Clock Gen 3 Click Board

How Does The Clock Gen 3 Click Board™ Work?

The Clock Gen 3 Click Board™ 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 Board™ 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.

The Clock Gen 3 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 the Clock Gen 3 Click Board™ 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)