MOSFET spec help

[dark]

Hi,

Please find the attached graph for MOSFET. I want to know if it is operated with a Vgs of 3.5V , then can we keep the Vds to 5V ? . In the graph the Vgs of 3V shows a Vds of merely 1.5V what does this means.....

Rgds

 

[MrAl]

Hi,

That's the 'on' resistance.

 

[dark]

Hi,

That's the 'on' resistance.

Hi, Thanks , so the manufacturer dosent shows full curves before just saturation voltage. Rgds

 

[Roff]

View attachment 68819

Hi,

Please find the attached graph for MOSFET. I want to know if it is operated with a Vgs of 3.5V , then can we keep the Vds to 5V ? . In the graph the Vgs of 3V shows a Vds of merely 1.5V what does this means.....

Rgds

Keep in mind that the drain current at the point you specified is about 35 amps. That's a power dissipation of
P=1.5V*35A=52.5W. If you raise Vds to 5V, the dissipation will be at least 175W. Even in the first case, you will have problems keeping it cool unless the current is low duty cycle.

 

[crutschow]

It would help if we knew what you are tying to do with the transistor.

 

[audioguru]

The graphs of the datasheet are for a "typical" mosfet.
But you cannot buy a typical one, you get whatever is available. It migh be much worse or much better.

 

[dark]

Keep in mind that the drain current at the point you specified is about 35 amps. That's a power dissipation of
P=1.5V*35A=52.5W. If you raise Vds to 5V, the dissipation will be at least 175W. Even in the first case, you will have problems keeping it cool unless the current is low duty cycle.

I will draw according to the package , What I need to know is , is the graph incomplete(or not necessary) for Vgs above 2.7V which dosent shows saturation.

It would help if we knew what you are tying to do with the transistor.

I am just switching a 5V/2A load(or less) with Vgs of 3.3V, the mosfet make is Irlml2502 .

Thanks

 

[audioguru]

Your Mosfet is a tiny little thing. With a Vgs of only 3.3V then a load of only 2A might be fine.
It is guaranteed to conduct 3.6A with a Vgs of 2.5V for 5 seconds when its junction is cooled to 25 degrees C somehow.
But it might get so hot that it desolders itself.

 

[Roff]

You don't need that graph. All you need is the attached spec. The max Rds(on) is 80mΩ, and that is with Vgs=2.5V. With Vgs=3.3V, your Rds will be less than 80mΩ.
Pdiss<.08Ω*2A
Pdiss<160mW.
The transistor will barely get warm.

 

[ronv]

I think I see what is bothering you.
I can't see anything that guarantees it will work at Vgs of 3.3 volts. But, from your curve we know that Vds will be below 0.1 volts at 2 amps and 3.3 volts gate to source so the power will be less that .2 watts, so temperature less than 20C above ambient.

Rolf must have found a better spec. I didn't see that line in this one.

https://www.electro-tech-online.com/custompdfs/2012/11/irlml2502.pdf

 

[Roff]

I think I see what is bothering you.
I can't see anything that guarantees it will work at Vgs of 3.3 volts. But, from your curve we know that Vds will be below 0.1 volts at 2 amps and 3.3 volts gate to source so the power will be less that .2 watts, so temperature less than 20C above ambient.

Rolf must have found a better spec. I didn't see that line in this one.

https://www.electro-tech-online.com/custompdfs/2012/11/irlml2502.pdf

The Rds(on) spec is near the top of p.2 in the datasheet you linked to.
I have never seen a switching-rated MOSFET that did not have an Rds(on) spec.

 

[dark]

Hi,

Please have a look at datasheet p.4 Maximum SOA , It dosent shows DC line !! . If I switch 5V@2A continuously will that be a problem .

@Roff ; I get it dissipitation wise it should be fine , but the datasheet is little tricky . Could anyone suggest me a better part with Vgs of 3.3 , Vds of 5V and Id=2A or more . I spotted NTD5867NL https://www.electro-tech-online.com/custompdfs/2012/11/NTD5867NL-DPDF.pdf , but this even dosent satates Rds on at 3.3V. Rgds

You don't need that graph. All you need is the attached spec. The max Rds(on) is 80mΩ, and that is with Vgs=2.5V. With Vgs=3.3V, your Rds will be less than 80mΩ.
Pdiss<.08Ω*2A
Pdiss<160mW.
The transistor will barely get warm.

Do you mean 2A*2A*.08Ω = 320mW?

 

[dark]

Hi,

Can we wire three or more MOSFETS in these configuration?
**broken link removed**

 

[dr pepper]

Sounds like power dissipation is bothering you.
Its not so much the on resistance thats the issue with heat issues, its more the switching speed, mosfet gates have capacitance it takes an amount of energy to charge and discharge this, slowing down switch on/off, this results in the fet spending more time in the linear state where it is dissipating power.
Do a google for mosfet switching.

 

[dark]

Sounds like power dissipation is bothering you.
Its not so much the on resistance thats the issue with heat issues, its more the switching speed, mosfet gates have capacitance it takes an amount of energy to charge and discharge this, slowing down switch on/off, this results in the fet spending more time in the linear state where it is dissipating power.
Do a google for mosfet switching.

I need to operate it continuous mode . Not with PWM or switching. If my load is say 2A and Volts 5A , then the MOSFET has to bear 10W continuously . I am not sure regarding this, probably designing a Load switch .

 

[audioguru]

I need to operate it continuous mode . Not with PWM or switching. If my load is say 2A and Volts 5V , then the MOSFET has to bear 10W continuously.

NO.
The power supply provides 10W. The Mosfet dissipates (2A*2A*.08Ω = 320mW and the load dissipates (10W - 320mW=) 9.68W.

 

[dark]

NO.
The power supply provides 10W. The Mosfet dissipates (2A*2A*.08Ω = 320mW and the load dissipates (10W - 320mW=) 9.68W.

Oh how foolish of me ... Thanks for correcting . Please have a look at the datsheet https://www.electro-tech-online.com/custompdfs/2012/11/irlml2502.pdf Page 8 Maximum SOA , there is no DC load specs can this be ignored. I just did some maths and found with 2A its die temperature comes out to be 150C ! ! is this ok. Rgds

 

[Roff]

Hi,

Please have a look at datasheet p.4 Maximum SOA , It dosent shows DC line !! . If I switch 5V@2A continuously will that be a problem .

You will never have 5V across the transistor when it is on, because your Ids is only 2A, and Rds(on)<.08Ω. Vds will be less than 160mV. As you correctly calculated, Pdiss<320mW. With RθJA<100°C/W, the junction temperature rise will be less than 32°C above the temperature of the PC board.

@Roff ; I get it dissipitation wise it should be fine , but the datasheet is little tricky . Could anyone suggest me a better part with Vgs of 3.3 , Vds of 5V and Id=2A or more . I spotted NTD5867NL https://www.electro-tech-online.com/custompdfs/2012/11/NTD5867NL-DPDF.pdf , but this even dosent satates Rds on at 3.3V. Rgds




Do you mean 2A*2A*.08Ω = 320mW?

Yes, you are correct. I had a brain fart.

 

[dr pepper]

Yes, you are correct. I had a brain fart.

Me too.

 

[dark]

You will never have 5V across the transistor when it is on, because your Ids is only 2A, and Rds(on)<.08Ω. Vds will be less than 160mV. As you correctly calculated, Pdiss<320mW. With RθJA<100°C/W, the junction temperature rise will be less than 32°C above the temperature of the PC board.

Yes, you are correct. I had a brain fart.

Thanks , its clear . Regards