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LM25117 An incorrect operation of the Lo-side driver

Kuramochi Tadahiko
Guru 28715 points
Other Parts Discussed in Thread: LM25117

Hi,

My customer is evaluating the LM25117.

But the Lo-side driver works an  incorrect operation when the SYNC frequency is dropped.

The waveform and condition is following;

- CH2(Green)：High-side Gate voltage

- CH3(Red)： SYNC signal

- CH4(Blue)：Lo-side Gate voltage

- Oscilating Frequency：300kHz

- Sync Frequency：241kHz

- This work has a tendency to occur with the heavy load than the light load.

1. When On-state of the SYNC signal is longer than Off-sate, does the Lo-side driver works an  incorrect operation ?

2. When the SYNC signal is Off-state more than fixed time, does the Lo-side driver works an  incorrect operation ?

3. Is there any reason that the Lo-side driver works an  incorrect operation?

If there is any lack of information please let me know.

Thanks and Regards,

Kuramochi

  • 0
    Guru 28715 points
    Could you give me any advise?
  • 0
    TI__Guru 58371 points
    Hi Kuramochi-san

    There are some requirements when applying external synchronization pulse to the LM25117. All the requirement should be met at RT pin
    - rising pulse should be greater than 3.95V
    - during falling time, RT pin voltage should be less than 1.25V, but greater than -0.3V
    - the pulse width should be less than 100ns
    - frequency should be within +/-10% of the frequency programmamed by RT resistor.
    Please check each items one by one.

    Regards,
    EL