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TAS5707 supply below 10V vs. blackouts

Lukas Osmancik
Prodigy 110 points
Other Parts Discussed in Thread: TAS5707

I noticed quite strange behaviour during testing my hardware with TAS5707+ARM M4+MEMS mic

Our cell powered device operates from 8.4 to 11V. TAS5707 should operates from 8V, but it has problems to operate properly below 10V! There are sound blackouts when some dynamic or loud sound is played. When the supply is 10V and above there are no problems.

I try to decrease modulation limit from 99.2 to 93.8 and it has effect that the device could play almost without blackouts with supply 9V, but it is far from operate at 8.4V. When I decrease power supply to 8.4V I hear some soft poping in speakers and amplifier isnt working. I must go to 8.7V, the poping disappears but there are big problems with sound blackouts.

My load are two 8Ohm speakers in series and additional 4.4Ohm series resistance as intrinsic safe protection.

 Thanks for any help or solution.

Lukas

  • 0
    Prodigy 110 points

    Here are my measurements on supply voltage

    Fig. 1 Ripples on supply voltage at 10V, when no data on I2S, no sound is playing

    Fig. 2 Ripples on 8.4V(different timebase) - no I2S data, but soft poping is present at outputs. It looks like it has tendency to start working (switching ripples fades in), but from some case it is cut-out and it causes a pop.

  • 0
    TI__Mastermind 22965 points

    Hi Lukas,

    This could be the UVLO (Under Voltage Lock out). If the Vcc falls below 7.5V, device will shut-down. 

    Try monitoring the supply voltage on the scope while playing the audio to check if the supply droops when loud sound is played. The battery may not be able to supply the peak current resulting in the supply sagging. This would especially be an issue at lower bass frequencies, in which case you can try implementing a high-pass filter using the Bi-Quads and see if it helps.

    How much bulk decoupling capacitance do you have for the TAS5707?

    -Ravi

  • 0 in reply to Ravi Singh
    Prodigy 110 points

    Thanks for reply.

    In my tests I use a regulated Voltage source instead battery. The speakers which i am using are high efficency industrial horns with quite weird frequency response.

    I think I have quite aggressive EQ on Bass and High frequencies to compensate horns attenuation. I will try to disable EQ or make it not so aggressive and add high pass to cut subbasses.

    The situation with shutdown causes even when no sound is playing - maybe EQ could cause subbas self resonances - I must check it.

    My bulk capacitance is 1440uF+100nF.

  • 0 in reply to Lukas Osmancik
    Prodigy 110 points

    Now I have only high pass (100Hz) on EQ section. It helps very slightly. The problem that the amplifier disable itself (poping) at supply level 8.6-8.7V still persists. I try to catch spikes on supply voltage, but there is nothing lower than 8.5V.

    There is amplifier waveform at output (to gnd) before filter inductance when poping

    There is amplifier waveform at output (to gnd) beyond filter inductance when poping

     

  • 0 in reply to Lukas Osmancik
    Prodigy 110 points

    I try scope /FAULT pin and there are short pulses. Maybe undervoltage detection is too sensitive and some disturbances on PCB causes its activation. 

  • 0 in reply to Lukas Osmancik
    TI__Mastermind 22965 points

    Hi Lukas,

    The UVLO has a fairly tight tolerance, and will only trigger if the supply drops below the trip-voltage. The FAULTZ tripping clearly indicates an issue.

    As a test, try running just one channel with the second muted & check if it helps. Further, a test with lower volume setting can be run as well.

    -Ravi