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STA400A Datasheet(PDF) 9 Page - STMicroelectronics |
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STA400A Datasheet(HTML) 9 Page - STMicroelectronics |
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9 / 117 page  9/117 STA400A OSCILLATOR BUFFER ELECTRICAL CHARACTERISTICS The Oscillator Pad Buffer is a single stage oscillator with an inverter working as an amplifier biased by an internal resistor (>1 MOhm). With an external PI network consisting of a crystal and two capacitors it works as oscillator, without the external crystal component it acts as input trigger. Pin XTI (analog pad buffer) is the input for the external clock source or for the quartz component, XTO is the oscillator buffer output pin to be connected to the external quartz. Oscillator Mode Specification (Guaranteed by Design) Condition: 27 MHz oscillation - PI quartz network connected to XTI and XTO (CA = CB = 16pF). Input Trigger Mode Specification (no crystal connected) (Guaranteed by Design) Condition: 27 MHz sine wave (0.5V amplitude, VDD/2 offset) applied to XTI. The external analog signal to be applied to the XTI input must be a sinusoid or a impulse wave centered at Vdd/ with 1V peak-to-peak amplitude. Minimum Oscillator Transconductance (Guaranteed by Design) The oscillator pad buffer can work with different crystal frequencies. To check if a given quartz can be used with this oscillator, the needed amplifier transconductance must be evaluated by the following formula: if the equation simplifies to: where Rm is the quartz equivalent series resistance, CA and CB the PI network capacitances and CO the quartz shunt capacitance. The transconductance of the oscillator pad given in the table above must be 8/9 times the transconductance calculated with the formula. Symbol Parameter Min Typ Max Unit Ci Current Consumption 450 µA Cp Power Consumption 810 µW DC Duty Cycle 49.07 49.60 49.86 % tstart-up Start-up Time 3 ms Symbol Parameters VL VH Hysteresis Unit Hys Hysteresis 0.631 1.123 0.492 V Symbol Parameters Min Typ Max Unit Ci Current Consumption 133 µA Cp Power Consumption 240 µW DC Duty Cycle 49.45 % Symbol Patrameters Min Typ Max Unit gmcrit 1236 µA/V gm cr i t R m ω 2 C A C B C A C O C B C O ⋅ + ⋅ + ⋅ () 2 C A C B ⋅ --------------------------------------------------------------------------------- ⋅⋅ = C A C B C == gm cr i t R m ω 2 C2 C O + () 2 ⋅⋅ = |
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