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

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-

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

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.

Si5341/40 Rev D Data Sheet

Functional Description

silabs.com | Smart. Connected. Energy-friendly.

Rev. 1.0 | 12