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I want need more clarification on MOSFET SOA, VDS and Id relation Motor Driver Peak Current 45A Voltage 48Vdc

I'm considering one MOSFET whose Id mention 113A at 100°C

1. Vds=Rds_onId is that correct to check the relation according to this Vds=0.007150 i.e. 0.355V and if I check the 0.42V on x axis the respective current approx. 40A on y axis (which is limited by Rds_on of MOSFET).that is so I'm not operating safely

2. I'm using 48V battery to drive my BLDC motor, so shall I consider 48V as Vds X axis (blue mark in SOA image) to obtain respective current on Y axis of SOA (red mark in SOA image Fsw 10 kHz and pulse time 100 us). So the current is only 50A. almost at the margin what I required

I've checked with some other mosfet also which has 180A current at 100°C according 1 step the resp current is 130A and by step to only 60A.

Above the rating the as per SOA,Mosfet get Damaged So please clarify which one of above step should be used to check mosfet safe operating Area.

also want to know when I will get to operate the mosfet at 113A,as mention in datasheet of MOSFET. or that is not practical

Waiting for a valuable reply Thanks!

enter image description here
IPB039N10N3 G datasheet link: https://www.infineon.com/dgdl/Infineon-IPB039N10N3G-DS-v02_03-en.pdf?fileId=db3a30431ce5fb52011d1ed1fd3915e0

enter image description here enter image description here

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  • \$\begingroup\$ What is your load? \$\endgroup\$
    – Voltage Spike
    Jul 28, 2021 at 20:44
  • \$\begingroup\$ Bldc motor which is driving the PUMP \$\endgroup\$ Jul 28, 2021 at 20:52

3 Answers 3

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50A steady state would be P=50A^2*3.9mΩ or 9.75W (which is probably too much for the package to take) Check 9.75W with the junction to ambient thermal resistance and make sure the package temperature stays below what it's rated for (ie calculate the package temperature from the dissipated heat).

As far as SOA, I get 100uS so keep the pulses equal to or shorter than that. I would also put this into a spice sim to double check the heating with a load for sanities sake.

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  • \$\begingroup\$ actually I'm using 2 MOSFET in parallel \$\endgroup\$ Jul 28, 2021 at 20:35
  • \$\begingroup\$ Could you please help me to understand which method should be use to check the MOSFET SOA step 1 or step 2 it's just for my reference only \$\endgroup\$ Jul 28, 2021 at 20:40
  • \$\begingroup\$ I'm still confuse in SOA, You've mention " I get 100uS so keep the pulses equal to or shorter than that" \$\endgroup\$ Jul 28, 2021 at 21:00
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On a log-log scale the SOA sloped limits represent constant max energy with equal space between the lines for log time scales. This is for peak energy flux in the chip.

The spec for 113A is for DC only with the caveats for margin and heatinsk.

The DC curve is for max power dissipation.

Adequate heat sinks are critical to maintain case temp limits well below limits as they have an Ron with a PTC pos.,tempco. This allows parallel use, but with very fast rise-times, not always so. This is only for pulse width with reasonable rise-times. Further reading is suggested on this subject.

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Here are the steps to validate a MOSFET’s operating conditions using SOA curve:

Identify the maximum V_DS and I_D ratings of the MOSFET from its datasheet. Locate these values on the SOA graph to ensure they fall within the safe operating area. For pulsed operations, consider the pulse width relative to time intervals indicated on the graph to ensure operation within safe limits. The time intervals listed next to each boundary line indicate how long the MOSFET can safely operate at certain conditions before thermal limitations are exceeded.

For an example using this graph with a frequency of 10kHz and a maximum voltage of 48V:

First, convert frequency to period: (T = 1/ period= 1/10kHz = 0.0001) seconds or 100μs. Locate V_DS at 48V on x-axis. Follow up vertically until you reach an intersection with a curve that corresponds closely to your operation period; in this case it would be between ‘100 μs’ and ‘1 ms’ lines. From this point follow horizontally to find out maximum allowable I_D without exceeding thermal limits.

To validate thermal operation:

Ensure that for given V_DS and I_D values during operation time (pulse width), you are within bounds of curves corresponding to those times or below them for safety margin. Check if continuous DC operations fall under DC line without surpassing it.

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