LM5071: Using in 3rd mode (min ripple) with transformer primary winding as inductor; not working at all

Atul Rathod1

Part Number: LM5071

We are using LM5071 part in 3rd mode (min ripple configuration) for the rating 6V,0.6A. We are using transformer primary winding as an inductor for the same. Below are some detials -

VIn= 24V

Vout= 6V, 0.6A

Fsw= 580Khz (RON=115K).

With the above configuration, the switcher is not working properly and giving 0.348V output. Please do let us know, why we are facing this issue, is there any resolution for this.

Please find attached datasheet of transformer.

750318836r00 Spec with 100mA per coil capacity 40uH.pdf

over 5 years ago

0 Darwin Fernandez over 5 years ago

TI__Mastermind 41780 points

Hi Atul,

Is your 24V powered at the VEE side or RTN side of the internal pass FET? Is UVLO above it's threshold? Also is VCC regulating above its threshold with no oscillations? Is the converter switching? What is the COMP behavior?

Lastly, is there a specific reference design you based your solution from? Do you have a schematic of your solution we can review?

0 Atul Rathod1 over 5 years ago in reply to Darwin Fernandez

Prodigy 20 points

Hello Darwin,

24V is constant input voltage to LM5071 IC. As you see, we have connected UVLO directly to 24V supply rail. So switcher will always be in active mode.

When we connect transformer, the switcher is not giving VCC and oscillations.

Thanks and regards,

Atul Rathod

0 Darwin Fernandez over 5 years ago in reply to Atul Rathod1

TI__Mastermind 41780 points

Hi Atul,

Can you send the schematic for review? Thanks!

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LM5071: Using in 3rd mode (min ripple) with transformer primary winding as inductor; not working at all