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# SOA calculations using ADM1270 for 40A inrush current

I have an application where I am controlling Inrush current of 40Amps; To control this I am using ADM1270 IC. This can be understood by following block diagram.

I have issue in Timing parameters to calculate capacitor values.

My spec are mentioned below

1. Vdc min.=16V
2. Vdc max=32
3. Vdc nom=28V
4. Idc max =3.33A@16V
5. Inrush current by EMI Filter and Converter = 40A
6. Output capacitor= 100-500uF(After Filter and Converter)
7. Amb Temp.=71°C
8. Power Good threshold=16
9. Voltage Foldback=15.2
10. UV=10% of 16V
11. OV=10% of 32
12. RPOWERUP = don’t know (static load resistance during system power up)?
13. P channel Mosfet Used to suit design is SPB80P06P G

Vds=-60V;Ids=-80A;Rdson=23mΩ @ 25°C and 36mΩ @ 150°C;θja=60K/W and θjc=0.6K/W

I did not get following things

1. MOSFET SOA Analysis – Short Circuit
• Graph of Op voltage Vs Power Dissipation
• Vout_wcp
• How it is going to protect by Short ckt operation
• How it is protecting converter and filter by 40A Inrush Current.
• In spread sheet and Datasheet Inrush Value is not considered.
• But I have to protect my converter and filter by 40A inrush current.
• Kindly help me for these calculations in detail
attachments.zip
Parents
• Hi Nitesh,

1. Vdc: Is this the voltage input of the DC-DC converter?
2. Idc MAX: If the current at input of DC-DC is held at 3.33A maximum, how is 40A inrush possible?

3. Is the inrush caused by the 500uF cap at the input of DC-DC?
4.  Why is there a need to put 500uF at the input of DC-DC?  What is DC-DC application?

5. What did you mean by "RPOWERUP" and "Vout_wcp"?

Thanks!

• Hi Nitesh,