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TPS2660: FLT Pin dosn't stay low during hic up mode

Part Number: TPS2660

Hi everone,

i'm using TPS2660 0 and everything is working fine. TPS26600 mode pin is left open, so it works as a circuit breaker with auto retry mode. FLT# Pin is pulled up with 4K7 resistor to OUT. Furthermore the FLT# pin is working on the anode of an optocoupler. If a fault condition happens, TPS26600 shuts down the voltage at OUT and FLT# pin is low. But: in hic up mode the fault pin goes up whenever the chip tries to put on the voltage on OUT and then goes low again when the fault persists. Reading datasheet page 22, figure 41 the FLT# pin is always low during fault condition as i expected.

What went wrong? Please let me know if you need any further information.

Thanks a lot.

Kind regards Thomas

  • Hi Thomas,

    Thanks for reaching out.

    What do you mean by hiccup mode? Can you please share test waveforms to understand the issue

    Best regards,

    Rakesh

  • Hi Rakesh,

    the hic-up-mode i thought the circuit breaker with AUTO RETRY. I can give you some scopes.

    Here we have the situation of overcurrent at out pin (1.5A). You can see the waveform on out pin (yellow), when the TPS26600 tries to put on the out pin although the overcurrent situation still exist. The green line is the waveform at FLT pin. The second image shows a detail. I thought it would stay low until the overcurrent situation is over.

  • Hi Rakesh,

    i can give you a cutout of the schematic. Think that helps.

    Best regards

    Thomas

  • Hi Thomas,

    Thanks for the update. I see that the current limit is set to 1.5A. What is the overload current ? 

    As you see, the output has reached 24V. So, the FLT/ goes high as per tPGOODR timing i.e., 20ms(approx)

    Can you capture zoom-out waveform including Vout, Current , FLT/ and Vin

    What is the load ? Are you controlling the load using FLT/ output ?

      

    Best regards,

    Rakesh

  • Hi Rakesh,

    let me explain first a littlebit about my application. After TPS26600 the fused 24V DC work directly on a halfbridge transmit stage. Let's say the 24V DC are modulated with a frequency of 1.2KHz. Now a highside FET switches the 24V to the transmit line, after that a lowside FET switches 24V (0) to to the transmit line. With the help of a deadtime generation it is guaranteed that both FET's never switch at the same time. Now we have a special kind of fault. During transmission the transmit line + and line - are shorted together. 1.2KHz are still working during fault! With the help of the TPS26600 the transmit halfbridge is shut down. But if FLT goes high again halfbridge works for the short time, transmits the signal and is shut down again. This effect is worse about device performance. I have developed a work around with the help of a retriggerable one shot, so the "regenerated" FLT signal is stable but it would be much smoother to solve the challenge at TPS26600 side.

    Kind regards
    Tom
    ------------------------------------------------------------------------------------------------------

    Lets have a look at the scopes (without workaround).
    a) current measured over a 1 Ohm resistor in case of described fault condition

    b) Vout at DR3/2 versus Vin in case of described fault condition

    c) FLT after the optocoupler versus Vout in case of fault

    d) Detail of scope c)

    e) Transmit line without fault condition

    f) Transmission line shorted + to - (FLT=high => peak! on line)

    g) Transmission line shorted + to -  detail

  • Hi Thomas,

    Thanks for sharing the info. I will get back by friday EOD this week.

    Regards

    Kunal Goel

  • Hi Thomas,

    Unfortunately your system is not clear to us. Also waveforms are not very informative. It would be helpful if you can share data like below:

    1. Please share diagram of system. Verbal explanation is difficult to visualize.

    2. can you share complete schematic regarding FLT pin like where it is going , what it is doing ?

    3. Please use a four channel scope and label the signals on scope shot. That helps in analyzing all important signals in one scope shot. Please capture VIN,VOUT,IIN,FLT like below so that we can see multiple retries and also capture at both zoomed in and zoomed out settings. 

    Regards

    Kunal Goel

  • Hi Kunal,

    thanks for your answer. I was on vacation.

    Unfortunately we don't have a 4 channel scope. But i will try to make some scopes with the help of the built in digital analyzer.

    Can you give me a seperate mail address? I don't want the forum to see the whole schematic and i must beg you to keep the schematic in confidence. Hope you understand this.

    Kind regards

    Thomas

  • Hi Thomas,

    We can use e2e private messaging. I have sent you friendship request.

    Regards

    Kunal Goel

  • Hi Kunal,

    actually accepted your friendship request. Doing Measurement this afternoon.

    Best regards

    Thomas