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MOSFET (Si/SiC) Forum Discussions

yadavjay
Level 1
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Level 1

Hello Team,

we are using BSS138 N channel MOSFET with gate turn on voltage of 3.3V. we need to calculate the turn on and turn off time for the BSS138 so that we require the gate plateau voltage with the Vgs of 3.3V range. Datasheet already has gate plateau voltage for Vgs of 0 to 10V testing range but we require the gate plateau for the testing range of 0 to 3.3V. 

yadavjay_0-1652238636133.png

above figure i can find that gate plateau voltage is given for the test condition 0 to 10V. I am operating gate signal with 3.3v. so please provide the Gate plateau voltage for the testing range of 0 to 3.3V or if you are having any graph of Vgs to Gate plateau voltage is also helpful.

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Pablo_EG
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Moderator

Hello yadavjay,

Thank you for posting on Infineon Community.

The plateau voltage of a MOSFET is the same regardless of the maximum driving voltage.
The plateau voltage can change with Id, Vdd, and junction temperature.

When the gate voltage of the MOSFET reaches Vth, the channel will start to conduct.
When the gate voltage reaches a point where all the Id can be conducted, the input capacitance Ciss will stop charging.
Instead, the voltage drop across the channel will decrease, and with it the reverse transfer capacitance will charge (Crss).
Once this is completed, Vgs will again climb, this time to its maximum value.

From the above explanation, I hope it is clear that Vplateau in your case is affected mainly by Id.

Based on Fig. 6 "Typ. drain-source on resistance" of the datasheet, at least 4.5V Vgs is needed to enhance the channel throughout the full current profile fully.
Therefore, using 3.3V will result in high losses, and the plateau will barely happen at high currents.
Alternatively, you could use the SPICE model we provide and assess the Vplateau at your specific Id, so that you can accurately measure the turn on/off times.

SPICE model

Best regards,
Pablo

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Pablo_EG
Moderator
Moderator 250 sign-ins 250 replies posted 25 likes received
Moderator

Hello yadavjay,

Thank you for posting on Infineon Community.

The plateau voltage of a MOSFET is the same regardless of the maximum driving voltage.
The plateau voltage can change with Id, Vdd, and junction temperature.

When the gate voltage of the MOSFET reaches Vth, the channel will start to conduct.
When the gate voltage reaches a point where all the Id can be conducted, the input capacitance Ciss will stop charging.
Instead, the voltage drop across the channel will decrease, and with it the reverse transfer capacitance will charge (Crss).
Once this is completed, Vgs will again climb, this time to its maximum value.

From the above explanation, I hope it is clear that Vplateau in your case is affected mainly by Id.

Based on Fig. 6 "Typ. drain-source on resistance" of the datasheet, at least 4.5V Vgs is needed to enhance the channel throughout the full current profile fully.
Therefore, using 3.3V will result in high losses, and the plateau will barely happen at high currents.
Alternatively, you could use the SPICE model we provide and assess the Vplateau at your specific Id, so that you can accurately measure the turn on/off times.

SPICE model

Best regards,
Pablo

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yadavjay
Level 1
5 sign-ins First like given First reply posted
Level 1

Hello Pablo,

Thanks for the Reply !

In my design the drain current Id will be less than 5 mA, Vdd will be 12V with this parameter can you provide the Gate plateau voltage or any graph of the gate plateau voltage vs Id ? or can we consider the nominal gate threshold voltage as gate plateau voltage that is 1 volt ?

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Pablo_EG
Moderator
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Moderator

Hello yadavjay,

We do not have such graphs, but we can find that out by using the simulation model I provided in my previous response.

I made a gate charge simulation with your specification (Id = 5mA)

 

Pablo_EG_2-1652945591842.png

Pablo_EG_1-1652945583390.png

As you can see, the plateau appears at 1.5V Vgs.
Any working point below 5mA would have a lower plateau voltage.

As mentioned, if you were to use the rated current (0.26A), the plateau would appear at 3.3V.

You can obtain the Id VS Vplateau graph by doing such simulations.

Best regards,
Pablo