ISO1228: Sink/source , output format

Hello Alex, 

The ISO1228 cannot change the output of a source type input. This is because the active state of a source type input is a short to GND. The MCU will need to invert the source mode logic internally the other truth table is needed. 

Best,
Andrew

hi Andrew

Iso1228 provide the I/O & SPI to monitor the DI input,

old design is use the MCU ,I/O to detect the DI input,

could the ISO1228 Use the same method? 

I use the MCU I/O to detect the source/ sink by ISO1228 I/O output without the SPI

Thanks?

HI Andrew

i need a solution ,how to use the MCU I/O to detect ISO1228 whenever is Source or SINK mode,thanks

please advise, thanks

Hello Alex,

There is no way for ISO1228 to differentiate between the SINK and SOURCE modes from the MCU side. An external isolation circuit would have to be implemented in order to differentiate between the two modes.  The sink source EVM would be the best layout to identify switch between both configurations (https://www.ti.com/tool/ISO1228EVM).

Why does the customer need to identify which mode the input is being used in? The OUTx pins will match the desired truth table shown in the initial post. 

To identify whether the inputs are in sink or source mode consider the following: ISOM8110 would be characteristically similar to 150060VS75000 (the green LEDs) so it is possible to use ISOM8110 to indicate when a sink or source mode input is active. This can be done either by replacing D15 and D14 in the schematic or one of the green LEDs (depopulated on the ISOM1228EVM) with an ISOM8110 footprint in your design. 

Best,
Andrew

hi Andrew

Due to old design is used the opto to detect the sink or source, and MCU to detect the Output of opto.

So, they don't want to change more,

they hope the iso1228 can follow old protocol as below

IN sink mode

input open, ISO1228 output low

input short, ISO1228 output high

IN source mode

input open, ISO1228 output low

input short, ISO1228 output high

thanks

Hi Alex

But our experimental results are not like that.

The two pictures below are in source mode; the black switch circle on the left represents an open circuit, yet the multimeter measures the OUTPUT as High.The black switch with a single line on the left represents a short circuit, yet the multimeter measures the OUTPUT as Low.

We followed the datasheet’s recommended wiring for SOURCE mode and used the ISO1228DFBEVM for testing.

Hello Ray, 

This behavior is likely due to the ISO1228DFBEVM. This EVM is the SINK mode EVM. By default, there LEDs on that EVM only support the SINK direction. Each LED needs to be turned around to be operating in SOURCE mode. The logic may be reversed because of some missed connection. 

The other ISO1228 EVM - ISO1228EVM - will support SINK and SOURCE mode configurations by providing 2 diodes (one for each direction) on the LEDx pins. 

Please include a schematic/diagram showing how you are connecting the switch, power supply and EVM. 

Hi Andrew

Below is the connection diagram. The secondary side follows the EVM’s default configuration without any circuit modifications.

Hi Andrew

I removed the switch and directly shorted the original switch connection points, but the test result still shows LOW; after removing the shorting wire, the output shows HIGH.

Thanks

Hello Ryan, 

I have tested this my self our lab just as a sanity check. OUTx remains 0V on the VCC2 side when the input terminal is open.

• In SINK mode (V1 = FGND and V2 = 24V), a short from IN1 to 24V delivers a HIGH at OUTx. 
• In SOURCE mode (V1 = 24V and V2 = FGND), a short from IN1 to 0V (or FGND) delivers a HIGH at OUTx. 

In both cases OUTx is a HIGH when INx is shorted with a wire to the intended state. The ISO1228EVM - which is sink/source mode capable - was used to test. 

Best,
Andrew

Hi Andrew

Can you provide your wiring circuit?

Thanks

Hi Ray,

Please give Andrew an additional day to respond.

Regards,
Aaditya

Hi Andrew

I have another question. Currently, we are using the ISO1228EVM to plan the circuit. We would like to define the external connection pin define for the power side V1 and V2 as fixed 24V and 0V for the customer, so that the customer does not need to reverse the input power when using SOURCE mode. Do you have any recommended circuit for this approach?

Or, do you know if there are commonly used labeling terms on machine enclosures to indicate that this terminal should be connected to positive or negative depending on the situation?

Hi Ryan, 

As you have noticed, the above EVM uses a bridge rectifier to ensure the voltage on AVCC is always 24V and AVSS is always 0V. The EVM connects all LEDx pins through diodes to V1. This configuration makes testing with the ISO1228 easier since a switch could be wired from INx to V1 for normal operation in both SINK or SOURCE mode, and only the V1 and V2 connections would be flipped to when changing modes. 

The bridge rectifier also prevents the possibility of reverse wiring and ISO1228 will not be damaged if V1 and V2 are flipped. It would just be in the other mode. Terminology such as FGND, COM1 and COM2 are typical names for these applications. 

Best,
Andrew

Hi Andrew

Thank you for your reply. I have another question to ask.

According to the "Device Functional Modes" in the datasheet, when (INx) = High, (OUT_EN) = High, (OUTx) = High.
Is this condition also the same in source mode?

Because when measuring in source mode with a voltmeter, the result (as shown in the figure) does not match what is written in the datasheet.

Could it be that I measured at the wrong test point? Or is 3.3V already considered as High?

Thanks.

Hi Ray. 

The voltmeter should be measuring from the input screw terminal to FGND. 

For clarity have added additional notes in the below table. Let me know if this is clear. 

Is the customer still seeing the reverse logic? Or do their results match the table above? 

Best,
Andrew

Hi Andrew

This explanation is clear, and our experiment results are consistent with what is described above.

Thanks