STCL132K Datasheet, PDF (7/20 Pages) STMicroelectronics – 32,768 Hz silicon oscillator

STCL132K
3
Operation
Operation
Use of the STCL132K silicon oscillator device is very simple. Once power is applied to V_CC
pin, a CMOS-compatible square wave output signal is provided on the F_OUT output pin (in
active mode the Chip Enable (CE) input pin must be at a logic high level).
3.1
Chip enable
This feature allows the user to stop the clock and significantly reduce the current
consumption when the application is put into power saving mode.
When used to clock the microprocessor in place of a crystal, the need for chip enable input
stems from a difference in the way microprocessors normally disable their clock. In the case
of a crystal or ceramic resonator, when going into power saving mode, the processor simply
opens the internal Xtal inverter feedback which results in stopping the crystal oscillations;
however in the case of the silicon oscillators this would not work and the oscillator would
continue to run. So in order to use this feature, one of the microprocessor's output pins must
be configured to control the silicon oscillator's Chip Enable (CE) input, see typical
application circuit diagram in Figure 2.
3.2
Note:
Transition to disable
At the moment when the Chip Enable (CE) input goes low, the oscillator's output F_OUT will
immediately go low; then during the disable period the output remains low.
For advanced microprocessor applications, other disable modes can be made available as
a product option (F_OUT completes the last clock period, and then remains low or provides 32
additional cycles before going low to allow the processor to complete the pipelined
instructions, etc.). Also, a product option with output in a high-impedance state to allow the
system to alternate between several oscillators connected in parallel can be made available.
Contact local ST sales office for availability.
3.3
Fast startup and stable wakeup from disable
The total startup time until oscillations internally stabilize and remain within specifications is
typically 90 µs, i.e. shorter than duration of the first three periods of the generated output
signal, see Section 5: DC and AC parameters. This means that 90 µs after power-on or
wakeup from disable a first valid period of the output signal occurs on the F_OUT pin and is
within the specified frequency and duty cycle range (in the meantime the output remains
low). This is in comparison to typically milliseconds for crystal oscillators.
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