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LM5101C: internal bootstrap diode specs

Yang Zhou76
Prodigy 60 points
Part Number: LM5101C
Other Parts Discussed in Thread: LM5101A

The datasheet doesn't include the curr rating of the internal bootstrap diode, what is it, such as peak current (better with duration specified). I am using it on a mass production platform, and not plan to parallel an external diode, assuming there is no resistor in series with the diode inside the chip. In the existing PCB design I don't have a resistor in series with the bootstrap cap (1uf) either, which means the peak curr through diode could be as high as 12V/1ohm =12A (1ohm is the diode resistance listed in datasheet). TY.

  • 0
    TI__Mastermind 20950 points

    Hello Yang,

    Thank you for your interest in the LM5101C. I am an applications engineer supporting this device and will work to address your questions.

    The bootstrap diodes in  the LM5101x half bridge drivers and other TI 100V half bridge drivers is intended for the purpose of charging the bootstrapr including the high peak currents involved. As you mention in your message, the very initial full charging cycle will be self limited by the diode resistance to ~12A. The LM5101x drivers have been used in literally millions of similar applications for decades.

    Once the converter is running and the HB-HS cap is initially charged, the following cycles will be much lower current peaks. The diode is capable of 100mA average current which is quite high for supplying the high side MOSFET gate charge requirement.

    Regarding sizing the bootstrap capacitor, please review the LM5101A datasheet section 9.2.2 on sizing the bootstrap capacitor. The 1uF capacitor is larger than most applications require, so review the value based on the MOSFET Qg and the switching frequency.

    Regards,

    Richard Herring