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TLV320AIC3106: Differential Line2R/R resistance in analog bypass mode

Gilbert Vellet
Prodigy 120 points
Part Number: TLV320AIC3106

In the datasheet, the input resistance is only given for analog inputs routed to ADC input. When the input is in analog bypass mode, it is routed to an output mixer instead. 

What is the input resistance on LINE2R, LINE 2L in differential and analog bypass modes when routed to HPROUT/HPLOUT through a mixer?

Here is the codec configuration:

Reg 20=0xF8 : Line 2L is not connected to ADC

Reg 23=0xF8 : Line 2R is not connected to ADC

Reg 37=0xC0 : Both DAC powered up, HPLCOM differential

Reg 38=0x04 : HPRCOM differential

Reg 40= 0xBC : output CM=1.65V, Line2L/R enabled in differential bypass mode, soft stepping 1 per fs

Reg 41=0x00 : Left DAC uses DAC_L1 path, Right DAC uses DAC_R1

Reg 45= 0x80 : Line2L routed to HPLOUT, 0 dB attenuation

Reg 62= 0x80 : Line2R routed to HPROUT, 0 dB attenuation

Reg 82=0x80 : DAC_L1 routed to LEFT_LOP/M , 0 dB attenuation

Reg 92=0x80 : DAC_R1 routed to LEFT_ROP/M , 0 dB attenuation

  • 0
    TI__Guru 62065 points

    Hi Gilbert,

    When in bypass mode, the analog inputs still go through the same input amplifier stage which sets the input impedance much like if it was routed to the ADC still.  Therefore, in a differential bypass mode, the differential input impedance is roughly 80kΩ.

  • 0 in reply to Collin Wells
    Prodigy 120 points

    Hi Collin,

    Is the differential input resistance fixed at 80kΩ or dependent on the attenuation level set in register 45 and 62? In a way it would be similar to what happen with the input resistance if the registers 20 and 23 would be enabled.

    Thanks

  • 0 in reply to Gilbert Vellet
    TI__Guru 62065 points

    Hello,

    Good question and I should have added that last time.  It will vary from 80kΩ (0dB) to 320kΩ based on the input attenuation settings.  Here are some rough numbers from one device we measured recently:  

    DIFFERENTIAL

    Gain (dB)

    CH1 (Ω)

    CH2 (Ω)

    0

    80048

    80363

    -1.5

    94944

    95189

    -3

    112836

    113177

    -4.5

    134160

    134530

    -6

    160780

    161020

    -7.5

    191190

    191330

    -9

    227700

    227740

    -10.5

    269890

    269710

    -12

    324420

    323100