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UCC27289: When the gate drive resistance is increased, the voltage cannot be boosted.

Shinichi Inoue
Guru 22281 points

Part Number: UCC27289

Dear Specialists,

My customer is evaluating UCC27289, and has a question.

I would be grateful if you could advise.

---

The FET is driven by UCC27289.
VDD=12.6V. 

When the high-side and low-side gate resistances were 2.2Ω, VHB-VHS (boot capacitor voltage)was 12V.

On the other hand, ringing was observed in the pulse of the HS-HO pin.

So the high-side and low-side gate resistances were set to 22Ω to mitigate ringing.

(The dead time is set 200ns for preventing short)

However, the voltage of VHB-VHS (boot capacitor) only rose to 6V to 7V and no longer reached 12V.

Even if the low side FET is turned on 100%, it only rises to 6~7V, not be 12V.

Is this behavior correct for the device?

Why doesn't the VHB-VHS (boot capacitor) voltage increase when the gate resistance is increased?

Could you please let me know what is the problem?

There is one thing that I am concerning.

I set the boot capacitor to 0.33μF. The recommended value is 0.1μF.

Is this the reason why the voltage doesn't increase?

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Genius 14135 points

    Hey Shinichi,

    Thank you for your question regarding the UCC27289.

    The capacitor should still charge to 12V. Did you change this capacitor to 0.33uF and the gate resistor to 22ohms at the same time or was the capacitor 0.33uF the whole time?

    Is there a resistor on VDD and an external diode as shown in this typical application circuit? If you could share your schematic that would be greatly appreciated. If you choose to place an external boot diode, you need to ensure that it has a lower Vf and fast recovery times, this is outlined in Section 8.2.2.2 External Bootstrap Diode and Series Resistor in the datasheet.

    With setting the boot capacitor to 0.33uF, you need to ensure that your bias (VDD) capacitor is sized larger as well to account for this. Section 8.2.2.1 Select Bootstrap and VDD Capacitor of the datasheet tells more about this and how the VDD capacitor should be at least 10 times greater than the boot capacitor and also placed close to the driver.

    Let me know what your schematic looks like and if you have any further questions.

    Thank you,

    William Moore

  • 0 in reply to William Moore
    Guru 22281 points

    Hi William,

    Thank you for your reply.

    I talked with the customer and obtained additional information.

    I would like to share, so please send me a friendship message

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi.

  • 0 in reply to Shinichi Inoue
    TI__Genius 14135 points

    Hey Shinichi,

    I have sent a friend request and this matter will be handled through messages.

    Thank you,

    William Moore