PWM IC current capability

[francis29]

Hi,
We are planning to use the PWM IC part from Texas Instruments UCC28C42D for driving MOSFET ( IPD90R1K2C3 from Infineon ) in an SMPS circuit.
the PWM IC datasheet does not provide any information on the current output capability of the Gate output pin.
How can we ensure that the PWM IC can Turn ON /OFF the MOSFET effectively for a particular ON time.

There is information regarding the RDSon. Does this info can be used?

 

[KlausST]

Hi,

datasheet does not provide any information on the current

you need to read the datasheet.
And if you don´t find it by reading, then you are free to use the PDF reader´s serach function. Easy to find the information by doing a serach on "current" and "out"..

First page says: 1 FEATURES:
"±1-A Peak Output Current"

also first page: 3 DESCRIPTION:
" and a ±1-A peak output current capability "

page 3 ...
page 4...
page 13..

... but indeed the R_DS_on resistance will be more useful for calculations.

Klaus

 

[andre_luis]

How can we ensure that the PWM IC can Turn ON /OFF the MOSFET effectively for a particular ON time.

The switching 'effectivenes' depends on the MOSFET capacitance Cg in addition with the PWM frequency.
The lower capacitance, the lower rising/falling time; and of couse, dissipation proportional to the switching frequency.

 

[francis29]

Hi,


you need to read the datasheet.
And if you don´t find it by reading, then you are free to use the PDF reader´s serach function. Easy to find the information by doing a serach on "current" and "out"..

First page says: 1 FEATURES:
"±1-A Peak Output Current"

also first page: 3 DESCRIPTION:
" and a ±1-A peak output current capability "

page 3 ...
page 4...
page 13..

... but indeed the R_DS_on resistance will be more useful for calculations.

Klaus

Thank you for the information.
I have seen the 1A peak current information. But my doubt is whether the IC can support 1A of current continuously.
In our design ( Non synchronous Buck converter, 920V input, 15V output ) the switching frequency is 46kHz and the minimum ON time of MOSFET is 354 nano seconds.
I just want to know this much small ON time is possible with this PWM IC.

For the RDSon calculations can you suggest some application notes / references.

 

[KlausST]

Hi,

But my doubt is whether the IC can support 1A of current continuously.

Driving a MOFET gate with "continuos current" makes no sense. The gate draws just a short peak then almost nothing.

For the RDSon calculations can you suggest some application notes / references.

Just do a search. Every MOSFET manufacturer provides them.
I don't have one by hand, so I'd have to search as well. Shouldn't be a big deal these days ;-)

Klaus

 

[cupoftea]

Its ohms law for switching current...they give you rds for ON and OFF....so you use ohms law, and you know the vcc you are giving it.

Eg if you have vcc = 10v...then rdson ON = 10R, so the current will be 1A...but soon the gate voltage will rise and there will be less voltage across the 10R....so drive current goes down.

UCC28C42 can do down to 354ns on time......it doesnt have a min on time.....but the comparator that trips will have a delay time.

Mind the tolerance aswell.

 

[andre_luis]

I have seen the 1A peak current information.

As said, you need take care about the MOSFET gate charging, and since the gate is modeled as an capacitor, the driver peak capacity is what define how long the transistor will lie within the ohmic region, and therefore, how much will dissipate.

 

[dick_freebird]

People have used the Unitrode PWMs as switching regulators.
Not a great idea for efficiency, the high side voltage drop is high
and the low side, not great. 800mA or so can be had if you don't
mind all that. I am not familiar with the CMOS / BiCMOS versions
output stage but the way it's spec'd makes me think MOS outputs.
With 25 ohms at 200mA in the limit table that's 5V drop on the high
side (peak current does not tell the "on" voltage drop story where
you care about it, if you're using the output as the SW node
directly). At 800mA on this CMOS version I think you'd have
almost no output from a 20V rail.

For driving FETs, all you need to know is in those rise time specs.
50ns at 1nF is pretty leisurely and you can pretty much scale
tr, tf by your_FET_Cgate/1n and see what risetime will look like.
If you want 300ns pulse width, you probably don't want a 3nF
gate capacitance malforming it with 150ns rise and fall. And
forget driving a 10nF beast.

 

[francis29]

People have used the Unitrode PWMs as switching regulators.
Not a great idea for efficiency, the high side voltage drop is high
and the low side, not great. 800mA or so can be had if you don't
mind all that. I am not familiar with the CMOS / BiCMOS versions
output stage but the way it's spec'd makes me think MOS outputs.
With 25 ohms at 200mA in the limit table that's 5V drop on the high
side (peak current does not tell the "on" voltage drop story where
you care about it, if you're using the output as the SW node
directly). At 800mA on this CMOS version I think you'd have
almost no output from a 20V rail.

For driving FETs, all you need to know is in those rise time specs.
50ns at 1nF is pretty leisurely and you can pretty much scale
tr, tf by your_FET_Cgate/1n and see what risetime will look like.
If you want 300ns pulse width, you probably don't want a 3nF
gate capacitance malforming it with 150ns rise and fall. And
forget driving a 10nF beast.

Planning to use SiC MOSFET. UCC28C42 Can be used to drive SiC MOSFETs?

Hard to find 1200V rated MOSFETs that are not SiC.