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Current limit for a di/dt greater than stated in datasheet?

Posted by: Harel Levy on 01/02/2022

Hello Everyone,

In my company we are changing all bias switchts to TOPSwitch-HX family so I have in my possession old designs and it turns out di/dt of the current designs are 4 times greater then the di/dt stated in the TOPSwitch-HX datasheet (specifically TOP254YN & TOP255YN).

Is there anyway to figure out the new current limit based on those higher di/dt's?

 

Best Regards,

Harel Levy.

Comments

Submitted by PI-Wrench on 01/10/2022

The data sheet for TOPSwitch-HX lists the current limit delay as 100 ns. You can use that information to calculate the current limit at your given di/dt.

Submitted by Harel Levy on 01/10/2022

Hi Wrench,

  • Care to elaborate on how exactly I can use the current limit delay information to calculate the current limit?
  • Is the value of I_limit in the data sheet for TOPSwitch-HX will be the same value with a much higher di/dt?

Thanks. 

Submitted by PI-Wrench on 01/11/2022

No, because of the current limit delay.  The current limit will be higher for a higher di/dt due to the delay time of the current limit comparator and the driver The extra current will more or less be the di/dt multiplied by the current limit delay.

Submitted by Harel Levy on 01/11/2022

Okay so let me use an example to see if I got it right:

Using the TOP255YN its typical current limit is 1.7A.

With a di/dt of 1.4 A/us and a time delay of 0.1us the real current limit will be at around 1.7 + 1.4*0.1 = 1.84A?

Submitted by PI-Wrench on 01/12/2022

What you would want to do it to use the current limit from the data sheet and subtract the extra portion due to the di/dt shown in the data sheet. Take this value and add the contribution due to your actual di/dt.