• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 31 subscribers
  • Views 1756 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TAS5630 offset voltage

Russell May
Intellectual 685 points
Other Parts Discussed in Thread: TAS5630, TAS1530, OPA1632, TAS5615, TAS5630B

Output offset voltage in BTL mode with AC-coupled inputs is specified up to 150mV. Is this also correct for PBTL mode? How can offset be minimized, or adjusted to zero?

 

  • 0
    Intellectual 685 points

    Update and more information: See forum topic "TAS5630 Over current protection problem." for some of it.

    We have a non-audio application in which we are trying to use a TAS5630DKD to drive a 50:1 transformer to develop 1500VAC while driving a  mostly-capacitive load up to about 100mA at 50 to 400Hz. We must be able to shut down the output voltage rapidly. Resetting the amplifier for this would open its outputs, which is likely to generate a high-voltage transient because of the transformer inductance, so the TAS5630 outputs are driven together to shut off the output voltage rapidly. I first attempted do this with a circuit intended to DC-couple the inputs of the TAS5630. That didn't work. Plan B is simply to  short-circuit the TAS1530 inputs. That seems to work, but output offset voltage is higher than desired.

    Our breadboard is now implemented by a TAS5615DKD EVM in which a TAS5630DKD has replaced the TAS5615, external R-C pairs (10uF, 100 ohms) have replaced the 10uF capacitors between the OPA1632 preamp and the TAS5630, 4.7-volt Zener diodes have been added across the TAS5630 inputs, 5KVA Transzorbs have been added from the TAS5630 outputs to ground, a common-mode choke and one-ohm power resistor are connected between the outputs and the transformer. The external R-C's are to allow us access to the circuit. The other items are to protect the TAS5630. The breadboard is driven by a 48V 10A power supply.

    With the EVM in PBTL mode and its A-B inputs both shorted to ground: DC output offset of the TAS5630 is about 0.13 volts. DC output offset with its inputs not shorted together is about 0.69 volts, producing about 500mA DC output current. Especially the latter situation seems undesirable, and it is unexpected because the TAS5630 is specified to have 0.15 volts maximum output offset voltage. The voltages go up about four percent when the transformer is disconnected.

    I would like to reduce the output offset voltage to reduce the DC output current or allow a lower resistance in series with the transformer.

     

     

  • 0 in reply to Russell May
    TI__Guru**** 189399 points

    Hi, Russell,

    I'm afraid we don't have a good suggestion on how to reduce the offset voltage. 

    In the past, I've noodled around on the idea of building a servo loop to zero out the offset voltage, but never tried actually building it.

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 685 points

    I also tried a dc servo but, lacking understanding of the internal circuitry of the TAS5630, I did not get it to work

    What appears to work, at least on one TAS5630 EVM,  is an adjustment through a 4.7Megohm resistor connected a TAS5630 input and to a trimpot which provides a maximum of about 1/12 VDD  (about 4 volts). This is a simple open-loop solution, without dc feedback.

    How stable this will be with temperature variation and on other TAS5630's is unknown yet. It has no effect if the TAS5630 inputs are shorted together. That is why I am interested in availability of the TAS5630B, mentioned in other threads.

    Without overall dc feedback, the overall amplifier gain is proportional to the TAS5630 voltage gain. That Is why I am interested in approximate min and max voltage gain, also mentioned in another thread.

    The TAS5630 EVM we are using right now has offset voltage within specification, and its adjusted offset voltage drifted less than 2mV over the weekend.

    The 0.13V and 0.69V offsets I mentioned previously might be from a damaged TAS5630. The protection diodes had been wired incorrectly. We have not yet tried to replace the TAS5630 in this hybrid TAS5615/5630 EVM.