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SI52146 датащи(PDF) 8 Page - Silicon Laboratories |
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SI52146 датащи(HTML) 8 Page - Silicon Laboratories |
8 / 20 page Si52146 8 Preliminary Rev. 0.1 Use the following formulas to calculate the trim capacitor values for Ce1 and Ce2. CL: Crystal load capacitance CLe: Actual loading seen by crystal using standard value trim capacitors Ce: External trim capacitors Cs: Stray capacitance (terraced) Ci : Internal capacitance (lead frame, bond wires, etc.) 2.2. CKPWRGD_PDB (Power down) Clarification The CKPWRGD_PDB pin is a dual-function pin. During initial power up, the pin functions as CKPWRGD. Upon the first powerup if the CKPWRGD is low, the device outputs will be disabled, but the crystal oscillator and I2C logics are active. Once CKPWRGD has been sampled high by the clock chip, the pin assumes a PDB functionality. When the pin has assumed a PDB functionality and the pin is pull low, the device will be placed in standby mode. 2.3. PDB (Power down) Assertion The PDB pin is an asynchronous active low input used to disable all clocks in a glitch free manner. All outputs will be driven low in power down mode. In power down mode, all outputs, the crystal oscillator and the I2C logic are disabled. 2.4. PDB Deassertion When a valid rising edge on CKPWRGD/PDB pin is applied, all outputs are enabled in a glitch free manner within two to six output clock cycle. 2.5. OE Clarification The OE pins are active high inputs used to enable and disable the output clocks. To enable the output clock, the OE pin needs to be logic high and the I2C output enable bit needs to be logic high. There are two methods to disable the output clocks: the OE is pulled to a logic low, or the I2C enable bit is set to a logic low. The OE pins is required to be driven at all time and even though it has an internally 100 k resistor. 2.6. OE Assertion The OE signals are active high input used for synchronous stopping and starting the DIFF output clocks respectively while the rest of the clock generator continues to function. The assertion of the OE signal by making it logic high causes stopped respective DIFF output to resume normal operation. No short or stretched clock pulses are produced when the clock resumes. The maximum latency from the assertion to active outputs is no more than two to six output clock cycles. 2.7. OE Deassertion When the OE pin is deasserted by making its logic low, the corresponding DIFF output is stopped cleanly, and the final output state is driven low. 2.8. SSON Clarification SSON is an active input used to enable –0.5% spread on all DIFF outputs. When sampled high, –0.5% spread is enabled on all DIFF outputs. When sampled low, the DIFF output frequencies are non-spread. Load Capacitance (each side) Total Capacitance (as seen by the crystal) Ce = 2 x CL – (Cs + Ci) Ce1 + Cs1 + Ci1 1 + Ce2 + Cs2 + Ci2 1 () 1 = CLe |
Аналогичный номер детали - SI52146 |
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Аналогичное описание - SI52146 |
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