The Differences Between Standby (ST) and Output Enable (OE) Options in Oscillators
Oscillators, including programmable and pin configurable devices, in the majority of the cases in their standard 4 or 6 pins packages, reserve pin 1 to a function called Output Enable (OE) or Enable/Disable (E/D). (Some vendors like Silicon Laboratories, Microchip, and others have a series of oscillators where the OE function can be chosen to be pin 1 or pin 2.)
Some vendors, in the same series or under another part number, have this pin 1 called Standby (ST), Power Down (PD), or Inhibit (INH).
So, what is the difference and when should each option be used?
In both cases, when this pin 1 is activated (it can be either “1” or “0”), it causes an output clock to become tri-stated or Hi Z (High Impedance); thus, allowing fewer oscillations in clock traces of PCB layers or allowing another clock source to feed the same device or any other application cases where the designer will want the clock to go to Hi Z.
The main difference between Output Enable and Standby functions is when the oscillator should retain the active state and drive the clock output again (to oscillate).
If the Output Enable (OE) function is selected, oscillation inside the component is not stopped, only the output circuitry within the oscillator is shut down (the oscillator output gate becomes Hi Z). The oscillator input current on the power supply line is almost the same as normal operating current.
If the Standby (ST) function is selected, all active circuitry within the oscillator is shut down. This results in the input current on the power supply line going to almost zero.
To resume oscillation, the oscillator must go through a startup period.
The vendors in their data sheet of the oscillators define the parameter called “Start-up time” in the range of 3 ms to 10 ms. This is rather a long time (vs. nanoseconds using OE option) and many applications where the performance and speed are critical can’t tolerate this delay.
On the other hand, for battery powered applications the critical issue is a battery life, so they can tolerate this relatively long delay to decrease overall power consumption of the circuitry.