WEBENCH® Tools/LM25118: LM25118 related detail reqired

Rajesh Thesiya64

Intellectual 330 points

Part Number: LM25118

Tool/software: WEBENCH® Design Tools

HI team,

We are designing a power supply using LM25118 IC which have below requirements.

1) Input voltage: 9V to 36V(down to 3V at the cold crank)

2) output voltage: 4V@7A and 12V@3A

3) what is the output voltage at our input voltage is 3V in cold crank condition?

please reply as soon as possible.

over 4 years ago

0 Garrett Roecker over 4 years ago

TI__Mastermind 21720 points

Hi Rajesh,

Thanks for reaching out with your question and considering the LM25118.

Regarding the output voltage, are theses two different variants of the board or is the output voltage dynamically controlled?

I'm not sure I understand question 3. The output voltage is dependent on the design not the input voltage.

Thanks,

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

hi garrett,

thanks for the quick response.

Regarding the output voltage, are theses two different variants of the board or is the output voltage dynamically controlled?

Rajesh-->> we are designing two separate board for both designs.

I'm not sure I understand question 3. The output voltage is dependent on the design, not the input voltage.

Rajesh-->> regarding this question I only ask about In cold crank condition my system is rebooting or not.

we are waiting for your soonest reply.

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Rajesh,

Thanks for explaining.

For the 12V output variant the VCC pin can be feed through a diode from the output voltage to ride through cold crank. Supply the VCC voltage externally will keep the device operating during cold crank. Check out the below application note.

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=snva741&fileType=pdf

For the 4V output variant the same approach of supplying the VCC voltage will allow the part to ride through cold crank. However the VCC voltage needs to be greater than 3.7V to keep the part alive. So a simple diode will not work. You can use the charge pump circuit below to double the output voltage to 8V and supply the VCC pin.

Please let me know if you have any questions.

Thanks,

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

hello Garrett,

Please find attached the Schematic for review.

Scheme 1:

Input voltage : 9V to 36V

Output voltage: 10V

Output current: 3A

Scheme 2:

Input voltage : 9V to 36V

Output voltage: 4V

Output current: 6A

Please review this attached schematic and give valuable suggestions.

we are waiting for your quick response.

sch_4V@6A_001.pdf sch_10V@3A_001.pdf

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Hi Rajesh,

The schematic for the 10V output application looks okay.

Regarding the 4V output condition there needs to be a supply to provide the VCC pin with enough voltage to run through the cold-crank voltage. I mentioned this in my previous post. It is possible to use a charge-pump to supply the VCC pin with enough voltage. Note the charge-pump output should be connected through a diode to the VCC pin.

Thanks,

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

Hello Garrett,

Thanks for quick response.

Do we required charge pump circuit for 10V supply also in cold cranking ? or design is ok for 10V.

If any reference design available for charge pump circuit then share me for 4V design.

We are waiting for your soonest reply.

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Hi Rajesh,

The 10V design will only require VOUT being connected to VCC through a diode. The 4V design is the only one that needs a charge pump.

Please see the attached picture of the charge-pump, sorry that it didn't post last time.

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

hi Garrett,

Thanks for a quick reply.

we have one query regarding cold crank condition.

--- In the input side of buck-boost converter we are planning to use electrolight bulk capacitor for cold crank conditions.

As you suggested charge pump circuit is worked in cold crank condition.

which option is best? or both option is required I cold crank condition.

we are waiting for a quick reply.

Regards,

Rajesh

0 Rajesh Thesiya64 over 4 years ago in reply to Rajesh Thesiya64

Intellectual 330 points

hello garret,

Please reply ASAP.

we are waiting for your feedback.

0 Rajesh Thesiya64 over 4 years ago in reply to Rajesh Thesiya64

Intellectual 330 points

hello garret,

we are also planning to use below the scheme using LM25118.

Scheme 1:

Input voltage : 3V to 4.2V

Output voltage: 4V

Output current: 6A

is it possible to do design the above specifications?

please share your feedback asap.

0 Youhao Xi over 4 years ago in reply to Rajesh Thesiya64

TI__Guru 68675 points

Hi Rajesh,

There is a similar e2e thread seemingly posted by your colleague:

https://e2e.ti.com/support/power-management/f/196/t/843454

Please refer to it and lets close this thread here.

Best Regards,

Youhao Xi, Applications Engineering

0 Rajesh Thesiya64 over 4 years ago in reply to Youhao Xi

Intellectual 330 points

hello Garett/youhao,

thanks for your quick reply.

as per your suggestion, we have implemented a charge pump circuit for the 4V output Scheme.

Input Voltage: 9V to 36V (3V at the cold crank circuit)

Output voltage: 4V@6A

please review our schematic and give valuable feedback. our circuit is work in cold crank condition.

0 Rajesh Thesiya64 over 4 years ago in reply to Rajesh Thesiya64

Intellectual 330 points

Hello Garrett/Youhao,

we are waiting for your reply ASAP.

0 Richard Fu22 over 4 years ago in reply to Rajesh Thesiya64

TI__Genius 17640 points

Hi Rajesh,

The engineer responsible for this part is currently out of office until the week of the 14th so please wait for his reply.

But if it helps, I see that your input voltage is not high enough for the VCC regulator and it violates its minimum operating voltage.

Thanks,

Richard

0 Rajesh Thesiya64 over 4 years ago in reply to Richard Fu22

Intellectual 330 points

hello Garrett/Youhao,

we are waiting for your feedback on our uploaded schematic.

IS this schematic is OK for 4V@6A? as per your suggestion, we have added a charge pump circuit.

Please share your feedback and Close this issue ASAP.

we are waiting for your soonest response.

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Hi Rajesh,

Capacitor C783 should be connected between cathode of D36 and the output to implement a output voltage doubling circuit.

Adding the charge pump will supply the VCC voltage during cold-cranking conditions.

Thanks,

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

hello Garrett,

Thanks for the quick reply.

As per your suggestion, we have updated the charge pump circuit with our schematic.

one query regarding the charge pump diode, we use CTS05S40 for the charge pump circuit. Is it ok?

Below is the updated schematic for your review.

we are waiting for your reply ASAP.

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Hello,

That diode should work fine. The schematic looks good as well.

Thanks,

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

hello Garrett,

One more thing-

reliability point of view - how these adjustments are reliable?

How confident TI on these settings to make the same Buck-boost works for 4V, 6A?

Because we are planning for Mass Production of 50,000 units we are producing in March 2020 and 500K in 2020-21.

So, we need to make sure that this given solution works in each and every condition and will not fail anyhow.

Let me know the reliability so we shall proceed with this given solution and submit the final schematic for review.

we are waiting for your reply ASAP.

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Rajesh,

We have used this charge-pump configuration in other reference designs and I have not observed any issues for those designs. As long as the VCC pin voltage is greater than the specified under voltage lockout parameter then the LM25118 should operate. Ultimately it is up to you to test the circuit to ensure that it meets your reliability criteria.

Thanks,

Garrett

0 Rajesh Thesiya64 over 4 years ago in reply to Garrett Roecker

Intellectual 330 points

hello Garrett,

I would like to understand the charge pump circuit.

There are two configurations for the charge pump circuit.

1) Diode input from VOUT pin and Capacitor connect to the SW node(Q10 Drain).

2) Diode input from the SW node(Q10 Drain) and Capacitor connect to the Vout pin.

Which configuration is suitable in our application? and Explain its working.

as per my understanding, Configuration 1 is right but you suggest Configuration 2.

Please reply and give a valuable solution.

0 Rajesh Thesiya64 over 4 years ago in reply to Rajesh Thesiya64

Intellectual 330 points

hello Garret,

Any Update on my quires?

we are waiting for your feedback ASAP.

0 Garrett Roecker over 4 years ago in reply to Rajesh Thesiya64

TI__Mastermind 21720 points

Rajesh,

Configuration 1 is correct. Sorry about showing configuration 2, I must have copied the wrong picture.

Please let me know if you have any questions.

Thanks,

Garrett

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WEBENCH® Tools/LM25118: LM25118 related detail reqired