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LMR36015: Minimum Switch On-Time

Victor Levy
Intellectual 2316 points
Part Number: LMR36015
Other Parts Discussed in Thread: LMR33620

Hello,

A customer of mine is working on the LMR36015,

The maximum current they will want to use is 300mA, Once load current is low as 150mA they are seeing a decrease in the frequency – see attached measurements:

They see the following frequencies at 24V nominal input:

 

Load

Frequency

0mA

8.6Khz

150mA

770Khz

300mA

830Khz

410mA & Above

1Mhz

 The output does stays at 11V.

Can you please advise if this is valid?

From my check the cause is because the Minimum Switch On-Time is reached – can you confirm?

  • 0 in reply to Victor Levy
    TI__Guru 57555 points

    Hello

    With an input of 24V and an output of 11V, your duty cycle is about 50%.

    So, you are not seeing the minimum on-time limitation.

    What you are seeing is the normal light-load mode for this device.

    At small loads the frequency is automatically reduced to provide high efficiency.

    You can see examples of this in the LMR33620 data sheet typical curves of frequency vs load current.

    If this behavior is not acceptable to the customer, then the "F" version of this device can be used.

    However, the "F" version will have poor efficiency at light loads.

    Thanks