 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
SY87729L Datasheet(PDF) 10 Page - Micrel Semiconductor |
|
||||||||||||||||||||||||||||||
SY87729L Datasheet(HTML) 10 Page - Micrel Semiconductor |
|
|
10 / 17 page  Micrel, Inc. SY87729L July 2011 10 M9999-072111-G hbwhelp@micrel.com Care should be exercised when selecting the value of P (Table 1) so that the voltage-controlled oscillator (VCO) of the fractional-N PLL is not driven out of range. The following conditions must be met: fVCO(min) < fREF × Fractional Division < fVCO(max) or or (408) 955-1690 ) fVCO(min) < fREF × ( ⎪⎭ ⎪ ⎬ ⎫ ⎪⎩ ⎪ ⎨ ⎧ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ + ± ± ± P Q 1 P Q 1 P Q P < fVCO(max) where, fVCO(min) = 540MHz fVCO(max) = 729MHz fREF = Frequency of the reference clock DivSel3 DivSel2 DivSel1 DivSel0 P 0 0 0 0 17 0 0 0 1 18 0 0 1 0 19 0 0 1 1 20 0 1 0 0 21 0 1 0 1 22 0 1 1 0 23 0 1 1 1 24 1 0 0 0 25 1 0 0 1 26 1 0 1 0 27 1 0 1 1 28 1 1 0 0 29 1 1 0 1 30 1 1 1 0 31 1 1 1 1 32 Table 1. DivSel Divider Setting Fractional-N Control This circuit controls the P/P-1 divider, selecting the appropriate divide ratio, either P or P-1, in the correct pattern. As explained in the example of Figure 2, controlling the P/P-1 divider amounts to generating a repeating binary bit stream. In that example, a “1” represents dividing by 4, and a “0” represents dividing by 3. The full cycle, “101,” says to divide by 4 twice, and to divide by 3 once. In the general case, the pattern “101” need not change based on the P divider value. To multiply by 14/3 instead of 11/3, for example, the same “101” pattern would be used, but we would alternate dividing by 5 and 4, instead of dividing by 4 and 3. The P value, in effect, represents the integer part of the multiplication factor. The repeating binary bit pattern really depends only on the number of times to divide by P, and the number of times to divide by P-1. We label the number of times to divide by P as QP, and the number of times to divide by P-1 as QP–1. The fractional-N synthesizer generates its output frequency as per this formula: fFNOUT = ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ± + ± ± 1 P Q P Q 1 P Q P × fREF In our figure two example, we multiply by 11/3, or 4 - 1/3. Matching against the formula, P = 4, QP–1 = 1, and QP = 2. The SY87729L accepts QP and QP–1 values from its MicroWire™ interface, where they exist as the 5-bit values “qp” and “qpm1.” Both values are unsigned binary numbers. QP and QP–1 are both constrained to be 31 or less, and their sum is also constrained to be 31 or less. That means that the denominator in the above formula must be 31 or less. As would be expected from the formula, setting QP to zero causes frequency multiplication exactly by P-1. Setting QP–1 to zero causes frequency multiplication exactly by P. The SY87729L behavior is undefined if both QP and QP–1 are both set to zero. In the general case, the length of the repeating binary bit pattern is QP + QP–1. It consists of QP “1”, and QP–1 “0.” |
Similar Part No. - SY87729L |
|
Similar Description - SY87729L |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
