ISO1540: I2C Slave device connected After ISO1540D Isolator Device not Working

JEBIN K JOHN

Part Number: ISO1540
Other Parts Discussed in Thread: INA237, , TCA9803

I have a design with ISO1540 I2C isolator. Recently, during software testing, we have come across an issue of an INA237 I2C slave device connected after the bi directional I2C translator ISO1540D is inaccessible.

We have found 2 major issues

Acknowledgement is failing up on reading the slave connected after ISO1540D (I2C block diagram attached)
After a few reads of this particular slave. the total bus is inaccessible like all slave sare inaccessible
Frequency of operation is 100kHz & time gap between 2successive read operation of INA237 is very quick / almost zero time gap.

Please find more details regarding the hardware implementation

We have 2 boards connected through aB2B interconnect. Master FPGA is placed on board 1. ISO1540D & inaccessible INA237 is place on board 2
Side 2 of ISO1540D is pulled to 5V through 4.7k resistor in board 2
Side 1 of ISO1540D is the long I2C bus connected to master FPAG & is pulled to 3.3v through 4.7k resistor in board 1.
In between Master FPGA & ISO1540D there is an I2C buffer TCA9803& a B2B interconnect.

Could you please help share your thoughts on this

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over 2 years ago

0 Vikas Jeevannavar over 2 years ago

TI__Expert 3046 points

Hi Jebin,

Thanks for reaching out and sharing the issue in detail.

Few concerns on the INA237 connections with Isolated I2C transceivers. V_IL of INA237 is 0.4V while V_OL1 of ISO1540 is 0.8V. The data read from INA237 not be successful on the side 1 connections. Side 2 of ISO1540 has lower V_OL. Please refer to [FAQ] Why is the logic LOW level output voltage, VOL1, up to 0.8V on Side1 of the ISO1540/ISO1541 and ISO1640/ISO1641 bidirectional I2C isolators? - Isolation forum - Isolation - TI E2E support forums
Also, please confirm that pull-up resistors are connected on side 1 of ISO1540. The schematic has pull up resistor after the TCA9803. They are required on both sides of I2C for operations. Please refer to 8.2.2 Detailed Design Procedure in datasheet.
Please share the screenshot of the scope readings for better understanding of the failure.

Thanks

Vikas J

Isolation

Isolation forum

ISO1540: I2C Slave device connected After ISO1540D Isolator Device not Working