LM5160: Secondary output voltage drop

Kuramochi Tadahiko

Guru 28715 points

Part Number: LM5160

Hi,

I'm evaluating LM5160 on LM5160DNTFBKEVM(Flybuck topology) and set external components based on calculator as attached.

LM5160FBKQuickStartCalculator - FinalVersion 20190625.xls

VIN=24V, Vout-pri=12V, ; Iout-pri=0A, Vout-sec=11.4V, Iout-sec=1.1A

Coupled Inductor: 744873680

This circuit is not working correctly, and secondary output voltage is 3V which is lower than setting voltage(11.4V).

This voltage drop depends on Iout-sec.

What is this voltage drop caused by?

I guess that the delay from SW-pri on to SW-sec off occurs because the delay also depends on Iout-sec.

Best Regards,

Kuramochi

over 4 years ago

0 Arief Hernadi over 4 years ago

TI__Mastermind 23815 points

Hi,

Would you be able to get a correct voltage at secondary with a lower current?

What is the primary output voltage at no load and with load?

Also make sure that the dot notation on the coupled inductor is applied correctly for flybuck topology.

Here is a user guide of our EVM as a reference

http://www.ti.com/lit/ug/snvu408a/snvu408a.pdf

Thanks

-Arief

0 Kuramochi Tadahiko over 4 years ago in reply to Arief Hernadi

Guru 28715 points

Arief-san,

Thank you for your checking.

>Would you be able to get a correct voltage at secondary with a lower current?

Yes, a correct voltage can be outputted at no load.

Secondary output voltage drops

>What is the primary output voltage at no load and with load?

Primary output voltage is constant(12V) with/without load.

>Also make sure that the dot notation on the coupled inductor is applied correctly for flybuck topology.

I have already checked it, and exchanged D1 and R1, moved C3.

So Vsw-sec phase is inverted for Vsw-pri phase as you can see.

Best Regards,

Kuramochi

0 Kuramochi Tadahiko over 4 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

Hi Arief-san,

How is this situation?

Best regards,

Kuramochi

0 Arief Hernadi over 4 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 23815 points

Hi,

At what load current does the voltage on secondary start dropping? Does it also change when you raise the VIN?

Maybe it is also a good idea to check it against the EVM

http://www.ti.com/lit/ug/snvu408a/snvu408a.pdf

The EVM suggest the load is around 400mA.

Thanks

-Arief

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LM5160: Secondary output voltage drop