We are developing a board based on ADRV9371-W/PCBZ, but we couldn't achieved to lock PLL2. Here are the similarities/differences:
- PLL1 is powered down, we are using in holdover mode. There is 122.88Mhz TCXO is supplied to VCXO_IN_P/N by DC coupled differential LVDS with external 100 ohm diff termination . REF inputs are floating as in ADRV9371 and REF_SEL is tied to GND. VCXO_VT and LF1 are floating as we are using TCXO instead of VCXO.
- VDD pins for used output buffers are tied to 3V3 and VDD pins for unused output buffers are floating(There is no info about it in the datasheet?).
- VDD pins (1, 10, 16, 20 and 72) are tied to 3V3 through EMI filter.
- LF2 are same as in ADRV9371 (1nF/470nF)
Here is the SPI write sequence:
- 0x000 - 0x3C
- 0x001 - 0x80
- 0x100 - 0x01
- 0x101 - 0x00
- 0x102 - 0x01
- 0x103 - 0x00
- 0x104 - 0x04
- 0x105 - 0x00
- 0x106 - 0x80 - Force holdover
- 0x107 - 0x00 - CP1 are tristate
- 0x108 - 0x81 - Diff VCXO active
- 0x109 - 0x00
- 0x10a - 0x02
- 0x10b - 0x00
- 0x200 - 0xE6 - Same as ADRV9371
- 0x201 - 0x87 - feedback divider is 32, we have also tried 30(0x08) with M=3 and N2=10
- 0x202 - 0x03
- 0x203 - 0x01
- 0x204 - 0x03
- 0x205 - 0x2A - Same as ADRV9371
- 0x206 - 0x00
- 0x207 - 0x00
- 0x208 - 0x09
- 0x209 - 0x00
- 0x300 - 0x329 are set.
- 0x32A - 0x32E are all 0x00
- 0x400 - 0x00
- 0x401 - 0x00
- 0x402 - 0x98
- 0x403 - 0x80
- 0x404 - 0x04
- 0x500 - 0x14 - PLL1 is powered down even if we activated force holdover.
- 0x501 - 0x6F - Ch(4-7-8-11-13) are used.
- 0x502 - 0x16
- 0x503 - 0x90 - Ch(4-7-8-11-13) are used.
- 0x504 - 0xE9
- 0x505 - 0x0A
- 0x506 - 0x00
- 0x507 - 0x04
- 0x00F - 0x01
and 0x508 status is 0x10 and 0x509 status is 08.
What we have tried:
- When we tried the same thing in ADRV9371 PLL2 is always locked if the M and N2 dividers are set to proper frequency for VCO, even if CP current(0x200) is set to min and max values.
- VDD pins for unused output buffers are AC coupled to GND by 100nF.
- We forced CP of PLL2 to pump-down and pump-up mode, 0V and ~1.80V were measured respectively.
Do you have any advice what is the problem?