• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 48 subscribers
  • Views 492 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

OPA564: Power stage with OPA564 as driver

OPA564: OPA564 circuitry fails continuously and output is shorting to ground

Bivin George
Expert 1057 points
Part Number: OPA564

Hi 

I'm using below circuitry on my custom card. But the circuit is failing continuously. I don't know why it is happening.

I'm enabling output only with 10% duty cycle at a repetition rate of 1Hz.

The load is a capacitive load of value (139.1, -57.48) (imepdance magnitude, phase angle degrees) at 51KHz & (565.4,-34 .23) at 63KHz output signal.

1. Is there any layout guidelines to be followed.

2. Is the input protection diode (BAT120S,115) selected proper.

3. What happens when EN pin toggles at PRF 1Hz , will it affect OPA564.

Please clarify.

  • 0
    Guru 140200 points

    Hi Bivin,

    what is the purpose of L13? What is its inductance?

    Does the circuit work when it runs continuously, without this enabling?

    Kai

  • 0
    TI__Guru* 93105 points

    Hi Bivin,

    When you state "I'm using below circuitry on my custom card. But the circuit is failing continuously. I don't know why it is happening" what exactly do you mean by failing continuously? Does this mean that the OPA564 is failing to preform electrically as you intend, or does it mean it is being catastrophically damaged and fails?

    If it is catastrophic damage, you have to be careful about the VSUPPLY, VDIGITAL power-supply sequencing as described in the datasheet Power Supplies section on Pg. 14. If the VDIGITAL comes after VSUPPLY the OPA564 my be damaged internally. Please check and make sure the supply power up, and power down sequences conform with what is shown in datasheet figure 36 B, or 36 C.

    Otherwise, I am not seeing anything about your OPA564 circuit that raises red flags. As Kai requested the inductance value of L13 is needed. When I do the AC math for your loads at appears as a series 74.8 Ohm + 26.6 nF load at 51 kHz, and a series 467 Ohm + 79.4 nF load at 63 kHz. The capacitances are significant, but the large resistances in series with them likely provides sufficient isolation (Riso) such that stability isn't the issue. This can always be explored more thoroughly if the trouble shooting requires that.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Expert 1057 points

    Hi

    Inductor used is SRP0320-R68K ; FIXED IND 680NH 7.4A 14.8MOHM SM.

    Please let me know whether inductance is an issue, will it affect stability.

    Board is getting damaged when restarted , ie when power up next time.  While working we found severe power dissipation issue.

    Please advice.

  • 0 in reply to Bivin George
    TI__Guru* 93105 points

    Hi Bivin,

    • Okay, that is a power inductor having a low 680 nH inductance. The output diode arrangement and inductor are often seen as part of a protection circuit in PLC applications. I don't see a problem there, but will let Kai comment as well in case I have missed something.
    • "Board is getting damaged when restarted, ie when power up next time" - that may be the result of the power up/down VDIGITAL and VSUPPLY sequence that can lead to OPA564 catastrophic failure. Please evaluate their timing relationship as I previously suggested.
    • The OPA564 has limited thermal power dissipation as all packages do but to different levels. OPA564 datasheet pages 22 to 24 provide a lot of good information about POWER DISSIPATION AND SAFE OPERATING AREA. That information should give you a good idea what kind of power dissipation the OPA564 can handle and how to maximize it.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • +1 in reply to Thomas Kuehl
    Guru 140200 points

    Hi Bivin,

    I fully aggree with Thomas and would add the following:

    Although the junction capacitances of Schottky diodes at the output are rather high, the circuit looks stable in the phase stability analysis.

    Not knowing the true nature of your "capacitive load" I would recommend to insert an isolation resistor of 10...22R between the output of OPA564 and the node where D5 and D8 are connected to each other.

    You should find out why the OPA564 is heating up. Increase the amplitude of input signal slowly from zero on and check the temperature of OPA564. Is it heating up proportionally to the input signal level or is there a trip point where the heat dissipation "explodes"? Scope the output of OPA564 during this test and check for oscillation or excessive ringing.

    Enhance the cooling, if the OPA564 heats up too much even under normal operation.

    Kai

  • 0 in reply to kai klaas69
    TI__Guru* 93105 points

    Hi Bivin,

    Please let us know about your progress finding the problem. A properly applied OPA564 should perform to the datasheet specifications, and should be reliable in operation.

    Regards, Thomas

    Precision Amplifiers Applications Engineering