TPS3808E: Some confusion about when SENSE pin input a under threshold voltage in first time start

Qin zhiqiang
Prodigy 80 points
Part Number: TPS3808E

Tool/software:

I use a reset IC, the part name is TPS3808EG30DBVRQ1(2.8V threshold), but when I give a under threshold voltage in first time start, why the IC output a high voltage?

In my opinion, there should output a low voltage, right?

CH1 : VCC  

CH2 : SENSE

CH4 : OUT

VCC = 3.3V, SENSE = 2 V

below picture is this IC timing sequence 

Looking forward to your reply.

  • 0
    TI__Genius 9880 points

    Hi Qin, Thanks for your question!

    Could you please share the top mark of the IC?

    Best,

    Sila Atalar 

  • 0 in reply to Sila Atalar
    Prodigy 80 points

    Hello Sila, please see this attached picture

  • +1 in reply to Qin zhiqiang
    TI__Genius 9880 points

    Hi Qin, Thanks for sharing the top mark. I just wanted to first make sure you have the correct device. It seems like TPS3808EG30DBVRQ1 is the correct OPN. 

    Your understanding is correct, normally the reset should be low when VDD:3.3V, Vsense:2V, and MR= High for TPS3808EG30DBVRQ1

    According to datasheet the RESET behavior at start-up is depend on both VDD and SENSE voltage. (When MR is High)

    1. VDD needs to higher than VPOR, which is 1V for TS3808E-Q1. 
    2. VDD_MIN =1.7V, and if VDD_MIN > VDD voltage >VPOR, the RESET should be asserting without checking the SENSE voltage. 
    3. If VDD> VDD_MIN, then SENSE voltage is the main input that will affect the output behavior

    (Please check section 8.4 Device Functional Modes for more information)

    Can you please keep VDD > VDD_MIN and Start Sense voltage from 0V, at this point Reset should be low. Increase the SENSE pin voltage gradually to see at what voltage it will become high? This way we can understand what voltage is de-asserting. 

    Thanks,

    Sila