Si5351A/B/C

4. I2C Interface

Many of the functions and features of the Si5351 are controlled by reading and writing to the RAM space using the I2C interface. The following is a list of the common features that are controllable through the I2C interface. A summary of register functions is shown in Section 7.

Read Status Indicators

Loss of signal (LOS) for the CLKIN input Loss of lock (LOL) for PLLA and PLLB

Configuration of multiplication and divider values for the PLLs, MultiSynth dividers

Configuration of the Spread Spectrum profile (down or center spread, modulation percentage)

Control of the cross point switch selection for each of the PLLs and MultiSynth dividers

Set output clock options

Enable/disable for each clock output Invert/non-invert for each clock output Output divider values (2n, n=1.. 7)

Output state when disabled (stop hi, stop low, Hi-Z) Output phase offset

The I2C interface operates in slave mode with 7-bit addressing and can operate in Standard-Mode (100 kbps) or Fast-Mode (400 kbps) and supports burst data transfer with auto address increments.

The I2C bus consists of a bidirectional serial data line (SDA) and a serial clock input (SCL) as shown in Figure 7. Both the SDA and SCL pins must be connected to the VDD supply via an external pull-up as recommended by the I2C specification.

 

VDD

>1k

>1k

 

Si5351

 

SCL

I2C Bus

SDA

 

4.7 k

INTR

 

I2C Address Select:

A0

Pull-up to VDD (A0 = 1)

 

Pull-down to GND (A0 = 0)

 

Figure 7. I2C and Control Signals

The 7-bit device (slave) address of the Si5351 consist of a 6-bit fixed address plus a user selectable LSB bit as shown in Figure 8. The LSB bit is selectable as 0 or 1 using the optional A0 pin which is useful for applications that require more than one Si5351 on a single I2C bus.

Slave Address

6

5

4

3

2

1

0

 

 

 

 

 

 

 

1

1

0

0

0

0

0/1

 

 

 

 

 

 

 

A0

Figure 8. Si5351 I2C Slave Address

Data is transferred MSB first in 8-bit words as specified by the I2C specification. A write command consists of a 7- bit device (slave) address + a write bit, an 8-bit register address, and 8 bits of data as shown in Figure 9. A write burst operation is also shown where every additional data word is written using to an auto-incremented address.

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Silicon Laboratories SI5351A/B/C specifications I2C Interface, I2C and Control Signals

SI5351A/B/C specifications

Silicon Laboratories SI5351A/B/C is a versatile, low-power clock generator and frequency synthesizer that has gained widespread popularity in various applications, including telecommunications, consumer electronics, and industrial control systems. These devices are primarily designed to provide precise clock frequency generation with low phase noise and jitter, making them ideal for high-performance applications.

One of the standout features of the SI5351 is its ability to generate multiple output frequencies simultaneously. Capable of producing up to three independent programmable outputs, the SI5351A/B/C can generate frequencies ranging from 8 kHz to 160 MHz. With its integrated phase-locked loop (PLL) technology, it achieves excellent frequency stability and accuracy, simplifying the design of frequency-dependent systems.

The device operates under a supply voltage range of 1.8V to 3.6V, allowing it to be used in battery-powered applications without excessive power consumption. The SI5351’s low current draw, typically as low as 25 mA, is especially beneficial in portable devices, extending battery life and enhancing overall efficiency. Furthermore, it features a programmable output driver, which can be set to various drive strengths, ensuring compatibility with a wide array of load requirements.

Configuration and control of the SI5351 are user-friendly, implemented via an I2C interface. This allows for straightforward integration into microcontroller-based designs. Moreover, the device includes an on-chip memory that stores settings, which streamlines the reconfiguration process when power cycling, minimizing setup time for developers.

Another significant advantage of the SI5351A/B/C is its output jitter performance, which is typically below 1 ps, resulting in clean output signals essential for high-speed data communications and precise timing applications. The SI5351’s integration of multiple synthesizer stages contributes to its impressive phase noise characteristics, making it suitable for demanding RF applications.

Additionally, the SI5351 devices offer programmable frequency stepping, allowing users to define custom frequency increments, which is particularly useful in applications requiring precise tuning or modulation. This flexibility, combined with its compact size and simple interface, makes the SI5351A/B/C an ideal choice for engineers seeking a reliable, cost-effective solution for generating clock signals in a myriad of electronic systems.

In summary, Silicon Laboratories SI5351A/B/C provides a robust, low-power solution for high-precision clock generation, characterized by its programmable outputs, low jitter, easy configurability, and broad frequency range, making it an excellent choice for both commercial and industrial applications across various sectors.