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LM5145: Could you please tell me any countermeasure to reduse high side gate ringing on EVM board?

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Replies: 6

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Part Number: LM5145

 Hello guys,

 One of my customers is evaluating LM5145 using  LM5145EVM-HD-20A (http://www.tij.co.jp/jp/lit/ug/snvu545a/snvu545a.pdf) for their new products.

 But they can't buy Infineon device dut to their distribution channel. So they replace BSC117N08NS5 for Q1 and BSC037N08NS5 for Q2 on EVM

with TI, CSD19531Q5A for Q1 and CSD19533Q5A for Q2. Also they change the following spec of EVM too.

1. EVM output voltage: 5V -> 12.5V.

2. Output capacitor: 47uF*7 -> 47uF*1.

3. Inductance, L2 , 3.3uF -> 15uF.

4. Switching frequency: 220kHz -> 370kHz

5. Input voltage: 24V

 When they measured effeciency of the EVM, the effeciency is about 90%. They thought it is low effeciency. So they cheched the gate voltage of Q1 and Q2.

As the result, they found Q1, the gate voltage of CSD19531Q5A(High side FET) was ringing dutring about 100ns with 5V swing  .

They think the high side NMOSFET, CSD19531Q5A could not be used with LM5145 because of high speed turn on/off characterstics.

 They wants know whether it is not good to use CSD19531Q5A for high side NMOSFET with LM5145 or not.

 Could you please give us any comment? And if you have any idea, could you please tell us any TI NMOSFET part number for the high side NMOSFET?

 Your reply would be appreciated.

 Best regards,

 Kazuya Nakai.

 

 

  • Hello guys,

    I'm Sorry. I forgot to tell you the FETs temperature. High side FET, CSD19531Q5A for Q1 temperature was about 110C and low side FET, CSD19533Q5A for Q2 was 90C.

    Best regards,
    Kazuya Nakai.
  • In reply to Kazuya Nakai59:

    Hello ,

    Can you please forward the Drive waveforms . Also did customer tried to use series resistance on drive output to slow down the FET.

    Ambreesh
  • In reply to Ambreesh Tripathi:

    Hello Ambreesh,

    Thank you for the prompt reply.

    Yes, the cusomer tried to insert 10ohm between LM5145 output and the high side MOSFET gate. Then gate votage ringing was improved but the effeciency improved was small.
    Could you please tell me your e-mail address because the customer doesn't want to disclose the waveform on E2E site?

    Thank you again and best regards,
    Kazuya Nakai.
  • In reply to Kazuya Nakai59:

    ambreesh@ti.com
  • In reply to Kazuya Nakai59:

    Will close this thread as it appears discussion continued through email.

    Thanks.

    David.

    Kind Regards,

    David Baba.

  • In reply to David Baba:

    Hello David,

    Thank you for the information.

    I could solve the issue with Ambreesh support.

    Best regards,
    Kazuya Nakai.

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