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TPS43060: bootstrap diode selection guide

Ikoma
Intellectual 940 points
Part Number: TPS43060

Hi Experts,

My customer is developing a boost converter with TPS43060. Its specification is:

input voltage 24V(+/-3%)
output voltage 36V(max)
output current 10A

Since datasheet doesn't show much explanation to select bootstrap diode, could you give me required specifications of the booststrap diode?
Exact example of part number of a diode is very helpful.

Thanks in advance

Regards,

  • 0
    TI__Guru**** 191445 points
    The TI EVM uses On Semi MBR1H100SFT3G Diode, Schottky Power Rectifier, 1A, 100V. There is some text in datasheet section 9.2.2.1 that describes the requirements, but I agree that it does not give much guidance.
  • 0 in reply to JohnTucker
    TI__Intellectual 940 points
    Hello John,

    Thanks for your reply. The datasheet only told about the diode requirement that "the external diode should have a breakdown voltage rating greater than the output voltage". How about current requirement?

    I see that TI EVM uses 100V, 1A schottky part. Since customer's design specification is different from the EVM, the customer users the "TPS43060/61 CCM Boost Excel Design Tool" and got passive components parameters according to the recommendation from the excel. For example, Cboot is 0.33uF +/-10% 50V part.

    I think some current flow the diode at just truning on the low side FET and charging Cboot. So, average current may be not so big like 1A. But I'm not sure how big the inrush current is.

    The customer is asking TI how to determine the minimum requirements of peak current, average current, peak surge current and Vf of the bootstrap diode. Is there any equation or theory for those parameters?

    Could you please help me to support this question.
    Regards,
  • 0 in reply to Ikoma
    TI__Guru**** 191445 points

    As you may know, I spend a lot of time on the e2e forums and often answer general questions.  I do not directly support TPS43060 though.   Let me see if I can direct your question to the proper person.

  • 0 in reply to Ikoma
    TI__Mastermind 46905 points

    1. the maximum voltage of the diode should be higher than the maximum voltage in SW，which is the VOUT adding voltage spike.
    2. the average current of the diode is fsw*Qg. Qg is the high side MOSFET driving Charge at VCC.
    3. the diode should be ultra-fast recovery, low reverse leakage diode.
    4. the inrush current of the diode is actually limit by the resistor in series with Vcc as suggested in the datasheet. or you can add a resistor in series with the diode to limit the inrush current during the startup period. the resistor is normally several ohms.

  • 0 in reply to Jasper Li
    TI__Intellectual 940 points
    Hello Jasper,

    Thanks for your support!

    1. Since the cathode of the diode is connected with BOOT, I think that (peak of SW)+(VCC + some margin)-(Vf of the diode) must be applied for the maximum voltage of the diode. May I have your recommendation of the margin for VCC?
    2. I see.
    3. Regarding ultra-fast recovery, how can I assess whether the diode is fast enough? Similary, may I have any recommendation of reverse leakage current? TI EVM uses On Semi MBR1H100SFT3G and its reverse current looks 40uA@Tj=25degC and 0.5mA@Tj=125degC. Is this enough specification?
    4. Understood the importance of the serise resistor.

    Regards,
  • 0 in reply to Ikoma
    TI__Mastermind 46905 points
    1. i would suggest the diode voltage rating is 1.2 * Vr, Vr is the voltage stress of the diode.
    3. i think a diode similar to 1N4148 should be OK for the application.