LM5158-Q1: Doubt about UVLO and other parameters

Hi Danielb,

Thanks for using the E2E forum.

I have checked your quick start calculator sheet and found that the selected Vin, min is 3.4V and you have selected the lower hysteresis value for the UVLO = 3.4V. The device will not turn on when your input voltage is 3.4V. 

kindly, select your Vin, min ≥ 3.7V to turn on the device.

Moreover, check your compensation network again, if the phase margin is less than 63 degrees because on the attach calculator I am not able to see bode plot. 

Reset seems okay to me.

Best Regards,

Hassan  

Thanks, Hassan. I changed VSUPPLY(min) to 3.7V and kept VUVLO_ON = 3.7V and VUVLO_OFF = 3.4V, but I still have doubts about it. Why Webench does not allow me to set VUVLO_OFF = 3.4V? The maximum value that WeBench allows me to set for VUVLO_OFF is 2.96V.

For these parameters, is LM5157 a better option than LM5158?

I will check the compensation network and post the results here.

Dear Hassan,

Please find attached the new sheet after I checked the compesation network. Is this design correct now? It is different from what I would get from Webench application:

See that the sheet has a inductor with 10uH and the webench provides 1uH. Why do we have this difference between applications?

Regards,

Daniel

0066.LM5157-58_Boost_Converter_Design.xlsx

Hi Daniel,

Thanks for the information.

I will come back to you tomorrow with answer. Thanks

Best Regards,

Hassan

Hi Daniel,

I have gone through your attached quick start calculator.

I have found that the phase margin is still lower than 63 degrees. Kindly, use the recommended values by the quick start calculator to have a phase margin greater than 63 degree. 

Regarding the difference in indictor value on webench and the calculator is due to the flexibility of selecting the ripple ratio on the calculator compare to the webench. If you reduce the ripple ratio in calculator, the inductor size will increase. 

Best Regards,

Hassan 

Dear Hassan,

I am sorry for the misconfusing. I corrected it. Could you please tell me if I am missing anything else?

For these parameters, is LM5157 a better option than LM5158?

0066.LM5157-58_Boost_Converter_Design-new.xlsx

Best regards,

Daniel

Hi Daniel,

Overall, your design look good now. 

I would recommend to use the LM5158 because it has higher output voltage capability compare to the LM5157, and your output voltage is 44V and max output limit for LM5157 is 48V, which are very close and any SW overshoot could cause a failure of the device.

Best Regards,

Hassan