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# What's the maximum over current limit of LTC4361?

Category: Datasheet/Specs
Product Number: LTC4361

Hi Sir,

What's the maximum over current limit of LTC4361?

I use the LTSPICE to simulate the LTC4361.

Vin 5V and use the short model.

When I adjust the Rsense to 9mohm, LTC4361 cannot work.

Rsense=9mohm

Rsense=10mohm, LTC4361 works.

• Rsns=10mΩ means you have a 5A circuit breaker.
Reducing Rsns to 9mΩ increases circuit breaker to 5.56A.

Your "SHORT" is only 1Ω, so it will draw 5A when turned on (given Vin=5V).
Add these two currents together and you get a total load current of 5.5A.

This means circuit breaker will trip at Rsns=10mΩ, but not at Rsns=9mΩ.

• Hi ,

We want to set the over current limit at 200A.

I modify the Ron=0.02. R2=0.00025

Vout is 5V. Is there anything I need to set?

• Hello ninasu,

my answer will largely be a repetition of what Ashapiro had written before.

The LTC4361 will turn off when the current over your shunt exceeds 200A. That will never be the case in your simulation because the resistance of your switch combined with the on state resistance of your FET will limit the current over the shunt to smaller values. So the LT4361 must not turn off in this situation.

Your simulation shows nevertheless a current peak which is above 200A. But this is not the current over the shunt, it's the current through the switch. And this is - for a very short time period - delivered from capacitor C1.

If you want to judge the correct behvaiour of the LTC4361 you should

- monitor the current through the shunt, not through the switch

- zoom much more into the time axis and check, if the width of the current pulse is 10µs (as required by the LTC4361) or if its only some ns.

best regards

Achim

• We want to set the over current limit at 200A.

With a current limit that high, you should be looking at hotswap controllers like the LTC4282 and ADM1278.

You will need to parallel multiple FETs to handle 199A of continuous current without overheating.
Hotswap controllers use a stronger gate pulldown for discharging multiple FETs.
And when you hit the current limit, you need to add TVS to the input to clamp inductive kick on the input.