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ADAU1787 HP_CTRL line out vs headphone output (HP1_MODE, HP0_MODE settings)

I am:

1) connecting the DAC output to low impedance ear bud speakers
2) looping the DAC outputs to the ADC inputs

When I switch (in real-time) between the HP_MODE line out and headphone out settings, I do not see any change in signal level neither case 1 nor case 2 above.

Other than the PB1_EN, PB0_EN, are there any other bits to make this setting functional?

Can I modify the setting in real-time?

I know the I2C interface is working in that my init works and my switch logic works for DAC mute (in real time).

How can I test whether this feature is working?

Thanks,

Dan

  • Hi Dan - those are the only two registers required to put the part into "headphone drive" mode. 
    I verified they can be changed in real-time using a test tone.If I try to drive headphone while in "line-out" mode, I get distortion
    and can see harmonics come up. Switching to HP_MODE causes the harmonics to go away, and I have more headroom when driving the 32 ohm headset. Hope that helps.