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[moved] UCC21521 Gate driver-Bootstrap

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kaanaydin

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Hi everyone,

I want to use TI UCC21521 half bridge driver to drive Sic mosfets.
**broken link removed**
In datasheet I saw a bootstrap circuit with negative bias.
kkuu.PNG
In this circuit.VDD voltage is supplying two of them.now my question is that, what will happen if I put three UCC21521 in my circuit to drive 3 halfbridge ? can I use VDD voltage for all of them ?

Maybe you can share your knowledges about bootstrap mechanism.

Thank you,thats really important for me :)
 

Hi,

VDD is referenced to VSS, so yes, you need only one VDD.

Klaus
 

KlausST said:
Hi,

VDD is referenced to VSS, so yes, you need only one VDD.

Klaus
Click to expand...

In this example, VDDB directly operating with the VDD voltage , and VDDA has a diode drop and resistance voltage drop. does it has any effects on operations ?
 

Hi,

Go the usual way:

Check what´s your VDD voltage.
Check what´s your worst case diode voltage drop.
Then calculate worst case VDDA voltage.
Check driver datasheet for specified VDDA range.

Klaus
 

KlausST said:
Hi,

Go the usual way:

Check what´s your VDD voltage.
Check what´s your worst case diode voltage drop.
Then calculate worst case VDDA voltage.
Check driver datasheet for specified VDDA range.

Klaus
Click to expand...

Thank you for your kindly answer. What do you think about bootstrap topology efficiency ? I can not use bootstrap %100 duty cycle but otherwise(without bootstrap), I must use another source and that means are place and money. What do you think ?

- - - Updated - - -

KlausST said:
Hi,

Go the usual way:

Check what´s your VDD voltage.
Check what´s your worst case diode voltage drop.
Then calculate worst case VDDA voltage.
Check driver datasheet for specified VDDA range.

Klaus
Click to expand...

Thank you for kindly answer. What about the efficiency of bootstrap topology ? I can not use the my circuit with %100 duty cycle but otherwise(without bootstrap) I must use another source.and thats means money and place. you should check figure 42,43,44 in datasheet
 

Hi,

It is the typical bootstrap circuit. It can´t go to 100% duty cycle.

Why do you think you need 100% duty cycle?

Klaus
 

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