SGTL5000- DC-Bias on linein using codec bypass

[max123]

Hi!

the SGTL can switch Line-In to HP-OUT using "codec bypass". We want to use this mode.

Our Problem: The SGTL does not switch the line-in DC-bias voltage on, if this mode is selected, which sounds horrible.  If we read from the line-in using the ADC prior to switching to this mode, the DC-bias is on. So there is a workaround, but it isnt pretty.

This looks like an error of some sorts in the linux driver.

According to the datasheet, there is no setting switch a DC-Bias to the line-in.  On the other hand, the driver seems to toggle some "reserved" bits.

How can we switch the DC-Bias on, without using the ADC first?

[max123]

Hi,

thanks for your answer!

The register "CHIP_REF_CTRL" is not used by the driver. Therefore, it should in default state, which should be ok for our application (0x00: GND=0,8V, BIAS_CTRL=Nominal, SMALL_POP=normal VAG ramp). We have no load on line-in and use a decoupling capacitor.

There is also no on/off setting for the DC-Bias. Maybe its in the "RSVD" bits?

[reyes]

Hi,

CHIP_REF_CTRL 0x0028 register controls the bandgap reference bias voltage and currents.

You can find more details on table 28 of the datasheet: https://www.nxp.com/docs/en/data-sheet/SGTL5000.pdf