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NBC12430FNR2 Datasheet(PDF) 8 Page - ON Semiconductor |
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NBC12430FNR2 Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 20 page NBC12430, NBC12430A http://onsemi.com 8 FUNCTIONAL DESCRIPTION The internal oscillator uses the external quartz crystal as the basis of its frequency reference. The output of the reference oscillator is divided by 16 before being sent to the phase detector. With a 16 MHz crystal, this provides a reference frequency of 1 MHz. Although this data sheet illustrates functionality only for a 16 MHz crystal, Table 9, any crystal in the 10−20 MHz range can be used, Table 11. The VCO within the PLL operates over a range of 400 to 800 MHz. Its output is scaled by a divider that is configured by either the serial or parallel interfaces. The output of this loop divider is also applied to the phase detector. The phase detector and the loop filter force the VCO output frequency to be M times the reference frequency by adjusting the VCO control voltage. Note that for some values of M (either too high or too low), the PLL will not achieve loop lock. The output of the VCO is also passed through an output divider before being sent to the PECL output driver. This output divider (N divider) is configured through either the serial or the parallel interfaces and can provide one of four division ratios (1, 2, 4, or 8). This divider extends the performance of the part while providing a 50% duty cycle. The output driver is driven differentially from the output divider and is capable of driving a pair of transmission lines terminated into 50 W to VCC−2.0 V. The positive reference for the output driver and the internal logic is separated from the power supply for the phase−locked loop to minimize noise induced jitter. The configuration logic has two sections: serial and parallel. The parallel interface uses the values at the M[8:0] and N[1:0] inputs to configure the internal counters. Normally upon system reset, the P_LOAD input is held LOW until sometime after power becomes valid. On the LOW−to−HIGHtransition of P_LOAD, the parallel inputs are captured. The parallel interface has priority over the serial interface. Internal pullup resistors are provided on the M[8:0] and N[1:0] inputs to reduce component count in the application of the chip. The serial interface logic is implemented with a fourteen bit shift register scheme. The register shifts once per rising edge of the S_CLOCK input. The serial input S_DATA must meet setup and hold timing as specified in the AC Characteristics section of this document. With P_LOAD held high, the configuration latches will capture the value of the shift register on the HIGH−to−LOW edge of the S_LOAD input. See the programming section for more information. The TEST output reflects various internal node values and is controlled by the T[2:0] bits in the serial data stream. See the programming section for more information. Table 9. Programming VCO Frequency Function Table with 16 MHz Crystal. VCO Frequency (MHz) MCount Divisor 256 128 64 32 16 8 4 2 1 M8 M7 M6 M5 M4 M3 M2 M1 M0 400 200 0 1 1 0 0 1 0 0 0 402 201 0 1 1 0 0 1 0 0 1 404 202 0 1 1 0 0 1 0 1 0 406 203 0 1 1 0 0 1 0 1 1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 794 397 1 1 0 0 0 1 1 0 1 796 398 1 1 0 0 0 1 1 1 0 798 399 1 1 0 0 0 1 1 1 1 800 400 1 1 0 0 1 0 0 0 0 |
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