The problem is this.
Circuit structure: LMX2491 + external loop filter+ VCO. Phase detector frequency is 40MHz.
I have verified the functionality of VCO. Verification method: Disconnect LMX2491, use a voltage source alone to supply power to the VCO, and adjust the voltage. The VCO can output the change frequency as the voltage changes, and the higher the voltage, the higher the frequency. It works as normal. Adjust the voltage range between 0.6 and 1.1V to correspond to my desired operating frequency.
After the two chips are connected together, the system does not work properly because the LMX2491 does not output the Vtune voltage signal properly, only about 0.01~0.03V. I checked all the registers and found nothing unusual. Then I tried setting the R28 register bit5 to 1 (the default is 0, and I think 0 is correct). The Vtune had a voltage signal, but it was too high for my default charge pump gain configuration of 3.1mA. In order to obtain the appropriate Vtune voltage value, I adjusted the charge pump gain. When it was set to 8, the Vtune voltage could work at about 0.9V. But the biggest problem is that PLL is not locked in any case. DLD detection is all low.
Attached are my 3 register configuration files, please help to check the other Settings are not correct. Thanks a lot.
R141 0x008D00
R140 0x008C0F
R139 0x008BA0
R138 0x008A00
R137 0x008900
R136 0x008800
R135 0x008700
R134 0x008600
R133 0x00850F
R132 0x0084A0
R131 0x008300
R130 0x008200
R129 0x008100
R128 0x008000
R127 0x007F00
R126 0x007E0F
R125 0x007DA0
R124 0x007C00
R123 0x007B00
R122 0x007A00
R121 0x007900
R120 0x007800
R119 0x00770F
R118 0x0076A0
R117 0x007500
R116 0x007400
R115 0x007300
R114 0x007200
R113 0x007100
R112 0x00700F
R111 0x006FA0
R110 0x006E00
R109 0x006D00
R108 0x006C00
R107 0x006B00
R106 0x006A00
R105 0x006901
R104 0x006890
R103 0x00673F
R102 0x0066FF
R101 0x0065C2
R100 0x00648E
R99 0x006340
R98 0x006207
R97 0x0061D0
R96 0x006000
R95 0x005F00
R94 0x005E0C
R93 0x005D4A
R92 0x005C20
R91 0x005B00
R90 0x005AC8
R89 0x005900
R88 0x005800
R87 0x005700
R86 0x005600
R85 0x005500
R84 0x005400
R83 0x005300
R82 0x005201
R81 0x0051C0
R80 0x005000
R79 0x004F00
R78 0x004EFF
R77 0x004D40
R76 0x004C00
R75 0x004B00
R74 0x004A00
R73 0x004900
R72 0x004800
R71 0x004700
R70 0x004608
R69 0x004500
R68 0x004400
R67 0x0043C0
R66 0x004200
R65 0x004100
R64 0x004000
R63 0x003F00
R62 0x003EA0
R61 0x003D00
R60 0x003C00
R59 0x003B00
R58 0x003A00
R57 0x003900
R45 0x002D00
R44 0x002C00
R43 0x002B00
R42 0x002A00
R41 0x002900
R40 0x002800
R39 0x00275A
R38 0x002642
R37 0x00256A
R36 0x002492
R35 0x002341
R34 0x002284
R33 0x002120
R32 0x002000
R31 0x001F32
R30 0x001E06
R29 0x001D00
R28 0x001C28
R27 0x001B08
R26 0x001A00
R25 0x001901
R24 0x001800
R23 0x001707
R22 0x0016D0
R21 0x001500
R20 0x001403
R19 0x0013E8
R18 0x00122C
R17 0x001100
R16 0x001025
R15 0x000F00
R14 0x000E00
R13 0x000D00
R12 0x000C00
R11 0x000B00
R10 0x000A00
R9 0x000900
R8 0x000800
R7 0x000700
R6 0x000600
R5 0x000500
R4 0x000400
R3 0x000300
R2 0x000201
R1 0x000100
R0 0x000018
R141 0x008D00
R140 0x008C0F
R139 0x008BA0
R138 0x008A00
R137 0x008900
R136 0x008800
R135 0x008700
R134 0x008600
R133 0x00850F
R132 0x0084A0
R131 0x008300
R130 0x008200
R129 0x008100
R128 0x008000
R127 0x007F00
R126 0x007E0F
R125 0x007DA0
R124 0x007C00
R123 0x007B00
R122 0x007A00
R121 0x007900
R120 0x007800
R119 0x00770F
R118 0x0076A0
R117 0x007500
R116 0x007400
R115 0x007300
R114 0x007200
R113 0x007100
R112 0x00700F
R111 0x006FA0
R110 0x006E00
R109 0x006D00
R108 0x006C00
R107 0x006B00
R106 0x006A00
R105 0x006901
R104 0x006890
R103 0x00673F
R102 0x0066FF
R101 0x0065C2
R100 0x00648E
R99 0x006340
R98 0x006207
R97 0x0061D0
R96 0x006000
R95 0x005F00
R94 0x005E0C
R93 0x005D4A
R92 0x005C20
R91 0x005B00
R90 0x005AC8
R89 0x005900
R88 0x005800
R87 0x005700
R86 0x005600
R85 0x005500
R84 0x005400
R83 0x005300
R82 0x005201
R81 0x0051C0
R80 0x005000
R79 0x004F00
R78 0x004EFF
R77 0x004D40
R76 0x004C00
R75 0x004B00
R74 0x004A00
R73 0x004900
R72 0x004800
R71 0x004700
R70 0x004608
R69 0x004502
R68 0x004400
R67 0x0043C0
R66 0x004200
R65 0x004100
R64 0x004006
R63 0x003F00
R62 0x003EA0
R61 0x003D00
R60 0x003C00
R59 0x003B00
R58 0x003A01
R57 0x003900
R45 0x002D00
R44 0x002C00
R43 0x002B00
R42 0x002A00
R41 0x002900
R40 0x002800
R39 0x002752
R38 0x00264A
R37 0x00253A
R36 0x002442
R35 0x002341
R34 0x002284
R33 0x002120
R32 0x002000
R31 0x001F32
R30 0x001E0A
R29 0x001D00
R28 0x001C1F
R27 0x001B08
R26 0x001A00
R25 0x001901
R24 0x001800
R23 0x001700
R22 0x001600
R21 0x001580
R20 0x001400
R19 0x001300
R18 0x00122C
R17 0x001100
R16 0x001025
R15 0x000F00
R14 0x000E00
R13 0x000D00
R12 0x000C00
R11 0x000B00
R10 0x000A00
R9 0x000900
R8 0x000800
R7 0x000700
R6 0x000600
R5 0x000500
R4 0x000400
R3 0x000300
R2 0x000201
R1 0x000100
R0 0x000018
R141 0x008D00
R140 0x008C0F
R139 0x008BA0
R138 0x008A00
R137 0x008900
R136 0x008800
R135 0x008700
R134 0x008600
R133 0x00850F
R132 0x0084A0
R131 0x008300
R130 0x008200
R129 0x008100
R128 0x008000
R127 0x007F00
R126 0x007E0F
R125 0x007DA0
R124 0x007C00
R123 0x007B00
R122 0x007A00
R121 0x007900
R120 0x007800
R119 0x00770F
R118 0x0076A0
R117 0x007500
R116 0x007400
R115 0x007300
R114 0x007200
R113 0x007100
R112 0x00700F
R111 0x006FA0
R110 0x006E00
R109 0x006D00
R108 0x006C00
R107 0x006B00
R106 0x006A00
R105 0x006901
R104 0x006890
R103 0x00673F
R102 0x0066FF
R101 0x0065C2
R100 0x00648E
R99 0x006340
R98 0x006207
R97 0x0061D0
R96 0x006000
R95 0x005F00
R94 0x005E0C
R93 0x005D4A
R92 0x005C20
R91 0x005B00
R90 0x005AC8
R89 0x005900
R88 0x005800
R87 0x005700
R86 0x005600
R85 0x005500
R84 0x005400
R83 0x005300
R82 0x005201
R81 0x0051C0
R80 0x005000
R79 0x004F00
R78 0x004EFF
R77 0x004D40
R76 0x004C00
R75 0x004B00
R74 0x004A00
R73 0x004900
R72 0x004800
R71 0x004700
R70 0x004608
R69 0x004502
R68 0x004400
R67 0x0043C0
R66 0x004200
R65 0x004100
R64 0x004006
R63 0x003F00
R62 0x003EA0
R61 0x003D00
R60 0x003C00
R59 0x003B00
R58 0x003A01
R57 0x003900
R45 0x002D00
R44 0x002C00
R43 0x002B00
R42 0x002A00
R41 0x002900
R40 0x002800
R39 0x002752
R38 0x00264A
R37 0x00253A
R36 0x002442
R35 0x002341
R34 0x002284
R33 0x002120
R32 0x002000
R31 0x001F32
R30 0x001E0A
R29 0x001D00
R28 0x001C28
R27 0x001B08
R26 0x001A00
R25 0x001901
R24 0x001800
R23 0x001700
R22 0x001600
R21 0x001580
R20 0x001400
R19 0x001300
R18 0x00122C
R17 0x001100
R16 0x001025
R15 0x000F00
R14 0x000E00
R13 0x000D00
R12 0x000C00
R11 0x000B00
R10 0x000A00
R9 0x000900
R8 0x000800
R7 0x000700
R6 0x000600
R5 0x000500
R4 0x000400
R3 0x000300
R2 0x000201
R1 0x000100
R0 0x000018