Do not populate bootstrap diode

Thread Starter

SiCEngineer

Joined May 22, 2019
320
Hi all,

Building the shcematic for the texas instruments GaN demo board and the bootstrap diode is designated as a "DNP" component. https://www.ti.com/lit/ug/snou140a/...ps%3A%2F%2Fwww.ti.com%2Ftool%2FLMG3410-HB-EVM

Why? Surely the upper gate drive needs the bootstrap capactior, or is there isoalted power supply providing the upper gate drive bias?

If it is left DNP, how would one bridge the connection across from the isolated power supply to the GaN driver? Surely just soldering some wire across would not be a good idea? Is it best that I include these in my design even if they are DNP?
 

AlbertHall

Joined Jun 4, 2014
11,524
Look at the connections from VDD on Q1 and Q2. They are each connected directly to their own isolated 12V supply.
See Q3 and Q4 at the bottom of the schematic.
 

Thread Starter

SiCEngineer

Joined May 22, 2019
320
Look at the connections from VDD on Q1 and Q2. They are each connected directly to their own isolated 12V supply.
See Q3 and Q4 at the bottom of the schematic.
Yes I get that, I tried to put that across in my message. I can see the isolated supplies - so this negates the need for the diodes? So why is it there?

Also, why is ISO_12V_L connected to ISO_12V_H in the upper FET? Would you not want to keep the two supply rails separate from one another?

Still, how would I bridge the connection across the diode if it was DNP,or should I just not connect it at all in my schematic?
 

AlbertHall

Joined Jun 4, 2014
11,524
Also, why is ISO_12V_L connected to ISO_12V_H in the upper FET?
I don't see where this is in the schematic. Can you give a component reference/pin number, please?

Still, how would I bridge the connection across the diode if it was DNP,or should I just not connect it at all in my schematic?
You shouldn't fit the diode or anything else in the DNP places.
 

Thread Starter

SiCEngineer

Joined May 22, 2019
320
I don't see where this is in the schematic. Can you give a component reference/pin number, please?


You shouldn't fit the diode or anything else in the DNP places.
Please see attached image. It shows for some reason that the L and H ISO supplies are connected at their positive terminals and then to the VDD. I don't see why it is not just the upper isolated supply which is connected there.
 

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Thread Starter

SiCEngineer

Joined May 22, 2019
320
Okay, so it looks like this is optional for bootstrap capacitor mode. We don't have to operate it in this mode. So what is the 0R resistor for? It says to replace with 20R in bootstrap mode but I don't understand the need for 0R>
 
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