PCM1808: PCM1808 VinL/R input limit

Nic Lin

Intellectual 2020 points

Part Number: PCM1808
Other Parts Discussed in Thread: OPA2134, PCM1804

Team,

Customer would like to input +/-2Vrms line in signal to PCM1808. However, the abs input voltage of VinL/R is VCC+0.3. VCC is 5V. +/-2Vrms is 5.656Vpp, which will exceed 5.3V. Could we just a simple resistance divider to attenuate the input signal? If not, any recommended solution to address this issue? Thanks.

Regards,

Nic

over 5 years ago

0 Ravi Patil over 5 years ago

TI__Expert 5645 points

Hi Nic,

The maximum input this device can accept without overflow or distortion in the digital output is the Full-scale voltage, which in this case would be 3Vpp.

The input voltage range for PCM1808 is as outlined below -

ANALOG INPUT: Input voltage=0.6 VCC Vp-p
Center voltage=(VREF) 0.5 VCC V

If you think the voltage can exceed this voltage, to be safe, you should provide some sort of external protection circuitry (zener diode, etc to clamp the input voltage within the input voltage range listed in the data sheet).

Finally, the maximum that you can input without damaging the device is < 6.5 V.

Best regards,
Ravi

0 Sadanori Kato over 5 years ago in reply to Ravi Patil

Guru 36510 points

Hi Nic-san,

Please refer to the following links when it is assumed that the input signal exceeds 3Vpp.

DEM-DAI1808
http://www.ti.com/lit/ug/sleu078/sleu078.pdf

PCM1808 Channel Separation
http://e2e.ti.com/support/audio/f/6/t/419141

Best regards,
Kato

0 Nic Lin over 5 years ago in reply to Sadanori Kato

TI__Intellectual 2020 points

HI Kato,
The problem is that it is powered by negative supply -AVcc. We need to use single-ended power supply. How should we do?

0 Sadanori Kato over 5 years ago in reply to Nic Lin

Guru 36510 points

Hi Nic-san,

As you know, AC coupling capacitors are used in DEM-DAI1808, so the single-ended power supply voltage can be used.
However, the reference voltage(0.5 x VCC) should be connected to the non-inverting input of OPA2134.

Best regards,
Kato

0 Nic Lin over 5 years ago in reply to Sadanori Kato

TI__Intellectual 2020 points

Per my understanding, reference voltage(0.5 x VCC) is input instead of output, why it needs to be connected to the non-inverting input of OPA2134?

0 Sadanori Kato over 5 years ago in reply to Nic Lin

Guru 36510 points

Hi Nic-san,

Please refer to the schematic around PCM1808 in DEM-DAI1808, so you can catch that the decoupling capacitors are only connected to VREF(common-mode voltage) pin.
Unfortunately I cannot judge whether the non-inverting input of OPA2134 can be connected directly to VREF pin of PCM1808 or not.
However, I think that PCM1808 can also do it since PCM1804 can do it.

Best regards,
Kato

0 Ravi Patil over 5 years ago in reply to Sadanori Kato

TI__Expert 5645 points

Thanks for the valuable inputs Kato-san.

Nic, I think you can connect the non-inverting input directly to VREF of PCM1808.

Best regards,
Ravi

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PCM1808: PCM1808 VinL/R input limit