LM5156-Q1: Schematic review

Hi Kygo,

It is recommended to use "LM5155/56 Boost Controller Quick Start Calculator" spread sheet for a new design.

For your questions, NMOS is more often used because it is cheaper than PMOS;

Spread spectrum selection pin can enable or disable “spread spectrum” function of LM5156.

Best Regards,

Feng Ji

Hi Feng

Thank you!

1.I have fill the "LM5155/56 Boost Controller Quick Start Calculator" ,please help to confirm if there is a problem.

2.Please help to review schematic , especially the UVLO part, because customer does not need UVLO, so UVLO PIN  is directly connected to BIAS PIN, is it OK?

 Copy of LM5155_56_Quickstart_Calculator_for_Boost_Converter_Design_V1_1_1.xlsx

Hi Kygo,

1. You should follow the calculated component value as the selected value provides only 21° phase margin. You should get more than 45° phase margin。

2. It is OK to to connect UVLO to BIAS.

Best Regards,

Feng Ji

Hi Feng

Thank you!

After I redesign the component value phase margin change to 50 degree.

Please help to confirm if there is good .2061.Copy of LM5155_56_Quickstart_Calculator_for_Boost_Converter_Design_V1_1_1.xlsx

Hi Kygo,

I think it is a good start point.

Best Regards,

Feng Ji

Hi Feng

Two question ,

1. The Gain margin is 20dB ,right?

2.If a customer currently wants to use PMOS, is it ok? What problems will it cause?
How should the SCH be changed when we use PMOS? THX

Hi Kygo,

1. The gain margin is the gain difference between 0 dB and the gain where phase is zero. The gain margin is marked with blue line, that is 15dB here.

2. People tend to avoid the use of PMOS whenever possible, as PMOS is more expensive. Sometimes PMOS are used where you can gain some benefit from the gate driver compared to NMOS. PMOS can be used here for sure, but the gate driver will be complicated.

Best Regards,

Feng Ji

Hi Feng

Thank you!

If we would like to change to PMOS  , how is the SCH needs to be changed