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UCC21750: Recommendation of Single End to Differential Device for IN+ and IN-

Shinichi Inoue
Guru 21701 points
Part Number: UCC21750

Dear Specialists,

My customer is considering UCC21750 and has a question.

I would be grateful if you could advise.

---

When using both IN+(10PIN) and IN-(11PIN),
We are thinking of using single-ended output from the control board (microcomputer) side, converting it to differential with a differential driver, and supplying it to IN+ and IN-.

If possible, could you please let us know the recommended single end to differential device.

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Expert 8185 points

    Hi Shinichi,

    IN+ and IN- inputs are not differential inputs, they are single ended wrt to GND. Please check device function mode table (section 8.4 of the datasheet) on how INP, INN along with other conditions on the OUTH/L status.

  • 0
    TI__Expert 7473 points

    Hi Shinichi San,

    We would recommend just tying the IN- to GND as the method you're suggestion would just add cost to the system and is not necessary. Please refer to section 9.2.2.2 (page 33) of the datasheet which says, " When only IN+ is used, IN- can be tied to GND"

    Please let me know if you have further questions.

    Hope this helps!

    Best,

    Pratik

  • 0 in reply to Pratik Adibatla
    Guru 21701 points

    Hi Sasikala and Pretik,

    Thank you for your reply.

    I understand.

    IN+ and IN- inputs are not differential inputs, 2 single end signals.

    The customer is also thinking PWM signal to IN-.

    Could you please advise. 

    ---

    My understanding, when using only IN-
    IN+: Direct 3.3V or 5V
    IN-: Input a signal that reverses PWM to the control board (microcomputer) side

    In this case, is it possible to pull-up IN- for a noise countermeasure.

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Expert 7473 points

    Hi Shinichi San,

    Adding low-pass filters to IN+, IN– pins can effectively increase the noise immunity and increase the signal integrity.

    Yes, separate single ended inputs can be used as mentioned in table 8-1 of datasheet.

    Yes, only using IN- works and tying IN+ to VCC works too. The problem is that it makes the driver default ON instead of default OFF. This can be solved with a pullup on IN- because this makes it so that if the MCU/controller is not actively driving the IN- pin, the IN- pin will pull high, turning the output off.

    Best,

    Pratik

  • 0 in reply to Pratik Adibatla
    Guru 21701 points

    Hi Pratik,

    Thank you for your reply.

    I understand a pull-up is required when using IN- in actual case.

    I'll share your suggestion with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi