LM3409 line regulation analysis

Subhash Chandra Sadhu

Other Parts Discussed in Thread: LM3409

Hi!

I am an Applications Engineer in the 3D ToF team. We recommend LM3409 to our customers for making current sources which drive LEDs/Lasers. One interesting aspect which is important for the system performance is to understand the line regulation of LM3409. We can subvert the effects of the output current ripple of LM3409, but the input power supply ripple can affect the system.
Could someone outline a methodology to calculate the AC impedance (or a step response) for LM3409 which can explain the effects of changing input supply voltage?

Thanks in advance!
-Subhash Chandra Sadhu

over 9 years ago

0 Clinton Jensen over 9 years ago

TI__Mastermind 25500 points

You may be able to used the attached and change the input voltage (top, in grey) and see how it changes for your application. All the things at the top in grey are input variables.

Otherwise the best way is to look at the datasheet curves and the % change they have. Most applications will have a similar curve.

~LM3409 ErrorAnalysis and Calculator.xls

0 Subhash Chandra Sadhu over 9 years ago in reply to Clinton Jensen

TI__Expert 3800 points

Thanks a lot for the xls. This seems pretty useful for designing a current source using LM3409.

One thing that I am looking for, is to understand the effect of ripple on the input supply voltage. Could you point me to some literature which shows how to analyse the effects of the input voltage ripple on the output current ripple?

Regards,
Subhash

0 Clinton Jensen over 9 years ago in reply to Subhash Chandra Sadhu

TI__Mastermind 25500 points

I am not aware of anything like that. But the LM3409 is hysteretic so it is extremely fast reacting so unless the input ripple is many volts or more it isn't likely to show up. Even if it is it would just shift the switching frequency along with the input ripple and the resulting current ripple would be fairly small.

0 Subhash Chandra Sadhu over 9 years ago in reply to Clinton Jensen

TI__Expert 3800 points

Thanks!
I now understand how to go about it. I guess it's an extension of the dynamic steady state analysis.

Regards,
Subhash

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LM3409 line regulation analysis