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Original question:

TPS92830-Q1: Blinking functionality

TPS92830-Q1: PWM input control for high power leds

idir douki
Prodigy 40 points
Part Number: TPS92830-Q1

Hello everyone,

I need to control high power leds: 350mA

I need to make them blink at a frequency of 20Hz and a duty cycle of 50%. To do this, I decided to control the 3 PWM inputs of the driver with GPIOs from an arduino.

The driver is supplied with 12V and the GPIOs of the arduino with 5V.

-> Is this a problem ?

The goal is to control the gate of the transistor with the PWM signal in order to control the LED.

-> Is my schema good ?

The problem is that I did some tests and it turns out that on the Gate of the transistor I find 12V permanently without even that the PWM is activated ... and when it is activated, the signal on the gate remains at 12V without varying.

Thank you for your help, 

Best regards, 

  • 0
    TI__Genius 15776 points

    Hi idir 

    Could you tell me application scenarios and the information of the project. 

  • 0 in reply to Frank Qiu
    Prodigy 40 points

    Hello Frank,

    The goal is to control the power LEDs (400mA each led) with a PWM signal at a frequency of 20Hz for example with a duty cycle of 50%.

    - On of the most important question, is also if it possible to change the current LED without changing the PWM signal ? Keep same PWM signal but increase or decrease current is possible ? 

    - Do i have to put special capacitor to use properlly the driver ? 

    Best regards, 

  • 0 in reply to idir douki
    TI__Genius 15776 points

    - On of the most important question, is also if it possible to change the current LED without changing the PWM signal ? Keep same PWM signal but increase or decrease current is possible ? 

    A: I think it's hard, because the peak current is setting by the resistor R27,R28,R29 and R25. If you want to keep the same PWM signal bet increase you have to change the resistance's value. So you may need a sliding rheostat or special circuit structure.

    - Do i have to put special capacitor to use properlly the driver ? 

    A:just reference the user guide design

    about the schematic: I the the source of the MOSFET is connected to the LED‘s cathode.

     

  • 0 in reply to Frank Qiu
    Prodigy 40 points

    I see, thank you !


    Yeah i did some bad job with the MOSFET in my schematic. The Drive, Source and Gate are not well connected to the driver. I Have corrected that point.

    I have an other question about the status of DERATE and DIAGEN.

    As i told you, i just want to control the gates with the 3 PWM input and nothing else.

    I'm not sure what i have to put on those two pins to make sure that the PWM input mode is always in fuction ?

    Best regards, 

    Idir 

  • 0 in reply to idir douki
    TI__Genius 15776 points

    Hi 

    As the describe in datasheet,DERATE and DIAGEN is used for protect and avoid fault open detect.So they have nothing to do with PWM input mode.

  • 0 in reply to Frank Qiu
    Prodigy 40 points

    Hello Frank, 

    Thank you for your feedback about my schematic. 

    I have new problems : when i check with the scope the FD pin or ICTRL pin, sometimes i find the PWM signal on those pin... how is it possible ? the soledring is good, no contacts between PWM pins and other pins. 

    I also find sometimes the PWM signal on FAULT pin too... 

    My setup :

    - >Derate = 0V (to disable current derating)

    -> Diagen = 0V (to disable open-fault diagnostics)

    -> FD = 2V

    -> PWM1,2,3 = 5V PWM signal at 10Hz and 50% duty cycle

    This causes the driver to operate completely randomly.

    Does something wrong with this schematic ?

  • 0 in reply to idir douki
    TI__Genius 15776 points

    As your schematic i see you connect the FD pin to Vin, so if you see a PWM wave form in FD pin, i think you have to check the input voltage is a constant voltage or not.