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TAS2781: TAS2781 Hybrid-Pro with TAS5825P Hybrid-Pro

Part Number: TAS2781
Other Parts Discussed in Thread: TAS5825P,



Just wanted to make sure if it is possible to have both the Hybrid-Pro from the TAS2781 and TAS5825P connected to each other like shown here:

In this application 2x TAS2781 and a TAS5825P share the same I2S LRCLK and BCLK and all operate at 1.8V IO-Voltage.

All the Hybrid-Pro PWM outputs are directly connected to each other in Open-Drain config and a Pull-Up resistor to 1.8V (resistor not shown).

All PWM outputs are set to 16-Step 192KHz and will use the LowPass-Filter suggested in PPC3 for the TAS5825P.


Alternative connection config:

All 3 Hybrid-Pro PWM outputs are set to Push-Pull outputs and are connected to a 3-Input OR-Gate with Push-Pull output, like the SN74LVC1G332. This output is then routed through the LowPass-Filter suggested in PPC3 for the TAS5825P.


The PPC3 Config:




Is this possible and is there anything specific that needs to be taken into account?


  • Hi FXtreme Logic engineer ;)

    I am checking with the team, but this should work as i believe both devices use the same circuit block for the class-H control

    your first suggestion is the correct one. no need for additional active components between the Amps and the boost. 

    short both of the PWM outputs together and then pass them through the low pass filter.


  • Hi Arthur:)

    Thanks for your reply!

    That's great to know, thanks. I assume that, although not necessary, it is possible to use the OR-Gate as described earlier?

    I see this as the best option as this way the output voltage of the Boost Converter is not affected by the extra e.g. 1K pull-up resistance needed with the Open-Drain config. It also appears that this is more efficient, as there will be no additional 1.8mA (1.8V IO) current draw from this resistor if an OR-Gate is used.


  • I’ll give a full answer shortly 



  • I heard from the TAS2781 designer, the Class-H block was taken from TAS5825P. I am waiting for a bit further confirmation that they are compatible. however I think it is safe to continue for now under the assumption that they are compatible

    It will be possible to use the OR gate solution that you mentioned. you will just need to solve the circuit to make sure that when PWM_CTRL = IOVDD and then PWM_CTRL = 0V that the correct boost voltages are being met. I believe this will be very much similar to the use case where there is a single device controlling the PWM_CTRL signal and the outputs are configured as "Push-Pull" 

    If you have not yet seen it this app note is a good reference 


  • This is all very helpful information, thanks!