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INA1620: Product recommendation request for headphone amplifiers.

Benjamin
Intellectual 290 points
Part Number: INA1620
Other Parts Discussed in Thread: TPS65131, , BUF634, BUF634A

Tool/software:

Hello,

I am looking for a recommendation of product(s) for a simple dual headphone amplifier device.

Here are our design specs and goals (Headphone driver specs are attached below):

  1. Purpose is to showcase our new consumer headphones, so low noise and distortion are important.
  2. Reliability also favoured (Eg hard to break by shorting output)
  3. Amps will be fed with single-ended audio signal
  4. Each device will have two stereo outputs (for two sets of headphones)
  5. Device is powered by 5V, but we can easily make up to +/-15V with TPS65131
  6. Each headphone amp should have a single volume pot, but we don't want to use a microcontroller, so volume control can come before the amp input (either with a stereo pot or VCA)
  7. Prefer not to use electrolytic capacitors

I am leaning towards the INA1620, but also considering something like a simple op-amp design with BUF634 or complimentary output driving transistors on the output.

Any advice on these parts or others?


  • 0
    TI__Guru* 77541 points

    Hi Benjamin,

    Benjamin said:
    Here are our design specs and goals (Headphone driver specs are attached below)

    INA1620 is a good option, but you did not specify the max. power that you are intend to drive. At higher temperature, the output current will be limited due to poorer dissipation, unless you have airflow or large surface area to dissipate the heat from the PCB surface at elevated temperature. 

    Benjamin said:
    also considering something like a simple op-amp design with BUF634

    BUF634A is an option to boost the output current, and it is better in specification than its predecessor, BUF634. However, I do not believe BUF634A has current limiting feature and current fold back protection or thermal shutdown feature. So you have to find a way to limit these overcurrent and temperature condition and limit the damage. May Use polymer fuse to limit and prevent these conditions.

    Benjamin said:
    complimentary output driving transistors on the output.

    The complementary approach will be ok, but you will have all the issues in both INA1620 and BUF634A combined. Basically, you are building an output stage in discrete components similar to  BUF634 topology, and increase the footprint of the audio amplifier. And you have to spend a great amount time to find tune the output behaviors. it is not recommended, unless you need to drive higher amount of current. 

    Benjamin said:
    Device is powered by 5V, but we can easily make up to +/-15V with TPS65131

    Using DC/DC switcher for precision or Hi-Fi audio is not recommended. You will be better off you use LDOs to step down the voltage or increase power rails with larger battery pack. If the switcher is designed correctly, you may be acceptable. 

    If you have other questions, please let us know. 

    Best,

    Raymond 

  • 0 in reply to Raymond Zhang1
    Intellectual 290 points

    Hi Raymond, thanks for your help

    Raymond Zhang1 said:
    INA1620 is a good option, but you did not specify the max. power that you are intend to drive.

    Max power of the driver is 20mW into 32Ohms, so i think we should be well within a safe zone with the INA1620 right? I can dedicate about 60cm2 of double sided PCB to each stereo amp 

  • +1 in reply to Benjamin
    TI__Guru* 77541 points

    Hi Benjamin,

    Benjamin said:
    Max power of the driver is 20mW into 32Ohms, so i think we should be well within a safe zone with the INA1620 right?

    If the max. power is approx. 20mW, the temperature rise will be approx. 13.1C/W * 20mW = 0.262W, and it should be safe. 

    You specified that max. input power is 20mW, so the output driving power has to be greater than 20mW. 

    I would still increase the PCB dissipation surface area and may consider to use 2oz copper (instead of 1oz Cu). 

    If you have other questions, please let us know. 

    Best,

    Raymond

  • 0 in reply to Benjamin
    TI__Mastermind 26965 points

    Hey Benjamin, 

    To add on to Raymond's comments I have tested the INA1620 EVM in the past to drive headphones into 3 ohms (very heavy load) and it worked very well. I tested with +/-4.75V though. With 32 ohms you will be a magnitude of 10 times lighter in regards to ohmic load with higher output voltage swings. This will come down to current limit drive on the output. The INA1620 can drive 145mA of current at room temperature. For my test I got a peak current of 128.98mA due to thermals and it was still very good on the EVM. 

    Here is a link to the Evaluation Module (EVM):

    INA1620EVM

    If you need more current drive you can parallel two INA1620's as shown in this app note here:

    Parallel INA1620 Headphone Amplifiers for Higher Output Power

    For my parallel amp test driving stereo I used two INA1620 EVM's wired up in parallel. See results on second slide below. I went from 24.97mW with a single amp vs 92.5mW with the parallel configuration. 

    My tests below I purposely drive the output into current clipping to measure the max I could drive with each configuration. I hope this helps with your design. 

    Best Regards, 

    Chris Featherstone