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SM74104: Maximum speed of SM74104 / LM5100 / LM5101 family?

Brian Machesney1
Prodigy 80 points
Part Number: SM74104
Other Parts Discussed in Thread: LMG1020, LM5101, , UCC27282, LMG1205

The ~20ns propagation delay times of these parts suggest that they could be operated at frequencies up to ~50MHz. If not, what is the upper frequency limit and what steps must be taken to ensure reliable operation?

  • 0
    TI__Genius 13445 points

    Hi Brian, 

    My name is Mamadou Diallo, from the High Power Drivers team.

    Please refer to the attached FAQ link discussing this topic:

    https://e2e.ti.com/support/power-management/f/196/t/788867?tisearch=e2e-sitesearch&keymatch=faq%3Atrue

    Please let us know if you have further questions or press the green button if this addressed your inquiry.

    Regards,

    -Mamadou

  • 0 in reply to Mamadou Diallo
    Prodigy 80 points

    Mr Diallo,

    Thanks for suggesting that item, which does answer part of the question, re: power dissipation. But, there must also be some maximum frequency that the device will deliver, which I hope is 1/tprop. I will drive a very light load, under 500pF. Sadly, the max frequency or minimum cycle time is never specified in gate driver IC data sheets.

    I understand your response to the earlier question, re: use of the LMG1020, but I need a combination high-side low-side driver.

    Also, can I use an external, isolated power supply to provide the bootstrap voltage for the SM74104 / LM5100 / LM5101 family? Or, is it not possible because of the integrated bootstrap diode?

  • 0 in reply to Brian Machesney1
    Prodigy 80 points

    Mr Diallo,

    The datasheets for the half-bridge drivers include a parameter tPW, the Minimum input pulse width that changes the output. This parameter sets an upper limit on the frequency at which the part will operate. Since the values range from 30ns to 50ns, the TI parts will not meet the high frequency requirements of my application.

  • 0 in reply to Brian Machesney1
    TI__Genius 13445 points

    Hello Brian, 

    Thanks for the additional details. 

    Have you considered LMG1205, or UCC27282? These devices might be better suited for what you are trying to do assuming high frequency switching >1MHz and light load situations. Depending on your requirements, these drivers can operate up to several MHz switching frequency.

    As far as using an external isolated power supply, you may do so while provisioning for an external Schottky (good for low reverse recovery) bootstrap diode because in the event of high frequency switching in combination with narrow pulse width signal on the low-side, the peak forward current and peak reverse current could be undesirably high for your application.

    Additionally, The tPW parameter specifies the minimum pulse width on the driver input that results in the driver output response following the input. 

    Typically, most devices have a maximum or typical value only specified but not minimum values because we do not production test this specific parameter. My colleague discusses this topic for UCC27282 on the thread below:

    https://e2e.ti.com/support/power-management/f/196/t/781219

    Please let us know if you have further questions.

    Regards,

    -Mamadou