Hi everyone,
I would just like to confirm the following understanding after reading some datasheets of eFuses I am evaluating for a 12V, 5A power bus.
The SOA protection implemented as power dissipation limiting, introduces a Maximum Startup Load requirement:
For the TPS25910, datasheet SLUSAR6D, page 17 equation 13 states: Rmin = (Vin^2) / 12
For the TPS2590, datasheet SLUS960G, page 11 equation (11) states: Rload > Rmin=(Vin^2)/12 again
I wanted to use the tps25910 preferably (or the TPS2590 instead) as output protection/enable for the 12V,5A power bus. Obviously both of them can operate at static maximum conditions, but apparently they cannot start the load for which I am designing. This is, my maximum input voltage is approx 13V, so both ICs lead to the following:
Rload > Rmin = (13^2)/12= 14.08 Ohm, which is the same as a maximum output current of 13V/14.08Ohm= 0.92A. Is this right? I mean, if my 12V,5A load is connected before I enable any of the ICs, then when I enable the ICs none of them will be able to start, and will enter a protection mode? Even though the device can withstand 12V,5A continuous?
As another question, If the load is completely resistive, lets say 12V/5A = 2.4Ohm, completely resistive, the current it will draw will increase up linearly as the output voltage ramp increases following the equation I_load = Vout/2.4, starting from 0A and reaching finally 5A. The power dissipated in the IC during startup would be P =(Vin-Vout)*I_load=(Vin-Vout)*Vout/2.4, which has a maximum when Vo=Vi/2=6V, which in turn yields Pmax = 15W. This is above the SOA power limit of 5W (for those two ICs...) but, is or is not the device capable of handling that power and make a reliable during the startup? It looks like a low power to handle for a short period of time, but SOA graphs are not provided.
If the device cannot candle that current even if the load is purely resistive, is there any way to aliviate this?
Also, f I am not wrong, if the device is already ON (device is active, Vout=12V with no load), then it is ok to connect a 5A load right? no startup problems rigth?
Do you recommend any other device for such a power rail? I am looking for eFuses (integrated FET).
Thank you very much for your help and solving my doubts.
