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LP8860-Q1: BOOST voltage setting

Kaji@PAN
Mastermind 7015 points
Part Number: LP8860-Q1

Hi,

I am creating a circuit using the LP8860-Q1 device.
I have one problem now.
The problem is that the output voltage rises during the BOOST START period during startup, but the input current flowing during this period is large.
I want to lower this current value.
One way is to lower the value of BOOST_INITIAL_VOLTAGE as much as possible. Then it has been confirmed that the current value drops.
So, the question is, the VF of the LED is 20V in total, is it possible to set the value of BOOST_INITIAL_VOLTAGE to 20V or less? For example, 16V.
In this case, disable BOOST OVP.
If the above is not possible, I would like to take a different measure. Is there any other way to reduce the input current?
Best regards,
  • 0
    TI__Genius 15776 points

    HI Kaji-San,

    I want to confirm some points,

    1)whether the input current is the current flow into VDD pin or not?


    2)the current is always large or only be large during startup period?

    3)could you offer your schematic and the part number of the MOSFET you choose

  • 0 in reply to Frank Qiu
    Mastermind 7015 points
    I'm a FAE for distributors of TI products, but I haven't provided any schematics from customers.
    1) No input current is flowing through the VDD pin.
    2) The intent of my question may not have been communicated.
    The period in the red frame below is the BOOST period. During this period, power is required to increase the voltage, and as a result, the input current is increasing.
    I would like to see how to reduce the input current during this period.
    As for the previous question, Could you answer whether the initial setting voltage of BOOST can be set lower than the voltage of the entire VF?
    Best regards,
  • 0 in reply to Kaji@PAN
    Mastermind 7015 points
    The input current I say is not the input current of the device itself. It is the current value on the input side of this whole circuit.
    There is a power supply that supplies power to the LP8860-Q1 circuit, but the problem is that the current limit of the power supply is caught.
    Best regards,
  • 0 in reply to Kaji@PAN
    TI__Genius 15776 points

    I think the max input current is based on the load of LED. 

    During the start-up period the load is open(you can see the PWM OUT is low in your red square), and the current is much lower than the full load situation(PWM OUT is constant high).

    From your describe If the supply can't satisfy the current during start-up, I think that may not suit your application.

    Initial voltage for adaptive voltage control mode must be higher than LED string voltage — otherwise the system may generate a boost overvoltage fault
    during VDDIO/EN pin toggling if the output boost capacitor is not discharged below the initial voltage before the next boost start-up.