LM5045: LM5045/46 for wide input voltage application (30 to 120VDC input and 48V DC output)

Johnson Pi

Part Number: LM5045
Other Parts Discussed in Thread: UCC2897A, ISO7420

Hi! Ti E2E,

My application is wide input voltage (30 to 120) VDC to 48VDC output. I wonder whether I can use LM5045/46 for this application. (It must have boost and buck function or say septic function.

Thanks,

Johnson

over 6 years ago

0 Johnson Pi over 6 years ago

Intellectual 470 points

I went to WebBench and try to design or simulate it in Full Bridge for this application but I cannot find or define the topology with full bridge using LM5045. Please advice it.

Thanks,

Johnson

0 Benjamin Lough over 6 years ago in reply to Johnson Pi

TI__Mastermind 26695 points

Hi Johnson Pi,

Thanks for your interest in LM5045. It appears that LM5045 does not a webench model available unfortunately. I suggest using the LM5045 design calculator to help with the power stage design. You can find the calculator on this page:www.ti.com/.../toolssoftware.

Best Regards,
Ben Lough

0 Johnson Pi over 6 years ago in reply to Benjamin Lough

Intellectual 470 points

Hi! Benjamin,

I downloaded the toolssoftware and found the file is "xmcd". What is the software? It is Mathcad or Mathlab?

Thank you,

Johnson

0 Benjamin Lough over 6 years ago in reply to Johnson Pi

TI__Mastermind 26695 points

Hi Johnson,

The calculator is a Mathcad file.

Best Regards,
Ben Lough

0 Johnson Pi over 6 years ago in reply to Benjamin Lough

Intellectual 470 points

Hi! Ti E2E,

As I mentioned at first for this topic, I need to design a converter with input voltage range from 30VDC to 120VDC. The LM5045 you suggested is good for 100V. How can I use it for 120V application?

Thanks,

Johnson Pi

0 Benjamin Lough over 6 years ago in reply to Johnson Pi

TI__Mastermind 26695 points

Hi Johnson,

You can use an emitter follower circuit with a zener tied to the base to limit the maximum voltage on the Vin pin. For reference, take a look at PMP7453: www.ti.com/.../PMP7453

The UCC2897A controller has a max Vin of 110V. In order to work up to 400Vin, the zener clamped emitter follower formed by R5, R7, R9, D6 and Q6 limits the maximum voltage applied to the Vin pin to less than 91V.

Best Regards,
Ben Lough

0 Johnson Pi over 6 years ago in reply to Benjamin Lough

Intellectual 470 points

Good idea!

Thanks,

Johnson

0 Johnson Pi over 6 years ago in reply to Benjamin Lough

Intellectual 470 points

Dear Ben,

I believe I don't need a controller or IC directly takes input voltage (over 120V) for Vin or Vcc. My fiscal (bias) circuit already have 12V bias circuit for controller . Then I can use LM5045 directly from input (30V to 12VDC) for power stage voltage and LM5045 always takes power from my local bias circuit.

Is it OK?

Thank you,

Johnson

0 Benjamin Lough over 6 years ago in reply to Johnson Pi

TI__Mastermind 26695 points

Hi Johnson,

This should be ok. Connect the 12V external bias circuit to both Vin and VCC pins.

Best Regards,
Ben Lough

0 Johnson Pi over 6 years ago in reply to Benjamin Lough

Intellectual 470 points

Hi! Ben,

You am in process of design use d I found in LM5045 application note, (page 25), Ti is using Si8420BB-D-IS, a digital isolator. But the IC, SI8420 has a water silk mark "Not Recommended for New Designs". I don't know what that means??

In TI prototye, did you really use it in your circuit? How does it performance?

Thank you,

Johnson

0 Johnson Pi over 6 years ago in reply to Johnson Pi

Intellectual 470 points

Si8410_20_21_Rev_1.5.pdfSorry for typo. See below,

Hi! Ben,

I am in process of design. And I found in LM5045 application note, (page 25), Ti is using Si8420BB-D-IS, as a digital isolator. But the IC, SI8420 data sheet has a water silk mark "Not Recommended for New Designs" in its data sheet. I don't know what that means??

In TI prototype, did you really use it in your circuit? How does it performance?

Thank you,

Johnson

0 Benjamin Lough over 6 years ago in reply to Johnson Pi

TI__Mastermind 26695 points

Hi Johnson,

What likely occurred is that the LM5045 EVM was released some years ago and sometime between the EVM release date and now, SI labs marked this isolator as NRND. I can't speak for Silicon Labs but generally this means this device is in the last stages of its product life cycle and they are recommending to not use this device in new designs/applications.I would suggest takaing a look at ISO7420. This isolator has been successfully used with LM5045 in past designs.

Best Regards,
Ben Lough

0 Johnson Pi over 6 years ago in reply to Benjamin Lough

Intellectual 470 points

Perfect!
Thank you for your input!

Johnson

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LM5045: LM5045/46 for wide input voltage application (30 to 120VDC input and 48V DC output)