SI5341_16 Datasheet, PDF (13/53 Pages) Silicon Laboratories – Low-Jitter, 10 or 4-Output, Any-Frequency, Any-Output Clock Generator

Si5341/40 Rev D Data Sheet
Functional Description
3.5.15 Digitally Controlled Oscillator (DCO) Modes
Each MultiSynth can be digitally controlled 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.
3.5.15.1 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 respectively by the amount specified in the FSTEPW.
3.5.15.2 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 fre-
quency 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.
3.6 Power Management
Several unused functions can be powered down to minimize power consumption. Consult the Si5340/41 Family Reference Manual and
ClockBuilder Pro configuration utility for details.
3.7 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 gen-
erate specific clock frequencies at power-up. Writing default values to NVM is in-circuit programmable with normal operating power sup-
ply 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 Si5340/41 Family Reference Manual for a detailed procedure for writing registers
to NVM.
3.8 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 3.3 V and 1.8 V host is supported. The SPI mode operates in either 4-wire or
3-wire. See the Si5340/41 Family Reference Manual for details.
3.9 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-pre-
programmed 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-pro-
grammed device will ship to you typically within two weeks.
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