• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 195 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMG1205HBEVM: Very slow J4 DC response (rise-fall time is abnormal) and a noisy waveform.

Alex Kor
Prodigy 10 points
Part Number: LMG1205HBEVM
Other Parts Discussed in Thread: LMG1205

Tool/software:

Hello! I am driving a LMG1205HBEVM with 0.166MHz PWM into a 60 Ohm load.
J1(Vin) = 6V
J2(PWM_IN) = 3.1V PWM (HI) via BNC; GND,GND,NC(LI) to ground.
J3(Vbus) = 12V
J4(Vout) 0V to 12V

As a function generator for PWM I am using a Portenta H7 (480MHz Cortex M7 core) programmed with a sawtooth waveform with a period of 10ms.
I am seeing a very slow J4 DC response (rise-fall time is abnormal) and a noisy waveform. What is the problem here?

  • 0
    TI__Genius 9790 points

    Hello,

    Is the blue trace connected to the EVM PWM input or is the green trace connected to the EVM PWM input?

    Can you measure the HI and LI input to LMG1205 and the HO and LO outputs? A scope shot showing HS and Vout can also help diagnose the issue. The EVM has tip and barrel test points to accurately measure these signals.

    Thank you,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 10 points

    Hi Walter,

    Blue is the PWM trace and green is J4(Vout). Unfortunately your suggestion didn't help.
    The fall time for the green waveform is questionable, it looks like the device is much slower than advertised.

    I'll try a more accurate function generator and report back on the forum.

  • 0 in reply to Alex Kor
    TI__Genius 9790 points

    Hello Alex,

    Vout is the output of the onboard buck converter circuitry so there will be delay in the fall time created by the output inductor and capacitors. The noise could be caused by the probe connection or the output inductance and capacitance ringing.

    Thanks,

    Walter