OPA569: Unexplained behavior of The Amplifier;s Current Flag and Output

Hi Ron,

the OPA569 could oscillate. Can you show a schematic?

Kai

Hi Kai,

Attached the schematic of the TEC driver. The OPA569 lines has an option of parallel connection with another OPA569 that is not on the attached schematic, but this is not in use.

I didn't see oscillation on the OPA569 output.

Thanks,

Ron

Hi Ron,

is there an inrush current issue?

Kai

Hi Kai,

There was an inrush current issue when I noticed these behaviors of the output and limit flag.

I forgot to mention that, at some point, for eliminating the influence of the thermal flag,  I disconnected the thermal flag from the enable and connected the enable input to a pull up so it will be constantly enabled..

The issues I described also happened when the OPA569 was constantly enabled.

Do you think that inrush current can explain this?

Thanks,

Ron

Hi Ron,

have you measured the inrush current?

Kai

Hi Kai,

I measured about 1.5A using a scope current probe. Due to bandwidth limitations of my probe, the current may have been higher.

Thanks,

Ron

Hi Ron,

is the power pad connected to GND? It looks like an overheating of chip, somehow, like a thermal shutdown.

Another issue could be the current limit function itself. There are two figures on page 10 of datasheet which show that the current limit activates from a slowly rising output current. This could be an indication that the OPA569 doesn't like sudden and instantaneous current changes in combination with the current limit function. It's only a guess.

In any case, I think it would be good design practise to provide some softstart for the TEC current and not to turn-on the TEC current with an extremely short rise time.

Kai

Hi Kai,

The power pad is connected to GND. I also didn't sense exceptional heating of the OPA569 during work.

I agree with you regarding the good design practice and OPA569 sensitivity to sudden current changes. I now changed the design to have a softstart and to avoid the inrush current. After the change I didn't notice the issues I described, but still, I don't fully understand the OPA569 behavior.

Thanks,
Ron

Hi Ron,

may I ask what is unclear to you?

Kai

Hi Kai,

It is mostly the current limit behavior I don't understand. When sudden high current changes occur, it remained flagging over current although the current returned to zero.

But, I guess it better to have a good design, without needing to understand what exactly goes wrong when you have a bad design :)

Thank you for your responses.

Ron