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OPA2348 can not drive the 32 ohm speaker

Mickey Zhang
Genius 12080 points
Other Parts Discussed in Thread: OPA2348, OPA314, OPA316, OPA1622, OPA1688, OPA1612

Hi Team,

The customer is using OPA2348 to drive a 32 ohm speaker. The power for the speaker is 8mW. But OPA2348 can not drive the speaker. The input signal is analog. The 
attachment is his schematic. The customer's VCM for OPA2348 is 400mV. The  output voltage value for OPA2348 is 32mV. 

Currently, the case that  the customer encountered is using the general op amp, not the audio op amp, andthe customer can only search for ways to solve this issue instead of changing to audio amp. 

Do you have any way to solve the issue?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

  • 0
    TI__Guru 60570 points

    Mickey,

    Driving 32ohm speaker with 400mV peak voltage would require 12.5mA peak output current which has to come from the supply voltage.  But having 5.23k resistor is series with supply would limit the output current to less than 1mA. Even without the 5.23k resistor OPA2348 could NOT drive 32ohm load since it is not designed to do so - its short-circuit current is +/-10mA.  See the graph of OPA2348 Vout vs Iout below.

    All in all, in order for the circuit to work in your application, you would have to remove the 5.23k resistor and use another op amp like OPA314 or OPA316 which have sufficient output current drive.  

    Our SoundPlus™ High-Fidelity op amps like OPA1622, OPA1612 or OPA1688 are designed specifically to drive 32ohm speakers but would require the minimum total supply voltage of at least 4V to 4.5V.