Device suggestion for +15V 5W and -15V 5W from 24V input

Hi  Jitendra,

What is the max VIN including transients? 

Thanks!

-Tahar

Hi Tahar,

24 V is regulated supply. Max VIN is 28V. Also the power mentioned, 5W, is peak power. Average combined power is 2 W.

Regards,

Jitendra

Hello Jitendra, 

I found couple devices from WVIN team, I assigned you post to them to comment more. 

https://www.ti.com/lit/ds/symlink/lmq66420.pdf?ts=1692639435323&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMQ66420

https://www.ti.com/product/LMQ66410

Thanks

Tahar

Hi Youhao,

Thanks for suggesting LMR36510. Yes, I need to have same part.

400 kHz switching frequency is comparable to the current frequency that we want to measure. Can you suggest part with higher switching frequency.

Regards,

Jitendra

Hi Jitendra,

What about LMR38020 with which you can program the frequency? 

Thanks,

Youhao

Hi Youhao, ok.

LMR38020 datasheet is not available. It is showing Error 404. Can you share it here?

Regards,

Jitendra

www.ti.com/.../LMR38020

Hi Youhao,

Thanks.

How can we do transient simulation of LMR38020 inverting buck boost.

Regards,

Jitendra

Hi Jitendra,

Use the transient model, and reconfigure the external circuit as an inverting buck boost.  You should also pay attention to the ground references.  I think 0V gnd of the model maybe a global 0V net, therefore, you may need to consider a level shift in setting up your Pspice model.  By doing the following:

1. Set IC GND pin to 0V, or connected to the Pspice GND symbol.

2. Set your actual system GND to be Vout, not connecting GND symbol.

3. Connect VIN source from VIN pin to Vout node which you assigned in above step.

The Vout from the simulation would be a positive voltage. The GND symbol is your actually negative output port if the Vout node is shifted down to 0V. 

Hope this clarifies,

Thanks,

Youhao

Dear Youhao,

Thanks. We are looking at it.

I need one more suggestion for the design. We expect 500mV/500 kHZ noise at the input of the regulator. What additional can I do to reject it nicely.

Regards,

Jitendra

Hi Jitendra,

You may consider to add an inductor to help filter it out. 

Thanks,

Youhao

Dear Youhao,

Thanks.

Webench suggested inductor value of 8.2uH for buck configuration. With 8.2uH, calculated current ripple is very small at 2MHz. Also section 9.2.2.4 in the datasheet says "Note that when selecting the ripple current for applications with much smaller maximum load than the maximum available from the device, use the maximum device current." Datasheet based calculation suggests to use much smaller value of inductor.

For simulation with 8.2uH, it seems device is not working in normal mode. Device behaved normally with 2.2uH in simulation.

Can you please suggest the good current ripple level for this device to choose proper inductor value?

Regards,

Jitendra

Hello Jitendra, 

Monday is a US holiday. 

Please expect some additional comments tomorrow. 

Regards, 
Denislav

Hi Jitendra,

Would you please share your Webench circuit, so I can understand the issue better? 

Thanks,

Youhao

Hi Youhao,

Files are attached.

Regards,

Jitendra

WBOperatingValuesDesign2.csv

Hi Jitendra,

I am studying this and will get back to you in the next few days.

Thanks,

Youhao

Dear Youhao,

How are you doing?

Do you have any suggestions for the inductor value and current rating. We want to finalize the inductor specs.

Regards,

Jitendra

Hi Jitendra,

Sorry for the delay.  The ic is 2~3A pk current capable, and your max load current is just 0.33A, about 10% of the capability, and it can be considered as "much smaller" or you can think it is still in normal range.  In my understanding, 8.2uH  should work, but 2.2uH may perform better according to the referred datasheet recommendations. Also, 2.2uH may be cheaper.

The Webench is based on EVM, a proven circuit design, and it may be limited to optimize the design.  However, it should work, at least getting you to a good start point.  We always recommend the customers to adjust the circuit by experiment to get better performance.

Wish you good luck in your project.

Best Regard,

Youhao