ISO124: iso124 not working as expected

Michael Stadtler

Prodigy 140 points

Part Number: ISO124

I breadboard an iso124 circuit and 2 TI dcpo1b 15v supplies. I double checked my connections.

I am using the plastic .1 gridded breadboard for thi prototype. - Is this possibly the problem?

I noticed in the app note that "no conductive materia ie traces can be undeneath the chip.

Along that same line how far away does the chip have to be from say a metal enclosure.

over 7 years ago

0 Tom Hendrick over 7 years ago

TI__Guru**** 168485 points

Hi Michael,

Welcome to our e2e forum! When you say the ISO124 is not working as expected, can you describe what you mean? What are you expecting and what are you seeing? Those plastic squeeze boards can be problematic, especially if they are old. Spacing will be dependent on your application.

0 Michael Stadtler over 7 years ago in reply to Tom Hendrick

Prodigy 140 points

Thanks for the quick response. I am using the circuit to isolate a DC signal. On the bench this a 5v supply. going to Vin refenced to high side ground. I am expecting the same DC signal at Vout refenced to low side ground. Any input 0 5v and output is stuck at 8.3v. I beleive my breadboard is ok , new but I am concerned with the metal being under the chip since a point was made in the app note, not to run any tracesunder the chip. Thanks

0 Tom Hendrick over 7 years ago in reply to Michael Stadtler

TI__Guru**** 168485 points

Hi Michael,

Can you give me a part number for the 15V supplies you are using? The app note regarding traces running under the chip is probably not something you need to worry about at this point in your debug process. Traces that run under the chip between the HV side and LV side will essentially reduce the creepage and clearance distance, which will in turn impact the isolation voltage. The metal strips in the squeeze board do have the same impact as traces, but you don't really seem to be dealing with any high voltage at the moment.

0 Michael Stadtler over 7 years ago in reply to Tom Hendrick

Prodigy 140 points

Hello again,

DCP011512DBP-ND IC REG ISOLATED +/-12V 41MA 7DIP are the 2 PS chips.

You are correct re: high voltage - this circuit is not.

I'll try a new ISO24 device next I think and maybe a perfboard wired prototype.

Thanik

0 Tom Hendrick over 7 years ago in reply to Michael Stadtler

TI__Guru**** 168485 points

OK - the isolated power supply chips should be fine. If you can draw up a schematic of your connections, I'd be happy to review them as well.

0 Michael Stadtler over 7 years ago in reply to Tom Hendrick

Prodigy 140 points

This circuit show a +24v supply, I will use in the final version. I am using +15v currently since I don't have the correct chips for +24v.

I am using a 0-7v DC supply for Vin with reference to ACOM U1-16.

Thanks again

0 Michael Stadtler over 7 years ago in reply to Michael Stadtler

Prodigy 140 points

0 Michael Stadtler over 7 years ago in reply to Michael Stadtler

Prodigy 140 points

What decoupling caps should I use on the +24 input 1uf or .47uf?
What decoupling caps should I use on the +/- 12v output 1uf or .47uf?

0 Tom Hendrick over 7 years ago in reply to Michael Stadtler

TI__Guru**** 168485 points

Hi Michael.

By the DCP011512DBP datasheet, 1uF on the input voltage and 0.47uF on the outputs.

0 Michael Stadtler over 6 years ago in reply to Tom Hendrick

Prodigy 140 points

Getting back to this design, was on another project.

The data sheet (below) reccomends .47uf for the 24v input part that I have. I only have 1uf caps will they work until I can get the .47uf. I realize they are just input capacitors, but I don't want to damage these parts.

For 5-V to 15-V input devices, a 2.2-μF, low-ESR ceramic capacitor ensures a good startup performance. For 24- V input voltage devices, 0.47 μF ceramic capacitors are recommended. Tantalum capacitors are not recommended, since most do not have low-ESR values and will degrade performance. If tantalum capacitors must be used, close attention must be paid to both the ESR and voltage as derated by the vendor.

0 Tom Hendrick over 6 years ago in reply to Michael Stadtler

TI__Guru**** 168485 points

Hi Michael,

The 1uF caps should be fine.

0 Michael Stadtler over 6 years ago in reply to Michael Stadtler

Prodigy 140 points

I am using the DCP022415DP in my design. I am unable to get any output voltage with +24 supplied. Can I email a schematic and layout to you for review?