Key facts
- Brand
- Analog Devices
- Model
- ADN2812
- Industry
- Electronics
- Documents
- 4
- Languages
- EN
- Last added
- 2012-08-02
Start here
Analog Devices AN-746 ADN2812 FDDI Support Application Note
The document describes the limitations of the ADN2812's default 'lock to data' operating mode when supporting the FDDI connection protocol. Specifically, it details how non-random bit patterns in the FDDI PCM states (Break, Connect, Next) cause frequency acquisition issues because they lack sufficient transitions at the target 125 Mbps rate.
To resolve this, the note provides a solution using an external reference clock to place the ADN2812 into 'lock to REFCLK' mode. It explains that in this configuration, the device locks its VCO frequency to an external reference rather than relying on data transitions, ensuring stable synchronization through the FDDI initialization sequence.
Analog Devices ADN2812 specifications
| Data Rate | 12.3 Mb/s to 2.7 Gb/s |
|---|---|
| Operating Temperature Range | -40°C to +85°C |
| Supply Voltage | 3.3 V |
| Supply Current | 235 mA typical |
| Package | 5 mm x 5 mm 32-lead LFCSP |
| Jitter Generation (OC-48) | 0.002 UI rms |
Source: Analog Devices ADN2812 Datasheet
All Analog Devices ADN2812 documents by type
Ratings, dimensions and ordering codes, for selection and design work.
How to use the product for one specific task, with worked examples.
Questions answered in these manuals
Why does the ADN2812 fail to support FDDI in its default mode?
The default 'lock to data' mode cannot handle the non-random, repetitive bit patterns (consecutive Q, H, and I symbols) generated during FDDI PCM states, which lack transitions at 125 Mbps.
From: Analog Devices AN-746 ADN2812 FDDI Support Application Note
How is the ADN2812 configured to support FDDI?
It must be programmed into 'lock to REFCLK' mode using an external reference clock, typically a 125 MHz system clock.
From: Analog Devices AN-746 ADN2812 FDDI Support Application Note
Does the ADN2812 require a reference clock?
No, the device automatically locks to all data rates without the need for an external reference clock or programming.
What is the typical supply current?
The typical power supply current is 235 mA.
What data rates does the ADN2812 support?
It supports continuous data rates from 12.3 Mb/s up to 2.7 Gb/s.
From: Analog Devices ADN2812 Clock and Data Recovery IC Datasheet
What is the supply voltage range for the ADN2812?
The device operates from 3.0 V to 3.6 V, with a typical value of 3.3 V.
From: Analog Devices ADN2812 Clock and Data Recovery IC Datasheet