Part Number: LMX2624-SP
I am having difficulty obtaining an RF output from the LMX2624-SP on a custom board. I have verified basic SPI communication using the TI EVM and TICS PRO software: register writes are successful (e.g., I can toggle the power-down bit in R0), but the PLL does not produce an output signal.
While debugging this, I noticed an apparent inconsistency between the LMX2624-SP datasheet and the TICS PRO register mapping related to the charge pump gain field.
According to datasheet SNAS849 (December 2024), page 42, Table 7-5 (R2 Register Field Descriptions):
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Bits [10:6] are labeled CP25V_IUP (charge pump gain)
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This implies a 5-bit field
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The table states that a value of 0x4 corresponds to a charge pump current of 1.5 mA
In TICS PRO, the EVM default charge pump gain is also set to 1.5 mA. Based on the datasheet description, I would therefore expect bits [10:6] of R2 to be programmed as 00100 (0x04).
However, when I inspect the register map in TICS PRO with the default settings, bits [10:6] are set to 11100, which corresponds to 0x1C (decimal 28). This does not match the value indicated in the datasheet for 1.5 mA.
Additionally, there appears to be a discrepancy in the defined width of the CP25V_IUP field:
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The datasheet states the field spans bits [10:6]
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TICS PRO shows the field spanning bits [10:8] only (see attached screenshot)
If the field truly spans only bits [10:8], then it would be a 3-bit field, which would be consistent with the maximum defined value in the datasheet being 0x7 (binary 111). This suggests the datasheet bit range may be incorrect, or that TICS PRO is applying additional internal encoding or offset.
Also, note that in TICS PRO, the available options span from 0mA to 15mA. In the datasheet, they only span from "unused" to 1.5mA. I wanted to verify which range of options is the correct one. I presume that perhaps the "15mA" in TICS PRO is referring to 1.5mA, and is simply missing a decimal point?
Given these discrepancies:
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Datasheet value for 1.5 mA: 0x4
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TICS PRO programmed value: 0x1C
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Datasheet field width: 5 bits
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TICS PRO field width: 3 bits
I would appreciate clarification on:
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The correct bit range for the CP25V_IUP field
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Whether TICS PRO applies any internal mapping or scaling to this field
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The correct way to manually program this field when not using TICS PRO
Clarifying this would help ensure the PLL is configured correctly and may explain why I am not seeing an RF output. Overall I would appreciate if the application engineer for this chip could get in touch to verify if I am programming the chip correctly, to avoid any other misunderstandings.
Thank you for your support.
