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TPS3839: question about RESET pin high logic level

Francesco Ladogana
Prodigy 150 points
Part Number: TPS3839
Other Parts Discussed in Thread: TPS61252, TINA-TI

Hi,

I want to use the TPS3839 to monitor the voltage of a LiPo battery so that when the battery voltage drops down to 2.9V the boost coverter I'm using (TPS61252) goes into shut down mode.

The boost converter Enable pin has a logic high threshold of 1V.

I have a doubt about the voltage level that the RESET pin of the TPS3839 assumes in its high logic state. Reading the datasheet of the component I thought that the RESET pin in its high logic state would simply track the voltage of the battery at the Vdd pin. But I've tried to simulate the component using the spice model on the TI website here ( http://www.ti.com/product/TPS3839 ) and it seems like the RESET pin voltage is being generated differently.

This is a simulation relative to the TPS3839G25 model with a 2.325V threshold voltage as an example. I've created a PWL waveform as the Vdd input. As you can see the RESET pin in its high logic state can assume a voltage higher than the Vdd value at the same time because it drops slower than Vdd.

Could you please explain how the RESET voltage is being generated by the TPS3839 when in its high logic state?

Thanks!

  • 0
    TI__Genius 12630 points
    Francesco,

    Interesting, I see what you mean! You are correct, the VOH (output voltage when logic high) should be VDD since this is a push-pull device. Is there anything connected to the /RESET output? There shouldn't be any pull-up resistor or capacitance connected. Can you provide your schematic? We will work to get this figured out ASAP. Thanks!

    -Michael
  • 0 in reply to Michael_DeSando
    Prodigy 150 points

    Hi Michael, 

    thanks for your reply.

    I simply imported in LTSpice the unencrypted model of the device taken from here: (http://www.ti.com/product/TPS3839/toolssoftware). 

    The schematic is as simple as you can get because I was just focused on confirming my understanding of the device behaviour.

    There's just a PWL voltage generator connected to Vdd and no load at all.

    In my project I want to connect RESETN to the enable pin of my boost converter and Vdd is the voltage of a 3.7V LiPo battery which will be provided through a voltage divider so that when the battery voltage is 2.9V it will match the particular threshold of the TPS3839 model I will choose.

    Could you please tell me if this is just a simulation issue? 

    Thank you!

  • 0 in reply to Francesco Ladogana
    Prodigy 150 points
    By the way, I've managed to try the encrypted model using Pspice and it seems to work as expected.
    So this issue is either with the unencrypted model or with the way LTspice imports it (although I've never had issues with the latter).
  • 0 in reply to Francesco Ladogana
    TI__Mastermind 30430 points
    Glad you got this figured out, Francesco.
    This is good information for us to have at TI. The models we have designed have been proven out in TINA-TI (and SIMPLIS). Neither of those software's have much of a learning curve if you are trying to utilize one of those for your next project.

    Let us know if you run into anymore issues that we can help you out on!
  • 0 in reply to Marshall_Beck
    Prodigy 150 points
    Ok thanks, I guess that you can't fix the unencrypted spice model to work with other simulators?
    By the way the most important thing is that it's clear how the device works.