LP5569: Buffer to fit between TCA9517 & LP5569

To which side of TCA9517 are you interfacing? Is the VCC level set to 5 V for both devices? Are there any fixed pull-up resistors on the other PCB that cannot be changed?

Regards,

Max

We are trying to connect TCA9517 B-side to LP5569 and the VCC is 5V on both sides of TCA9517. 

We have a 4.7K pull-up on TCA9517 B-Side. which we don't prefer to change. but we would like to consider this change as last option if nothing works.  

At LP5569 side PCBA is on proto stage and is open for changes.

Since we are having two buffers before TCA9511 the Low-level voltage is offset three times and we don't have control over pull-up of the buffers. hence we are planning to break the chain by the added isolator. the Isolator VCC1&2 are the same 5V rails and GND1&2 are the same ground. 

The VIL and VOl level ISO1540 and LP5569 are not compatible however the ISO1540 an open drain, in that case, if we use a proper pull-up we could have control over the Low-level voltage. 

Please review and share your comments. 

Hi Thiagarajan,

I would not recommend the solution using ISO1540. The Vol of this device mis-matches with LP5569 in a similar way to the origial problem with TCA9511 to LP5569. I do not have a simple solution to suggest right now. We don't have any buffers that would be compatible with these thresholds that works at 5V Vcc. I am going to gather more information on LP5569 to see what work-arounds may be possible before suggesting something too complex. I will give you an update within the next couple of days.

Regards,

Eric

Thanks Eric,

Correction a typing error, we are using P/N:TCA9517ADGKR on the mainboard. We are open for BOM Level changes on Mainboard and we have 4.7K pull-up on B-Side of TCA9517. 

The Visual alarm indicator is on the prototype stage, we are open for any change to use LP5569. Mainboard sources 5V to Visual alarm indicator PCBA. 

Hi Thiagarajan,

Thanks for the update and figure. We're looking in to possible BOM changes that would allow everything to remain within spec. It's possible we may have to suggest a more complex work-around than the buffer we were hoping for. 

The team in charge of LP5569 is out on holiday. I will continue looking into this as some clarification here could vastly simplify the issue. 

I will be in touch before the end of the week.

Regards,

Eric

Hi Eric,

Thanks for your reply. I have tried below options and tested options of ADUM1250 and TCA9517 and found them working. I am going to try ISO1540 options tomorrow. 

Please review this approach and share your suggestions. Also, we are still interested on your suggestion to fix after discussion with the LP5569 team.

Hi Eric,

we have tested all three options (ADUM1250m ISO154 & TCA9517) and they are all working. 

Please review this approach and share your suggestions. Also, we are still interested in your suggestion to fix after discussion with the LP5569 team.

Hi Thiagarajan,

Glad to hear these methods worked! I will review the solution and relay any suggestions early next week. I will also let you know what I learn from the LP5569 team. I appears that they will be back from holiday early February.

Regards,

Eric

Hi Thiagarajan,

Sorry for the delay. The LP5569 is China-based and are not back from Holiday yet. I believe it was extended due to the situation there. I will inform you if I learn anything of interest regarding this device in you application.

Regards,
Eric