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LM9061: Problem while testing basic functionality

Greg Novitzki
Prodigy 40 points
Part Number: LM9061
Other Parts Discussed in Thread: TPS2595, TPS25982, TPS2663

Hi

I am new to electronic design and I think I am missing something fundamental but...
I intend to use LM9061 to limit max current through an electric motor (DC controled with PWN).
I mounted a circuit on a breadboard based on a reference design to test how the controller works (and to roughly choose Rthr).

with R2 and R3 at 107R the limiting current should be around 2.5 A.
I set my lab bench to limit current to 4A (it is max 5A).
The controler turns on and off with the ON/OFF signal but when i bypass R1 to ground instead of Latching Off, the controller keeps Gate at 4V above source.

What can i do wrong to cause it?

  • 0
    TI__Guru* 95551 points

    Hi Greg,

    Welcome to E2E!

    Can you please share a test waveform of Vin, Source voltage of Q1, input current and GATE voltage of Q1 when R1 is grounded.

    Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 40 points

    Screen 1

    On screen 1 yellow (CH1) is Vin, Q1 source voltage is light blue (CH2), Q1 Gate voltage is dark blue (CH4), Purple (CH3) is subtraction of Ch2 from Ch4 so Q1 Source-Gate voltage.

    Screen 2

    I could not measure at one time the input current becuse i was shorting circuit through osciloscope ground while measuring voltage drop on resistor in series on Vin (not on previous circuit drawing). I measured it while other probes were disconected. Also i could not use 1Ohm resistor becuse I dont have any high power ones ( I have burnt two small ). Instead I measured it on 39 Ohm 5Watt one. It is the lowest resistance, high power resistor i have on hand. So the current was limited to 0.4 A by that resistor

    But I thing what the problem could be. While shorting the resitor R1 the Vin drops to around 6,8 Volt (measured by multimeter - confirmed roughly by ch1 waveform). My power supply shows in this moment 17.7V.        I was convinced that Vin is that measure (on power supply). But according to LM9061 datasheet 7.0-6.2V range is absolute no go zone. So I understand it is main culprit of the problem.

    But on the other hand in the event of undervoltage according to the datasheet it should also go into LatchOFF mode which should be only able to reset by raising Vin to acceptable level and providing Low level  and then high on ON/OFF pin.

    So i am still confused but I'll try some more powerful power source (which will not sag so low as my power supply)
    Tell me what you think is going on

    Best Regards
    Greg

  • 0 in reply to Rakesh
    Prodigy 40 points

    Today i hooked up the circuit to a battery bank. I shorted the output to ground ... and i blew a transistor. I am fairly sure the supply voltage did not dipped significantly below 24V (nominally there was 25V). I was controlling the values on oscilloscope. Unfortunately I did not record the waveform. It was second transistor that day. While i was blowing the earlier i had not set up all the measurements.
    There is something going horribly wrong with the setup or with the driver.

    Until some help from your side I have to consider other solution to my application

    Best regards

    Greg

  • 0 in reply to Greg Novitzki
    TI__Guru* 95551 points

    Hi Greg,

    Sorry, I did not fully understand the issue. Do you mean that during output short circuit, the supply source Vin is collapsing ? what is the current limit the source is set for ?

    As you mentioned that you are new to the design. Can you pick integrated solutions to use directly. Below are the recommendations based on voltage and current ratings.

    1. TPS2595 for 12V, 4A 

    2. TPS25982 up to 24V, 15A

    3. TPS2663 up to 60V, 6A

    Regards, Rakesh

  • 0 in reply to Rakesh
    TI__Guru* 95551 points

    Hi Greg,

    Please let me know if you have any update/questions on the above suggestions.

    Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 40 points

    Hi

    Long story short. As electronic circuit breaker the lm9061 works as intended with additional flyback protection of transil diode between transistor source and gnd.

    And one of your suggestions looks like would be also adequate to my needs.

    Thanks for the help
    Greg