7. Dynamic PLL Changes
7.1 Revisions B and A
It is possible for a PLL to become unresponsive (i.e., lose lock indefinitely) when it is dynamically reprogrammed or changed via the
serial port. Reprogramming/changing the N divider does not affect the PLL. Any change that causes the VCO frequency to change by
more than 250 ppm since Power-up, NVM download, or SOFT_RST requires the following special sequence of writes. Changes to the
following registers require the following special sequence of writes:
• XAXB_FREQ_OFFSET
• PXAXB
• MXAXB_NUM
• MXAXB_DEN
• M_NUM
• M_DEN
1. First, the preamble:
Write 0x0B24 = 0xD8
Write 0x0B25 = 0x00
Write 0x0502 = 0x01
Write 0x0505 = 0x03
Write 0x0957 = 0x17
Write 0x0B4E = 0x1A
2. Wait 300 ms.
3. Then, perform the desired register modifications.
4. Write SOFT_RST - 0x001C[0] = 1
5. Write the post-amble:
Write 0x0B24 = 0xDB
Write 0x0B25 = 0x02
7.2 Revision D
The Revision D preamble and postamble values for updating certain registers during device operation have changed after Revision
B. Either the new or old values below may be written to Revision D or later devices without issue. No system software changes are
necessary for legacy systems. When writing old values, note that reading back these registers will not give the written old values, but
will reflect the new values. Silicon Labs recommends using the new values for all Revision D and later designs, since the write and read
values will match.
The device revision can be determined in the setting DEVICE_REV, register 0x0005.
DEVICE_REV = 0x02 or higher: New Values
Revision
D
Preamble: 0x0B24 = 0xC0, 0x0B25 = 0x00
Revision
D
Postamble: 0x0B24 = 0xC3, 0x0B25 = 0x02
Note that revision B and earlier devices must continue to use the original values for these registers:
DEVICE_REV = 0x00 or 0x01: Old Values
Revision
B
Preamble: 0x0B24 = 0xD8, 0x0B25 = 0x00
Revision
B
Postamble: 0x0B24 = 0xDB, 0x0B25 = 0x02
Si5341, Si5340 Rev D Family Reference Manual • Dynamic PLL Changes
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.3 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • July 26, 2021
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