MAX9768 nearest replacement

Hi Derek,

Thanks for the suggestion. Unfortunately, the customer doesn’t have space for the suggested part as it would take two channels for the stereo. We need to have a mono class D amplifier with a size similar to or close to the size 4mmx4mm. Also to be more specific, the power requirement on the amplifier output would be somewhere between 3-8W would be acceptable ( eg:- 3W or 5W or 8W, etc). Please help us to suggest the nearest possible device. 

Best regards,

Jonathan

Hi Derek,

Thank you for the help.

This part is not suitable for the Mono channel requirement. It's only for the stereo. We were are able to find part # TPA2028D1 suitable for a 4 Ohm loudspeaker with 3W output. But for an 8 Ohm load, it will provide better performance till 800mW only.

This IC seems to be perfect for our application apart from the 8-ohm limitation.  So could you please suggest a similar part that can perform at the same level @ 8 Ohm?

Best regards,

Jonathan

Hi Derek,

Thank for clarifying this. But  our system is already built and in production. The gain we have set on the previous design is 16.1dB (since max9768 having fixed internal gain of 20dB, we need to reduce it to 16dB by the use of feedback pin at the input by adding -4dB). But in the suggested part , I can see only 2 x available gain settings ( 20 & 26 dB).

• Please suggest, is there any way to do this with the TPA3139  or suggest something which meets the requirement
• Or let us know how to control or reduce the gain to 16dB without degrading the audio performance.
• What is the power output, if we can operate TPA3139 in Mono mode?

Please note, our PVDD voltage is VBAT=7.2V

Best Regards
Sharvy

Hi Sharvy,

TPA3139 Gain setting can not be adjusted, it is fixed by internal.

The easy way is to adjust input level. Do you think it is possible way for your systerm?

Regards,

Derek

Hi Derek,

I check internally. We couldn't  adjust this at codec level at the moment. Any changes on the codec level would change our entire inventory. Could you please let us know, what are the method to adjust the gain at the input of this audio amplifier without compromising the audio performance, before it fed to the audio amp.

Also, please let us know if any suggestions on different part numbers.

Best Regards,

Sharvy 

Hi Derek,

As you recommended we have added a resistor at the input & recalculated the gain accordingly. Please let us know, our approach is correct or not.

• Assume we are using the gain 20dB. So as per datasheet, the internal input impedance is Zi = 40kOhm .
• As per parameters given on the datasheet (section 8.2.2.4 Input Resistance) we can derives the Zf as 400K
• Our required gain at the output of audio amp ( TPA3139 ) 16dB. So, we have to trim down the input to -4dB.
• So as recommended by TI , if we increase the input impedance let's say Rin as 14 KOhm, the effective input impedance ( Rin+Zi) will increase. We will add this resistor (Rin) between the input capacitor & the input pin of the audio amplifier. So at the output of the audio amplifier,  effectively we will be able to reduce the gain to 16dB. This is calculated based on the inverting amplifier gain ratio formula (refer below the basic diagram of adding resistor).

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Best Regards

Sharvy

Hi Sharvy,

Adding resistor between capacitor and input pin will increase capacitor charge time, it may have pop risk. 

Hi Derek,

Can you please give your thought on how to implement your suggestion of adding resistor on input to reduce the input level?

Best Regards

Sharvy

Hi Derek,

I am very new to the audio design.

• Can you please verify & confirm below resistor values are correct to produce -4dB attenuation on gain at the input of audio amp?
• Also, please let me know what are the side effects which you think this solution might have? 
• Do you think, if we need any unity gain buffer (op-amp) after this divider network?

Best Regards

Sharvy