While looking at USB 3.0 Host Controller reference design, I came across this circuit:
They used LL4148 diode in this design.
Note: PONRST goes directly to the Host Controller IC.
I'm trying to understand the idea behind why is this circuit used.
To my understanding, when when 3V3AUX_in = 3.3V, the PONRST pin is 3.3V, and the capacitor is charged.
Now, if we assume that we lost the power, 3V3AUX_in will be 0V, and for some short period of time PONRST pin will still be 3.3V because it takes time to discharge the capacitor.
Since LL4148 Forward Voltage is maximum 1V, when PONRST=3.3V, the Anode of D5 is 3.3V and the Cathode is 0V and the diode will not conduct.
In the meanwhile, the capacitor will start discharging to GND untill the voltage reaches 1V and now the diode will conduct and the discharging will be faster. thus, we will discharge the PONRST pin faster and maybe protect the PONRST pin from being powered while the IC itself is not powered.
Is my analysis right?
Also, is it okay to replace this diode with CDBQR0130L-HF?