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[FAQ] Maximum Operating Frequency

Prodigy 10 points

Replies: 1

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Part Number: LM5114

What is the maximum operating frequency of this gate driver (LM5114BMF/NOPB)? I would like 24 MHz.

Maximum operating/switching frequency of a gate driver depends on many factors including load, external gate resistance, supply range, package type, in other words maximum power dissipation capability the driver, etc. Turning on/off power FETs requires the driver to dissipate some power internally from the formula: P = Qg * VDD * Fsw. You will notice that all the factors previously mentioned are directly proportional to the power dissipated within the junctions of the driver.

For example, assuming no gate resistance & operating at room temperature Ta = 25C; you're driving a 50nC total gate charge load, at VDD = 10V and Fsw = 24MHz; the driver will dissipate about P = 10V*50nC*24MHz =  12W.

Tj = (P * RθJA) + Ta

where Tj = Junction temperature; RθJA = Junction-to-ambient thermal resistance; Ta = ambient temperature => Tj = 12W*108.1°C/W(SOT-23 package) + 25C = 1,322.2°C which is well above the Recommended junction temperature specified for this device.

To reduce the power dissipated at the junctions of the driver, an external resistance between the driver's output  and the power FET, this external resistor has the benefit of reducing part of the gate-charge related power dissipation in the driver's package and sharing it into the external resistor itself.

For that high of a switching frequency however, I would strongly recommend LMG1020 with its datasheet copied below.

Please let us know if you have further questions by posting on e2e.

Regards,

-Mamadou

  • HI Shinji,

    Thanks for your interest in our driver, my name is Mamadou Diallo, I will help answer your question.

    Maximum operating/switching frequency depends on many factors including load, external gate resistance, supply range, package type, in other words maximum power dissipation capability the driver, etc. Turning on/off power FETs requires the driver to dissipate some power internally from the formula: P = Qg * VDD * Fsw. You will notice that all the factors previously mentioned are directly proportional to the power dissipated within the junctions of the driver.

    For example, assuming no gate resistance & operating at room temperature Ta = 25C; you're driving a 50nC total gate charge load, at VDD = 10V and Fsw = 24MHz; the driver will dissipate about P = 10V*50nC*24MHz =  12W.

    Tj = (P * RθJA) + Ta

    where Tj = Junction temperature; RθJA = Junction-to-ambient thermal resistance; Ta = ambient temperature => Tj = 12W*108.1°C/W(SOT-23 package) + 25C = 1,322.2°C which is well above the Recommended junction temperature specified for this device.

    To reduce the power dissipated at the junctions of the driver, an external resistance between the driver's output  and the power FET, this external resistor has the benefit of reducing part of the gate-charge related power dissipation in the driver's package and sharing it into the external resistor itself.

    For that high of a switching frequency however, I would strongly recommend LMG1020 with its datasheet copied below.

    Please let us know if you have further questions.

    Regards,

    -Mamadou

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