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LMX2491: No output on CPout

Ruixin Feng
Intellectual 2535 points

Part Number: LMX2491

Tool/software:

Hi team,

customer used LMX2491 as FMCW modulation with below register configuration. The scanning frequency is from 1.5Ghz to 1.515625GHz. The issue is CPout=0V, and TRIG1 is high. And this is a occasional issue. could you pls help to check the configuration and see if any problem here? Thanks!

Register Value
92 0x74
91 0x00
90 0x00
89 0x00
88 0x00
87 0x00
86 0x00
99 0x40
98 0x17
97 0x70
96 0x3F
95 0XFF
94 0XEE
93 0XF0
106 0X80
105 0X19
104 0X78
103 0X00
102 0X00
101 0X00
100 0X00
113 0X23
112 0X30
111 0XC0
110 0X00
109 0X00
108 0X08
107 0X34
120 0X64
119 0X00
118 0X01
117 0X00
116 0X00
115 0X00
114 0X00
24 0XFF
23 0XFF
22 0XFF
21 0X80
20 0X00
19 0X00
18 0X2C
17 0X00
16 0X25
84 0X20
83 0X05
82 0X02
81 0XD8
80 0X33
79 0X33
78 0X00
77 0X7F
76 0XCC
75 0XCC
74 0XDA
73 0X80
72 0X00
71 0X00
70 0X24
69 0X00
68 0X02
67 0XD8
66 0X00
65 0X00
64 0X00
63 0X00
62 0X80
61 0X00
60 0X00
59 0X02
58 0X01
39 0X3A
38 0XFA
37 0X17
36 0X5A
35 0X41
34 0X84
33 0X20
32 0X00
31 0X2A
30 0X06
29 0X00
28 0X14
27 0X08
26 0X00
25 0X01
2 0X02

Rayna

  • 0
    TI__Guru** 116790 points

    Hi Rayna,

    What is fosc and fpd?

    It would be great if you can provide the configuration in TICS Pro format like below.

    Suggest read the EVM user's guide to study how to setup the configuration for frequency ramp.

    www.ti.com/.../snau160

  • 0 in reply to Noel Fung
    TI__Intellectual 2535 points

    Hi Noel,

    Fosc and Fpd is 40MHz. VCO output is from 1.5Ghz to 1.515625GHz. customer use their own board so I'm sorry I don't have the TICS pro format.

    Is there any more test we can do now? Since it's an occasional issue, we keep the issue now.

    Thanks!

    Rayna

  • 0 in reply to Ruixin Feng
    TI__Guru** 116790 points

    Hi Ruixin,

    I loaded their configuration in TICS Pro, there are some errors in their configuration.

    Below register is 2's compliment, this value is 33-bit long, so the value = 2^33 - Extended_Fractional_Numerator (Equation 1 in the datasheet).

    suggest make RAMP_LIMIT_HIGH to a higher frequency, for example 5000MHz.

    Based on their configuration, below is their ramp waveform

    Suggest change the configuration to:

  • 0
    TI__Intellectual 2535 points

    Hi Noel,

    could you pls export your suggested configuration for customer reference? thanks a lot!

    Rayna

  • 0 in reply to Ruixin Feng
    TI__Guru** 116790 points

    Here you are.

    Fullscreen LMX2491.txt Download 
    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	0x006917
R104	0x006870
R103	0x00673F
R102	0x0066FF
R101	0x0065EE
R100	0x0064EE
R99	0x006343
R98	0x006230
R97	0x0061C0
R96	0x006000
R95	0x005F00
R94	0x005E08
R93	0x005D35
R92	0x005C30
R91	0x005B00
R90	0x005A28
R89	0x005900
R88	0x005800
R87	0x005700
R86	0x005600
R85	0x005500
R84	0x005400
R83	0x005300
R82	0x005200
R81	0x005100
R80	0x005000
R79	0x004F00
R78	0x004EBC
R77	0x004D00
R76	0x004C00
R75	0x004B00
R74	0x004A00
R73	0x004900
R72	0x004800
R71	0x004700
R70	0x004608
R69	0x004500
R68	0x0044C6
R67	0x004300
R66	0x004200
R65	0x004100
R64	0x004000
R63	0x003FD0
R62	0x003E00
R61	0x003D00
R60	0x003C00
R59	0x003B00
R58	0x003A01
R57	0x003900
R45	0x002D00
R44	0x002C00
R43	0x002B00
R42	0x002A00
R41	0x002900
R40	0x002800
R39	0x00273A
R38	0x0026FA
R37	0x002510
R36	0x00245A
R35	0x002341
R34	0x002244
R33	0x002120
R32	0x002000
R31	0x001F32
R30	0x001E0A
R29	0x001D00
R28	0x001C14
R27	0x001B08
R26	0x001A00
R25	0x001901
R24	0x001800
R23	0x001703
R22	0x0016E8
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	0x000202
R1	0x000100
R0	0x000018

  • 0 in reply to Noel Fung
    TI__Intellectual 2535 points

    Hi Noel,

    Customer will check their configuration.

    In LMX2491 EVM UG, Figure 9 comment that "VCO output limit range must be greater than the ramp range". It's a little confusing here. Based on your comments, my understanding is ramp range need to be larger than VCO output range. which is correct?

    Thanks!

    Rayna

  • 0 in reply to Ruixin Feng
    TI__Guru** 116790 points

    Hi Ruixin,

    Below is the ramp limit.

    It should be greater than the ramp range. In this case ramp range is 1500MHz to 1562.5MHz.,