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TPS61088: Doubt about output Short-Circuit Protection TPS61088

Leo86
Intellectual 255 points
Part Number: TPS61088
Other Parts Discussed in Thread: PMP9779, , TL331, TPS61178

Hi, 

I am trying to put the protection circuit in my project that uses the TPS61088. I used the application note "Output Short-Circuit Protection Solution for the TPS61088" that uses the PMP9779 board.

In my project I did the following scheme.

My doubt is why I need to put the RC circuit, on the P channel MOSFET transistor in the Q4 scheme above,
to avoid inrush (as explained in topic 2.4 of the application note SLVA819), if the TPS61088 already has a starting 
protection configurable by the capacitor on the SS pin?.

regards,
  • 0
    TI__Mastermind 40080 points 


    My doubt is why I need to put the RC circuit, on the P channel MOSFET transistor in the Q4 scheme above,
    to avoid inrush (as explained in topic 2.4 of the application note SLVA819), if the TPS61088 already has a starting 
    protection configurable by the capacitor on the SS pin?.

    --》 This  inrush current has nothing to do with the SS, it is uncontrollable. IQ=Vin/Rdson at initial, if the VGS of the FET turn-on slowly, 
    the Rdson will be bigger. thus the Iq_inrush controlled.
  • 0 in reply to Helen chen
    Intellectual 255 points


    I am using a microcontroller to control the MOSFET channel P. if I apply a PWM to try to make the MOSFET start more slowly, do I need to use the RC circuit?

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    I suggest you keep the space for R and C.

  • 0 in reply to Helen chen
    Intellectual 255 points

    Hi Helen,

    I put a discrete solution for control inrush current in mosfet channel P "Q4". You have any suggest?

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    It seems OK.

  • 0
    Intellectual 255 points

    Hi Helen.

    I am having some problems implementing the short circuit protection. As in the conversations above I need to protect my circuit and I am trying to put the detection part of PMP9779 (TL331) in my project.

    When connecting my plate with the comparator circuit under normal conditions (without short circuit). The TL331 has the output at level "0". However, when I make the short circuit, the TL331 output goes to "1", indicating that there is a short circuit. However, when I remove the short circuit, strangely the TL331's output does not return to "0", always staying at "1". Why is this happening?


    (No short circuit)

    pin1 (TL331) = 109mV

    pin3 (TL331) = 0V

    pin4 (TL331) = Low level

    (With short-circuit)

    pin1 (TL331) = 109mV

    pin3 (TL331) = 250mV

    pin4 (TL331) = High level

    However, when removing the short circuit

    pin1 (TL331) = 109mV

    pin3 (TL331) = 0V

    pin4 (TL331) = High level (The pin is still high)

    I didn't understand the "because" that happens.

    best regards!

     

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    This is because of the hysteresis, you can connect R16 to EN signal, then recycle the EN signal.

  • 0 in reply to Helen chen
    Intellectual 255 points

    Hi Helen,

    Let me see if I understand.

    The hysteresis control must be done by the ENABLE of the TPS61088. The ENABLE pin of the TPS61088 is connected to one of the IOs (OUTPUT) of my microcontroller.

    To do the hysteresis control, should I connect as shown in the figure below ?.


    To control hysteresis I must monitor the output of the TL331 through a microcontroller input (SENSE, when "1" short-circuit, when "0" normal). When a short circuit happens the TL331 level goes to HIGH, at that moment I put LOW level on the ENABLE (TPS61088) and LOW on the MOSFET channel P to disconnect the load, after doing this I put the HIGH level of the ENABLE again, to recycle the sign?

    best regards!

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    Hi Leo,

    I can't see you schematic clearly. Please check the below PMP9779 schematic. We pull the EN signal low, then release it to high.

  • 0 in reply to Helen chen
    Intellectual 255 points

    Hi Helen,

    My circuit to detect the short circuit, using microcontroller.

    As you can see, I am relying on PMP9779. However, I control the MOSFET channel P which disconnects the load with the TPS61088 using a microcontroller.

    When starting the system, the microcontroller put HIGH LEVEL in the ENABLE (tps61088). When a short circuit occurs, the TL331's output goes to
     LOW LEVEL, then the input from the SENSE microcontroller reads the TL331's output status and (turns off the MOSFET and puts LOW LEVEL in ENABLE,
     "disconnecting the load"). Then to recycle the signal from the TL331, the microcontroller sets HIGH LEVEL.

    Is this how the operation for the TL331 circuit works?
  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    Hi Leo,

    Yes, for the PMP9779, we need to make sure the "+" is lower than "-" for successful start up.  if not recycle the EN, the "+"will be higher than "-" after OCP.  so the start up will failed.

    So you need to check the logic after OCP happens.

  • 0 in reply to Helen chen
    Intellectual 255 points

    Hi Helen,

    My logic to control the disconnection of the load in a short circuit condition and recycle the tl331, I'm not sure if I'm doing the recycling right.

    if(!SENSE)               // Read pin4 TL331. If pin4 TL331 is "0" (VO_TL331 = L = 0V)
    {                                // NORMAL OPERATION
         ENABLE(1);        // ENABLE TPS61088  
         CSD25404_ON;  // ENABLE MOSFET CSD25404
    }
    else
    {                                  // Pin4 TL331 is "1" (VO_TL331 = H). Then SHORT-CIRCUIT
         ENABLE(0);          // DISABLE TPS61088
         CSD25404_OFF;  // DISABLE MOSFET CSD25404 

         ENABLE(1);          // Do you enable the EN of TPS61088 to recycle the TL331?
    }

    When the OCP (short circuit) happens the first time, I put "0" in the EN of the TPS61088 and consequently recycling the TL331, as shown in the red line of the code.

    Even trying to recycle (ENABLE=1), the Vo_TL331 signal does not return to the condition when the short-circuit is removed. Why does it happen?

    Am I correctly recycling the TL331?

    Best regards!

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    Dear Sir,

    The logic seems OK.

    How about the reference voltage Vref? It should be present before the EN signal high.

  • 0 in reply to Helen chen
    Intellectual 255 points

    Hi Helen

    The VREF reference voltage is already available at startup, without any problem.

    For some reason, when the short-circuit happens and I try to recycle the TL331 the current is not cut and it increases a lot. I expected to disconnect I don't understand why it happens if I'm doing the right logic...

    Helen, the PMP9779 implemented solution, does it auto shut off and auto power on ?.                                I could make a system like SLVA889 (Improving Boost Converter Reliability Using the TPS61178x Hiccup Mode Short Protection). Or is this system completely different from PMP9779?

    Best regards!

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    It seems the disconnect FET doesn't completely turn off.

    Maybe it is caused by the delay of the MCU. Please check the TTL331 output signal to the MCU output control signal delay time. It should be within 10us.

  • 0 in reply to Helen chen
    Intellectual 255 points

    Helen,

    Could I make a system like SLVA889 (Improving Boost Converter Reliability using TPS61178x Hiccup Mode Short Protection) using TPS61088 and the circuit proposed by PMP9779?

  • 0 in reply to Leo86
    TI__Mastermind 40080 points

    Actually you can directly use TPS61178, just an external FET needed!

  • 0 in reply to Helen chen
    Intellectual 255 points

    Hi Helen,


    But could I do the same thing that the TPS61178 does with the circuit (TPS61088 + PMP9779)?

  • 0 in reply to Leo86
    TI__Mastermind 46905 points

    Hi Leo,

    sorry for the late as Helen had left TI.

    may I know what is input voltage/ output voltage and current in your application. the TPS61178 is a better solution if current capacitor is too large.