Post Go back to editing

Connecting to 8 ohms speaker

Category: Hardware
Product Number: MAX9860
Hi,
 
I am looking at MAX9860 as a replacement for an existing design of ours. I have few questions.
 
1. The current design have an 8 ohms speaker but the MAX9860 seems to be specked for 16-32 ohms speakers. Can an 8 ohms speaker be driven by MAX9860? (I guess this would load the output driver more. So I cant use max gain for DAC output?)
2. Is there an output over power limit function?
3. We use a single MEMS mic (Knowles SPH6611LR5H-1). All I have to do is AC couple this to MICLP with MICLN AC coupled to AGND? 
 
Thanks,
Kay
  • Hello, Kaushalya,

    1. The MAX9860 is intended to drive a mono headphone speaker.  It is able to drive an 8Ω speaker, but the volume would be much lower than what can be provided by a speaker amplifier.  The output will also likely become more distorted at lower power than with a 16Ω - 32Ω speaker.

    If you look at the "HEADPHONE OUTPUT POWER vs. LOAD RESISTANCE" plot on page 9 of the datasheet, you can see that the "sweet spot" for output power is tuned for a 16Ω load.  The output power line is illustrating the maximum power at a specific THD+N level, and the performance decreases quickly as the impedance goes below 16Ω.

    2. There is no output over power limit function, because the MAX9860 cannot provide enough power to cause damage.

    3. Yes, this is the appropriate method for using a single-ended microphone.

    I am more familiar with legacy Maxim products so I don't have complete Analog Devices lineup information, but perhaps a CODEC with dedicated 8Ω speaker outputs would be more suitable for your application, like the MAX98089 or the MAX98090.

  • Thanks Ed,

    I can see your point regarding the 8 Ohms speaker. I have missed the Output power Vs load resistance graph. Thanks for pointing it out.

    Cheers,

    Kay