Question about gate driver specifications

Thread Starter

geekoftheweek

Joined Oct 6, 2013
692
I would like to use the MIC5021 https://ww1.microchip.com/downloads/en/DeviceDoc/20005677A.pdf for a project, but having never worked with gate drivers before I have some learning to do.

Is the gate on voltage referenced to the circuit 0V (ground) or to VDD? I want to use a 50A capable FET, but most seem to need 10V above the source to turn on. VDD will be around 13 Volts from a car battery so the gate voltage would need to be 23 Volts to ground.
 

jpanhalt

Joined Jan 18, 2008
11,088
This:
1604950569537.png
Implies the boosted gate is relative to Source ≈ Vdd in a high side application.

And this muddies the water a little for that assumption:

1604950774727.png

However, the boost at 12V is only about 6V to 7V, which suggests that these values are relative to ground:

1604950942700.png.
 

jpanhalt

Joined Jan 18, 2008
11,088
The device is like ones I have used. It has a charge pump and goes above Vdd, but by how much? See the middle image (Figure 3-2) posted from the DS.

EDIT:
It appears the amount is about 50% of VDD (@36V increase is 39%, @ 12V, increase is 50%). Note 2 says at "DC". If that applies to the PWM, presumably at less than 100% duty cycle, it might be higher.

EDIT2:
I worried about that question, and here is the answer (Source: Datasheet):
1604957672502.png
 
Last edited:

Ian0

Joined Aug 7, 2020
3,275
The type you want is known as a high-side driver.
If you are driving it with a square-wave it can do its own charge pump.
If you look at circuits for half-bridge drivers such as IR2104, and IR2153 you will see the difference between the high-side and the low-side circuits, and how you can include a charge-pump
 

Thread Starter

geekoftheweek

Joined Oct 6, 2013
692
However, the boost at 12V is only about 6V to 7V, which suggests that these values are relative to ground:
View attachment 221879
That was what I was suspecting. I was thinking there would be some sort of notation if it was referenced to VDD, but maybe there was an "unwritten rule" I was missing.

I totally missed this in the datasheet. Thanks!

In all reality the circuit should only draw anywhere from 1A to 5A when working correctly. This is going to be a test device and I need a safety margin to allow for shorts to ground (one of the most common issues in the tested equipment) which is where the 50A thought came in. After a little more looking it looks like an IRLZ34 will handle things and with a .003 ohm sense resistor it should cut out at 16A.
 

Thread Starter

geekoftheweek

Joined Oct 6, 2013
692
Another option I have is since I will be using a ‎MAX4173TESA connected to an ADC pin of a PIC microcontroller to measure current I could possibly use the PIC's PWM to create my own charge pump. If I connect to both an ADC and comparator of the PIC I could use the comparator to detect overloads and shut down the PWM in an interrupt. I'll do some experimenting there also.
 

Thread Starter

geekoftheweek

Joined Oct 6, 2013
692
@jpanhalt thanks. I'll look around some more and see if I can find Microchip's information. I played with the idea before, but got lost in the math and since I really didn't need it at the time I didn't put a whole lot of effort into it. A gate driver sounds a little easier than trying to light a light bulb which is what I was trying the last time around..
 
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