TPA6203A1: The outputs have non-equal bias

Hi,
This is one of those cases in which you'll have to post your schematic and board files for anyone to even begin to venture a guess. After that, 'scope screen shots of various parts of the circuit may be called for...

B'rgds,
Mike Tripoli

Hi Yasein,

Welcome to E2E, thanks for your interest in our devices.
As Mike mentioned it is necessary a schematic and scope screenshots in order to provide you better support. Besides, If it is possible you could provide us the board files to review them.

Best Regards
José Luis Figueroa
Audio Applications Engineer

Doc1.pdf

Hello 

Thanks for quick response.

Attached is the schematic of the circuit that I am testing. As I mentioned in my post, this is just the fully differential amplifier implementation of the recommended circuit for 8Ohm load. The AC characteristics of the circuit are fine and input is amplified by 8 times. Thus, the scope output does not provide any gain. However, the DC characteristics are problematic. The  DC voltage value at the Bypass pin is around VDD/2 -0.1, and it is valid for 3V < VDD < 5V. I guess this value is expected. The DC voltage measurement at VO- is VDD and at VO+ pin is 0V (with respect to GND pin). This bias causes large current flow on the speaker, and it heats up. I guess the common mode internal amplifier is not functioning properly and causes unbalanced bias at the output pins.

I check whether input affects the bias by shorting VI+ and VI- pins. The bias is still there. I also added input DC blocking caps in front of R2 and R3, but it was not the cause. Furthermore, I removed the decoupling cap from BYPASS pin, which did not affect the bias. Also, I decreased the gain by increasing R2 and R3 to 20k. The bias is not affected.

The evaluation module measurements indicate that VO+ and VO- pins have equal bias, which is the of voltage on the BYPASS pin.

So, I am out of solutions and need your advice to proceed with TPA6203A1 device.

Best Regards

Yusein Ali

Hi Yusein,

It is always recommended adding DC blocking capacitors if using a differential input source that is biased from 0.5V to Vdd-0.8 or in single-ended input application.
I noticed that you are connecting the IN+ feedback network to Vo+ and IN- feedback network to Vo-, but they should be connected to reverse. I mean positive input (IN+) to Vo- and the negative input (IN-) to Vo+.
Please let me know if this solves your problem.

Best Regards
José Luis Figueroa
Audio Applications Engineer