SI5341 Datasheet, PDF (37/56 Pages) Silicon Laboratories – LOW-JITTER, 10-OUTPUT, ANY-FREQUENCY, ANY-OUTPUT CLOCK GENERATOR

Si5341/40
5.5.16. Digitally Controlled Oscillator (DCO) Modes
Each MultiSynth can be digitally controlled to so that all outputs connected to the MultiSynth change frequency in
real time without any transition glitches. There are two ways to control the MultiSynth to accomplish this task:
Use the Frequency Increment/Decrement Pins or register bits
Write directly to the numerator of the MultiSynth divider.
An output that is controlled as a DCO is useful for simple tasks such as frequency margining or CPU speed control.
The output can also be used for more sophisticated tasks such as FIFO management by adjusting the frequency of
the read or write clock to the FIFO or using the output as a variable Local Oscillator in a radio application.
5.5.16.1. DCO with Frequency Increment/Decrement Pins/Bits
Each of the MultiSynth fractional dividers can be independently stepped up or down in predefined steps with a
resolution as low as 0.001 ppb. Setting of the step size and control of the frequency increment or decrement is
accomplished by setting the step size with the 44 bit Frequency Step Word (FSTEPW). When the FINC or FDEC
pin or register bit is asserted the output frequency will increment or decrement respectivley by the amount specified
in the FSTEPW.
5.5.16.2. DCO with Direct Register Writes
When a MultiSynth numerator and its corresponding update bit is written, the new numerator value will take effect
and the output frequency will change without any glitches. The MultiSynth numerator and denominator terms can
be left and right shifted so that the least significant bit of the numerator word represents the exact step resolution
that is needed for your application.
5.6. Power Management
Several unused functions can be powered down to minimize power consumption. Consult the Si5341/40 Family
Reference Manual and ClockBuilder Pro configuration utility for details.
5.7. In-Circuit Programming
The Si5341/40 is fully configurable using the serial interface (I²C or SPI). At power-up the device downloads its
default register values from internal non-volatile memory (NVM). Application specific default configurations can be
written into NVM allowing the device to generate specific clock frequencies at power-up. Writing default values to
NVM is in-circuit programmable with normal operating power supply voltages applied to its V_DD and V_DDA pins. The
NVM is two time writable. Once a new configuration has been written to NVM, the old configuration is no longer
accessible. Refer to the Si5341/40 Family Reference Manual for a detailed procedure for writing registers to NVM.
5.8. Serial Interface
Configuration and operation of the Si5341/40 is controlled by reading and writing registers using the I²C or SPI
interface. The I2C_SEL pin selects I²C or SPI operation. Communication with both 3.3V and 1.8V host is
supported. The SPI mode operates in either 4-wire or 3-wire. See the Si5341/40 Family Reference Manual for
details.
5.9. Custom Factory Preprogrammed Devices
For applications where a serial interface is not available for programming the device, custom pre-programmed
parts can be ordered with a specific configuration written into NVM. A factory pre-programmed device will generate
clocks at power-up. Custom, factory-preprogrammed devices are available. Use the ClockBuilder Pro custom part
number wizard (www.silabs.com/clockbuilderpro) to quickly and easily request and generate a custom part number
for your configuration. In less than three minutes, you will be able to generate a custom part number with a detailed
data sheet addendum matching your design’s configuration. Once you receive the confirmation email with the data
sheet addendum, simply place an order with your local Silicon Labs sales representative. Samples of your pre-
programmed device will ship to you typically within two weeks.
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