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OPA1632: Impedance and o/p voltage requirement is 600 Ohm and 12 Vrms.

Part Number: OPA1632
Other Parts Discussed in Thread: LM4902, , TLV320AIC14K


Hi ...

We are using TLV320AIC14KIDBTR, LM4902MM/NOPB and OPA1632DR in our audio processing card.

The input to the TLV320AIC14KIDBTR  will be MIC or 1.5 Vrms differential.

The output of the TLV320AIC14KIDBTR will be given as an input to LM4902MM/NOPB or OPA1632DR through analog DPDT switch.

The output of the LM4902MM/NOPB will be interfaced to a Headphone(1.5 Vrms, 150 Ohm).

The output requirement for OPA1632DR is 12 Vrms @ 600 Ohm.

Kindly suggest us that what should be the V+ and V-  voltage levels and the current requirements for 12 Vrms output  at 600 ohm load ?

Can the output of OPA1632DR be directly connected to 600 ohm 12 Vrms load ?


Is there any impedance matching circuit required in between ?

Requesting you to review the attached schematics and give your feedback.

Warm Regards,


  • Hello Manjunath,

       I will be reviewing the OPA1632. If you would need a schematic review of the LM4902, I would suggest creating a new thread linking the LM4902 device part number to the question, so the thread will be placed in the appropriate TI team. 

      12Vrms translates to about 34V differential at 600 ohms or 17Vpp at each output at 30mA of current. The amplifier should be able to handle this, but with lower loads and higher currents, comes with a decrease to output voltage range of the amplifier (claw curve). Also, no need for impedance matching with this audio amplifier. 

       For schematic review of the OPA1632, I would suggest a +/-15V power supply and a 0.1uF or 1uF decoupling capacitor at the output of VOCM pin to filter any high-frequency noise that could couple into the signal path through the VOCM circuitry. The gain settings seem to low for 1.5Vrms differential to 12Vrms differential for the OPA1632 or is there a previous gain stage?

    Thank you,

  • Hi ...

    Thank you for the reply and valuable suggestions given.

    Will the +/-15V power supply to be connected to VOCM pin ?


    Should it be connected to V+ and V- pins ?

    Since VOCM pin is a output pin, can we connect power supply to it ?

    The previous stage of OPA1632 is TLV320AIC14K codec. The output of TLV320AIC14K codec is connected as input to OPA1632.

    The DAC gain of TLV320AIC14K codec can be configured to max 20 DB through software. Is this enough ?

    Or do we need to adjust the gain using Rf and Rg resistors provided in the datasheet of OPA1632 ?

    Warm Regards,


  • Hello Manjunath,

      +/-15V would be set to power supplies Vs+ (15V) and Vs- (-15V) for maximum output voltage range.

      VOCM sets the output common mode voltage. Thus, VOUT+ and VOUT– swing symmetrically relative to VOCM. It is best to set VOCM to mid-supply, which in this case would be to ground for optimal distortion performance. For this device, and most FDAs, it is recommended to add a bypass capacitor(s) to ground either 0.1uF or 1uF to reduce noise. Some examples below:

      Thank you for the additional information. Yes, that should be enough gain. Correct, I would suggest adjusting RF and RG to unity gain 390Ohms each as you have shown from the datasheet.

    Best Regards,