Minimum operating voltage of USB pendrive?

[udhay_cit]

I need to interface a pendrive (not a specific manufacturer) with my handheld equipment. The instrument is powered with 4 AA size battery. The maximum output of the battery pack will be 4*1.4V = 5.6V. The minimum output voltage is 4*1.1V = 4.4V. The cutoff voltage of the battery is 4*0.9V = 3.6V but i will not allow the system to access the pendrive when the battery voltage below 4.5V.
I need to know what will be the minimum & maximum operating voltage of a pendrive? I can reduce the 5.6V by using a simple zener diode. But what can i do for minimum voltage without using a boost circuit?

regards
Udhay

 

[FvM]

USB spec requires devices to operate with Vbus of 4.4 V to 5.25 V. Beyond this range it's a matter of hope.