Design stability Check LM5118

Sanjeev Kumar093

Prodigy 50 points

Other Parts Discussed in Thread: LM5118

Hi All,

I am using LM5118 in one of my application. With following specification I simulated this on TI webench

Vin:5V-8V

Vout: 12V

Iout:4A

while simulating the below message popup

As per the above message what I understood that For design stability I need to Improve the Phase margin. But I am unable to get this information from the Datasheet. Can anyone Help me to stabilize the design or to improve the phase margin.

Thank you.

Regards,

Sanjeev Kumar

over 11 years ago

0 Kevin Ip over 11 years ago

TI__Intellectual 2155 points

Hi Sanjeev,

I used the LM5118 quick start calculator

and found these values to use:

Rfbb = Rfb1 = 1000 ohms

Rfbt = Rfb2 = 8756 ohms

Rcomp = 29.3 Kohms

Ccomp1 = Czero = 28 nF

Ccomp2 = Cpole = 3.9 nF

Setting these values as a CUSTOM component in the schematic gave the following OpVal results:

Phase Marg = 61.6deg

Cross Freq = 5.15kHz

0 Sanjeev Kumar093 over 11 years ago in reply to Kevin Ip

Prodigy 50 points

Hi Kevin,

Thanks for your quick Reply,

Actually we are using this regulator in Automotive Application where our actual requirement is as mention Below

Vin:5V-48V

Vout: 12V

Iout:4A

Is this compensation component value will work for higher input voltages too?

And if any special guidelines for EMC/EMI has to be taken, Please let us know. It will be a great help if you can share some PCB Layout gerber or board file for the same.

Thank you.

Best Regards,

Sanjeev Kumar

0 Kevin Ip over 11 years ago in reply to Sanjeev Kumar093

TI__Intellectual 2155 points

Hi Sanjeev,

I'm afraid not - for the new design conditions you will need to find the compensation values again and check stability.

Regarding the PCB layout, have you tried the new WEBENCH PCB Export feature? It can provide a known good layout populated with your WEBENCH design components.

0 Sanjeev Kumar093 over 11 years ago in reply to Kevin Ip

Prodigy 50 points

Hi Kevin,

Thanks for your Comments.

Regards,

Sanjeev Kumar

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Design stability Check LM5118