• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 1119 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC27211 Leak Vout

T Kishi
Genius 4425 points
Other Parts Discussed in Thread: UCC27211

Hi

My Customer use UCC27211.

Not enterd the PWM,but Voltage is generated.  (Load = OPEN)

Vout in the circuit of the above will occur. (About 3.5V)

What causes do you think?

Regard

T Kishi

UCC27211.pdf

  • 0
    TI__Mastermind 41310 points

    T Kishi,

    I have moved your post to the AC/DC and Isolated DC/DC forum.

  • 0
    TI__Intellectual 2910 points
    T Kishi,

    When the output half-bridge is in high-impendance state (both FETs turned OFF), the switch node can float up to a positive voltage. The voltage it floats to is determined by the balance of the leakage currents and the Cds capacitance of the bridge FETs.

    That said, I would like to understand this specific setup better. Please confirm:
    1. Is the +12V VDD supply enabled?
    2. Is the +48V main supply enabled?
    3. Does the 3.5V at Vout vary with time, or with variation to VDD or main supply?

    - Daniel
  • 0 in reply to Daniel Ruiz
    Genius 4425 points
    Hi

    Thank you for reply.

    >>When the output half-bridge is in high-impendance state (both FETs turned OFF), the switch node can float up to a positive voltage. The >>voltage it floats to is determined by the balance of the leakage currents and the Cds capacitance of the bridge FETs.
    　⇒In other words Do you mean how GateDriver even the possible phenomenon?

    1.Yes. It is applied to 12V.
    2.No. It is not applied to 48V.
    3.Yes.When VDD= 9V, 3.5V drops.

    Regard
  • 0 in reply to T Kishi
    TI__Intellectual 2910 points
    Thank you for providing more details. I can now better address your question.

    The switch node voltage (Vout) is floating up due to the charging of the series combination of the bootstrap capacitor and the Coss of the low-side FET through the integrated bootstrap diode. Hence, the Vout value varies with changes in VDD. This will be common in half-bridge configurations with a high-side bootstrap supply and should not be a design concern.

    I hope this clarifies the situation. If not, let me know, and I will try to explain further.

    - Daniel