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LM5108: driver current question

Nan Zhang
Intellectual 1895 points
Part Number: LM5108

hi team,

     Here are some questions from customers,could you please help me to figure out these?

1. Does the internal bootstrap link of LM5108 have a current-limiting design? If so, please help confirm the current limit value and provide a design reference point for the current limit circuit inside the chip.
Cause of the problem: The main consideration is that when the bootstrap capacitor is charged for the first time, it will instantly pull a large current from VDD, which affects the current supply design of VDD and the current limiting design considerations on the link.
2. What are the restrictions on the maximum source and sink current of 1.6A/2.6A of LM5108? The internal design of the chip?
When the high-side driver is turned on, topology should be the current drawn from the bootstrap capacitor. So should the maximum drive current be determined by the energy storage of the bootstrap capacitor?
3. When the bridge arm is turned off, which part of the chip is the Vgs leakage circuit?

yours

nan

  • 0
    TI__Genius 12435 points

    Hey Nan,

    Thank you for the question regarding the LM5108.

    1. There is not an internal current-limiting circuit. There aren't any defined specifications regarding the current limit on this circuitry. If current from VDD is a concern, a Rboot resistor can be added in series with this to help with that. Please refer to this document about Bootstrap Circuitry at this link for more information.

    2. The peak current testing is done in almost a shorted to ground setup because of the no load test conditions stated in the datasheet. This is done to see the maximum current that the device withstands. If you refer the this functional block diagram you can see that the bootstrap capacitor is not connected directly to the gate. When reaching current higher than this spec of 1.6A/2.6A, you begin to see thermal issues with the devices components.

    3. For the Vgs leakage circuit, when the low side switch is turned off, the bootstrap diode is what is blocking current.

    Let me know if you have any further questions.

    Thank you,

    William Moore