Clock Gen 3 Click features a low power self-contained digital frequency source providing a precision frequency from 1kHz to 68MHz, set through a serial port. This Click board™, an I2C configurable clock generator, features the LTC6904 from Analog Devices and requires no external components other than a power supply bypass capacitor, and it operates over a single wide supply voltage range of 2.7V to 5.5V. The LTC6904 features a proprietary feedback loop that linearizes the relationship between digital control settings and frequency. It has many features that make it attractive for various applications such as a microcontroller clock source, clock source for a switched capacitor filter, or general replacement for a DAC/VCO combination.
Clock Gen 3 Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.
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 peripheral address and it can be selected by an onboard SMD jumper labeled as ADD SEL allowing selection of the peripheral 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.
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