what resistor values for the output pins

DickCappels

Joined Aug 21, 2008
6,587
The resistors are there to reduce the chance of destructive ringing and oscillation on the gate of the MOSFET.

You may notice that there are no examples in the datasheet in which gate resistors are not used.

Whether you can connect the sink and source pins together does not appear to be addressed in the datasheet. That could save one resistor if it doesn't break the driver.
 

DickCappels

Joined Aug 21, 2008
6,587
Unfortunately, people talk of zero ohm resistors. How's that for setting things up for confusion?

If you find excessive ringing on the gate, which would manifest itself as poor efficiency of the MOSFET, you may wish to try the resistor.
 

BobaMosfet

Joined Jul 1, 2009
1,207
There is this circuit with no resistors straight from the datasheet.
View attachment 177348
You need to learn how to read a schematic. There are at least 3 resistors shown in the image you posted (Rin, Rsouce, and Rsink). As for 'zero-ohm' resistor that is a lie and a myth. There is no such thing (unless you want to call it a conductor). Resistors serve one and only one purpose- to resist the flow of current. Out of this manifests many valuable things related to manipulating the reciprocal relationship between voltage and current.
 

djsfantasi

Joined Apr 11, 2010
6,799
As for 'zero-ohm' resistor that is a lie and a myth. There is no such thing (unless you want to call it a conductor).
I’m not clear as to what you mean. I get that the name “zero-ohm resistor” is meaningless. However, as a component, they most certainly exist. Mouser has many (10,000+) zero-ohm resistors for sale. So does DigiKey!
 

DickCappels

Joined Aug 21, 2008
6,587
If I read the datasheet correctly, only one of the output devices (source and sink) are on at a given time. Only one of the lines is a low impedance at a time, so with 8R resistors there would be 8 ohms in series when the gate is being charged and held high and different 8 ohms while the gate is discharged and held low.
 

BobTPH

Joined Jun 5, 2013
2,538
It is a gate driver. All it is designed to do is charge the gate of a MOSFET. Take the total gate charge and divide by 10 to get the time this takes.

Current stops flowing once the gate is charged. It can be left on for as long as you like. It

Bob
 

crutschow

Joined Mar 14, 2008
25,398
If they are identical value, I see no reason for separate source and sink resistors (unless they are being used to minimize shoot-through currents).
 

Audioguru

Joined Dec 20, 2007
11,249
If the gate driver IC is very close to the gate pin of the Mosfet then there is no inductance in series and there will be NO RINGING. Therefore then the sink and source pins of the gate driver IC can be connected directly to the gate pin of the Mosfet with NO RESISTORS.

The datasheet shows the fast waveform produced (with some overshoot) by the Mosfet when there is NO RESISTORS. The overshoot would become ringing if there is some series inductance caused by distance between the driver IC and the Mosfet.
 

jpanhalt

Joined Jan 18, 2008
10,222
Here's another viewpoint (see attached, AB-9). Use what you need to reduce ringing to what you find acceptable. You can use a diode to speed up turn-off, if necessary. Unfortunately that pdf is no longer on the Fairchild site, so far as I know. I see no reason for multiple resistors as shown.
 

Attachments

Audioguru

Joined Dec 20, 2007
11,249
A wire or trace has series inductance that is reduced if it has a very short length. The inductance resonates with the gate to ground capacitance of the Mosfet which causes the ringing. Adding a series resistor slows the rise and fall times and reduces the Q of the LC tuned resonance.
 
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