How does it work?

Clock Gen 3 Click uses the LTC6904 IC, 1kHz to 68MHz Serial Port Programmable Oscillator from Linear Technology. The LTC6904 is a low power self-contained digital frequency source providing a precision frequency from 1KHz to 68MHz, which is set by the I2C interface operaing up to 3.4 Mbps. This Click board™ features on-board I2C address jumpers, pull-up resistors, a power supply bypass capacitor, and a power LED. The maximum frequency error is 1.1% or 1.6% when operating with a flexible power supply voltage range from 2.7V to 5V, which makes it suitable for 3.3V and 5V MCUs.

In most frequency ranges, the output of the Clock Gen 3 Click is generated as a division of the higher internal clock frequency. This helps to minimize jitter and subharmonics at the output of the device. In the highest frequency ranges, the division ratio is reduced, which will result in a greater cycle-to-cycle jitter as well as spurs at the internal sampling frequency. Because the internal control loop runs at 1MHz to 2MHz without regard to the output frequency, output spurs separated from the set frequency by 1MHz to 2MHz may be observed. These spurs are characteristically more than 30dB below the level of the set frequency.

The LTC6904 communicates with the MCU using the standard I2C 2-wire interface. The two bus lines, SDA and SCL, must be HIGH when the bus is not in use. If the I2C interface is not driven with a standard I2C compatible device, care must be taken to ensure that the SDA line is released during the ACK cycle to prevent bus contention. The LTC6904 can respond to one of two 7-bit addresses. The first 6 bits (MSBs) have been factory programmed to 001011. The address pin, ADR (Pin 4) is programmed by the user and determines the LSB of the slave address and it can be selected by an onboard SMD jumper labeled as ADD SEL allowing selection of the slave address LSB.

This Click board™ can be supplied and interfaced with both 3.3V and 5V without the need for any external components. The onboard SMD jumper labeled as VCC SEL allows voltage selection for interfacing with both 3.3V and 5V microcontrollers. More information about the LTC6904 can be found in the attached datasheet. However, this Click board™ comes equipped with a library that contains easy to use functions and an example that may be used as a reference for development.

Specifications

Pinout diagram

This table shows how the pinout on Clock Gen 3 Click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
	NC	1	AN	PWM	16	NC
	NC	2	RST	INT	15	NC
Output Enable	OE	3	CS	RX	14	NC
	NC	4	SCK	TX	13	NC
	NC	5	MISO	SCL	12	SCL	I2C Clock
	NC	6	MOSI	SDA	11	SDA	I2C Data
Power Supply	3.3V	7	3.3V	5V	10	5V	Power Supply
Ground	GND	8	GND	GND	9	GND	Ground

Onboard settings and indicators

Maximum Ratings (Limiting Conditions)

Software Support

We provide a library for the Clock Gen 3 Click on our LibStock page, as well as a demo application (example), developed using MikroElektronika compilers. The demo can run on all the main MikroElektronika development boards.

Library Description

The library contains basic functions for working with Clock Generator 3 click.

Key functions:

• void clockgen3_set_freq( float freq ) - Sets Frequency
• void clockgen3_config( uint8_t cfg ) - Configuration

Examples description

The application is composed of three sections :

• System Initialization - Initializes I2C module and set GS pin as OUTPUT
• Application Initialization - Initializes driver init and configuration Clock Generator click
• Application Task - Adjusts different frequencies every 3000ms.

void application_task ( )
{
    mikrobus_logWrite( ">> Set Freq = 12.000 MHz", _LOG_LINE );
    clockgen3_set_freq( 12000.0 );
    Delay_ms( 3000 );
    mikrobus_logWrite( ">> Set Freq = 8.000 MHz", _LOG_LINE );
    clockgen3_set_freq( 8000.0 );
    Delay_ms( 3000 );
    mikrobus_logWrite( ">> Set Freq = 5.500 MHz", _LOG_LINE );
    clockgen3_set_freq( 5500.0 );
    Delay_ms( 3000 );
    mikrobus_logWrite( ">> Set Freq = 2.700 MHz", _LOG_LINE );
    clockgen3_set_freq( 2700.0 );
    Delay_ms( 3000 );
    mikrobus_logWrite( ">> Set Freq = 800 KHz", _LOG_LINE );
    clockgen3_set_freq( 800.0 );
    Delay_ms( 3000 );
    mikrobus_logWrite( ">> Set Freq = 200 KHz", _LOG_LINE );
    clockgen3_set_freq( 200.0 );
    Delay_ms( 3000 );
    mikrobus_logWrite( "----------------------------", _LOG_LINE );
}

The full application code, and ready to use projects can be found on our LibStock page.

Other mikroE Libraries used in the example:

• I2C library
• Conversions Library
• UART Library

Additional notes and informations

Depending on the development board you are using, you may need USB UART click, USB UART 2 click or RS232 click to connect to your PC, for development systems with no UART to USB interface available on the board. The terminal available in all MikroElektronika compilers, or any other terminal application of your choice, can be used to read the message.

mikroSDK

This Click board™ is supported with mikroSDK - MikroElektronika Software Development Kit. To ensure proper operation of mikroSDK compliant Click board™ demo applications, mikroSDK should be downloaded from the LibStock and installed for the compiler you are using.

For more information about mikroSDK, visit the official page.

Resources

Downloads