Part Number: TAS5825M
I'd like to use one of these parts for a sonar application, generally in the 40-80kHz range, and at high power. Equivalent load to the amp will be around 2 ohm (maybe 4 depending on how important that is). Running at BTL or PBTL is fine, we will probably use PBTL to accommodate a lower value load. We were planning on 24VDC power, 192kHz.
We've done some experiments with the 5756 but reaching published power levels in this frequency band has been difficult. It's pretty good though overall.
Which of these parts would be most suitable? It seems that the TAS5825 is a newer, smaller design with fewer external components, but fidelity isn't quite as good (though 0.03% THD vs 0.007% probably isn't a big deal). Rds is about the same, so I'd expect similar thermal properties, and power handling and efficiency seems to also be about the same. Switch frequency is the same. Flexibility with experimenting with modulation type on the 5825 is helpful for experimentation. Also the lack of external coupling of the DAC to power section of the 5825 (compared to the 5754/6) makes the circuitry a bit simpler.
Any other important differences I should be aware of? One unknown is how each amp responds to a non-speaker-load in this frequency range; while the equivalent is about 2 ohms, the piezo load is quite reactive, so both magnitude and phase change quickly with frequency, and it's unclear how the closed-loop control will respond.
Thanks for any guidance.
If you are using a 2 ohm load it would definitely be recommended to use PBTL as the minimum load impedance for BTL is 3.2 ohms vs PBTL has a minimum load impedance of 1.6 ohms.
The TAS5825 would be recommended for evaluation over the TAS5756/54 as it has our most advanced and flexible digital processing flow and the PPC3 software offers the most ease of use in configuring and evaluating our device.
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In reply to Luis Fernandes de Pina:
Thanks! Is the DSP core available at 192kHz? I recall it wasn't in the 5754/6, so that would be nice.
Is there any notable difference in raw performance between the devices in this frequency band, and with this load? THD, power capacity, efficiency, etc. How do they compare? Is there a difference in the control loops that would affect this band?
I didn't see any substantial differences from a look at the datasheets but sometimes subtle things make a big difference, especially when it's a nonstandard design like this.
In reply to Joe454:
The DSP can support 192kHz sampling. We not do not have performance data for ultrasonic frequency as since this is device is primarily aimed at audio applications our datasheet has performance data for audio frequency bands. Since typical load applications are 4-8 ohms we typically only have performance measurements for those loads as part of our device validation.
In regards to the control loop differences in the devices it would be hard to say how they would affect the ultrasonic frequency band as ultrasonic performance is not something that is part of our validation and verification process for our devices.
Ok thanks, I suppose I'll have to buy an eval of each and try it.
I just checked the Process Flows document, and it appears that the only setup that supports 192kHz is Process Flow 8, which has no DSP capability. Am I misinterpreting this? LIke the 5754/6, it appears that there is no DSP for configurations using 192kHz, but I could be mistaken.
(192kHz input can be used, but only if it's downsampled)
For 192K process flow, as you can see in PPC3 GUI, the resource is much less due to the limitation of MIPS.
In reply to Alix Wan:
Yes, I understand there is much less resource available at 192kHz, but I was under the impression that this part had some DSP capability at this rate, but it appears to have none, like the 5754/6. It's fine, I just wanted to be sure I understood.
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