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Technical question about TPS70950

Djordje Radivojevic
Prodigy 100 points
Other Parts Discussed in Thread: TPS709

Hi,

In our application we are using Linear Regulator TPS70950. Design is made according to TI datasheet. Main issue is related to Enable pin of TPS70950 and how it is used or should be used, do we have some changes regarding the way of using that pin.

  •    This is proposed application from Texas Instruments side for TPS76950 linear regulator. Please see image below, took from datasheet.

Figure 1 Proposed application circuit

  •    According to datasheet ENABLE pin can be left floating to enable the device (AS WE DID), please see table below.

Table 1

  •    We made our design according to application TI proposal.          
        

Figure 2

   On all sample boards that we made we didn't notice any problem with enabling linear regulator (TPS70950), our circuit worked fine. Now we produced significant number of PCBs, with recently bought chips, and we have a problem that on all boards TPS70950 chip doesn’t want to produce +5V on its output, for 7.2V<Vin<12V, if ENABLE pin is left floating. If we add pull-up resistor to EN pin circuit works fine, chip is enabled and +5V is on output pin.

  • What can be cause of this behavior?
  • Is it possible that new chip on market has different behavior than previous version?
  • What is changed about specification and way of use of  TPS70950 Enable pin (revision note), and if is changed from which date of production that change  is applied?

Thank you in advance for you help,

Djordje

  • 0
    TI__Guru 55940 points

    Hi Djordje,

    We have not made functional changes to the TPS709 family.  Are there any additional leakage paths on the new boards by the enable pin?  

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 60 points

    Hi, 

    I meet a similar issue with the 3v3 member of TPS709 components family.

    I use the TPS70933 (WSON package version) with a 12V<Vin<24V.

    Due to the high Vin value, we didn't connected the ENABLE pin. (and according to the datasheet, that's not an issue as the chip is designed to automaticaly Enable itself if that pin is left not connected)

    It's IMPOSSIBLE to obtain a Vout when Vin is above a certain voltage value. (while Vin is <7V --> Everything os OK)

    It seems that when the Vin voltage value is close to the Absolute Max Rating of the Enable pin (and above), something goes wrong inside the chip, and Vout becomes disabled...

    Where the issue we meet could come from?

    Is it "REALLY" confirmed that on the ref design, there is no issue with high Vin AND Enable pin left not connected?

    Regards

    Yannick

  • 0 in reply to Yannick RUIZ
    TI__Guru 55940 points

    Hi Yannick,

    Could you please share your load current condition?  Also, would it be possible to share a scope probe with Vin, Vout and if possible Iout?

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 60 points
    I did manage setting the Vin using a stabilized laboratory power supply in order for me to test at different Vin voltages values...

    Iout is 17,5mA

    When working, Vout is "pure" 3.3Vdc. Perfect!
    When not working, Vout is a steady 0V!! no glitches, no ripple, nothing!

    I identified a Vin range where the Vout starts to decrease... Then to increase (above the 3.3V!), then to be disabled.

    Once at this step, the only way to make the TPS70933 generate a 3.3Vdc again is to apply a Voltage on the Enable pin (I used a cell coin battery)...


    It seems that a Vin above Venablemax blows the Enable "auto bias" that is used when it is left unconnected !


    I didn't saved the oscilloscope captures but had observed them...
    I'll try to make some with a board I have...


    Regards
    Yannick
  • 0 in reply to Yannick RUIZ
    Prodigy 100 points
    Hi, I had problem with enabling TPS7095 when Enable pin is left not connected. After consultation with TI we found that ICs that we bought are not original. After that we ordered components from Reliable supplier and after that we didn't have that kind of problem. Best regards, Djordje