What is the difference between Quiescent current & shut down current. I have searched a lot but didn't find valid answer. As per as my knowledge Quiescent current is the small current which flows when device is in inactive state. Both appears to be similar, but datasheet is provided with different set of values for both. Please let me know the difference.
"Quiescent current" is the nominal (average) current used while "on" in a minimal state, such as an amplifier IC which is on and ready to work, but not currently amplifying anything. This is the minimum average current the device will consume while "on" and can be used for a minimum power consumption (maximum battery life) estimation.
"Shutdown Current" is the current used while the shutdown pin is asserted. Many IC's have a shutdown feature, and asserting this puts it into a low-power "sleep" state. The advantage to having a "shutdown" feature, usually is that it can be turned on and off with one logic signal, "plays nice" with other devices that may still be on, and wakes up quickly. More advanced IC's can allow certain features to remain running while in "shutdown", such as a PIC microcontroller and some of it's peripherals (real-time-clock-calendar, low-speed clock, interrupts, etc.) Shutdown is primarily used to save power and extend battery life.
Quiescent current is the steady-state output current which flows by virtue of a steady-state input bias, while "shutdown current" is, I believe, more commonly referred to as "leakage current" and is the output current which flows when the device's output is turned OFF.