SNAA449 June   2025 LMX2820

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Various Options in Instant Calibration
    1. 2.1 When Delay for Instant Calibration Needs to be Increased From 2.5μs to 5μs
    2. 2.2 Generating the Lookup Table for Instant Calibration With the VCO Doubler
    3. 2.3 Reading Back the Instant Calibration Lookup Table Through SPI
    4. 2.4 Writing the Lookup Table Through SPI
    5. 2.5 Dealing With Case When Phase Detector Frequency is Changed Without Re-generating the Lookup Table
  6. 3Summary
  7. 4References

2.4 Writing the Lookup Table Through SPI

  1. Power off the supply and on.
  2. Load Default 6GHz tics pro file with 100MHz as input OSCIN.
  3. Write the following registers
    1. R70
      1. DBLBUF_PLL_EN(R70<4]) = 1
      2. DBLBUF_CHDIV_EN(R70<5]) = 1
      3. DBLBUF_OUTBUF_EN(R70<6]) = 1
      4. DBLBUF_OUTBUF_EN(R70<7]) = 1
    2. R1
      1. INSTCAL_DBLR_EN (R1[1])=1
      2. INSTCAL_EN (R1[0]) = 1
    3. R4
      1. LUT_GEN_SEL (R4[15]) = 1
    4. R36
      1. PLL_N (R36[14:0] = 28
    5. PLL_NUM
      1. R42(MSB),R43(LSB) as 250 (NUM)
    6. PLL_DEN
      1. R38(MSB),R39(LSB) as 1000(DEN)
    7. INSTANT_PLL_NUM
      1. R44 and R45; R44(MSB),R45(LSB) as 2^30 (2^32*(NUM/DEN) INSTCAL_PLL_NUM)
    8. Toggle FCAL
      1. FCAL_EN (R0[4] =0
      2. FCAL_EN (R0[4] =1
      3. FCAL_EN (R0[4] =0
  4. INDEX_TEST(R106[10]=1), INDEX_WR_RD(R106[11]=0)
  5. For Index = 0 to 519
    1. Write INDEX_NO(R106[9:0]) =Index
      1. Ensure INDEX_WR_RD(R106<11]) = 1
      2. Ensure INDEX_WR_RD(R106[11]) = 0
      3. Write stored value for INDEX_TEST_WRDATA_37_32(R107<5:0])
      4. Write stored value for WRDATA_31_16(R108<15:0])
      5. Write stored value for INDEX_TEST_WRDATA_15_0(R109<15:0])
  6. After writing to LUT, make INDEX_TEST(R106<10]) as 0.

After above steps, LUT writing is done and user can change the frequency of output faster just by writing the required N.F and INSTCAL_PLL_NUM with PFD not changed. Writing to R0 is needed for the N.F change to take place as doubler buffering is enabled. This can help in faster setting behavior.