LM5145: 23VDC @ 5A output, 24VDC to 60VDC input, 72VDC input withstanding

Hello Dave,

Suggest using low ESR ceramic on the input and place close to the FETs as recommended in the datasheet.

You can change the output capacitor in WeBench by selecting alternate component when you "click" on Cout in the schematic.

Please note, that the LM5145 is a voltage mode controller, therefore the output capacitor and its ESR is important in the compensation design. If you arbitrarily change Cout and its ESR, you may find the loop will be unstable.

Alternatively you can use the online calculator in the link below, enter your selected Cout and ESR and it will calculate the new compensation components for you.

www.ti.com/.../lm5145design-calc


Hope this helps?

David.

David,

Thank you for the capacitor information. I'm afraid that the WEBENCH tool does not support this specific scenario. I created the power supply in the Quickstart Calculator, but when I tried to use the WEBENCH tool to change some of the components, it responded that my input and output specifications would not work with  the LM5145. The WEBENCH question has been posted to the WEBENCH forum. I would like to go ahead with the Quickstart Calculator design, as long as TI can vouch for the Quickstart Calculator results? Could you please verify that my input and output specifications are appropriate for a LM5145 design and that the Quickstart Calculator results are valid?

Hello Dave,

I think we should stick with the calculator to help with your design?

I checked the latest Calculator for the LM5145.  It will come down to your selected switch frequency, RDSon top and Bottom FET, LDCR and the Toff min [max].  The off time for the LM5145 is quite good, so you should be fine if you select a switch frequency of ~250kHz with RDSons ~10mR and below.  I have attached the latest spreadsheet, if the Vin min turns red (when you increase the Sync Frequency cell, Increase RDSons and LDCR ), you will know you have violated the Toff min specification for the LM5145.

Hope this helps answer your question?

David.

8883.LM5145 Wide Vin Synchronous Buck Controller Quickstart Calculator r12-7.xlsm

David,

I downloaded your spreadsheet. I noticed that it is recommending (33) 10uF capacitors. This is not really feasible. This is why I was asking about changing the Cin and Cout recommendations from the TI tools. I started looking at the LM5145 when I noticed that in section 9.2.3 (page 45) of the data sheet there is a design (Design 3) very similar to our requirements, except the input starts at 28VDC. It uses a switching frequency of 440 kHz (smaller inductor and far fewer caps needed). Now that you have validated the spreadsheet tool, it looks like I should be able to select a frequency between 250kHz and 440kHz and use the spreadsheet to help select the final component values?