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Original question:

ClockPro and CDCE925

CDCE925: Calculating N, P, Q, R for CDCE925

Chris Burrell83
Prodigy 110 points
Part Number: CDCE925
Other Parts Discussed in Thread: CLOCKPRO

I have seen the question and would like to ask further about the algorithm to use to find the values for the CDCE925.

The strategy for increasing N / M isn't what TI Clock Pro does, neither is trying to get R=0.

For example, if I calculate all the N / M values for 36.800 MHz output given a 27MHz crystal, TI Clock Pro gives N / M of 3312 and 486 respectively, but my own program, which calculates all possible values of N / M I find that 4048 and 495 are the highest values for N / M.

On further investigation there are lots of other instances where this happens.  It is not obvious what is being optimized in TI Clock Pro.

I understand that there is a fixed frequency loop filter in the CDCE925 and that TI don't want to give away any IP, but is it possible to provide enough information to at least allow an algorithm that produces the same results as TI Clock Pro so it can be used to generate values "on the fly"?

All suggestions gratefully received.

  • 0
    TI__Mastermind 18070 points

    Hi Chris,

    Unfortunately I'm not able to locate source code of clockpro and can't tell the algorithm used for this calculation. But as long as the calculation is based on datasheet 10.2.2.2 and the VCO frequency is within the range there should be no problem.

    Regards,
    Hao

  • 0 in reply to Hao Z
    Prodigy 110 points

    Hi Hao,

    Thank you for your reply and also thank you for looking for the source code.

    I have done some more investigation and found the original patent for this which has helped.

    In the below list for target frequency 36.818 using a 27MHz reference crystal there are lots of possible answers...

    Results for 36818000
    P_Div= 3, M= 11, N=  45, P=2, Q=16, R=  4, Er=182, vco=110.45, Magic=2454545
    P_Div= 3, M= 22, N=  90, P=2, Q=16, R=  8, Er=182, vco=110.45, Magic=1227273
    P_Div= 3, M= 33, N= 135, P=2, Q=16, R= 12, Er=182, vco=110.45, Magic=818182
    P_Div= 3, M= 44, N= 180, P=2, Q=16, R= 16, Er=182, vco=110.45, Magic=613636
    P_Div= 3, M= 55, N= 225, P=2, Q=16, R= 20, Er=182, vco=110.45, Magic=490909
    P_Div= 3, M= 66, N= 270, P=2, Q=16, R= 24, Er=182, vco=110.45, Magic=409091
    P_Div= 3, M= 77, N= 315, P=2, Q=16, R= 28, Er=182, vco=110.45, Magic=350649
    P_Div= 3, M= 88, N= 360, P=2, Q=16, R= 32, Er=182, vco=110.45, Magic=306818
    P_Div= 3, M= 99, N= 405, P=2, Q=16, R= 36, Er=182, vco=110.45, Magic=272727
    P_Div= 3, M=110, N= 450, P=2, Q=16, R= 40, Er=182, vco=110.45, Magic=245455
    P_Div= 3, M=121, N= 495, P=2, Q=16, R= 44, Er=182, vco=110.45, Magic=223140
    P_Div= 3, M=132, N= 540, P=2, Q=16, R= 48, Er=182, vco=110.45, Magic=204545
    P_Div= 3, M=143, N= 585, P=2, Q=16, R= 52, Er=182, vco=110.45, Magic=188811
    P_Div= 3, M=154, N= 630, P=2, Q=16, R= 56, Er=182, vco=110.45, Magic=175325
    P_Div= 3, M=165, N= 675, P=2, Q=16, R= 60, Er=182, vco=110.45, Magic=163636
    P_Div= 3, M=176, N= 720, P=2, Q=16, R= 64, Er=182, vco=110.45, Magic=153409
    P_Div= 3, M=187, N= 765, P=2, Q=16, R= 68, Er=182, vco=110.45, Magic=144385
    P_Div= 3, M=198, N= 810, P=2, Q=16, R= 72, Er=182, vco=110.45, Magic=136364
    P_Div= 3, M=209, N= 855, P=2, Q=16, R= 76, Er=182, vco=110.45, Magic=129187
    P_Div= 3, M=220, N= 900, P=2, Q=16, R= 80, Er=182, vco=110.45, Magic=122727
    P_Div= 3, M=231, N= 945, P=2, Q=16, R= 84, Er=182, vco=110.45, Magic=116883
    P_Div= 3, M=242, N= 990, P=2, Q=16, R= 88, Er=182, vco=110.45, Magic=111570
    P_Div= 3, M=253, N=1035, P=2, Q=16, R= 92, Er=182, vco=110.45, Magic=106719
    P_Div= 3, M=264, N=1080, P=2, Q=16, R= 96, Er=182, vco=110.45, Magic=102273
    P_Div= 3, M=275, N=1125, P=2, Q=16, R=100, Er=182, vco=110.45, Magic= 98182
    P_Div= 3, M=286, N=1170, P=2, Q=16, R=104, Er=182, vco=110.45, Magic= 94406
    P_Div= 3, M=297, N=1215, P=2, Q=16, R=108, Er=182, vco=110.45, Magic= 90909
    P_Div= 3, M=308, N=1260, P=2, Q=16, R=112, Er=182, vco=110.45, Magic= 87662
    P_Div= 3, M=319, N=1305, P=2, Q=16, R=116, Er=182, vco=110.45, Magic= 84639
    P_Div= 3, M=330, N=1350, P=2, Q=16, R=120, Er=182, vco=110.45, Magic= 81818
    P_Div= 3, M=341, N=1395, P=2, Q=16, R=124, Er=182, vco=110.45, Magic= 79179
    P_Div= 3, M=352, N=1440, P=2, Q=16, R=128, Er=182, vco=110.45, Magic= 76705
    P_Div= 3, M=363, N=1485, P=2, Q=16, R=132, Er=182, vco=110.45, Magic= 74380
    P_Div= 3, M=374, N=1530, P=2, Q=16, R=136, Er=182, vco=110.45, Magic= 72193
    P_Div= 3, M=385, N=1575, P=2, Q=16, R=140, Er=182, vco=110.45, Magic= 70130
    P_Div= 3, M=396, N=1620, P=2, Q=16, R=144, Er=182, vco=110.45, Magic= 68182
    P_Div= 3, M=407, N=1665, P=2, Q=16, R=148, Er=182, vco=110.45, Magic= 66339
    P_Div= 3, M=418, N=1710, P=2, Q=16, R=152, Er=182, vco=110.45, Magic= 64593
    P_Div= 3, M=429, N=1755, P=2, Q=16, R=156, Er=182, vco=110.45, Magic= 62937
    P_Div= 3, M=440, N=1800, P=2, Q=16, R=160, Er=182, vco=110.45, Magic= 61364
    P_Div= 3, M=451, N=1845, P=2, Q=16, R=164, Er=182, vco=110.45, Magic= 59867
    P_Div= 3, M=462, N=1890, P=2, Q=16, R=168, Er=182, vco=110.45, Magic= 58442
    P_Div= 3, M=473, N=1935, P=2, Q=16, R=172, Er=182, vco=110.45, Magic= 57082
    P_Div= 3, M=484, N=1980, P=2, Q=16, R=176, Er=182, vco=110.45, Magic= 55785
    P_Div= 3, M=495, N=2025, P=2, Q=16, R=180, Er=182, vco=110.45, Magic= 54545
    P_Div= 3, M=506, N=2070, P=2, Q=16, R=184, Er=182, vco=110.45, Magic= 53360
    P_Div= 4, M= 11, N=  60, P=2, Q=21, R=  9, Er=182, vco=147.27, Magic=2454545
    P_Div= 4, M= 22, N= 120, P=2, Q=21, R= 18, Er=182, vco=147.27, Magic=1227273
    P_Div= 4, M= 33, N= 180, P=2, Q=21, R= 27, Er=182, vco=147.27, Magic=818182
    P_Div= 4, M= 44, N= 240, P=2, Q=21, R= 36, Er=182, vco=147.27, Magic=613636
    P_Div= 4, M= 55, N= 300, P=2, Q=21, R= 45, Er=182, vco=147.27, Magic=490909
    P_Div= 4, M= 66, N= 360, P=2, Q=21, R= 54, Er=182, vco=147.27, Magic=409091
    P_Div= 4, M= 77, N= 420, P=2, Q=21, R= 63, Er=182, vco=147.27, Magic=350649
    P_Div= 4, M= 88, N= 480, P=2, Q=21, R= 72, Er=182, vco=147.27, Magic=306818
    P_Div= 4, M= 99, N= 540, P=2, Q=21, R= 81, Er=182, vco=147.27, Magic=272727
    P_Div= 4, M=110, N= 600, P=2, Q=21, R= 90, Er=182, vco=147.27, Magic=245455
    P_Div= 4, M=121, N= 660, P=2, Q=21, R= 99, Er=182, vco=147.27, Magic=223140
    P_Div= 4, M=132, N= 720, P=2, Q=21, R=108, Er=182, vco=147.27, Magic=204545
    P_Div= 4, M=143, N= 780, P=2, Q=21, R=117, Er=182, vco=147.27, Magic=188811
    P_Div= 4, M=154, N= 840, P=2, Q=21, R=126, Er=182, vco=147.27, Magic=175325
    P_Div= 4, M=165, N= 900, P=2, Q=21, R=135, Er=182, vco=147.27, Magic=163636
    P_Div= 4, M=176, N= 960, P=2, Q=21, R=144, Er=182, vco=147.27, Magic=153409
    P_Div= 4, M=187, N=1020, P=2, Q=21, R=153, Er=182, vco=147.27, Magic=144385
    P_Div= 4, M=198, N=1080, P=2, Q=21, R=162, Er=182, vco=147.27, Magic=136364
    P_Div= 4, M=209, N=1140, P=2, Q=21, R=171, Er=182, vco=147.27, Magic=129187
    P_Div= 4, M=220, N=1200, P=2, Q=21, R=180, Er=182, vco=147.27, Magic=122727
    P_Div= 4, M=231, N=1260, P=2, Q=21, R=189, Er=182, vco=147.27, Magic=116883
    P_Div= 4, M=242, N=1320, P=2, Q=21, R=198, Er=182, vco=147.27, Magic=111570
    P_Div= 4, M=253, N=1380, P=2, Q=21, R=207, Er=182, vco=147.27, Magic=106719
    P_Div= 4, M=264, N=1440, P=2, Q=21, R=216, Er=182, vco=147.27, Magic=102273
    P_Div= 4, M=275, N=1500, P=2, Q=21, R=225, Er=182, vco=147.27, Magic= 98182
    P_Div= 4, M=286, N=1560, P=2, Q=21, R=234, Er=182, vco=147.27, Magic= 94406
    P_Div= 4, M=297, N=1620, P=2, Q=21, R=243, Er=182, vco=147.27, Magic= 90909
    P_Div= 4, M=308, N=1680, P=2, Q=21, R=252, Er=182, vco=147.27, Magic= 87662
    P_Div= 4, M=319, N=1740, P=2, Q=21, R=261, Er=182, vco=147.27, Magic= 84639
    P_Div= 4, M=330, N=1800, P=2, Q=21, R=270, Er=182, vco=147.27, Magic= 81818
    P_Div= 4, M=341, N=1860, P=2, Q=21, R=279, Er=182, vco=147.27, Magic= 79179
    P_Div= 4, M=352, N=1920, P=2, Q=21, R=288, Er=182, vco=147.27, Magic= 76705
    P_Div= 4, M=363, N=1980, P=2, Q=21, R=297, Er=182, vco=147.27, Magic= 74380
    P_Div= 4, M=374, N=2040, P=2, Q=21, R=306, Er=182, vco=147.27, Magic= 72193
    P_Div= 4, M=385, N=2100, P=2, Q=21, R=315, Er=182, vco=147.27, Magic= 70130
    P_Div= 4, M=396, N=2160, P=2, Q=21, R=324, Er=182, vco=147.27, Magic= 68182
    P_Div= 4, M=407, N=2220, P=2, Q=21, R=333, Er=182, vco=147.27, Magic= 66339
    P_Div= 4, M=418, N=2280, P=2, Q=21, R=342, Er=182, vco=147.27, Magic= 64593
    P_Div= 4, M=429, N=2340, P=2, Q=21, R=351, Er=182, vco=147.27, Magic= 62937
    P_Div= 4, M=440, N=2400, P=2, Q=21, R=360, Er=182, vco=147.27, Magic= 61364
    P_Div= 4, M=451, N=2460, P=2, Q=21, R=369, Er=182, vco=147.27, Magic= 59867
    P_Div= 4, M=462, N=2520, P=2, Q=21, R=378, Er=182, vco=147.27, Magic= 58442
    P_Div= 4, M=473, N=2580, P=2, Q=21, R=387, Er=182, vco=147.27, Magic= 57082
    P_Div= 4, M=484, N=2640, P=2, Q=21, R=396, Er=182, vco=147.27, Magic= 55785
    P_Div= 4, M=495, N=2700, P=2, Q=21, R=405, Er=182, vco=147.27, Magic= 54545
    P_Div= 4, M=506, N=2760, P=2, Q=21, R=414, Er=182, vco=147.27, Magic= 53360
    P_Div= 5, M= 11, N=  75, P=2, Q=27, R=  3, Er=182, vco=184.09, Magic=2454545
    P_Div= 5, M= 22, N= 150, P=2, Q=27, R=  6, Er=182, vco=184.09, Magic=1227273
    P_Div= 5, M= 33, N= 225, P=2, Q=27, R=  9, Er=182, vco=184.09, Magic=818182
    P_Div= 5, M= 44, N= 300, P=2, Q=27, R= 12, Er=182, vco=184.09, Magic=613636
    P_Div= 5, M= 55, N= 375, P=2, Q=27, R= 15, Er=182, vco=184.09, Magic=490909
    P_Div= 5, M= 66, N= 450, P=2, Q=27, R= 18, Er=182, vco=184.09, Magic=409091
    P_Div= 5, M= 77, N= 525, P=2, Q=27, R= 21, Er=182, vco=184.09, Magic=350649
    P_Div= 5, M= 88, N= 600, P=2, Q=27, R= 24, Er=182, vco=184.09, Magic=306818
    P_Div= 5, M= 99, N= 675, P=2, Q=27, R= 27, Er=182, vco=184.09, Magic=272727
    P_Div= 5, M=110, N= 750, P=2, Q=27, R= 30, Er=182, vco=184.09, Magic=245455
    P_Div= 5, M=121, N= 825, P=2, Q=27, R= 33, Er=182, vco=184.09, Magic=223140
    P_Div= 5, M=132, N= 900, P=2, Q=27, R= 36, Er=182, vco=184.09, Magic=204545
    P_Div= 5, M=143, N= 975, P=2, Q=27, R= 39, Er=182, vco=184.09, Magic=188811
    P_Div= 5, M=154, N=1050, P=2, Q=27, R= 42, Er=182, vco=184.09, Magic=175325
    P_Div= 5, M=165, N=1125, P=2, Q=27, R= 45, Er=182, vco=184.09, Magic=163636
    P_Div= 5, M=176, N=1200, P=2, Q=27, R= 48, Er=182, vco=184.09, Magic=153409
    P_Div= 5, M=187, N=1275, P=2, Q=27, R= 51, Er=182, vco=184.09, Magic=144385
    P_Div= 5, M=198, N=1350, P=2, Q=27, R= 54, Er=182, vco=184.09, Magic=136364
    P_Div= 5, M=209, N=1425, P=2, Q=27, R= 57, Er=182, vco=184.09, Magic=129187
    P_Div= 5, M=220, N=1500, P=2, Q=27, R= 60, Er=182, vco=184.09, Magic=122727
    P_Div= 5, M=231, N=1575, P=2, Q=27, R= 63, Er=182, vco=184.09, Magic=116883
    P_Div= 5, M=242, N=1650, P=2, Q=27, R= 66, Er=182, vco=184.09, Magic=111570
    P_Div= 5, M=253, N=1725, P=2, Q=27, R= 69, Er=182, vco=184.09, Magic=106719
    P_Div= 5, M=264, N=1800, P=2, Q=27, R= 72, Er=182, vco=184.09, Magic=102273
    P_Div= 5, M=275, N=1875, P=2, Q=27, R= 75, Er=182, vco=184.09, Magic= 98182
    P_Div= 5, M=286, N=1950, P=2, Q=27, R= 78, Er=182, vco=184.09, Magic= 94406
    P_Div= 5, M=297, N=2025, P=2, Q=27, R= 81, Er=182, vco=184.09, Magic= 90909
    P_Div= 5, M=308, N=2100, P=2, Q=27, R= 84, Er=182, vco=184.09, Magic= 87662
    P_Div= 5, M=319, N=2175, P=2, Q=27, R= 87, Er=182, vco=184.09, Magic= 84639
    P_Div= 5, M=330, N=2250, P=2, Q=27, R= 90, Er=182, vco=184.09, Magic= 81818
    P_Div= 5, M=341, N=2325, P=2, Q=27, R= 93, Er=182, vco=184.09, Magic= 79179
    P_Div= 5, M=352, N=2400, P=2, Q=27, R= 96, Er=182, vco=184.09, Magic= 76705
    P_Div= 5, M=363, N=2475, P=2, Q=27, R= 99, Er=182, vco=184.09, Magic= 74380
    P_Div= 5, M=374, N=2550, P=2, Q=27, R=102, Er=182, vco=184.09, Magic= 72193
    P_Div= 5, M=385, N=2625, P=2, Q=27, R=105, Er=182, vco=184.09, Magic= 70130
    P_Div= 5, M=396, N=2700, P=2, Q=27, R=108, Er=182, vco=184.09, Magic= 68182
    P_Div= 5, M=407, N=2775, P=2, Q=27, R=111, Er=182, vco=184.09, Magic= 66339
    P_Div= 5, M=418, N=2850, P=2, Q=27, R=114, Er=182, vco=184.09, Magic= 64593
    P_Div= 5, M=429, N=2925, P=2, Q=27, R=117, Er=182, vco=184.09, Magic= 62937
    P_Div= 5, M=440, N=3000, P=2, Q=27, R=120, Er=182, vco=184.09, Magic= 61364
    P_Div= 5, M=451, N=3075, P=2, Q=27, R=123, Er=182, vco=184.09, Magic= 59867
    P_Div= 5, M=462, N=3150, P=2, Q=27, R=126, Er=182, vco=184.09, Magic= 58442
    P_Div= 5, M=473, N=3225, P=2, Q=27, R=129, Er=182, vco=184.09, Magic= 57082
    P_Div= 5, M=484, N=3300, P=2, Q=27, R=132, Er=182, vco=184.09, Magic= 55785
    P_Div= 5, M=495, N=3375, P=2, Q=27, R=135, Er=182, vco=184.09, Magic= 54545
    P_Div= 5, M=506, N=3450, P=2, Q=27, R=138, Er=182, vco=184.09, Magic= 53360
    P_Div= 6, M= 11, N=  90, P=1, Q=16, R=  4, Er=182, vco=220.91, Magic=2454545
    P_Div= 6, M= 22, N= 180, P=1, Q=16, R=  8, Er=182, vco=220.91, Magic=1227273
    P_Div= 6, M= 33, N= 270, P=1, Q=16, R= 12, Er=182, vco=220.91, Magic=818182
    P_Div= 6, M= 44, N= 360, P=1, Q=16, R= 16, Er=182, vco=220.91, Magic=613636
    P_Div= 6, M= 55, N= 450, P=1, Q=16, R= 20, Er=182, vco=220.91, Magic=490909
    P_Div= 6, M= 66, N= 540, P=1, Q=16, R= 24, Er=182, vco=220.91, Magic=409091
    P_Div= 6, M= 77, N= 630, P=1, Q=16, R= 28, Er=182, vco=220.91, Magic=350649
    P_Div= 6, M= 88, N= 720, P=1, Q=16, R= 32, Er=182, vco=220.91, Magic=306818
    P_Div= 6, M= 99, N= 810, P=1, Q=16, R= 36, Er=182, vco=220.91, Magic=272727
    P_Div= 6, M=110, N= 900, P=1, Q=16, R= 40, Er=182, vco=220.91, Magic=245455
    P_Div= 6, M=121, N= 990, P=1, Q=16, R= 44, Er=182, vco=220.91, Magic=223140
    P_Div= 6, M=132, N=1080, P=1, Q=16, R= 48, Er=182, vco=220.91, Magic=204545
    P_Div= 6, M=143, N=1170, P=1, Q=16, R= 52, Er=182, vco=220.91, Magic=188811
    P_Div= 6, M=154, N=1260, P=1, Q=16, R= 56, Er=182, vco=220.91, Magic=175325
    P_Div= 6, M=165, N=1350, P=1, Q=16, R= 60, Er=182, vco=220.91, Magic=163636
    P_Div= 6, M=176, N=1440, P=1, Q=16, R= 64, Er=182, vco=220.91, Magic=153409
    P_Div= 6, M=187, N=1530, P=1, Q=16, R= 68, Er=182, vco=220.91, Magic=144385
    P_Div= 6, M=198, N=1620, P=1, Q=16, R= 72, Er=182, vco=220.91, Magic=136364
    P_Div= 6, M=209, N=1710, P=1, Q=16, R= 76, Er=182, vco=220.91, Magic=129187
    P_Div= 6, M=220, N=1800, P=1, Q=16, R= 80, Er=182, vco=220.91, Magic=122727
    P_Div= 6, M=231, N=1890, P=1, Q=16, R= 84, Er=182, vco=220.91, Magic=116883
    P_Div= 6, M=242, N=1980, P=1, Q=16, R= 88, Er=182, vco=220.91, Magic=111570
    P_Div= 6, M=253, N=2070, P=1, Q=16, R= 92, Er=182, vco=220.91, Magic=106719
    P_Div= 6, M=264, N=2160, P=1, Q=16, R= 96, Er=182, vco=220.91, Magic=102273
    P_Div= 6, M=275, N=2250, P=1, Q=16, R=100, Er=182, vco=220.91, Magic= 98182
    P_Div= 6, M=286, N=2340, P=1, Q=16, R=104, Er=182, vco=220.91, Magic= 94406
    P_Div= 6, M=297, N=2430, P=1, Q=16, R=108, Er=182, vco=220.91, Magic= 90909
    P_Div= 6, M=308, N=2520, P=1, Q=16, R=112, Er=182, vco=220.91, Magic= 87662
    P_Div= 6, M=319, N=2610, P=1, Q=16, R=116, Er=182, vco=220.91, Magic= 84639
    P_Div= 6, M=330, N=2700, P=1, Q=16, R=120, Er=182, vco=220.91, Magic= 81818
    P_Div= 6, M=341, N=2790, P=1, Q=16, R=124, Er=182, vco=220.91, Magic= 79179
    P_Div= 6, M=352, N=2880, P=1, Q=16, R=128, Er=182, vco=220.91, Magic= 76705
    P_Div= 6, M=363, N=2970, P=1, Q=16, R=132, Er=182, vco=220.91, Magic= 74380
    P_Div= 6, M=374, N=3060, P=1, Q=16, R=136, Er=182, vco=220.91, Magic= 72193
    P_Div= 6, M=385, N=3150, P=1, Q=16, R=140, Er=182, vco=220.91, Magic= 70130
    P_Div= 6, M=396, N=3240, P=1, Q=16, R=144, Er=182, vco=220.91, Magic= 68182
    P_Div= 6, M=407, N=3330, P=1, Q=16, R=148, Er=182, vco=220.91, Magic= 66339
    P_Div= 6, M=418, N=3420, P=1, Q=16, R=152, Er=182, vco=220.91, Magic= 64593
    P_Div= 6, M=429, N=3510, P=1, Q=16, R=156, Er=182, vco=220.91, Magic= 62937
    P_Div= 6, M=440, N=3600, P=1, Q=16, R=160, Er=182, vco=220.91, Magic= 61364
    P_Div= 6, M=451, N=3690, P=1, Q=16, R=164, Er=182, vco=220.91, Magic= 59867
    P_Div= 6, M=462, N=3780, P=1, Q=16, R=168, Er=182, vco=220.91, Magic= 58442
    P_Div= 6, M=473, N=3870, P=1, Q=16, R=172, Er=182, vco=220.91, Magic= 57082
    P_Div= 6, M=484, N=3960, P=1, Q=16, R=176, Er=182, vco=220.91, Magic= 55785
    P_Div= 6, M=495, N=4050, P=1, Q=16, R=180, Er=182, vco=220.91, Magic= 54545

    None of them provide the required result, so this is an interesting case..

    The answer TI Clock Pro produces is the one where M/N are highest but not at the expense of a higher magic number; in other words TI Clock Pro chose M=506 and N=3450 rather than M=495 and N=4050 just because the Magic number is lower.

    Where the result yields R=0 then its ok to choose that one, but select N/M to be high.

    I hope this helps anyone else.

    Regards,

    Chris