Digital Isolators, what is Isolated Power?

Hello all,

May I ask what this feature is/does? The LTM2884CY-PBF is out of stock and I am looking for alternatives and wanted to know if this is a “must have”. I found this IC and it seems to work well with our application but does not have the Isolated Power feature: ADUM4160BRIZ-RL.

Please let me know what you think!

Thank you.


Hi entechbob,

If you are asking what the “Isolated Power” feature is, it means that it can pass power from the Host side to the Device side across an isolated barrier. This allows one to power isolated devices from the host without having to provide a separate power supply for the device.

Essentially, the LTM2884CY#PBF is a single-device interface providing both power and USB communication across an isolated barrier to an end device.

The ADUM4160BRIZ-RL provides an isolated USB interface, but it does not provide power across that barrier, so each side will require its own supply. You can make something functionally equivalent to the LTM2884CY#PBF by designing in both the ADUM4160BRIZ-RL and a separate isolated power supply. We can help you select such a device, if interested.

The most similar item we have in stock is the NMUSB202MC-R7. It is functionally very similar, but the board layout is not the same, and the height is significantly taller (14.5mm vs. 5.2mm).

So, if your device side (downstream side) does not have its own supply, you need to provide that either with an integrated device (isolated power and USB communication) or with a separate supply.

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Hello David_1528,

Thank you, this is good information and explains it well!

This NMUSB202MC-R7 looks good! Is the board layout and pin layout the same thing? This one says Voltage-Isolation 3000VAC, does that equal 2100Vrms? My hope is that I drop this in and retrace the pcb and it works similar if not the same as the LTM2884CY-PBF.

I am also interested to see how difficult it would be to configure the ADUM4160BRIZ-RL and a separate isolated power supply as we have already ordered samples to test.

Thank you for your help!


Hi entechbob,

Board layout includes pin layout, but may also affect dimensions of the layout, including gaps in the board for the isolation barrier. I have not looked at the differences there yet, as I was only considering functional comparison.

Regarding voltage, when one specifies AC voltage, there is generally an assumption of RMS, so it is 3000Vrms.

An important difference between the LTM2884 and the NMUSB202MC is that the LTM2884 can be powered from anywhere between 4.4V and 16.5V, whereas the NMUSB202MC must be powered by 4.5V to 5.5V (the standard USB voltage). If your system provided a higher voltage (which allows for higher power delivery across the isolation barrier) then you would need to alter your power source to drop it to 5V for the NMUSB202MC.

Additionally, the LTM2884 has a couple of low-power 3.3V outputs (one on the host side {Vlo1} and one on the device side {Vlo2}) which can be used for auxiliary functions. If your original design used either of those pins, then you would have to find another way to provide these features.

Finally, the LTM2884 has a “Suspend Power” pin and an “ON” pin, which either turn off the DC/DC converter (suspend power) or disable the power and communication through the isolation barrier (not “ON”), respectively. The NMUSB202MC does not have these features, so if used in your original design, one would either lose these features (which would use more power in idle state), or you would have to figure out a work-around with external circuitry to accomplish similar functionality.

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Thank you for such a detailed response, sorry it has taken so long to get back to you!

I have ordered samples of the NMUSB202MC because the wider voltage range on the LTM2884 is not a must have. At least for now! Also, our original design does not take advantage of the other features, but I will keep these in mind!

As of now, I have the samples of the ADUM4160 and have gotten it to work, however, we have learned we do need the Isolated Power feature or a separate isolated power supply. Before you had mentioned you had a few devices in mind for such a task, may I ask for your recommendation?

Thank you!



Just as an update:

I have gotten samples of these ICs

Hopefully, one of these compliments the ADUM4160 - please let me know what you think.

Thank you,


Hi Entechbob,

The LTM2884 produces a 5V isolated supply at up to either 500mA or 200mA, depending on whether you power it with ≥ 8.6V or 5V, respectively.

If you only power the primary side with 5V, then any of these would be reasonable candidates. Any of these will take a 5V input and give an isolated 5V output with at least 200mA of current. Differences include form-factors, isolation voltage (all of these are ≥ 3kV), ripple voltage, max output current, efficiency, temperature ratings, and additional optional features.

If you want one which can take a higher input voltage (18V or more) and output 5V with at least 500mA, then these are some options. Variations are similar to those above.

Finally, here are a few more if you are supplying right around 12V on the primary side.

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Sorry, just saw your post. First glance looks like each of those should work, though only the PRM3W-E12-S5-S can handle the wider full input range of the LTM2884.

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Again, thank you so much for such a detailed answer. I just tested this ITR0305S05 and it is all good!

I really appreciate your time helping me with this, thank you and take care until the next time!