TLP250 OR BOOTSTRAP IC (IR2110 etc.) for MOSFET GATE DRIVING

[gsecer]

Hello everybody;

I am designing a BLDC motor driver.

As I know there are various set-ups for mosfet gate driving, but I am familiar with two methods:

1. Using Optocoupler such as TLP 250:
2. Using Bootstrap ICs such as IR2110

My application requires high side gate driving naturally. I am a little bit confused about above 2 methods.

First of all, when someone use TLP250 for high side gate driving, he/she should connect the output ground of optocoupler to the floating node which is source of the high side MOSFET. Is this a problem or does it work just fine?
Another question is that:
My motor operates at 48 V max. TLP 250 says its output supply is 35V max. Does this yield any problem?
Last question is that it is known that when you use a bootstrap ICs, bootstrap capaacitors are not charged for %100. Is it true? What is the explanation of this?
I really understand that bootstrap capacitors are not charged when motor operates at very low speeds but when %100 pwm is appled and motor rotates at its no load speed what is the reason of problem?

Any help and idea is appreciated very much.

Thank you

 

[FvM]

Re: TLP250 OR BOOTSTRAP IC (IR2110 etc.) for MOSFET GATE DRI

First of all, when someone use TLP250 for high side gate driving, he/she should connect the output ground of optocoupler to the floating node which is source of the high side MOSFET.

Yes. Where do you think to connect output VCC of the optocoupler?

 

[hakeen]

Re: TLP250 OR BOOTSTRAP IC (IR2110 etc.) for MOSFET GATE DRI

You cant use 48V for TLP250.H e can have abs max 35v, Recommended 30v. 48V is above both. I know some new generation optocouplers have abs max 40v,but even this one would be not enough. Woud it be possible to have lower voltages with ur motor?

 

[gsecer]

Re: TLP250 OR BOOTSTRAP IC (IR2110 etc.) for MOSFET GATE DRI

Hello everybody;

First of all, thanks for your replies.

My first question is stupid actually. When I look at it now, I say what a shame

My designated driver is attached to this post.

I want to ask some question which are not silly this time I think.

*Should I use any diode anti-parallel to the gate driving resistor? If yes, what does it bring? I examined some of the application notes, but didnt meet something like this. However, some guys say put a anti parallel diode.

*Should I put a series resistor next to bootstrap diode? Why do we need such thing? Does not it reduce the voltage between bootstrap capacitor?

*I want to measure phase currents. This is why I use shunt resistors between source of the low level FETs and my power ground. Now I am a little bit confused about whether I should connect COM pin of IR2110 to my power Ground or to other side of the shunt resistor.

 

[FvM]

Re: TLP250 OR BOOTSTRAP IC (IR2110 etc.) for MOSFET GATE DRI

My first question is stupid actually.

I don't think so. There are ways to use a TLP250 as highside driver, but it needs a floating supply or some
kind of bootstrap circuit similar to IR2110. Besides TLP250 maximum supply voltage you have to care also for
maximum MOSFET gate voltage.

As a first remark, your schematic has errors related to VB/VS and bootstrap diode connection. I think
they are obvious when you look at the circuit suggested in the datasheet.

FET gate drivers are ususally designed with symmetric drive current. It guess you are referring to a diode
that speeds up switch off? It may be used to assure sufficient deadtime, but it's most likely unwanted to
have too fast switch off. It mainly generates inductive overvoltages and causes EMC problems.

A bootstrap series resistor would act as a current limiter, but also reduce the maximum duty cycle.

The shunt resistor voltage drop would be hopefully small compared to IR2110 VCC, so you better connect IR2110
to common ground.