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TPS61060: VFB

Kuramochi Tadahiko
Guru 28715 points
Part Number: TPS61060

Hi,

I'm understanding that VFB is 250mV(typ) when ILED is high.

On the below schematic, I think that ILED should be 120mA(0.25V/2.1Ω), however actually ILED is 200mA and VFB is 0.43V.

Is this correct working?

If yes, please let me know mechanism of this behavior.

If no, what is this behavior caused by?(Is duty ratio too small?)

Best Regards,

Kuramochi 

  • 0
    TI__Intellectual 1985 points

    Hi Kuramochi,

    If the device is operating normally, the only way Vfb can be somewhere between 0.25V and 0.5V is when ILED is tied to high (brightness control enabled) and short low pulse are injected into ILED pin to control the brightness. You can refer to section 8.4.2 "Digital Brightness Control (ILED)" for more detail.

    I have not tried using this device with such high current. What kind of LED are you using? red LEDs? the forward voltage seems really low with 200mA flowing through it. One thing you can try is using a higher value of Rs and see how the device behaves.

    I am in the process of getting an EVM to try out your configuration, but I might have a problem getting the type of LED you are using.

    Regards

    H L

  • 0 in reply to Hak-Leong Ng
    Guru 28715 points
    HL-san,

    Thank you for your support.

    This problem was solved.
    The cause was what duty control signal is too high speed(100kHz).

    Best Regards,
    Kuramochi
  • 0 in reply to Kuramochi Tadahiko
    TI__Intellectual 1985 points

    Hi Kuramochi-san,

    Thanks you for the feedback. By the way, when you mentioned "duty control signal", which signal is this and where does it apply to the device? I did not see any external control signal in the schematic.

    Regards
    H L

  • 0 in reply to Hak-Leong Ng
    TI__Intellectual 1985 points
    Hi Kuramochi-san,

    I will close this case if you have no other questions.

    Regards
    H L