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LM5109B: About power supply sequence

Junya Kato
Expert 1635 points
Part Number: LM5109B

Hello Team,

Even if power is supplied to HB in ten or more seconds after power input to VDD, is there a problem with device?

Best regards,
Kato

  • 0
    TI__Mastermind 23105 points

    Hello Kato,

    Thank you for your interest in the LM5109B. I am an application engineer with High Power Drivers at TI and will work to answer your questions.

    There is not an issue with the LM5109B with applying the HB with a time delay from the VDD rising. I do have some questions about the application.

    Most applications have a bootstrap supply for the high side with a diode from VDD to the HB pin. The HB to HS capacitor is charged when the low side driver output goes high and the HS pin is switched to the ground, or VSS potential. In your application is there the bootstrap supply with boot diode for the HB bias supply? Is there the 10 second delay from the VDD rising to the LI input signal, which results in the delay from VDD to the HB supply being applied?

    Is the case of the initial power up of VDD and some delay on the driver input pulses. There is a path from VDD thru the boot diode charging the HB capacitor which will result in the HS node rising if both MOSFETs are off, if there is a high impedance on the HS node. This will not be a problem for the driver, but is an expected observation until the low side FET is turned on.

    Regards,

    Richard