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SM5170 Datasheet(PDF) 7 Page - Nippon Precision Circuits Inc |
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SM5170 Datasheet(HTML) 7 Page - Nippon Precision Circuits Inc |
7 / 10 page SM5170AV NIPPON PRECISION CIRCUITS—7 Reference Frequency Divider (R-counter) Structure The reference frequency divider generates a compar- ator frequency signal (FR), which is input to the phase comparator, by dividing the reference oscilla- tor frequency input either from an external signal on XIN or from a crystal oscillator connected between XIN and XOUT. The reference frequency divider is comprised of a fixed divide-by-4 prescaler and a 16-bit reference counter. Reference counter frequency data and LD setting The reference counter which determines the refer- ence frequency divider ratio is set by bits 1 to 16. The lock detect signal output is set by bit 20. Reference frequency divider example If the VCO output is (fVCO), the crystal oscillator frequency is 14.4 MHz and the channel bandwidth (fCH: comparator frequency (fR)) is 25 kHz, then the reference frequency divider ratio R is given by: Therefore, the reference counter count is 144 (0000000010010000)2 . LD output The output on LD is set by bit 20. Bits 15 to 19, bits 21 to 22 Bits 15 to 19 have no meaning, and should be set to 0. Bits 21 and 22 are factory test bits and should also be set to 0. Frequency settings Prescaler A (= 4) Reference counter B Reference frequency divider ratio R = A × B = 4 × B Counter set ranges Prescaler A = 4 Reference counter B = 5 to 65535 Reference frequency divider ratio range R = 20 to 262140 Figure 5. Reference counter data and LD output setting format Reference Counter (16bit : 5 to 65535) 12 345 678 9 10 11 12 13 14 15 16 17 MSB 18 19 20 21 22 23 LSB 22 222 222 22 2222 15 14 13 12 11 10 98 76 5432 22 10 Control bits Not used (set to 000) 24 LDpin Set bit Test bits (set to 00) R Xtal f CH ----------- Xtal f R ----------- 14.4 0.025 ------------- 576 4 144 × === = = Bit 20 LD output 1 N o r mal unlock signal output (normal operation) 0 Unlock signal output OFF, LOW -level output |
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