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Original question:

CSD19534Q5A: IDS measurmant method for ASO (Are of Safety Operation) confirming.

CSD19534Q5A: Is there any MOSFET which has shorter Td(off) and tf than CSD19534Q5A?

Kazuya Nakai59
Guru 20670 points
Part Number: CSD19534Q5A
Other Parts Discussed in Thread: LM5145, CSD19533Q5A

 Hello guys,

 One of customers is evaluating CSD19534Q5A with LM5145. But they is serching for any MOSFET which has shorter Td(off) and tf than CSD19534Q5A (Td(off)=20ns, tr=6ns) because LM5145 dead time

between low side MOSFET=on->off and high side MOSFET=off->on is very small (14ns).

 Could you please tell me that any NMOSFET which meets the following condition?

 VDS =80V~100V

 ID=30~50A

 VGS=+/-20V

 RDS(on)=less than 20mohm

 td(of)=less than 20ns

 tr=less than 6ns

 Ciss=less than 1300pF

 Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.

   

  • 0
    TI__Mastermind 32345 points

    Hi Nakai san,

    Thanks for continuing to promote TI FETs at your customer. The switching times published in the FET datasheets are of limited usefulness. The LM5145 includes adaptive dead time control to prevent cross conduction of the FETs. I have also attached a spreadsheet with a list of all 80V to 100V TI FETs in 5x6 QFN. The CSD19533Q5A has a td(off) time of 16ns. Please refer to this blog:

    FETS_80V_100V_5X6_QFN.xlsx

  • 0 in reply to John Wallace1
    Guru 20670 points
    Hello John,

    Thank you for your reply and listing those recommended FET.

    LM5145 adaptive dead time control checks only the low side FET gate voltage before high side
    turning on. The control sequence is the below.
    1. Turning low side FET off.
    2. Checking whether the low side FET gate voltage is less than Vgs(th) or not.
    3. Waiting the dead time (14ns(typ)) after the gate voltage is less than Vgs(th).
    4. Turning high side FET on.

    The customer uses CSD19534Q5A for both, high side and low side FET with LM5145.
    Also they worry about a shoot through (high side and low side FET are on status at same time)
    because the total time(26ns typ) of the FET td(off) and tr is more than the dead time (14ns).
    I know that those are limited usefulness as you said.
    But they just want to know how long does the FET to get Ids=0A after the gate voltage drops to lower than Vgs(th).

    Do you have any data about the time?

    Thank you and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 32345 points
    Hello Nakai san,
    I can do some calculations to estimate the switching times in the customer's application using the internal gate resistance and charge of the FET along with the LM5145 controller gate driver specs. Can you please provide a summary of the customer's requirements: Vin, Vout, Iout, switching frequency, and output inductor value. I will also try to find out the test conditions used for measuring the switching times in the FET datasheet.
  • 0 in reply to John Wallace1
    Guru 20670 points
    Hello John,

    Thank you very much for your kind support.

    Their application conditions are the follows.

    Vin=30V~45V.
    Vo=12.5V.
    Iout=4.5A.
    fsw=550kHz.
    Inductor value= 8.2uH.

    If you need any additional information, could you please let me know?

    Thank you very much again and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 32345 points
    Hi Nakai san,
    I am going to send you an email outside of e2e with my latest information.
  • 0 in reply to John Wallace1
    Guru 20670 points
    Hi John,

    Thank you very much for your off line mail.

    I will close this thread.

    Thank you again and best regards,
    Kazuya Nakai.