Gate Driver ICs Forum Discussions

[KelvinCao]

Hi,

We used 1EDN7550U in our design to work as a high side switch, the schematic is as the below picture:

After I got the prototype board and did testing, I found 1EDN7550U didn't switch at all, I have tried to pull IN+ to 3.3V high,

it didn't switch, I have tried to input a 3.3V PWM signal to IN+, it didn't switch either, the pin 4 of MOSFET is about 48V,  supply +5V is OK, and I also have tried to connect VDD to a 12V supply, it didn't switch either,  would you tell me what is wrong with the design?

Thanks 

Kelvin

[KelvinCao]

Any Infineon application engineer comes to response this question? it is urgent to me.

From my prevous experiences, TI''s engineer will response within 12 hours.

Kelvin

[Meghana]

Hello Kelvin,

Apologies for the delay.

To drive a high side switch, we need to either have a bootstrap circuit or the secondary side supply ground should be referenced to the source of the MOSFET. Can you please let me know if the +5V supply's GND is connected to the source of Q60? 

If not, then that is the reason for not observing the output on the secondary side of the IC. Either you can use a bootstrap circuit as shown in below image or use an auxillary supply whose GND is referenced the high side MOSFET source to supply the gate. 

Please feel free to contact us if you have further questions on this topic. 

Regards

Meghana

[KelvinCao]

Hi Meghana,

Very nice to get your response.

Yes, we used a bootstrap circuit just like you pasted, but I am not sure the circuit connection is right or not, on board, VDD(5V)/VBUS (Q47.4)share the same Ground,  in other words, on board, the PGND/SGND connected together, would you help to check the circuit connection I pasted is right or something wrong? 

Thanks

Kelvin

[Meghana]

Hello Kelvin,

From the schematic snippet shared here, I'm not able to verify the charging path of the bootstrap capacitor. Can you please share the complete schematic here?

Regards

Meghana

[KelvinCao]

There are many pages of the completed schematic, I can pasted the schematic related to high side switch here, below is the 5V circuit schematic, it is referenced to signal name GND, 5V is already ready before the software  tries to switch on high side MOSFET Q60 by pull the signal BAT_O_CTRL to HIGH.

Below is the completed high side switch circuit schematic, I would like to give some explanation, DC supply inputs comes from connector P_BAT and is reference to GND also, DC power supply goes through the MOSFET Q47 then goes to Q60, I suppose Q60 will be switched on by the U40 and the DC voltage should be tested at the Pin of Q60.3.

Thanks

[KelvinCao]

Hi,

I got you mail message but failed to reply you, my mailbox is: kelvin.cao@otis.com

kindly feel free to set Webex call meeting.

Thanks!

[KelvinCao]

Hi Meghana,

Thanks for your Webex call, you said you will send me a mail to summarize the explanation at the meeting call, right?

Actually I am not sure I understood you explanation, especially for you said I should add an isolated power supply , this isolated power supply should supply the power of driver and do charging for boot strap capacitor.

Because the IN+ signal is referenced to controller GND, if driver IC is powered by the isolated power supply, how the driver IC works?

Thanks

Kelvin

[Meghana]

Hello Kelvin,

Based on our discussion over call and other details that were shared with us so far, we have drafted our recommendation in the attached ppt. 

Please check and let us know if you have more questions. 

Regards

Meghana

[KelvinCao]

Thanks! it helps us a lot!