OPA564: OPA564 Abnormal when powered on

cyan zhou

Part Number: OPA564

In below design, when powered on, Vout Pin have V+ output voltage, which causes N-MOS couldn't operate the ON/OFF control.

this is used in fiber laser project, there're many pieces of this abnormal.

we don't sure if there is design mistake.

and, please help check if there's a reflow soldering Temperature curve about OPA564?

Thanks!

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Cyan,

oops, C78 means an output short circuit at high frequencies. And it can easily ruin the phase margin. Have you carried out a phase stability analysis?

And what about R60? Is it zero? Could turn U21 into trouble, again because of loss of phase margin.

Kai

0 Thomas Kuehl over 5 years ago

TI__Guru* 93105 points

Hello Cyan,

Is this a new application of the OPA564 for you, or is it one that has been in production for some time and is now having the problem?
You mention "In below design, when powered on, Vout Pin have V+ output voltage, which causes N-MOS couldn't operate the ON/OFF control." Does the OPA564 normally operate as a linear amplifier i.e. the output has a linear range of output levels that it produces, or is it supposed to operate with the output either high or low providing ON/OFF control?
What voltage is pin 5 of the OPA564 at when the Op amp is first powered and Vout locks up at V+?

There isn't a specific reflow soldering curve for the OPA564. TI provides more general documents on the subject of reflow solder:

https://www.ti.com/lit/an/snoa292j/snoa292j.pdf

https://www.ti.com/lit/an/scea041/scea041.pdf

Certainly, if the underside PowerPad is not properly soldered to the PC board that could cause problems.

Regards, Thomas

Precision Amplifiers Applications Engineering