LM61460: LM61460 WEBENCH trouble

Hi Alex,

I double checked it and got same result, it support current over 3A.

LM61460 is a 6A converter which is overkill for 2A load. LM61440 or even LMR33620 should be more cost-effective if load current only 2A.

B R
Andy

Hi Andy, 

LM61440 WEBENCH solution for 5V@2A not generated  as well.

The problem's the  WEBENCH generated solution for LM61460/LM61440 in the November/December 2020 ( I have a schematic)  and problem came only this January. Seems the LM61460/LM61440 models has been updated .  

Hi Andy, 

You are correct. Seems model has been updated. We are looking into the change and your design requests. We should be able to get back to you by mid of next week with any updates on this. Hope this is fine.

Best Regards,

Bhushan

Hello Alex,

We have fixed the issue. Please note that the fix will be available on TI website after the production release. 

We will let you know once it is updated.

Thanks and Regards,

Atul

Hi Atul,

Thanks for the info. Can I use LM61460 model to simulate LM61440?

Hi Alex,

I will not suggest to use LM61460 model for LM61440. As stated by Bhushan in above reply, both models are being updated and corrected. I would suggest to wait for next Webench release (by mid of FEB) so that you have updated designs (for both the devices). We will notify you once the changes are available on ti.com.

Kindly note that electrical simulation is only available for LM61460 and not for LM61440.

Currently electrical simulation for LM61440 is not in pipeline as well.

Thanks and Regards,

Atul

Hi Atul,

I already made PCB for LM61460 based on the WEBENCH version available in November/December 2020. PCB production expected to start next week, but you wrote WEBENCH update will be available 2 weeks later.... 

Hi Alex,

As you have mentioned you are using the November/December 2020 version of Webench design for your application then it should be fine. I would strongly suggest to thoroughly test the designs on bench(on PCB) before PCB production. 

In January there was an update on LM61460 for better component selection (enhancement). But we observed that update is messing with few design creation and needs a correction. As Atul has mentioned this issue is already resolved on internal servers. Kindly let me know if I can share the design report from internal servers with you for your input condition for further reference. Please note that there will be few difference due to an update. 

On Webench we can always save our designs (or design reports) or open the older design as well. I have shared few steps below on how to do it. Kindly let me know if this helps.

Accessing Older Designs :

After we login into Webench power designer (below link), go to my designs to open older designs.

Webench Power designer : https://webench.ti.com/power-designer/

Saving the designs and design report:

Open Webench design and click on share designs to generate the public link. This link will serve as gateway to your design. We can always print design reports from Export tab as well. 

Best Regards,

Bhushan

Hi Bhushan,

The question's can I rely on the WEBENCH simulation results I made in November/December or not?

This is why  I ask TI Team help me to verify my designs with the updated models. Can you assist? Actually it's 4 configurations only .

It also due to fact we want to switch from LM61460 to LM61440.

Hi Alex,

To answer the specific question on November/December design, yes you can rely on those designs. But before going into any production I will still recommend to test designs on board.

On your second query, can you share your schematics/designs with us? So that the our product expert can review and assist you. As you are planning to switch from LM61460 to LM61440, I will recommend this review. 

Meanwhile on Webench model update, it will be available in in mid of FEB on ti.com. But for your immediate reference, I created the design for input conditions shared on the post on internal servers for LM61440 and attached the report below.

/cfs-file/__key/communityserver-discussions-components-files/196/WBDesign9624.pdf

Best Regards,

Bhushan

Hi Bhushan,

Thank you very much for the support. We're under high pressure with start of production date and your assistance is quite useful.

The design you sent use approx. 400 KHz switching frequency and relatively big coil, but in my design the space is limited this is why I ask you to generate design with the next  requirements :

1. VIN = 9V ... 32V

2. I OUT = 1.2 A .. 2,5A 

3. Switching frequency 800 KHz ( possible to increase to 1 MHz but better keep 800KHz for the better efficiency)

4. Coil is Coilcraft  XAL4030-472 

Could you please check LM61440 design stability for the min and max load?

Hi Bhushan,

Thank you very much for the support. We're under high pressure with start of production date and your assistance is quite useful.

The design you sent use approx. 400 KHz switching frequency and relatively big coil, but in my design the space is limited this is why I ask you to generate design with the next  requirements :

1. VIN = 9V ... 32V

2. I OUT = 1.2 A .. 2,5A 

3. Switching frequency 800 KHz ( possible to increase to 1 MHz but better keep 800KHz for the better efficiency)

4. Coil is Coilcraft  XAL4030-472 

Could you please check LM61440 design stability for the min and max load?

Hi Alex,

Thanks for providing the above inputs conditions. I created the design for input conditions shared above on internal servers for LM61440 and attached the report below.

For LM61440 9-32-5-1.2A --Fsw 800kHz,

WBDesign6774_1P2A.pdf

For LM61440 9-32-5-2.5A --Fsw 800kHz,

WBDesign6775_2P5A.pdf

Let us know if you have any other queries.

Best Regards,

Shaheen S M

Hi Shaheen,

Thanks a lot for the assistance.

The Second case for LM61440  is : 

1. VIN = 18V ... 32V

2. VOUT = 1,55V

2. I OUT = 1,7 A .. 2,2A

3. Switching frequency 800 KHz ( possible to increase to 1 MHz but better keep 800KHz for the better efficiency)

4. Coil is Coilcraft  XAL4030-472 

Hi Alex,

Please find below the report for above mentioned conditions  with LM61440  device.

Input: VIN = 18V ... 32V, Vout=1.55V , 1.7A with 800kHz 

WBDesign6773_1P7A.pdf

Input: VIN = 18V ... 32V, Vout=1.55V , 2.2A with 800kHz 

WBDesign6777_2P2A.pdf

Regards,
Shaheen S M

Hi Shaheen,

Hi Shaheen,

Thanks a lot for the assistance.

The Third case case for LM61440  is : 

1. VIN = 18V ... 32V

2. VOUT = 4,2V

2. I OUT = 2 A .. 4A

3. Switching frequency 800 KHz ( possible to increase to 1 MHz but better keep 800KHz for the better efficiency)

4. Coil is Coilcraft  XAL7070-332 

Hi Shaheen,

Do you expect the troubles with Third case ( see above )?

Hi Alex,

Please find below the report for above conditions. WEBENCH designs are getting created for above inputs on internal servers.

VIn=18V to 32V Vout=4.2V Iout=2A with Fsw=800kHz device:LM61440 

WBDesign6779_2A.pdf

Vin=18V to 32V Vout=4.2V Iout=4A with Fsw=800kHz device:LM61440 

WBDesign6779_4A.pdf

Hi Shaheen,

Thanks. Just last case left and I want to discuss  it separately.

I need the power supplier with the next spec.;

VIN = 18V ... 32V

2. VOUT = 3,3V

2. I OUT = 0,3A .. 1A

I selected the same LM61440. , because it was already used in the Case 1... Case3.  Is it possible to get the stable design for this spec for the 800KHz and Coilcraft  XAL4030-472  .

Maybe you can offer more efficient  ( and available from distributors) , automotive qualified solution in the same VQFN-HR package?

Hi Alex,

Please find the WEBENCH design report for above input condition. 

WBDesign67811A.pdf

The design is stable on WEBENCH for 0.3A to 1A load. However, It's recommended to get this reviewed from our product experts. 

For answering your second query, We are moving this post to product experts .

Regards,

Shaheen S M

Hi Shaheen,

In the last design for 3,3V  the output capacitors 2x100uF ( GRM32ER60J107ME20K) is too big  and I can't fit it on existing PCB layout. 

Can I ask you to check the design stability and voltage ripple with 2 x 22 uF ( GRM21BR61E226ME44L ) ?

.......... and one more :  in designs  you sent yesterday  for LM61440  5V@2.5A and 5V@1.2A the different  output capacitors has been used. I think it's not correct to estimate phase/gain margin.  Actually it the same 5V BUCK regulator and the output current can vary from 1,2A to 2,5A

Hi Alex,

Above mentioned input condition(Vin:12 to 32V , Vout=5V,Iout=2A with fsw=800kHz ) is working fine for  LM61460 on our internal servers. This updates will be available on ti.com by next WEBENCH release(tentatively mid feb).

I'm attaching the design report for your immediate reference.

WBDesign6786.pdf

Hi Alex,

We don't have GRM21BR61E226ME44 in WEBENCH database. However, We have used custom part for cout(2*22uF) for testing 3.3V design on WEBENCH. 

Please find the report for your reference.

WBDesign6787_C_22u.pdf

Hi Shaheen,

Will the WBDesign6787_C_22u.pdf stable at 0,3A as well?

Please find below the report for 

For LM61440 9-32-5-2.5A --Fsw 800kHz with XAL4030-472  inductor

WBDesign6788.pdf

For LM61440 9-32-5-1.2A --Fsw 800kHz with same inductor and Cout

WBDesign6789_1P2A.pdf

Thanks a lot!

Last question left :  Will the WBDesign6787_C_22u.pdf stable at 0,3A as well?

HI Alex,

Above design for 0.3A is entering into PFM mode of operation and is stable on WEBENCH.

Regards,

Shaheen S M

Hi Shaheen,

OK. Thanks.