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TINA/Spice/TIDA-01573: Design of and selection of components on Evaluation Board TIDA-01573

Rainer Baettig33
Prodigy 130 points
Part Number: TIDA-01573
Other Parts Discussed in Thread: TINA-TI, LMG1020,

Tool/software: TINA-TI or Spice Models

To whom it may concern -

My questions relate to the evaluation board TIDA-01573 for the FET driver LMG1020.

Referred documents:

1.  C10, a bypass cap for the LMG1020, is rated to 85°C. Can you recommend a suitable replacement rated to 125°C?

2.  R1, R2, the output resistors at OUTH and OUTL of the XLMG1020 have a value of 0 Ohm (!). Can R1 and R2 be omitted? The data sheet of the  LMG1020 states that a single resistor of not less than 2 Ohm can be used instead of R1 and R2 (and OUTH and OUTL be shorted). Is this a viable solution, or is there a stringent reason using two 0 Ohm resistors?

3.  What is the function of the shunt resistors R5-R8 parallel to the laser diode? Are they just for board testing if there is no laser? Can R5-R8 be omitted?

I will be very grateful for any information you can provide on these questions.

Best wishes,

Rainer

  • 0
    TI__Genius 12990 points
    Hi Rainer,

    Welcome to e2e!
    Im an apps eng with this device and will help answer your questions.
    1) any X7R 0306 package ceramic cap should work up to 125C
    2) for high frequency operation above 1MHz its recommended to use 2 ohm gate resistors to reduce the internal current consumption when instantly switching between OUTH and OUTL
    3)These resistors act as a dummy load so you dont have to solder a laser achieve full functionality - when using a laser diode these resistor should be removed

    hope this answers your questions, let me know if you have any more
    thanks,
  • 0
    Prodigy 130 points

    Hi Jeff,

    Thank you for the very good and rapid feedback.

    Further to question 2):

    The reference design TIDA-01573 implements R1 and R2 as 0 Ohm resistors. 0201L (0.6mm x 0.3mm) components are chosen.

    I am a bit confused why one should go to the trouble of using these rather inconvenient 0201 SMD resistors of 0 Ohm. Can one replace them by short lengths of PCB traces and tie OUTH and OUTL to the FET gate using a single gate resistor of ~2 Ohm (as suggested in the data sheet to suppress inductive ringing)? Would that sacrifice rise time?

    Best wishes, Rainer

  • 0 in reply to Rainer Baettig33
    TI__Genius 12990 points

    Hi Rainer,

    thanks for your update!

    This TIDA's recommended key system specifications keep the max switching frequency at 1MHz.

    The resistors are there for flexibility in rise/fall time. They are 0201 to reduce loop inductance.

    The 2 ohm resistors on OUTH and OUTL limit the internal shoot-through current as OUTH/OUTL switch from one state to the other (VDD to GND will see 4 ohms at the instant of shoot-through). If using a 2 ohm resistor its recommended to put the resistor on the pin rather than tying together OUTH/OUTL then putting a 2 ohm at the gate. Using a resistor greater than 0ohms in the gate loop will limit the rise time depending on your GAN ON threshold voltage. If you have inductive ringing you can play around with the resistor values to fine tune how much ring your system can afford.

    hope this help answer your question, feel free to ask more.

    thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 130 points

    Hi Jeff,

    thanks for the information. I am still somewhat doubtful if I understand the design correctly.

    The TIDA-01573's BOM lists the resistors on OUTH and OUTL as 0 Ohm, not 2 Ohm.
    Thus, as far as the BOM and schematics are concerned, OUTH, OUTL and the FET gate are essentially tied together.

    Questions:
    * Does the BOM reflect TIDA-01573 as manufactured? Or are in reality R1, R2>0Ohm?
    * If R1 and R2 are in fact 0 Ohm, is it then ok to emitt them ?

    Incidentally the BOM contains another 0 Ohm resistor (R10, the coupling resistor
    at the input of the LMG1020). The above questions apply to this component as well.

    I will be grateful for any further guidance.
    Best wishes,
    Rainer

  • 0 in reply to Rainer Baettig33
    TI__Genius 12990 points
    Hi Rainer,

    thanks for sharing your concern.
    In order to achieve a 1-2 nanosecond pulse as the TIDA supports the gate resistance needs to be minimal in the TIDA case R1=R2=0R. You can emit R1 and R2 if needed for longer pulses.

    R10 is used to disconnect the AND gate buffer U3 from the circuit. By removing R10,R9 and populating R3 you can bypass the AND gate or pulse shortener.
    does this help your concerns, let me know if you have any more questions,
    thanks,
  • 0 in reply to Jeffrey Mueller
    Prodigy 130 points

    Hi Jeff,

    Thank you very much, great feedback - this clarifies a lot.

    I will tag the this thread as "resolved".

    I will consider replacing the 0 resistors by some higher value as I am willing to sacrifice rise time.

    Best wishes,

    Rainer