WEBENCH® Tools/LM5088-Q1: LM5088-Q1 WEBENCH Problem

Sergey Shusharin

Part Number: LM5088-Q1

Tool/software: WEBENCH® Design Tools

Hello. I am designing a power supply circuit with an operating voltage range of 18-65 volts and a current limit of 7 amperes on the LM5088-1 microcircuit. I assembled a printed circuit board. It works stably, protection against short circuit on the output works. But, for some reason, the chip fails when the input voltage rises above 45 volts and makes a short circuit at the output. Burns without noise and smoke. just lost generation on the gate. Burned 3 chips. I can not understand where the error was, did everything as suggested by the designer. The transistor took IRF3710 choke srp1265a-330m at 33 uh and 8 amps. Who can tell what the error is?

over 5 years ago

0 Sergey Shusharin over 5 years ago

Intellectual 260 points

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hello,

I apologize, I accidentally hit the wrong button before replying.

How are you applying 45V to the input, and how are you changing the voltage? Would it be possible to take an oscilloscope waveform measurement from input to ground at a lower voltage? The cause of this type of damage is typically ringing on the input pin which causes an over voltage.

In terms of layout you want to keep the input capacitors as close as possible to the device. Also, you want to have a large ground plane on the top layer of the board in order to help dissipate heat as well as keep your parasitic loops as small as possible.

Best Regards,
Katelyn

0 Sergey Shusharin over 5 years ago in reply to Katelyn Wiggenhorn

Intellectual 260 points

Katelyn thanks so much for the tip. . Unfortunately, I can not yet take measurements, because all 3 chips burned

0 Sergey Shusharin over 5 years ago in reply to Sergey Shusharin

Intellectual 260 points

I forgot to say that I will need a current of 7 amps for a short time, no more than 10 seconds. Its main mode of operation will be a current of 0.5-1 amps. Therefore, I was not particularly worried about the heat sink. As soon as the spare chips come, I will listen to your advice and check the bounce on the input and output. In my circuit, there are two electrolytic capacitors for 33 uF with low ESR and 4 ceramic capacitors of 2.2 uF in parallel with them. It seems like I followed all the rules of PCB layout. For me, the main thing is that when a short circuit at the output of the chip would not burn out

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hello,

How are you connecting the board to the power supply? Is this through long cabling? Because this can also create a higher risk for the input to see ringing.

I agree that from a component selection perspective the input capacitance should be sufficient. However, you still want to place the capacitors (at least 1 or 2) directly next to the IC in order to minimize any inductance in the traces since the input loop of your dc-dc converter will have a switching current.

Best Regards,
Katelyn

0 Sergey Shusharin over 5 years ago in reply to Katelyn Wiggenhorn

Intellectual 260 points

Hello. Cables from the laboratory power supply, the length is short. Once again, I redraw the scheme, please see if I did everything right?

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hello,

Thank you for sharing your updated layout. This looks better. Ideally you would take one of your input capacitors and rotate it horizontally to be directly next to the IC. The ground pad can connect to ground by creating a ground plane connected to the DAP. Also, the pin directly below is the EN pin, so you can move these resistors slightly further away to make room for the capacitor.

Second, you will want to add a ground plane on the top layer to connect to the DAP. Again this should be cocnnected to ground pins as well and the ground side of your input capacitor.

Please let me know if you have any additional questions.

Best Regards,
Katelyn

0 Sergey Shusharin over 5 years ago in reply to Katelyn Wiggenhorn

Intellectual 260 points

Good day. Thank you very much, I redid the scheme according to your recommendations. Please look at the picture of the PCB, is it worth it to change something else?

0 Sergey Shusharin over 5 years ago in reply to Sergey Shusharin

Intellectual 260 points

The designer offered me such a circuit. The frequency is 246 KHZ. The input voltage range is 18-70 VOLTS

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hello,

Thank you for sharing again. The input capacitor placement looks much improved. A couple additional recommendations:

Add thermal relief vias underneath the ground DAP.
You could rotate the feedback resistors such that the DAP can be connected to the ground plane and the ground pads of the feedback resistors.

Please feel free to let me know if you have any questions.

Best Regards,

Katelyn

0 Sergey Shusharin over 5 years ago in reply to Katelyn Wiggenhorn

Intellectual 260 points

Thank you very much for the recommendations. I turned the feedback resistors. And the perforations under the microcircuit were already present, they were simply not displayed in the P-cad. Please look again my scheme?

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hello,

Thanks for sharing. The resistors look good. My one question is what are the two components highlighted below:

Best Regards,

Katelyn

0 Sergey Shusharin over 5 years ago in reply to Katelyn Wiggenhorn

Intellectual 260 points

Good morning. Left diode shottky MBR20200, right transistor MosFet IRF3710

0 Sergey Shusharin over 5 years ago in reply to Sergey Shusharin

Intellectual 260 points

I beg your pardo. But let me ask one more question, will the situation improve with the reliability of the scheme, if I additionally add mass filling in the top layer of the top, or leave one fill of the bottom layer? I am afraid that the additional screens in the upper layer of a smaller area, as well as the fill under the throttle will affect the stability of the chip, what do you think?

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hello,

The mass filling should not effect the stability, but it should improve the stability.

Best Regards,

Katelyn

0 Sergey Shusharin over 5 years ago in reply to Katelyn Wiggenhorn

Intellectual 260 points

Hi, thank you. Tomorrow I will order printed circuit boards to the factory, as soon as I assemble and test I will report the results.

0 Katelyn Wiggenhorn over 5 years ago in reply to Sergey Shusharin

TI__Genius 11040 points

Hi,

Thank you for sharing. Please open a new thread when you share these results, and you can link to this thread.

Best Regards,

Katelyn

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