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TPS61181A: TPS61181A - FAULT signal

Jose
Intellectual 305 points
Part Number: TPS61181A
Other Parts Discussed in Thread: TPS61181EVM-259

Hi,

We are finishing a project with the TPS61181A.


When we were going to connect the FAULT signal to the microcontroller, we found that the signal was designed to control the gate of a Mosfet, and not for direct connection to a GPIO of a microcontroller.

How can we read the status of the FAULT signal from the GPIO of a microcontroller running at 3.3V?

Thanks.

regards

Jose

  • 0
    TI__Mastermind 31230 points

    Hi Jose,

    The FAULT pin can be used as a pFET gate driver for fault protection, and it can also be used as signal output for fault report.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Intellectual 305 points

    Hi Patrick,

    The question was how do you connect the FAULT signal to a GPIO of a microcontroller running at 3.3V ?

    regards

    Jose

  • 0 in reply to Jose
    TI__Mastermind 31230 points

    Hi Jose,

    I think the simple method is adding a resistor divider net to regulate the voltage to be within 3.3V.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Intellectual 305 points

    Hi Patrick,

    I don't see how you can solve the problem with a voltage divider.

    A microcontroller powered at 3.3V will have VOH > Vdd-0.7 > 2.6V and VOL < 0.6V.

    Let's assume the Vin voltage of TPS61181A of 12V.

    With the Fault signal, it can be at approx. 12V or 6V depending of beeing High or Low.

    If I calculate the voltage divider to have e.g. 0.5V for Vfault= 6V then I will have 1V for Vfault = 12V ... it doesn't work!

    If I think to command a Mosfet, for example with Vgs of 1.7V (typ) and that can be between 0.8V and 2.0V (Vgs min and max)  I will have the same problem.

    That is, if for a 6V Vfault, I have Vgs of 0.5V, I will have Vgs and 1V for a 12V Vfault ... it doesn't work.

    So without an OPAMP serving as a comparator with a reference voltage I see no solution.

    The problem is that for cost, BOM and board space reasons I cannot add this OPAMP circuit.

    So I ask what other solution there might be to solve the problem.

    regards

    Jose

  • 0 in reply to Jose
    TI__Mastermind 31230 points

    Hi Jose,

    May I have a look at your schematic? What's your Vbat for now?

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Intellectual 305 points

    Hi Patrick,

    We are using the TPS61181EVM-259 demo board, and have varied the Vbat between 11V and 15V which will be expected in our future application.

    My previous description assumed that we would connect the voltage divider input that you suggest to TP3 on the demo board, and the voltage divider output to the GPIO of the microcontroller.

    regards

    Jose

  • 0 in reply to Jose
    TI__Mastermind 31230 points

    Hi Jose,

    Another method is that you can add a Zener diode near fault pin, and series a large resistor between Vbat and Fault pin to limit the current through diode. When no fault, the voltage on Fault pin is low, when fault occurs, Fault pin floating and the Zener diode will regulate the voltage within 3.3V and the large resistor will forbid large current through diode.

    BR

    Patrick