LM5143-Q1: Bode plot measurement

wenjun yang

Intellectual 360 points

Part Number: LM5143-Q1
Other Parts Discussed in Thread: LM5143

Tool/software:

Hi,TI experters

when LM5143 use to Two-Phase, Single-Output Buck Regulator 3.3V,how test gain margin and phase margin.

I place to injection point is 1 ,or 2 or 1&2 .I am uncertain.

10 months ago

0 Timothy Hegarty 10 months ago

TI__Guru 73102 points

Hi Wenjun,

You will need to change to a setup with a feedback resistor divider (not a fixed output setting) and inject at the top of the upper feedback resistor using the conventional technique. Injecting where you have indicated will also impact the current sense, so it won't give a correct result.

Regards,

Tim

0 wenjun yang 10 months ago in reply to Timothy Hegarty

Intellectual 360 points

Hi，Timothy

Thanks for your reply

your mean is inject at the top of the upper feedback resistor using the conventional technique.But from datasheet can fix output with no
external feedback resistors ,as below config

in this condition ,where is injection position.I don't understand

0 Timothy Hegarty 10 months ago in reply to wenjun yang

TI__Guru 73102 points

You will need to install the external feedback resistors - there will be no change to the bode plot.

0 wenjun yang 10 months ago in reply to Timothy Hegarty

Intellectual 360 points

Hello,Timothy

Could you help to mark onto the image of my use case ,in case that I disunderstanding your mean.

thank you very much

0 Timothy Hegarty 10 months ago in reply to wenjun yang

TI__Guru 73102 points

Wenjun, you need to connect the resistor divider Rfb1 and Rfb2 from Vout to FB (corresponding to the third row in the table above). This will allow you to make bode plot measurements. It's not possible with a fixed output setting (set by FB1 tied high or low).

Tim

0 wenjun yang 10 months ago in reply to Timothy Hegarty

Intellectual 360 points

Thanks for your kindly support

I understood,for two phase fixed output,We want to evaluate the power supply stability. If we cannot measure the bode plot, do you have any other suggestions?

+1 Timothy Hegarty 10 months ago in reply to wenjun yang

TI__Guru 73102 points

Yes, you can measure the bode plot - you just need to use the adjustable output setting with feedback resistors. The result will be equivalent to the fixed output setting you want to use, as the gain only depends on the ratio of the feedback resistances, not the actual values.

0 wenjun yang 10 months ago in reply to Timothy Hegarty

Intellectual 360 points

Thank you very much,Tim

0 Timothy Hegarty 10 months ago in reply to wenjun yang

TI__Guru 73102 points

Thank you too, Wenjun.

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LM5143-Q1: Bode plot measurement