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TRS3243: V+ pin connection

Takashi Onawa
Genius 13200 points
Part Number: TRS3243

Hi Team,

I have a quick question about the other side of cap connection.

According to the datasheet, it can be connected to Vcc or GND, but which is better normally?
When connecting to Vcc side, they have been seeing some glitch noise on CP output, so they want to connect it to GND. So they want to know if there is any side effect will be expected or not.

Figure 8. Typical Operating Circuit and Capacitor Values
A. C3 can be connected to VCC or GND.

Regards,

Takashi Onawa

  • 0
    Guru 277650 points

    C3 needs a low-impedance connection to a stable voltage. Both VCC and GND are suitable.

    If you have a ground plane but no VCC plane, GND might be better. But I doubt that you will be able to eliminate the noise; switching power supplies always have some ripple.

  • 0 in reply to Clemens Ladisch
    TI__Genius 13200 points

    Hi Clemens-san,

    Thank you for your prompt response on this.

    They have already confirmed that it will be solved by connecting GND. They put Ferrite bead in front of Vcc pin and it seems that it causes the glitch noise issue. Due to the bead, we saw some glitch noise between the bead and Vcc pin as well.

    I have one more question to close this issue. I need to explain that to close.

    Can you explain why connecting C3 to GND solve this issue?

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    Guru 277650 points

    In theory, both power rails should behave the same. I'd have to guess that there is a difference on how they are routed on that particular board.

  • 0 in reply to Takashi Onawa
    TI__Mastermind 46627 points

    Hi Takashi,

    Clemens is correct on why VCC or GND are suitable.

    For your question on why connecting to ground solves this it could be due to the ferrite bead adding more inductance to the VCC pin + the layout could cause some unexpected transient noise to occur. I am not sure if a supply decoupling capacitor was added between VCC and ground (close to the pins as possible) in the design but this capacitor could also affect the noise. Since the ground connection has potentially less parasitic elements it could have less noise generated than the VCC line - but this is just an idea and its probably just best to work with the ground plane for this application.

    Please let me know if you have any other questions!

    Best,

    Parker Dodson