LM51772: schematic review

Hi Jeff,

Thanks for reaching out. We'll get back to you with some feedback by today.

Thank you and best regards,
Bryan

Hi Jeff,

Thanks for waiting. Could you please attach the filled out LM51772 BuckBoost Quickstart Calculator Tool?
This would greatly help us achieve a proper evaluation of the schematic to make sure it's right for your application.

Thank you and best regards,
Bryan

Hi Bryan,

FYI.

LM51772_Buck-Boost_Quickstart_Tool_V1_1_0 (2).xlsm

Hi Bryan,

I only fill output = 5V, but actully our Vout may have Vout = 5V/9V/12V/20V/24V/48V.

Actully we concern about the recommend inductor value. seem need higher inductor value when Vout is low.

Thanks!

Jeff

HI Jeff,

as you can see for the 48V the inductor gets to small - you should select the 6.8uH.
This would be good also for the 48V.

Do you need the 5A also for 5V output - usually this is less for USB-PD.

I assume you will control the output voltage via I2C:

In this case FB-IN should be connected to AGND and FB to VCC2 - this enables the internal FB divider which can be controlled by I2C

Connection of DRV1 does not work the way it is connected but components are DNP - so not critical as long as this function is not needed.

Resistor at CFG1 does disable I2C - please check

All connections with the light green rectangle and TP_xxx are unclear - ensure this have the proper connection and components.

Note: cap at VCC2 needs to have the value from the Datasheet with considering DC-Bias.

Note2: AGND and PGND need connection point at Thermal pad

Excel sheet shows Iimiter and CDC of but components are place - please check again - also check required components at CDC and ILIMCOMP pin.

Best regards,

 Stefan

Hi Stefan,

I would like to ask C26/C27 50V is enough for 48V design?

May I need choose 100V to get more design margin?

Thanks!

Jeff

Hi Stefan,

Still have some question need check with you.

1. If FB pin no need connect to external divider resistor, how to LM51772 check Vout voltage? Via pin19 ISNSN/(VOSNS)?

2.CFG1 connect to VCC2 dierectly? or need a pull high 10k or 100k resistor?

3. AGND and PGND if using 0ohm connect to each others, which size do you recommend? or how many current rating for this connection?

4. SYNC and DTRK connect to VCC dierectly? or need a pull high 10k or 100k resistor?

5. For inductor have any DCR limitation? Now we found 6.8uH DCR about ~23mohm, is it okay? any side effect?

Thanks!

Jeff

Hi Stefan,

Sill have have question on item 5.

I using the calculate tool to fill about 25mohm inductor DCR, but can't find Efficiency red line as below.

We want check the Efficiency diff for the inductor DCR.

0537.LM51772_Buck-Boost_Quickstart_Tool_V1_1_0 (2).xlsm

And we choosing below 80V MOSFET is fine? Anything need notice?

https://www.infineon.com/dgdl/Infineon-BSZ0602LS-DataSheet-v02_02-EN.pdf?fileId=5546d462700c0ae601708b98b9631427

Thanks!

Jeff

Hi Stefan,

If my d1esign change to input 36V, is it possible reduce for inductor value?

Also can reduce input/output capactior? or suggest keep as 48V design?

8816.LM51772_Buck-Boost_Quickstart_Tool_V1_1_0 (2).xlsm

Thanks!

Jeff

HI Jeff,

sure, you can make the inductor smaller. Ensure it does not get marked red in the inductor field.

When asking for reducing the capacitor - do you mean the voltage rating or the capacitance.

Voltage rating should be ~ 30% above the max voltage on the cap.

Capacitance: depends on the the required ripple you can allow.

Best regards,

 Stefan