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Inquiry regarding LM5022 PMP7763 reference circuit

Other Parts Discussed in Thread: LM5022

Hello, all

Now we have some inquiries regarding LM5022 PMP7763 reference circuit from our customer.

Please refer to the items below, and feedback us with your comment.

We have designed our own board which is based on PMP7763 reference circuit.

However, the output voltage was not observed.

In order to find the solution to resolve this issue, please let us clarify;

1) Why VCC pin is tied to GND via 1uF capacitor

2) Why RT resistor is 243kohm? (We assume that the switching frequency is very low)

We thank you in advance for your information.

Best regards,

  • Hi,

    Thanks for your interest in TI's product. Here are answers to your questions:

    1) 1uF capacitor is the decoupling capacitor connecting to internal linear regulator which also supplies power to the lower side FET driver.

    2) Switching frequency should be selected to meet your design goals such as efficiency and size of the converter. High switching frequency reduces the size, however it increases switching loss. Lower switching frequency gives lower switching loss but the converter size will be bigger. Trade-off between size and efficiency should be made for your application requirements.

    Thanks.

    Haifeng 

  • Hello, thank you for your reply.

    I have some additional inquiries from our customer. Please refer to the items below, and feedback us with your comment.

    1) With regard to the schematic of PMP7763, it seems that the power is not supplied for internal regulator and low side FET driver. Is this normal usage of this device?

    We assume that LM5022 could not startup on this configuration.

    2) Do you have any particular reason why you selected this switching frequency for PMP7763 reference design?

    We thank you once again for your information.

    Best regards,

  • Hi

    For the first question, it is normal configuration, and it can startup in this configuration. Actually this reference design was built and tested, check out the test results at http://www.ti.com/tool/PMP7763.

    For the second question, as I mentioned switching frequency should be selected based on the size and efficiency requirements. You can choose different frequency from this reference design to achieve your design goals.For this particular reference design, the VIN is up to 800V, and 1500V MOSFET is used, that might be one reason that the designer choosed this frequency.

    Thanks.

  • Hello, thank you for your continuous support.

    Since they are facing on difficult situation to start up their own design, they would like to try to evaluate actual PMP7763 board.

    Please let us clarify whether we could purchase this board now.

    We thank you once again for your information.

    Best regards,