This is an assembly guide for Analog Devices ADuM4160-based full/low speed.
USB Isolator kits, released in October 2009, have been popular among PC-based test instrument users, software-defined radio operators, and DIY audio builders, to name a few. It is a reliable and quite affordable way to provide galvanic isolation between the host PC and USB peripheral.
In this manual, we’ll give you a walkthrough of the best Adum4160 USB Isolator Kits and give step-by-step instructions on building a USB isolator kit and also talk about tweaking and modifying the circuit for certain applications.
Top 7 Adum4160 USB Isolator Assembly on Amazon
Both “Isolator Only” and “Full” Kits are covered.
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Adum4160 USB Isolator Assembly Guide
|When the parts kit arrives in the mail, it usually looks like one on Photo 1 (click on it to make it bigger). Parts are in the lower compartment, PCB – in the middle of the bag, and connectors are on the top.|
“Full Kit” on the right contains more parts, as well as one extra connector. No matter which kit you are building, dealing with small unmarked parts is inevitable. These parts are also lightweight so sneezing into a pile of parts is not recommended.
Some parts are mounted on a tape – it is a generally good idea to keep them this way until the moment you are ready to solder them.
The easiest way to get parts out of the bag is to cut the bag along the long edge with scissors. Connectors can stay in the bag for now. For the next several steps, a pair of tweezers and a magnifier glass will be helpful.
|Photo 1. USB Isolator Kits|
|Photo 2 shows small parts of the kit. Again, the “Isolator Only” set is on the left aligned in a single column. Two columns on the right are the “Full” set. Here is the list: 1. A pair of 0.1″ headers with 2 pin jumpers.|
Used to program USB speed on both sides of the isolators. They will be soldered very late in the build, together with connectors – for now, it’s best to put them away.2. Analog devises ADuM4160 IC, the heart of the circuit.
Wide 16-pin SOIC package, clearly marked on the top. Usually comes on a tape, but may be packaged differently, for example, in a piece of IC “tube”. This is the largest of small parts, you won’t miss it.3. 1MOhm 1206 resistors.
Three on a tape, marked “105″ (or “501″ if you are holding it upside down) on top. Usually black in color, but may also be blue.4. 24Ohm 1206 resistors. Four on a tape, marked “240″, “24R0″, or similar. Usually black in color, but may also be blue.5. 0.1uF 1206 ceramic capacitors.
Four on a tape in the “Isolator Only” set, five in the “Full” set. Tan in color, no markings. Very hard to distinguish from number 6 in the “Full” set, the only way to avoid mix-ups is to keep them separated. The rest of the parts are present only in the “Full” kit.M
ost of them have distinctive shapes and are therefore easily identifiable, but beware of the number 6! 6. 3300pF 1206 ceramic capacitor. One on a tape. Tan in color, no markings.
Very hard to distinguish from number 5, the only way to avoid mix-up is to keep them separated.7. Linear Technology LT1376-5 buck controller IC. SO-8 package, marked on top. Usually comes in a piece of IC tube.8. 6-10uH inductor, Sumida CDRH5D18 or similar. May be marked differently.9. 1N4148 diode.
The stripe on the case marks a negative pin.10. MBRS130 diode. The stripe on the case marks a negative pin.11. Tantalum low-ESP input capacitor. Marked with 2 numbers, first indicating capacitance, second-rated voltage. In the picture, 22-35 means 22uF, 35V.
The stripe on the case marks a positive pin. D-size package, usually black but may be tan, like number 12. To distinguish between them, read the second number, which indicates voltage. The input capacitor is usually rated to 35V, output – only to 10V.
Also, the capacitance value of the input cap is around 20uF, whereas the output cap has 68-100uF.12. Tantalum low-ESP output capacitor. Marked with 2 numbers, first indicating capacitance, second-rated voltage. In the picture, 686 means 68uF, and 10 means 10V.
The stripe on the case marks a positive pin. D-size package, usually tan but may be black, like number 11. To distinguish between them, see the description for number 11.
|Photo 2. USB Isolator Kit Parts|
The kit has been designed for easy assembly. Parts are big enough to be placed without the aid of a a microscope and soldered by hand. If you are unfamiliar with SMT soldering, watch this excellent SMT Soldering 101 video by Curious Inventor.
Don’t be scared – the parts you will be dealing with are quite a bit bigger. Nevertheless, be extra careful with multi-pin parts placement – once 3 pins of a part are soldered to PCB, fixing misalignment becomes very difficult.
I’m using ordinary temperature-controlled soldering iron, similar to the one used in the video above. A flux pen or a bottle of liquid flux (which is really rosin diluted in alcohol) and a brush is also necessary – the secret of successful SMT soldering is generous flux application.
Solder wick is helpful when too much solder was applied accidentally. A pair of good tweezers is very helpful. Boom-mounted lighted magnifier is nice to have but optional.
|Step 1. The first piece to solder is ADuM4160. Photo 3a shows the correct placement – a notch on the case is facing the power supply side of the PCB. Photo 3b shows pins aligned to pads and a corner pin soldered.|
If after making this joint pins become misaligned, heat the solder joint, melt the solder, and re-align the part. When everything is good, turn PCB around, check alignment, solder another corner pin, and check alignment again – if misaligned, heat up the joint and re-align.
When alignment is good, continue soldering the remaining pins on this side (Photo 3c), then turn PCB around and finish another side.
When all pins are soldered, run a dental pick or X-Acto knife between pins to check for bridges and then inspect your work under a magnifier. Photo 3d shows the final result. A couple of pins on this picture hold a little bit too much solder, however, there are no bridges so they can be left alone.
|Photo 3. Soldering ADuM4160|
|Step 2 (“Full” kit only). If you are building a “Full” kit, it’s now time to mount LT1376 IC. “Isolator only” builders please skip stepping 3. |
The soldering technique is similar to Step 1 – align, solder a corner pin, check alignment, solder second corner pin, check alignment again, solder remaining pins, and finally inspect for bridges with a dental pick and magnifier glass.
Photo 4 shows LT1376 mounted on the board in the proper orientation. This IC doesn’t have a notch; instead, it has a small taper on the lower (on the photo) edge of the package. Don’t use package markings for reference – they can be printed upside down.
|Photo 4. Soldering LT1376|
|Step 3. In this step, I will be soldering 24 Ohm resistors. Four of them need to be placed on both sides of ADuM4160 IC. Photo 5a shows where they need to go – I placed little red asterisks to the left of each place to make it easier to find in the photo. |
Before making the shots, I cleaned up flux residue from the PCB with 99% IPA AKA rubbing alcohol using an old toothbrush. It’s not really necessary during assembly unless the generous application of flux makes it difficult to recognize part positions.
You may also notice that I wiped off extra solder from ADuM4160 pins with solder wick. Soldering 1206 resistors are much easier than SO packages ( ADuM4160 and LT1376 ). The part has only 2 pads to solder and at the same time big enough to handle with a pair of decent tweezers.
All that is necessary is to apply flux to the pads, then add a small amount of solder to one pad, apply more flux, place the part, melt the solder while holding the part in place, check alignment and then solder the other pad.
The key to success here is the correct amount of solder – this amount shall be small. Also, the first pad is somewhat harder to do than a second, therefore when deciding which one to start with, pick one which has more empty space around – as you can see in Photo 5a, I picked pads facing away from ADuM4160. Photo 5b shows a closeup of two pads with the correct amount of solder applied.
Photo 5c shows a pair of resistors with one side soldered. Don’t forget the second pair on the other side of ADuM4160 and then solder the other sides of all 4 resistors. Don’t forget to apply flux from time to time. Photo 5d shows the final result.
|Photo 5. 24 Ohm resistors|
|Step 4. Next, I will be placing 1M 1206 resistors. Using the technique described in the previous step, place 2 resistors next to speed selector jumpers and one next to ADuM4160, as depicted in Photo 6.||Photo 6. 1M resistors placement|
|Step 5. Four 0.1uF 1206 capacitors are placed on both sides of ADuM4160. If you are building a “Full” kit, the fifth cap goes next to LT1376. On Photo 7, 4 caps around ADuM4160 are marked with asterisks, and the fifth one is marked with the number “5″. |
After finishing this step, builders of the “Isolator Only” kit may skip to Step 15, where connector placement is shown.
|Photo 7. 0.1uF capacitors placement|
|Step 6 (“Full” kit only). Sumida CDRH5D18 inductor goes next. This part has a lot of thermal capacity so if you can, bump your soldering iron temperature a little. |
First of all, flip the part around and take a look at the pads. Even though the inductor is non-polar, there is a way to solder it incorrectly by placing inductors’ pads across PCB pads.
Don’t make this mistake – if you do, de-soldering would be a pain. Second, it is very hard to attach the whole pad to the PCB with a soldering iron – the part is basically a piece of iron and has a large thermal capacity; in addition, pads tend to separate from the case if you overheat it.
The easiest way to mount this inductor is to solder two opposite corners, where inductor wire is attached to the pad. Two asterisks on Photo 8 are marking soldering points.
|Photo 8. Inductor placement|
|Step 7 (“Full” kit only). MBRS130 Shottky diode is polar – it has a stripe on its package indicating a negative terminal. Photo 9 shows the correct orientation with an asterisk placed next to the negative terminal. |
You may also note a solder bridge from this terminal to the adjacent capacitor – this is normal. If you get one while soldering this part – don’t worry, there is an actual trace below it.
|Photo 9. MBRS130 placement|
|Step 8 (“Full” kit only). 1N4148 diode is also polar – see Photo 10 for correct placement.||Photo 10. 1N4148 Placement|
|Step 9 (“Full” kit only). 3300pF capacitor, non-polar, accessible from either end (see Photo 11). You won’t have any trouble soldering it.||Photo 11. 3300pF capacitor placement|
|Step 10 (“Full” kit only). Last step on this side of the board – placing input and output capacitors. |
Tantalum caps are polar and have familiar stripes on their packages; however, unlike diodes, the stripe marks a positive terminal. Photo 12 shows correct placement with asterisks placed close to positive terminals.
|Photo 12. Input and output capacitor placement|
|Step 11 (both kits). In the previous step, we mounted the last SMD piece. We now need to solder several thru-hole parts. Photo 13 shows speed selector jumpers placement.||Photo 13. Speed selector jumpers placement|
|Step 12 (both kits). Two USB connectors go next. This completed the build for “Isolator Only” builders. To complete the “Full” build, one last step is necessary.||Photo 14. USB Connectors|
|Last step(“Full kit” only). Barrel power connector. This concludes the build.||Photo 16. Barrel Connector|
|Testing the isolator||After the board is built, it’s a good idea to wash it in 99% IPA and check for power-to-ground shorts. Don’t forget to install speed selector jumpers – they have to be set to the same speed on both sides of the isolator. |
Unless you need to isolate low-speed devices, such as a keyboard or mouse, set them to Full speed. If you have built a Full kit, you need to find a suitable wall wart. The power supply accepts a wide range of input voltages; it is important to have a positive supply on the center contact of the power supply’s barrel connector.
A PC and some USB devices are also necessary to test the isolator, a USB cable or two may come in handy as well. I usually use a USB flash disk with a large archive on it.
When the disk gets detected by OS, I run “Archive check”, generating a lot of traffic while archiving program performs the integrity check of data passing through the isolator. The picture on the left shows my test setup.
For best results, connect them in the following order: power first, then host, then peripheral. If your peripheral is not detected or the PC gives detection errors, reconnect it while leaving power and host connected.“Isolator Only” kit has many more powering options.
Please refer to the “Tweaking” section for some ideas. The testing procedure is similar. What to do if the circuit doesn’t work? Checking everything with an ohmmeter is a good idea. Also, very common detection error issues, as well as ways to remedy them, are described in this article.
USB isolator breaks the galvanic connection between USB host and peripheral. Among other things, this means whatever power and ground noise that exists on one side won’t affect the other.
In many cases, the source of noise is the PC power supply, however, I heard about noisy peripherals too. One of my customers has a stage lights controller connected to his laptop adding interference to music playing from the laptop’s audio port – the issue was remedied with a USB isolator.
In many cases, isolating peripheral from PC ground reduces noise to undetectable levels. However, for very sensitive equipment, such as USB oscilloscopes, extra steps must be taken to ensure signal integrity.
The photo on the left shows 1KHz analog calibrator waveforms displayed on Bitscope 310 USB DSO. Signal amplitude from top to bottom changes from 4V to 400mV to 40mV to 4mV p-p.
The left column shows the waveform with the USB port of the instrument isolated, right column waveforms were obtained with the instrument directly connected to the same USB port of the same PC.
The results can be easily interpreted – while the 4V signal looks pretty much the same on both pictures, smaller signals show more and more noise, and the 4mV signal on a directly connected Bitscope is hard to interpret, let alone measure.
The photo on the right shows the arrangement. In order to reduce interference to the minimum, the isolator is powered by the oscilloscope’s 5V regulated power supply. Also, the peripheral cable is kept as short as possible.
I recommend using a similar arrangement for high-end audio applications – to obtain the best results, don’t use the isolator’s own power supply, use the power supply of the peripheral, a battery, or a super clean power source made for audio.
If you don’t have the power supply on your isolator board, the standard way to power the peripheral side is to connect +5V to “Vbus” pad and ground to “Agnd” pad. As you can see in the previous picture, it is also possible to use a barrel connector ( not included in the “Isolator Only” kit, available in the store ) by running a wire from “Vin” to “Vbus”.
It is also possible to power the isolator from a 3.3V supply by connecting it directly to “VDD2″ pin of ADum4160 (it’s more convenient to solder a supply wire to a capacitor connected to this pin).
It is also possible to bypass the power supply. The “Shdn” (as in shutdown) pad is provided for this purpose. By connecting “Shdn” to the ground LT1376 turns off completely. The photo on the left shows the wiring with an asterisk placed near the jumper from “Shdn” to “Agnd”.
Optionally, you can run a wire from “Vin” to “Vbus” to use a barrel connector – make sure you use a 5V supply in this case! There is also a way to build a linear power supply on the board.
USB isolator kit from Circuits At Home is an inexpensive and handy addition to PC-based measurement instruments, software-based radio, or computer feed for audio devices.
Building the kit is easy. If you are having trouble building yours, please let me know!
FAQs About Assembling Adum4160 USB Isolator Kits
How does a USB isolator work?
This USB isolator separates your computer’s data lines and power supply, fully protecting your USB devices and data signals from electrical noise, high voltage spikes, surges, and ground loops for up to 3000V, which could otherwise damage your equipment.
What are USB isolators?
A USB Isolator is a device that prevents computer noise from reaching USB equipment connected to a PC. This is especially relevant when using noise-sensitive audio devices like USB Digital-to-Analog Converters (DACs) and USB-to-S/PDIF converters (DDCs).
Are USB ports isolated?
USB is a popular PC interface due to its widespread industry support and simple structure (only four wires in a USB cable). It is simple to electrically isolate a USB controller that connects to your embedded system via the SPI interface. The SPI interface operates at any speed and is made up of simple, unidirectional signals.