ADUM1250 bi-dir isolator

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Hi,

 

i have an eeprom on my PCB that i wished to additionally protect, so i put it in isolated circuit. So i added a isoalted DC/DC 3.3V to 3.3V converter (1W), and a ADUM1250 bidirectional isolator to isolate i2c communication and i have pull up resistor on both side of i2c. I checked i2c on the primary side (the left side which has MCU on) with osciloscope, and the I2C signal gets sent, but nothing comes out on the secodanry side of ADUM. If i remove ADUM isolator and just brick connections with wire, the i2c on eeprom works. But with ADUM isoaltor, nothing gets through. Could it be that ADUM is damaged or is tehre something else im missing (i always use full ESD protection when handling components and sodlering).

 

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Last Edited: Mon. May 11, 2020 - 09:05 AM
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Do you have pull-ups on the input side? And decoupling on the power rails.

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Last Edited: Mon. May 11, 2020 - 08:32 AM
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I don't see how the ADUM1250 will protect your eeprom - it will isolate it though.

C19 is drawn backwards. 

Have you verified all of your connections and that you are getting the correct voltages? Some of the little isolated converters have a very noisy output - have you checked this?

 

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Show the mystery secondary supply & its hookup  to everything.  Do you get the volts from it?

 

how much are your pullups?

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Last Edited: Mon. May 11, 2020 - 08:50 AM
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Klemko wrote:
i wished to additionally protect

"Protect" from what, exactly?

 

Rather than link to a distributor, it's generally best to go direct to the manufacturer's site for the datasheet - and other supporting materials:

 

https://www.analog.com/en/products/adum1250.html

 

Have you checked against the application notes, examples, reference designs, etc there?

 

For specific discussions about the Analog Devices part, go to the Analog Devices forums; eg,

 

https://www.analog.com/en/products/adum1250.html#product-discussions

 

EDIT

 

Have you read the bit in the datasheet which tells you about the differences between "Side 1" and "Side 2" ... ?

 

 

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Last Edited: Mon. May 11, 2020 - 09:10 AM
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Yes there are all neccesery pullups(4.7k) and decoupling capacitors on power lines. Protect from overvoltage(up to 1kV) on the primary side. There are sensitive data saved on eeprom, that need to be available even if there is 230VAC short on primary side. I discovered problem. I used DC/DC converter from XP Power, IE0303S, and even thought this one is supposed to be 3.3V output according to datasheet, its actuialy a 5.1V output. I removed it and add teh ADUM back int ocircuit and bricked primary 3.3V and GND to secondary 3.3V_s and GND_s and now it works. So i need t ofind a better DC/DC converter. 

Thanks fortips.

 

Below is diagram with additional DC/DC, for clarification. Al lthe capacitors are ceramic, so no need to worry about orientation.

Last Edited: Mon. May 11, 2020 - 09:08 AM
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Yes, it was converters fault. The output was 5.1V instead of 3.3V according to datasheet.

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Klemko wrote:
Al lthe capacitors are ceramic, so no need to worry about orientation.

Sure, but choose a unipolar capacitor symbol and do the reader of your schematics a favour.

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Those power supply specs sound kinda crummy (my comment in # 4 was why I was wondering)

 

Load Regulation • 10% for a 20-100% load change(5) (3.3 V models ±20%) Setpoint Accuracy • ±3%

 

Not that you have a load variation, but that implies the overall accuracy is poor

 

5. Operation at no load will not damage unit but it may not meet all specifications.

Since it is a 300 ma supply, you may be considered close to "no load"

 

Maybe there is a better one that is still cheap.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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These isolated converters tend to be rather cheap 'n' cheerful. Some brands are better than others. One gotcha is that they tend to couple the switching frequency across to the load side due to the transformer winding capacitance - this can find its way back home through weird and wonderful paths causing much mayhem along the way.

 

For example - similar spec converters from pduke and xp power. the xp frequency was around 300kHz and the transformer design must've been better as the coupled energy was much lower. THe pduke was around 120kHz. Different enough that the EMC tests needed to be redone. Apart from that, they were functionally identical.

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Also--Did you find, or notice, there is a version (ADM3260) that has the isolated power supply built in?  It has some limited capability for powering external stuff too (pin VISO)

It looks like it costs about  $1.10 more @ 1000   ...might be worth a look.

 

https://www.analog.com/media/en/technical-documentation/data-sheets/ADM3260.pdf

 

VISO Secondary Supply Voltage Output for Digital Isolator Isolated Side Power and External Loads. The output voltage is adjustable from 3.15 V to 5.25 V.

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Last Edited: Tue. May 12, 2020 - 02:17 AM
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Kartman wrote:
These isolated converters tend to be rather cheap 'n' cheerful

 

Royer oscillators are fun to ponder there should be an educational kit for kids. However, I can only frown on there use as they drive the core into saturation, sort of like putting a quick but frequent short on the power supply (300k crowbars per second). One of the past outfits I worked at made truckloads of the things. The so-called current fed models cost more, and few sold.

 

https://en.wikipedia.org/wiki/Royer_oscillator

 

 

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Last Edited: Tue. May 12, 2020 - 03:36 AM