I have a circuit which uses an Enpirion ER3105DI to step an input voltage down to +3.73V. The input voltage can be either +24V or +5V depending on the power supply being used.
In some circumstamces there is a possibility that the power supply could drop as low as +4.5V, which is less than 1V above the desired output voltage. I am concerned that in this situation the performance of the regulator could be impacted, and would like to quantify this.
I've scoured the datasheet and unfortunately there is no information about the dropout voltage of this chip, or about performance of the chip when Vin is close to Vout.
What is the dropout voltage for this device? Are there any documents discussing best practice for input voltage compared to output voltage for this range of buck converters?
Regarding the ER3105DI dropout voltage; to make it easier for calculation you can consider the Rdrop =920mOhm at worst case.
To calculate Vout (V)= Vin(V) - Iload(A) *Rdrop(Ohm)
in this case, the device is subjected to 100% duty cycle.
So i don't recommend to work at the max loading condition when Vin=4.5V to avoid the Vout not to drop lower than your desired Vout.
But in general the device performance will be affected under the Full duty cycle condition where the controller doesn't have enough duty cycle to do the required regulation and also the efficiency, load transient will be affected too.