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TAS5630 output voltage

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

Measurements of a TAS5630DKD2EVM show that no-load usable output voltage in PBTL mode is limited to about 29.4Vrms with a 50VDC power supply or 28.1Vrms with a 48VDC power supply. Those are where the output waveforms start to have noise bursts at their high and/or low peaks. Some older and not quite comparable measurements of a TAS5615 EVM, indicate it would output about 2Vrms more. Do these figures seem typical?

Would using output filters (15uH, 0.68uF) like those in the TAS5615 EVM reduce modulation noise to increase the usable output voltage, maybe to the level that the TAS5615 EVM delivered? I don't need all of the power that a TAS5630 can deliver but I do need as much output voltage as possible.

  • 0
    TI__Guru**** 189399 points

    Russell,

    I think changing the inductor would actually push the cut-off frequency out, resulting in less attenuation of the modulation noise.

    Your voltage measurement seems a little low to me.

    Can you try loading the outputs and see if you get the same voltage swing as depicted in the d/s?

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 685 points

    Unfortunately I cannot easily test a TAS5630 in a TAS5615 EVM now. I did check output voltage with no load and with a 10 ohm load.

    Checking for noise bursts is somewhat subjective, and the adjustment is touchy using the available signal generator, but nevertheless it seems appropriate for determining usable output voltage. The following measurements were done using a 60Hz sine-wave generator and 48 Vdc 10A power supply, on one TAS5630 EVM in PBTL mode.

    Noise bursts occur for over 28.0 Vrms output into no load. When a 10 ohm load (300 watt resistor) is applied, output drops about 0.15 Vrms and there are noise bursts.

    Noise bursts occur for over 27.0 Vrms output into the 10 ohm load, and output rises about 0.15 Vrms when the load is removed.

    Modulation noise, off-center DC output  voltage, output DC voltage offset, and imbalance between positive and negative voltage gains reduce output voltage capability, but this particular TAS5630 EVM seems to be pretty good for all of these aspects. Modulation noise is about 0.7 Vp-p, output voltages are nearly centered (about 23.6 Vdc), output offset voltage is about 0.15 Vdc, positive and negative voltage gains are almost precisely equal.

    48 Vdc power supply noise is about 0.2 Vp-p at about 400KHz with no load, presumably from the TAS5630's modulator. That 400KHz rides on about 0.6 Vp-p at 120Hz when the 10 ohm load is applied. The power supply has remote sensing so its average output at the EVM  (48.04 Vdc in this case) does not change significantly regardless of the load.

  • 0 in reply to Russell May
    TI__Mastermind 18510 points

    Russell, when do the noise bursts occur?  I expect they are around the peak output, and they may be intentional noise skipping rather than noise.

    Output pulses require a minimum off time so BST caps can be recharged, so there is a maximum duty cycle that can be achieved during a normal switching cycle.  Of course, such a maximum would limit available output voltage.  So, when the internal feedback loop drives the duty cycle to its maximum, the device begins to skip pulses to avoid the equivalent of hard clipping.  Distortion increases, but it remains around 0.5% until pulse skipping reaches continuous operation at 1/3 of the normal switching frequency.  That is the limit for this action, and it is the onset of true clipping.  At that point distortion naturally increases as the output clips harder and harder.

    Check the frequency of the noise you are seeing.  If you are using the nominal 400kHz switching frequency, and the noise is in fact pulse skipping, you should see 133kHz switching when this happens.  Please let me know what you find.

    Best regards,

    Steve.

  • 0 in reply to SteveCrump
    Intellectual 685 points

    The noise bursts occur near the high or low peaks of the waveforms. This morning the onset with no load was at about 28.15 Vrms, at the low peak of the B-D output which was at about +3Vdc. Maximum magnitude was then about 15Vp-p, from about -4V to +11V. Waveform was approximately triangular and period was 15 usec.That is about 66 kHz. This noise burst lasteds about 500usec. Everything except the period changes as the input signal increases: Next the A-D output gets noise bursts near its high peak, then both outputs get noise bursts near both peaks, then the amplifier starts to clip so the noise happens just before and after the clipped outputs. Absolute maximum magnitude is about 20Vp-p on both outputs at both peaks near clipping.

  • 0 in reply to Russell May
    Intellectual 685 points

    Typos corrected:

    The noise bursts occur near the high or low peaks of the waveforms. This morning the onset with no load was at about 28.15 Vrms, at the low peak of the B-D output which was at about +3Vdc. Maximum magnitude was then about 15Vp-p, from about -4V to +11V. Waveform was approximately triangular and period was 15 usec.That is about 66 kHz. This noise burst lasts about 500usec. Everything except the 15 usec period changes as the input signal increases: Next the A-C output gets noise bursts near its high peak, then both outputs get noise bursts near both peaks, then the amplifier starts to clip so the noise happens just before and after the clipped outputs. Absolute maximum magnitude is about 20Vp-p on both outputs at both peaks near clipping.

  • 0 in reply to Russell May
    Intellectual 685 points

    I checked a TAS5615 EVM in which the TAS5615 was replaced by a TAS5630, which makes it a hybrid EVM.

    The replacement was done twice. The original TAS5615 was damaged by our load-transient testing. The first replacement  TAS5630 had high output offset voltage. The second replacement also had high output offset voltage. I assume these were related to the output offset voltage being sensitive to leakage at the inputs. After more thorough cleaning, output offset voltage was acceptable (0.12 Vdc).

    The noise bursts for this EVM were subjectively similar to those for the first EVM. Onset of noise bursts was at about 28.1 Vrms. Absolute maximum magnitude was less, about 10 Vp-p. Period was longer, about 20 usec (50kHz).

    Russ

     

  • 0 in reply to Russell May
    Intellectual 685 points

    Here are some results from another repaired TAS5630 EVM with no load and 48 Vdc power supply.

    Output offset was initially high (up to 0.9 Vdc) after the TAS5630 was replaced, with outputs at about 26Vdc. This was after cleaning twice with alcohol.

    Output offset after thorough cleaning was good (0.043 Vdc), with outputs at about 23.8 Vdc. This was after cleaning twice with running water and brush.

    Onset of noise bursts was at 28.24 Vrms output. Absolute maximum magnitude of the noise was about 16 Vp-p with 15 usec period (66kHz), near the high peak of one output..

     

  • 0 in reply to Russell May
    TI__Mastermind 18510 points

    Russell, I want to be sure I understand the circumstances for the noise bursts.

    - Output voltage around 28Vrms;

    - Noise bursts occur with 10ohm load but not with no load.

    Is that correct?

    With 48 to 50 V PVDD, and peak signal around 40V, this is probably not pulse skipping as the output nears clipping.  I am wondering if it is OCP caused by some strange load condition.

    Please remind me of the LC filters you are using.  Are they still the standard EVM filters?

    Can you post the impedance of your resistor loads vs. frequency, including above the audio band?  Maybe if these are ordinary wirewound they have significant inductance.  Of course, speakers all include significant inductance, so unless the inductance is huge it should not be a factor.  Maybe there is some other anomaly in their impedance.

    Best regards,

    Steve.

  • 0 in reply to SteveCrump
    Intellectual 685 points

    Output voltage is about 28 Vrms.

    Noise bursts occur with no load or 10 ohm load.

    No load should not be strange. 10 ohm resistor load should not be strange.

    LC filters are what is built into the EVMs. The first and third EVM's are TAS5630 EVMs. The second EVM is a TAS5615 EVM with TAS5630 IC.

    Load impedance with no load is 10 Megohms (DVM input impedance) between outputs, presumably up to about 30 kHz, and 10 Megohms (oscilloscope input impedance), presumably up to about 400MHz,  from each of the two PBTL outputs to ground. Inductance would be from about three feet of 24 ga wire each direction to the DVM.

    10 ohm load adds a 300 watt Ohmite rheostat (end-to-end) and about one foot of 20 ga wire each direction to the rheostat.

    Measured resistance and inductance of the rheostat versus frequency are:

    9.765 ohms, 13 uH at 120Hz; 1 kHz : 9.766 ohms, 13.0 uH at 1kHz ; 9.769 ohms, 13.04 uH at 10kHz;  9.820 ohms, 12.93 uH at 100kHz.

     

     

  • 0 in reply to Russell May
    Intellectual 685 points

    Measurements for two more EVM's: One is a TAS5630EVM with TAS5630 IC. The other is a TAS5615 EVM with TAS5615 IC.

    Onset of noise bursts for the TAS5630 EVM is at about 28.22 Vrms with no load. Absolute maximum noise burst magnitude is 16 Vp-p. Noise period was bout 15 usec (66K kHz).

    Onset of noise bursts for the TAS5615 EVM is at about 30.0 Vrms with no load, 29.0 Vrms with 10 ohm load. This is about 1.5 to 2 Vrms higher than the four EVM's with TAS5630's in them, including the hybrid EVM. Noise burst amplitude was less than 10 Vp-p. Noise period was over 15 usec, but indistinct because the noise was mixed with the only slightly lower 400 kHz modulation voltage.  48 Vdc power supply current with no load was about 80 mA, noticeably less than 120 to 180 mA for the EVM's with TAS5630's in them.