ISO1228: Verification of Rthr Resistor Values for ISO1228 Digital Isolator.

Hardware Team

Part Number: ISO1228

Dear Technical Support Team,

I am currently working with the ISO1228 digital isolation device and would like to confirm whether our chosen external resistor values are appropriate for safe and reliable operation.

Our configuration is as follows:

Rsource: 1 k ohm

Rlim: 0 ohm

Rthr: 180 ohm

Additional series resistor: 430 ohm(connected across the common line)

Input voltage: 12 V for all four input channels

I would like to request your guidance on the following points:

Are these resistor values acceptable for proper and safe operation of the ISO1228 device?

Will operating the device with these resistor values affect the long-term reliability or life expectancy of the IC?

9 months ago

0 Andrew J 9 months ago

TI__Mastermind 34580 points

Hello,

Thank you for reaching out. At first glance the parameters look good, however, this would be easier to confirm if you could provide a drawing or schematic of the applications input side.

8.2.4.1.2 Voltage Thresholds shows the details to calculate if the design will reach your desired thresholds. We also provide an excel calculation tool at ISO1228-CALC Calculation tool | TI.com

Best,
Andrew

0 Hardware Team 9 months ago in reply to Andrew J

Prodigy 10 points

Hello,
I’ve attached my block diagram and schematic for your review. Please let me know if everything appears correct or if any adjustments are needed.
Thank you.

0 Andrew J 9 months ago in reply to Hardware Team

TI__Mastermind 34580 points

Hi, Thank you for sending schematics. Please allow me a day to review and get back to you.

0 Andrew J 9 months ago in reply to Andrew J

TI__Mastermind 34580 points

Hello,

Thank you for including the schematics. The above diagram should work.

Please note that for the current limit feature needs an RPAR at each input channel to properly limit the current. The current design should be okay, however, the ISO1228 input will scale linearly (no current limit) without an RPAR.

Best,
Andrew

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ISO1228: Verification of Rthr Resistor Values for ISO1228 Digital Isolator.