Isolated Power for the Gigaspeed Realm: Designing with the ADN462x Family

We glimpsed just how many factors are at play when selecting a digital isolation solution for your gigaspeed application in the first blog of this Gigaspeed Isolation series. The first step is knowing what considerations to make when choosing an isolated gigaspeed LVDS device—but what’s next?

We concluded that a robust design calls for much more than just the right level of isolation; it must also optimize for size, power, and signal integrity. This post will consider isolated power solutions for designs using the ADN462x family of 2.5Gbps LVDS devices.
 

Gigaspeed Isolated LVDS: Why Choose ADN462x?

Although there are traditional solutions that support the isolation of gigaspeed digital signals, such as optical fiber or serializer/deserializer (SerDes) circuits, these can be bulky or add unwanted complexity to a design.

The gigaspeed LVDS isolation ADN462x devices overcome many of these challenges, offering different levels of isolation and robustness. Depending on the application requirements, you may require functional, basic or reinforced isolation.

Learn more about the different types of isolation in this article.
 

Considerations When Selecting a Power Solution

Even if you restrict your search to only Analog Devices, Inc. (ADI), you’ll find a wide variety of isolated power solutions available. With options for robustness, efficiency, integrated features and package formats, that support space saving footprints, and different levels of creepage and clearance—how’s a designer to choose?

Your power solution selection should depend on a holistic view of the design requirements, which may include some of the following:

• Output voltage range
• Output power
• Efficiency
• Temperature rating
• Package size, creepage, and clearance
• Isolated voltage (Viso)
• Working voltage (Viowm)
• Integrated features that improve output accuracy

Understanding the overall requirements is a bigger blog that we’ll go into depth on soon, but here we will just focus on the isolation of HDMI 1.3a.
 

Power for Gigaspeed Applications in Digital Healthcare

HDMI display output for patient care equipment is one application that utilizes the ADN4624 2.5Gbps LVDS isolator. In digital healthcare, isolation is usually needed between a display and the source equipment to ensure safety of the both the patient and the medical attendant. HDMI signals are in the gigaspeed realm, which makes the ADN4624 an excellent choice.
 

Figure 1: Technical diagram of an HDMI 1.3a isolated design

Figure 1 shows the different building blocks for an HDMI 1.3a isolated design. You can see the ADN4624 2.5Gbps isolated at the core, which requires a 1.8V supply for operation. From the high-level block diagram, we can see that the power delivery to the primary side of the isolation barrier is 5V, delivered through the USB-C connector.

In addition to this 5V supply there is also a requirement for 3.3V and 1.8V as shown. As an example these voltage levels can be delivered through the ADP1707 a highly stable and accurate linear dropout regulator. Sufficient power must also be delivered to the circuity located on the secondary side.

Finally, the HDMI 1.3a protocol consists of various other signals that also need to be isolated, as seen in Figure 2.

Figure 2: Table of signals needing isolation in a typical HDMI 1.3 digital healthcare implementation
 

Powering HDMI 1.3 with ADuM4070

ADuM4070 meets all the above requirements while maintaining galvanic isolation. This is a 2.5W regulated DC-to-DC isolated power supply controller with an internal MOSFET driver combined with an external push-pull transformer. ADuM4070 has a built-in pulse width modulation (PWM) feedback feature with compensation, making it an ideal solution where output voltage stability and high efficiency is required.

Come back next month to dive into LTspice and other ADI simulation tools, which can support and expedite your design process for isolated gigaspeed signals.