LM3488: Control loop stability

Anton Kocherov

Part Number: LM3488
Other Parts Discussed in Thread: LM5122

Hello, I develop power source for a heating (input 12 V, output :8A, 24 V;Fswitch 500kHz). But i don't undurstand how to design control loop. i can't found correct values for R6, R7 and C9. For configuration of the scheme presented in PDF output voltage is only stable 22 V (but divider is designed for 25 V in this config) on load around 8 ohms How i can calculate R6, R7 and C9 values? Datasheet don't contain information about it, it has only 2 reference design.7802.DC-DC.PDF

over 5 years ago

0 Garrett Roecker over 5 years ago

TI__Mastermind 21720 points

Hi Anton,

Thanks for reaching out with your question and for using the LM3488.

I would suggest trying the following values for the compensation

R7 = 400Ohm

C9 = 330nF

Looking at the power level of the application and the step-up ratio of ~2 please take a look at the LM5122. This will help to improve the efficiency of the design.

Thanks,

Garrett

0 Anton Kocherov over 5 years ago in reply to Garrett Roecker

Prodigy 210 points

Hello, I tried R7=400 Ohm and C9=330nF. Operation is't stable. And then i tried R7=330 Ohms and C9=1uF. Operation Operation is't stable. R6 is 2kOhm for both cases.

0 Garrett Roecker over 5 years ago in reply to Anton Kocherov

TI__Mastermind 21720 points

Hello Anton,

To help debug the issue it will be helpful to have some waveforms

Can you please provide the DR pin, the output voltage and the COMP pin voltage during operation?

Thanks,

Garrett

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LM3488: Control loop stability