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cross mob
Ext-jsatishk
Level 1
Level 1
5 replies posted 5 likes given First like received

Can you please share the formaulas to calculate the number of parallel MOSFET is required?

Please guide me for below example.

Continuous current is 100A at 90deg C and 200A at 25DEg C,  short circuit current is 800A ,Vds is 100V. Consider the part IPT015N10NF2S. Can you please advise how many parallel MOSFET is required for Charging and Discharging in  60V BMS application

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1 Solution
cynic_bandera
Employee
Employee
5 questions asked First question asked 100 sign-ins

Ok, let´s calculate it step by step:

1. Thermal management.  You declared 90°C ambient temperature and 100A. Let´s define the thermal budget. If we assume Tj operation at 130°C (must be lower than 175°C abs max), So dT=Tj-Tc, Td=40°C. We can calculate how much power we can dissipate from one MOSFET, Pdis=dT/RthJA, RthJA=62K/W (with the min footprint). Pdis=0.64W we can dissipate from one MOSFET.

2. Let´s calculate how much current we can get from one MOSFET. Rdson(Tj=130°C)=2.145 mOhm. Pdis=I^2 *Rdson. So, I = 17,34A from one MOSFET.

3. Let´s calculate MOSFETs number N=Itot/I. N =100A/17,34A, So N=6pcs

4. You make the same for 200A and 25°C and check the number

5. Check SOA and SC. For your application it´s suitable to use LinearFET with wide SOA, You calculate energy you dissipate and reaction time of your protection (50us for example) and check how many MOSFETs you need based on SOA. Increase MOSFET number if it´s needed by SOA.

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4 Replies
vigneshkumar
Moderator
Moderator
Moderator
250 sign-ins 50 solutions authored 100 replies posted

Hi

THanks for posting on Infineon community

If Continuous current considered.

                            FETs in parallel

vigneshkumar_0-1691052760008.png

 

 

Based on your spec ,1 MOSFET is sufficient.

 

If Short circuit current considered:

 

Calculate the Eoff energy during the turn-off transistion

convert the nonlinear power dissipation to pulse power to verify with SOA specified in datasheet

Ppulse

vigneshkumar_1-1691052760008.png

 

Plot calculate pulse power dissipated on SOA , get the current value for 60V, if we assume,we get 400A at that voltage we need 2 MOSFETs to handle 800A short circuit currrent.

 

General Suggestion:

  • Reduce the short circuit detection time
  • Switch of the MOSFETs with high sink current at gate
  • Use clamping circuit or freewheeling circuit
  • Use Wide SOA MOSFETs

Regards

Vignesh

 

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cynic_bandera
Employee
Employee
5 questions asked First question asked 100 sign-ins

Ok, let´s calculate it step by step:

1. Thermal management.  You declared 90°C ambient temperature and 100A. Let´s define the thermal budget. If we assume Tj operation at 130°C (must be lower than 175°C abs max), So dT=Tj-Tc, Td=40°C. We can calculate how much power we can dissipate from one MOSFET, Pdis=dT/RthJA, RthJA=62K/W (with the min footprint). Pdis=0.64W we can dissipate from one MOSFET.

2. Let´s calculate how much current we can get from one MOSFET. Rdson(Tj=130°C)=2.145 mOhm. Pdis=I^2 *Rdson. So, I = 17,34A from one MOSFET.

3. Let´s calculate MOSFETs number N=Itot/I. N =100A/17,34A, So N=6pcs

4. You make the same for 200A and 25°C and check the number

5. Check SOA and SC. For your application it´s suitable to use LinearFET with wide SOA, You calculate energy you dissipate and reaction time of your protection (50us for example) and check how many MOSFETs you need based on SOA. Increase MOSFET number if it´s needed by SOA.

Hi Cynic,

 

Thanks for your detailed explanation, its really helpful for me to understand. I have a doubt on selction of Tj, Depends on which condition we need to take the Tj value. In the bove example you have considered Tj value 130deg C , how you selected these value?

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You can operate up to abs max Tj=175°C, but it´s an abs maximum. The temperature affects Rdson, it´s getting higher, and it affects the reliability (big theory with calculation and measure behind), It affects SOA. 120-140°C is used by my practical experience to count on the three mentioned factors.

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