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TRS3253E: TRS3253E

Anderson Silva99
Prodigy 20 points
Part Number: TRS3253E

Hi.
I'm using the IC TRS3253E in a project and is appearing something about -9V in the pin "V-" (3) instead -5.5V.

This project consist in a CPU connected to TRS3253E.

All the charge pump capacitor are ok (100nF) and the power supply is 3,3V.

Some PCB's worked very well (appear -5-5V in pin "V-") but others have -9V in this pin "V-" (3).

I've verified that when I connect a 10K resistor from pin DIN2 (5) to GND these boards work very well (appear "-5,5V" in "V-"(3) ).

So I've imagined that the problem could be some reference... But I'm not sure.

Do you have any ideia what could be the reason of this problem?

Is this voltage (V-) created only by the charge pump capacitors? Or something can affect this value?

If the DIN pins don't have referente it could happens?

Thanks.

  • 0
    TI__Mastermind 47675 points
    Hi,

    That is strange. Is V- the only sign of the device not behaving properly?

    A few questions to help diagnose:
    Do you have a waveform of V- while the device is active? We can look at that to see if the charge pump is switching properly.
    What is the logic level being used at VL and DIN? These should be the only references for the device besides Vcc and GND.
    When driving DIN HIGH, what is the voltage at the corresponding Vout? This should match the value at V-.

    Regards,
    Eric
  • 0 in reply to Eric Schott1
    TI__Guru 62910 points
    Hi Anderson,

    I just wanted to check back in on this - were you able to resolve this issue? If not, have you had a chance to look more into Eric's feedback above?

    Max
  • 0 in reply to Max Robertson
    Prodigy 20 points
    Hi Max.
    Thank you for your feedback.
    I have read your questions and I have not answered you because I was trying to understand the problem ...
    Anyway ... Let me tell you what happened here with this issue ...
    My application consists of a PCB connected to a PC by usart interface (RS232).
    As I told you before, it is appearing -9V in TRS3253E "V-" pin of some boards.
    Trying to look at the problem I saw that when I putted the scope in the pin 5 (Din_2) the problem disappear. So I've imagined that was missing some reference. So I putted a 10K resistor from this pin to the ground (just to test) and the problem was solved.
    But there's no problem with reference. I have checked all pins and connections and all of them are ok.
    So I kept looking for the problem and when I unconnected the TRS3253E "23" pin (Dout_2) the problem is solved too (unconnected this pin from RS232 cable).
    As I'm not using this pin in my application, the problem was solved just by taking off this pin. So it's all ok now. But I'm still not sure what was happening ...
    Maybe the PC is drainning too much current in this pin and the IC TRS3253 is becoming crazy ...
    But it's all ok right now, as I told you before, because I'm not using this pin (23).
    Thank you very much.

    Regards.

    Anderson Silva
    V2Com
  • 0 in reply to Anderson Silva99
    TI__Guru 62910 points
    Anderson,

    Thanks for your explanation - I'm glad to hear that this is resolved! My guess is that this was indeed related to differences in loading on the DOUT2 pin causing the charge pump voltages to vary. It sounds like pulling DIN2 to a low level (meaning DOUT2 was driven to V+) was the fix, so the issue may have only been something that showed up when DIN2 was high. If you didn't have any pull-ups or pull-downs on DIN2 initially to bias it to a particular logic level then you may have had some percentage of boards where it was normally low and some where it was normally high (and therefore showed the different V- voltage).

    I hope this makes sense, and please just let us know if you have any further questions.

    Regards,
    Max