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Buck Converter Switching Pin and Voltage Output

Electrical Engineering Asked by GuneyBoss on November 26, 2021

By using rohm’s BD9G341AEFJ-LB buck switching regulator, we want to take 5V. In datasheet BD9G341AEFJ-LB’s datasheet
the example circuit given like

enter image description here

But we had to try circuit that is in Image-2, because of component absencity. Before trying this circuit we simulated at PSPice and it worked well except of some current ripple.

enter image description here

When we powered circuit in real it gives us 24V at output despite Vin 24V, too. First question, despite we tried PSPice and worked problemless, why did we take this 24V? Does it components value?

And we tried to measure the LX pin with oscilloscope in ac coupling mode. The screen of oscilloscope isenter image description here (Forgive me I haven’t better oscilloscope)

In dc coupling mode already oscilloscope gives us 24V DC. Second question, Is voltage ripple normal? And at the datasheet example circuit, by setting RT resistance to 47k ohm frequency can set 200kHz, that is, if we look to oscilloscope screen, should frequency equal to 200kHz? Or Is frequency is equal to 200kHz?

Last situation as of 05 August

According to last comments and ROHM technical service, I made these:

I found closest components values as possible like in adviced circuit in the datasheet(Image-1) . At the end, I obtained circuit that in below and results.

enter image description here

And layout like that:
enter image description here

When I supplied VCC with 24V, there was a fluctuating in LX pin between 0 to 1 V during first 20 seconds . And then abruptly I saw 24V at output. Before soldering all components, I controlled again the board and there wasnt any short circuit or different situation.

According to ROHM technical service, when I said this situation to them. They wanted me remove schottky barrier diodes one lead if you use RB095B-90. But why this problem occurs, they didnt tell. Im waiting a response,again. I will inform in here.enter image description here

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