TAS5611A

Hi Sean,

AC coupling is highly recommended with the TAS5611A.

The common mode voltage on the input pins ramps during startup. Although the VI_CM pin ideally ramps with the common mode voltage of the input pins, this voltage reference can be very sensitive to external loading and may cause issues and performance degradation. A buffer on this node Is most likely required in order to use VI_CM as a reference.

Also any mismatch between the common mode voltage of the TAS5611A and the input stage will cause a DC offset on the output which can cause asymmetrical clipping and a shutdown due to the protection circuitry.  

Your best bet is to try this setup to see if it will meet your requirements.

Is there a specific reason for removing the DC blocking caps?

Best Regards,

Matt

Hi Matt,

Thank you for the informative response.

I am trying to design a variable bipolar dc power supply by putting the TAS5611A inside of a global feedback loop.  I want to use the TAS5611 because it is a convenient package complete with built-in pwm conversion, gate drive, and efficient H-bridge.  

I am not sure if the device has some sort of protection against high levels of DC output.  Also, I would like to know if there would be a problem with using a significantly lower switching frequency than the recommended 390kHz, i.e. 50kHz or so.

Sean

Hi Sean,

The FPWM frequency of the TAS5611A has 3 fixed setting (400KHz, 333KHz and 300KHz).

If it was possible to run the PWM slower, 50Hz would require a very large LC filter since the cutoff frequency should be around a factor of 10 lower than the PWM switching frequency of the amp for good attenuation for EMI.

The audio performance would also be unusable and the signal bandwidth would be limited since the PWM is so slow.

Best Regards,
Matt

Matt,

I know it is not intended for the purpose, but I want to use the device for variable (slowly changing) DC.
That's why I wanted to know if it had bandwidth to DC without input capacitors.

The datasheet says it can be syncronized to an external frequency.

Sean

Hi Sean,

Can you share a bit more about the application and what you are trying to drive with this supply?

The TAS5611A will support DC. There is no protection circuitry to shut down the output or input due to DC offset so from that aspect it should meet your needs.

As for using an external synchronization to 50Hz this may work however It has not been tried before.

What is your goal with a 50Hz PWM rate? Power savings?
There is a tradeoff between switching losses and ripple voltage/current losses at the output as you go lower in PWM frequency.
At 50Hz, the gate drive losses will be low due to fewer switching transitions, however the ripple current at the output will increase for a given inductance value for the LC filter. Therefore, a very large inductance is required.

This large inductance will also slow the response time of the supply.

Best Regards,
Matt

Matt,

I'm building a +/- 20v/10a dc power supply.  I am using a 240W 24V PSU to supply the TAS5611A, which will give out a regulated +/- 0-20V at up to 10A.  According to the efficiency graphs, using device at the recommended frequency into a 2 ohm load will not yield enough headroom with the 24V/10A supply, so I would like to experiment with frequencies as low as 50KHz (not 50 Hz) so I don't eat up as much of the 4V of headroom on the supply.

The input control is an analog voltage, which feeds into a type III compensated error amplifier along with the feedback, which is the differential output voltage from either side of the PBTL output filters.  If compensating this proves too difficult, I will take the feedback directly from the TAS outputs.

Sean