TPS55010: Help finding transformer for use case

Hi John,

I had a quick look and couldn't find any of the transformers going to high frequencies supporting the 3.6V input. 750313527 from WE goes up to 1.2MHz, but support only from 4.5V on the primary side. I shall take a look if there are any alternate ones and get back to you.

Does the customer want to run at 1MHz to reduce output ripple? Could they consider using a lower switching frequency and increase output cap to reduce ripple?

Best regards,

Varun

Hi Varun,

Thanks for the quick response! Looking at their power tree, there looks to be a 5.8V regulated rail available. Do you think that could work better? Its within the 2.98 to 6.0V recommended range, but not sure if it would have a negative effect on regulation. Let me know your thoughts.

John

Hi John,

I think the 5.8V rail can help. The TPS55010 can run off the 5.8V rail and regulate the primary output to ~ 4.5V. That should be enough to meet the primary voltage range of the transformer.

Best regards,

Varun

Hi Varun,

I thought the output voltage was a combination of the resistor divider on the input, the turns ratio, and the Schottky diode drop on the output. Is there a way to make sure the output is closer to 5.0V? That is what they need, and you mention ~4.5V above. Is that just a limitation of what transformers are available? Couldn't we set the voltage higher on the input side so that we can get closer to 5.0V on the output?

Thanks,

John

Hi John,

The primary side output voltage should be 

and the secondary side output voltage (V_OUT) should be 

The transformer I suggested requires at least 4.5V on the primary side. Given the turns ratio of this particular transformer, I was thinking of shorting terminals 4 & 7, and connecting the output to 6 and 8. This would mean the turns ratio (3-1:6-8) would be around 0.751.  

The secondary side charges only when the low side FET of the TPS55010 conducts. The voltage across the primary side winding during this low side phase should be the primary voltage of TPS55010 . If the primary side is at 4.5V, the secondary voltage between terminals 6-8 would be around 6V. Maybe 2 diodes in series can be used on the secondary side to bring the voltage down to 5V.

Best regards,

Varun

Hi Varun,

Thanks for the detailed response! That helped me a lot. I think the only issue is he doesn't have 4.5V available. So it would require 2 diode back to back, and another regulator in addition to this regulator. He only has 3.6V and 5.8V available in his power tree. Is there a better device we should consider?  Or a different transformer? 

John

Hi John,

The 4.5V can be generated using the TPS55010 as below. 

The RHS and RLS can be set as 44.2KOhm and 10KOhm to get 4.5V.

As an alternative to the transformer, I'm thinking a coupled inductor could also be used. The turns ratio would be 1:1 for a coupled inductor. A coupled inductor having around 2 to 2.5uH inductance on the primary side should be enough.

DC-DC converters having low negative current limit values and FPWM mode could also be used as an alternative to TPS55010. But I don't think they may help as the problem seems to be with finding the right transformer part.

Best regards,

Varun

Thank you so much, sharing this with the engineer now!

John

Sure. Let me know if any further assistance is required.

Best regards,

Varun