TAS5634: Lowest PWM frame rate?

Hi Luis,

Okay, I missed the 'stuck at fault' condition. The reason I ask is that I was throwing around some wild ideas about how to drive the PWM inputs of a TAS5634. I would like to use an IC with a higher PVDD rating, to achieve absolute maximum output power into 4ohm load. I always found it strange that this IC has higher voltage rating on its PVDD supply pins over the TPA3255. But having asked this question before I am assured that it is true. To this end I would need to drive PWM into the IC. However TI only seems to recommend using the multi-channel DSP oriented PWM modulators. I have no need for such complexity and instead just need a simple PWM modulator, for just a single channel. All the DSP work filtering and such will already be achieved elsewhere in the system. I am forced to consider a PWM modulator in this case simply to make use of the TAS5634. As I can not find such an simple PWM modulator from TI, I was.......wait for it, considering using a low power TPA Class D chip, and simply not bootstrapping the HI output. I'm fairly convinced that the propagation delays and dead time associated with this low cost approach could be worked around. However it is clearly far from ideal. The problem was that the low power TPA ICs do not run at the same switching frequencies as the TAS5634. In fact they fall outside the defined PWM frame rate range. So it looks like this is out of the question anyway.

The truth is I am now genuinely having to start to look at another vendor. I can not achieve high enough output power levels at 4ohm from the TPA3255. It runs out of steam and would lead to high THD levels in combination. It is a shame as it is the last 10V's or so of PVDD span that causes these limitations. The TAS5634 can squeeze a little more out of the IC package and from experience I am convinced that I can manage the heat dissipation associated with this approach.

In fact I would also like to experiment with using multiple TPA3255 or TAS5634 ICs in parallel. 'What on earth'? you may ask, but actually I have already successfully done this with another vendor's Class D IC (STmicro). This vendor also used a fixed frame rate. In this situation, I was successfully able to parallel the outputs of 2 ICs,  (After the LC filter), so space and cost is a consideration. Have TI actually tried this before. I think for a fixed frame rate architecture this will probably work and a common clock would only improve upon this?

What I can say is that I have already experimented with the TPA3255 running very close to maximum PVDD voltages. It get hots! very hot. Hence the reason why I would like to experiment with parallel IC both running in PBTL mode. It's simply a matter of spreading the heat load and keeping THD under control to some extent. 

All the above would apply also to the TAS5634 with a nudge better power performance. 

As an adjunct, I have been wondering what TI are doing in the class D area. Many vendors are now upgrading and expanding the class D portfolio. The focus seems to be on compact and higher operating voltages and improved efficiency with lower RDS on. Having said this I am very pleased with TI's internal subsystem. They work well and have for the most part proved to be robust. 

I simply need lower RDS on, higher operating voltages and IC packaging that allows me to dissipate the heat. I am desperately trying to avoid going towards a discrete class D solution as there are so many advantages to using ICs.

What can TI say about this situation. Let us not forget Infineon are out to grab your customers, this is clear.

Thanks Luis, 

I think you have confirmed what I already thought. Seems I did not miss anything from your portfolio. I understand that probably I am directly sitting in the niche. I am developing pro-audio systems, and naturally high output power levels are always needed.

Having said this, I would like to offer some further feedback: I have never understood why TI do not offer the driver stage from within the TPA / TAS systems and expose the gate drive directly (pre and post level shifter). This would potentially allow niche customers to raise the working voltage of the power stage and potentially even use GANFETs as well. 

If I am not mistaken today the only offerings are fully integrated ICs, but the protection features etc within the controller part of the ICs, and CBC3 mode for example are undeniably useful. Other vendors have and still do offer these parts of their system as separate ICs. Why not TI? After all it will be hard to know exactly what your customers need as a final solution and for niche cases offering a combined analog IN PWM modulator with clock distribution options, built in feedback with exposed compensation, and all the protection features of the driver would be certainly something I would jump at, where it available.

Just my 2 cents.

All the best. Feel free to mark as resolved back to my experiments

Aidan