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# LTC4380 Short Circuit Protection

Hi,

Customer is planning to use LTC4380 for the power rail of 28V/9.57A. Based on the spreadsheet calculator, the required MOSFET SOA is VDS= 39.2V, IDS = 21.11A & Time = 88.8ms.

Currently with wide SOA MOSFET selection is either IXTK200N10L2 or IXFB210N30P3.

Question:

1) Under VDS= 39.2V, IDS = 21.11A & Time = 88.8ms condition, is heatsink required?

2) Is there any way to lower down the SOA requirement? Using other surge stopper? Any recommendation?

Thanks in advance.

• Hello

>> ...power rail of 28V/9.57A...the required MOSFET SOA is VDS= 39.2V, IDS = 21.11A & Time = 88.8ms

Can you explain, how did you get to VDS= 39.2V, IDS = 21.11A & Time = 88.8ms specification?

>> 1) Under VDS= 39.2V, IDS = 21.11A & Time = 88.8ms condition, is heatsink required?

This is hard to tell generally. It depends on your board and especially on your layout. When you have a big multilayer board with 6 Layers and a lot of vias for MOSFET, it would help.
Do you really need 88.8ms in current limited short circuit?
This would mean over 268W or 23.8J worst case.
I think the IXFB210N30P3 is heavily oversized. Especially the high VDS makes high Cgs and Cgd.
IXTK200N10L2 with some heatsink seems better choice. But it has Ron 11mOhm,
which produces 1W in normal operation. This also could be handeled wit relatively small heatsink. For short circuit condition a copper one has much higher thermal capacity than aluminum so it could be smaller.

• Hi Alex,

VDS= 39.2V, IDS = 21.11A & Time = 88.8ms

this one is calculated by using the LTC4380 calculator sheet.

Do you really need 88.8ms in current limited short circuit? This one is calculated.

In short, if using IXTK200N10L2, as long as the board can handle 1W during normal operation, no heatsink require right?

• Hi JohnsonCheah,

1. Not sure if heatsink is required. It may depend on your layout like Alex mentioned.

2. I don't know if SOA requirements can be lowered down especially if you're operating at 10A. You may also take a look at LTC4368 since it has an application that can go up to 10A output current.

• Hi Alex,
I run the simulation and the simulated current is in microampere range during short load.

Do you know why?