Post Go back to editing

About LTM4646 Power Dissipation

Category: Hardware
Product Number: LTM4646

Hi I am using LTM4646.

In Figure 11 of the datasheet, is the power loss value single output?
Or is it the sum of the dual outputs?


I am using it below.
1. Input +12V
2. Output +4.15V
3.Composite output by connecting output 1 and output 2

About 0.43A of +12V flows when the output is unloaded.
The loss is about 5.16W.
The output is normal at 4.15V.
My device gets hot. Is it normal?

If it is normal, it would be helpful if you could tell me if there is a way to reduce power consumption.


Best regards.

  • Hello,

    I'm assuming it is sum as it is either a dual 10A output or single 20A output load which is the output current in the figure is up to 20A.

    You can try your design in LTPowerCAD to have an idea how it will behave.

    When you say hot, what is the temp?

    You can try increasing your switching frequency and see if it reduces power consumption. Make sure your EXTVCC is at 5V as it is an LDO. If the EXTVCC is high, it will consume a lot of wasted power.

  • Hello, Mr.Jhun

    thank you for your answer.

    I understand that the figure is the total.

    RFREQ was set to 115Kohm, switching frequency was 350kHz.
    I changed the RFREQ to 30Kohm and the switching frequency to 1.3MHz.

    As a result of the change, it became about 2.4W (0.2A/12V) from about 5.16W (0.43A/12V) at no load.
    It is roughly the same as the power loss in the figure.

    The surface temperature also went from 71 degrees to 55 degrees.

    As you pointed out, increasing the switching frequency reduced the power consumption.
    Thank you.

    EXTVCC is unknown because it does not create a test pin on the board.

    Best regards.