ADS1248 stops converting in BURST test

Jiri,


I don't know much about the surge test you're doing, but I assume that it's associated with IEC 61000-4-4. I don't have any specific solutions, but there are things to try. I'll list them and you can re-run tests to see if any of them help.

I see that you already have a large series resistance with the inputs (10k). I would expect that the series resistance helps quite a bit and would have thought that this would have prevented problems with the input surge. I would not increase the resistance. This is already quite a bit and you need to consider any input leakage (both from the device and any protection diodes) reacting with the series resistance.

I'd remove the EMI/RFI filters on the inputs. Generally I don't use any inductors in the input filtering and with the surge, I'm not sure if the filters help or hurt the device with the surge test. I would replace them with a short and see if it helps.

I would definitely remove the inductor between the supply lines (L5). This could likely give you more problems. With digital currents, this will likely give far more supply noise and spiking because the L(dI/dt) that occurs.

Another thing about the supplies is that you can add a TVS between the supplies. Even if the surge comes from the input pins, the discharge path will go to supply or ground, and you would still need to make sure that these supplies stay within operating range. The TVS could help keep the supplies from rising too far above ground.

I see that you have the BAS70 schottky diodes on the inputs. Is there a reason that you have them on some of the inputs, but not others? I would also consider using the BAV199 instead. These are much lower in leakage and would give less error with leakage currents reacting with series impedance. Another possibility would be to add extra ESD devices to the front end. I've seen both TPD1E10B06 and TPD2E001 recommended for other IEC tests, but I'm not sure how they would do in the surge test.

I would also consider adding capacitive filters to analog inputs (instead of the RFI/EMI filters with inductance) this might help decrease the voltage rise from the surge test especially with the series input resistance. Take a look the ADS1248EVM and see what we use for differential and common-mode input filtering.


Joseph Wu

Joseph,

everythink is OK now. I shorted a inductor and resistor in power supply and add capacitor to RESET wire.

Jiri