LM5118: LM5118 : buck boost converter output regulation issue.

Raj B

Part Number: LM5118
Other Parts Discussed in Thread: LM5170

Tool/software:

LM5118 Buck boost converter

We follow all the steps for the design for LM5118 buck boost converter, however the output regulation is not maintained. specifications: Input voltage range 8V to 30V DC. and output is 10V ,1A.

I am getting 4.37V output when the input 12V is given. Also, it does not maintain the regulation. When I give 24V DC input, output is 6.25V output. Pls suggest.

9 months ago

0 Stefan Schauer 9 months ago

TI__Guru 58641 points

Hi Ray,

thank you for using the E2E forum.

Can you share more details:

- Schematic

- Scope plots showing:

- VIN

- VOUT

- SS

- COMP

- both side of the inductor

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

Pls could you share your email ID .

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

Hi,

you can send a private message if you click on my avatar icon and select send private message.

Please drop a note here to let me know to check the private message inbox.

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

Stefan,

I sent you private message.

Best Regards,

RajB

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

HI RAj,

can you let me know the load condition while doing the measurements.

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

There is no load at output at the time off measurements. you can see Jumper J4 that is open now. if I close this it will supply voltage to U3 and U4. however I did not close J4 since I am not getting regulation and 10V.

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

HI Ray,

something is triggering a restart of the controller as you can see from the continuous ramping up of the SS pin voltage.

This might be due to the overshoot on Vcc.

What is the part number of the Cap you have used on Vcc? Esp. what is the effective capacitance considering DC Bias?

Can you check if there is a change if you increase the capacitance there.

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

Part# of the Cap is GRM188R71E105KA12D. I shared the schematic with all part# to you.

Regards,

Rajesh

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

Hi Ray,

please check the DC bias derating of this cap

at 10V it has only 400nF left.

at 20V it has only 200nF left.

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

Hi Stefan,

This design is from TI reference design and I have shared the reference schematic with you.

Regards,

RajB

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

Hi Raj,

thanks for the info - I will check with the owner of the LM5170 EVM.

Have you checked already the behavior with increasing the effective cap on VCC.

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

Hi Stefan,

I checked the behavior with increasing the effective cap on VCC, however no change at the output. I got the same result.

Regards,

RajB

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

Hi Rai,

on how many boards to do you see this behavior?

Have your already replaced the LM5118? If yes, does it still show this issue after replacing it?

Best regards,

Stefan

0 Raj B 9 months ago in reply to Stefan Schauer

Prodigy 55 points

Hi Stefan

I have tested on one board only since I have assembled only one board , I have not replaced LM5118 on this board. shall I replace LM5118 on this board?

Best regards

RajB

0 Stefan Schauer 9 months ago in reply to Raj B

TI__Guru 58641 points

Hi Raj,

yes, please replace the LM5118 or test on another board to ensure this is not just related to one device.

Maybe the device was damaged during the assembly or any test case.

Best regards,

Stefan

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LM5118: LM5118 : buck boost converter output regulation issue.

LM5118 Buck boost converter