LM5175: Design review

mauprs

Part Number: LM5175
Other Parts Discussed in Thread: LM5176, TPSM5601R5H

Dear Support, my design (name: 56000080200) has this specification : Vin=20-30V, Vout=24V, Iout=20A, max ambient temperature 60°C (based on LM5175 or LM5176). Typical operating condition (24/7/365, every day) is Vin=24V, Vout=24V, Iout=8A but, in same conditions Vin can go down / up until 20V / 30V and Iout can become 20A; so I design it for Iout=20A and my target is to reduce LM517x power loss. I need design (schematic) review so I want share schematic, part list and my questions. Can you send a mail (or other) to attach documents ?

over 2 years ago

0 mauprs over 2 years ago

Prodigy 40 points

56000080200_Design review.pdf 56000080200_WiringDiagram.PDF 56000080200_PartList.pdf I attached (in this box) documentation for design review. My questions are in "56000080200_Design review" doc. Thanks

0 EM over 2 years ago in reply to mauprs

TI__Genius 11215 points

Hello,

Thanks for reaching out. We are currently taking a look at your inquiry and will come back to you as soon as possible, thank you for your patience.

Kind regards,

0 mauprs over 2 years ago

Prodigy 40 points

Hello EM, do you have any news?

+1 Stefan Schauer over 2 years ago in reply to mauprs

TI__Guru 60211 points

Hi,

can you please share the filled out quickstart calculator as well.

Regarding your questions so far:

1. Boot sequence. TPSM5601R5H starts when Vin=12V, so Vbias = 9V; when Vin=20V LM5175 starts, so when LM5175 starts VBIAS is present. In reverse order power off sequence. Do you think it is right this power on/off sequence ?

There is no issue if Vbias is available before Vin

2. Rsense. From “LM5175 Datasheet” formula Rsense @ 20 ampere seems to be rated 9,9W while from “LM5175 Buck-Boost Quickstart Tool -- r9” seems 2,52W-2,86W. Which is right power for Rsense ?

Can you point me to the location in the datasheet where teh Rsense is rated with 9.9W

3. Inductor selection. Do you think it’s a best choice an inductor for Iout=10A typ (1,3-1,8uH) or Iout=20A max (0,7uH)?

I would go for the higher inductance to reduce the max inductor current - for more margin to the saturation current.

4. Inductor polarity. XAL1580-741ME has pin 1 (marked) that seems to indicate “direction of terminals and start (short) lead. Connect high dv/dt here for lowest EMI”. Do you think I connect it in the right side ?

Yes, the pin 1 marking indicates the short or longer lead. To get that information please check the inductor datasheet or contact the inductor manufacture.
For EMI the short lead should be on the side where the higher dv/dt is happening - in this case it might be at the input side.
If you have EMI issue later when testing you can also rotate the inductor and test again.

5. Mode. CCM, Hiccup Enabled is suitable for this application? In overload condition my target is reduce heating so Hiccup seems good. DCM mode (rather than CCM) could reduce power loss ?

DCM will have advantages in low load condition only.

6. Snubbers. Are there good snubbers connections?

It is good to have footprint for a snubber at SW1 and SW2 - in case need the components can be added without layout modifications.
But this are already placed.

7. Diode_boot (D4 and D5). Do you think BAS316 is a good choice ?

Briefly checked the datasheet - look OK for me

8. Diode_FET (D3 and D6). Do you think SK5C0A is a good choice ?

Briefly checked the datasheet - looks OK for me

9. Heatsink. Do you think I should use an heatsink (for mosfets)?

Check the power loss with the Quickstart calculator - what is the heating expected for the MSOFET? What copper area do you have on the PCB to spread the heat.

10. Design Review. Do you suggest modifications? Can I prototipe my pcba?

Ensure kelvin connection bewteen CS /CSG and the Sense Resistor

Follow the layout rules of the Datasheet

0 mauprs over 2 years ago in reply to Stefan Schauer

Prodigy 40 points

Pag_24_lm5175_Datasheet_Rsense.xlsx

0 mauprs over 2 years ago in reply to Stefan Schauer

Prodigy 40 points

000_LM5175 Buck-Boost Quickstart Tool -- r9_10-30V 24V20A 500KHz.xlsm

0 mauprs over 2 years ago in reply to Stefan Schauer

Prodigy 40 points

000_LM5175 Buck-Boost Quickstart Tool -- r9_18-30V 24V10A 500KHz.xlsm

0 mauprs over 2 years ago in reply to Stefan Schauer

Prodigy 40 points

0 mauprs over 2 years ago in reply to Stefan Schauer

Prodigy 40 points

I Stefan. Thank you for your reply. Following "Quickstart Tool" in two significant configuration. I Attach "RSense datasheet formula". In xls "Pag_24_lm5175_Datasheet_Rsense" you find some test for "RSense datasheet formula" and you can see 9,9W when Vin=10V. I wait your new considerations. Thank you

0 Stefan Schauer over 2 years ago in reply to mauprs

TI__Guru 60211 points

Hi,

sorry, still can not follow or thinking in the wrong direction.

- in the datasheet the power loss is 1.8W

- in your application Vin min is 18V per Excel sheet and 20V per spec above - so why do you consider 10V ?

Best regards,

Stefan

0 mauprs over 2 years ago in reply to Stefan Schauer

Prodigy 40 points

I consider (also) 10V because I have 2 app. The first one (appA) with Vin min 20V; the other (appB) with Vin min 10V. So I think, Rsense_appA is 2,8W while Rsense_appB is 9,9W. Is it right ?

+1 Stefan Schauer over 2 years ago in reply to mauprs

TI__Guru 60211 points

Hi,

thanks, now i got it, yes, this is right.

So for the 10W you should consider to have some Resistors in parallel to get the Energy more distributed.

Best regards,

Stefan

Power management

Power management forum

LM5175: Design review