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  • TI Thinks Resolved

LMG1020: Can I use LMG1020 with 4.5V DC Supply?

Part Number: LMG1020

 I need very fast capacitive load driver for 60MHz pulse ( duty: 50% ) with 1nF Capacitive Load and very low Rise/Fall/Propagation Delay.

I Think LMG1020 is the closest solution for fast driving. 

However 5Vdd power supply is little higher value that I need.

My Ideal requirement Vout is 0 to 4V but I think it is too low to use lmg1020 driver.

Can I use LMG1020 with 4.5V supply? ( I know 4.75 V is minimum but TINA-TI simulation is OK with 4.5V dc supply)

If it is impossible I want to use simple mosfet inverter (buffer) to change voltage swing level with very fast response time

Could you recommend CMOS pair applicable 60MHz 4V pulse? or Other solutions for nanosecond pulse capacitive load driver?

Thank you.

  • Hi Sangbeom,

    Welcome to e2e!! Thanks for asking about LMG1020, Im an apps engineer and will help.

    LMG1020 has a VDD recommended minimum of 4.75v. The device should function above UVLO turn on max of 4.33v.

    Using VDD at 4.5v only leaves about 200mV headroom before the driver reaches UVLO condition in which the driver would be disabled. Regardless, let me look into the reliability at 4.5V and update you.

    You can use a simple level shifter on the output, between the driver and the fet with a seperate 4V supply. You can also use higher gate votlage fet. Are you using a GAN fet?

    Thanks,

    Jeff

  • In reply to Jeffrey Mueller:

    Since validation testing is only done inside the datasheet spec limits being able to determine if there are issues at 4.5V when there are transient undershoot and across temp and process is difficult. TI recommends 4.75V minimum (with no abs max) and if operating at 4.5V the long-term reliability performance will need to be evaluated in the application. However operating with a value outside of datasheet spec, datasheet performance is not guaranteed. Can you use a voltage divider on the output instead of the buffer?

    Thanks,

    Jeff

  • In reply to Jeffrey Mueller:

    Thanks for your kind help.

    Unfortunately, I can't use voltage divider. I think voltage divider with resistor may degrade 60MHz pulse transient and RMS current consumption with capacitive load. 1ns~2ns Rising Time with 1nF load is very important factor for me.

    For more detail, I need to charge and discharge the 1nF capacitor very fast pulse with almost perfect transient with precised timing.
    I want to use LMG1020 as a kind of digital buffer for capacitive load. ( Yeah, I need VERY high current 4V out Logic buffer. XD)

    A traditional level shifter IC is not applicable for this situation(1nF/4V/60MHz) due to It's low current supply ability.
    So as I mentioned first, I'm considering to use simple MOSFET buffer for level shift purpose. (1nF Load / 2ns rising time must be achieved)

    Discrete BJT Buffer may be a solution, then I think I don't need to use LMG1020 for logic buffer.
    ( I'm not good at discrete design and also I want to keep design as small as possible. This is my very last solution at this time)

    In conclusion, I think I should change my questions.
    Is there 4V~5V Logic Buffer for 1nF Load with 2ns Rising Time?

    I will post my questions to logic forums.

    Thank you.

  • In reply to Sangbeom Jeong:

    Hi Sangbeom,

    The divider will draw more RMS current but if decoupling is tight the peak current capability shouldn't be affected too much since instantaneous peak current will rush into the gate capacitance which looks like a short when dischaged.
    The driver for the discrete BJT buffer would still turn the BJT on very fast as long as the pull up resistance is below 0.5 ohm.
    Can you use LM5114 at 4V?

    Thanks,

    Jeff

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