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LP5860T: What are VCC and VLED supplying?

Derek
Mastermind 9792 points
Part Number: LP5860T

Tool/software:

Hello,

   This product has two high side voltage inputs: VCC and VLED. What does each supply internally? For an application that is flashing the LEDs, which of those rails should get the bulk capacitance that supplies the LEDs?

We are using this driver to supply qty. 50 RGB LEDs. Nominal Vforward is 3.2V for each LED. We have access to different power rails: 3.6V, 5.0V, etc. What would be the most efficient rails to use for VCC and what would be best to use for VLED?

Regards,

Derek 

  • 0
    TI__Mastermind 23150 points

    Hi Derek,

    Our expert is currently out of office. I will ask another expert to help on this thread. He will respond to you later. Thanks for your understanding.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    TI__Expert 5560 points

    Hi Derek,

    As shown in the block diagram the VCC provides the power voltage for internal analog and digital circuit, the VLED provides the power voltage for all the LEDs through the internal high side FET. The VCC and VLED can be connected together if the voltage level satisfy the requirement below.

    • For the VCC, when the maximum current setting for the output is larger than 75mA. the VCC voltage should be higher than 3.3V. But the current capability is not critical (<10mA). 

    • For the VLED, As it will provide the power voltage for all the LEDs, so its current capability should be higher enough to provide the total current, e.g. when every current sink's max current set as 100mA, then the current capability of the VLED should be higher than 100mA * 18 = 1.8A.
      • And the voltage level of VLED should be higher than the sum of (Vforward of LED + voltage drop on the highside FET + max VSAT), in which the voltage drop on the highside FET = Rdson of the FET * total LED current, the Rdson and VSAT can be found in the datasheet EC table (as shown below).
      • And the real VLED voltage should be selected as close to the calculated value through the formula above to minimize the power dissipation on the LED driver, as the main power dissipation of the driver = (VLED - Vforward of LED) * sum of the current.

    Best regards,

    Felix