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MOSFET (Si/SiC) Forum Discussions

User22280
Level 1
First question asked
Level 1
Hi teams,

if I use 2 pcs BSC059N04LS6 in parallel, how to calculate the Equivalent Qrr?
Double the original value or keep the same?

Thanks

Best regards
From Mia
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1 Solution
Pablo_EG
Moderator
Moderator 250 sign-ins 250 replies posted 25 likes received
Moderator
Hello MIA,

Thank you for posting on Infineon Forums.

When paralleling two MOSFETs, the current load will be shared between both devices (provided they have the same characteristics and are at the same Tj)
There will be some discrepancy due to the gate voltage time offset.
The body diodes will also share half of the load each.
I understand that it is difficult to picture how the Qrr differs from one setup to another.
This is why I made a simple simulation to verify this.

5252.attach

I used the device part number you are using, BSC059N04LS6.
You can find the simulation model here: https://www.infineon.com/cms/en/product/power/mosfet/12v-300v-n-channel-power-mosfet/bsc059n04ls6/#!...
The setup is a double pulse test circuit.
I performed one simulation with a single MOSFET as well as parallel MOSFETs, and the result is the following:

5253.attach

We can see that the peak reverse current is 7.1 A for the single and 11.3 A for the parallel version.
In terms of Trr, the single version had about 9 ns while the parallel version had about 10 ns.
If we apply the following approximation: Qrr = Trr*Irr_pk / 2
Qrr single = 31.5 nC
Qrr parallel = 56.5 nC

We can see that the relationship is not strictly an x2 multiplication, but it is quite close. (x1.8)

Please note that Qrr is very dependant on Id and di/dt, and the latter will be dictated by the stray inductance of your board mainly.
I suggest you make a simulation with your specific parameters in order to have the best approximation possible.
I used Simetrix but Infineon's models can be used in other simulators such as LTSpice.

Please let me know if you have any doubt.

Best regards,
Pablo

View solution in original post

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1 Reply
Pablo_EG
Moderator
Moderator 250 sign-ins 250 replies posted 25 likes received
Moderator
Hello MIA,

Thank you for posting on Infineon Forums.

When paralleling two MOSFETs, the current load will be shared between both devices (provided they have the same characteristics and are at the same Tj)
There will be some discrepancy due to the gate voltage time offset.
The body diodes will also share half of the load each.
I understand that it is difficult to picture how the Qrr differs from one setup to another.
This is why I made a simple simulation to verify this.

5252.attach

I used the device part number you are using, BSC059N04LS6.
You can find the simulation model here: https://www.infineon.com/cms/en/product/power/mosfet/12v-300v-n-channel-power-mosfet/bsc059n04ls6/#!...
The setup is a double pulse test circuit.
I performed one simulation with a single MOSFET as well as parallel MOSFETs, and the result is the following:

5253.attach

We can see that the peak reverse current is 7.1 A for the single and 11.3 A for the parallel version.
In terms of Trr, the single version had about 9 ns while the parallel version had about 10 ns.
If we apply the following approximation: Qrr = Trr*Irr_pk / 2
Qrr single = 31.5 nC
Qrr parallel = 56.5 nC

We can see that the relationship is not strictly an x2 multiplication, but it is quite close. (x1.8)

Please note that Qrr is very dependant on Id and di/dt, and the latter will be dictated by the stray inductance of your board mainly.
I suggest you make a simulation with your specific parameters in order to have the best approximation possible.
I used Simetrix but Infineon's models can be used in other simulators such as LTSpice.

Please let me know if you have any doubt.

Best regards,
Pablo
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