OPA1637: Maximum output

Hi Jonah,

As you have mentioned, unfortunately, the datasheet only offers Figure 6-4 Total Harmonic Noise and Distortion up to 10VRMS with RL=2k,10k, and the datasheet does not specify nor offer THD+N performance plots beyond this amplitude where performance starts to degrade.  We currently don't have data beyond this amplitude with a 600-Ω load.

Thank you and Regards,

Luis

Someone put this on the data sheet for a reason: "The OPA1637 also features high-voltage capability, which allows the device to be used in ±15-V supply circuits without any additional voltage clamping or regulators. This feature enables a direct, single amplifier for a 24-dBm differential output drive (commonly found on mixers and digital audio interfaces) without any additional amplification."

Can you find that person and ask for their data? "[W]here performance starts to degrade" is different than the graph taking off into unusable THD.

Thanks.

Hi Jonah,

I will re-verify to see if data is available beyond the 10-VRMS amplitude with the development team. For RL = 10k and 2k load, the data would be relatively close to the performance shown above.

However, for the 600-ohm load case, and 12.5 VRMS output,  the condition approaches current limit drive capability.  The typical short circuit current limit of the device is 31mA typical spec (not minimum spec), and the current drive will be approaching ~30mA.  The device needs to operate at a conservative current output well below the output short circuit current capability.

Thank you and Regards,

Luis

Thanks for looking into it. The 12.5Vrms/24dBu question is aimed at the 2K/10K load condition; the 600 ohm performance is a secondary interest. I wouldn't expect this part to perform well as a 600 ohm line driver, and would be impressed if it could do 9Vrms cleanly into that load. But it's important to know where exactly the response pivots into distortion, and this is the only FDA in the TI stable that is advertised for pro audio line level and is lacking that data point. There is no reason to cut the graph off when THD starts to climb. We want to see the slope.

HI Jonah,

I have contacted the validation team, let me see if we can find more data or perform a test.

Please allow a couple of days.

Thank you and Regards,

Luis

Cool!

Hello Jonah,

There is no data immediately available on our database. 

I only have a THP210EVM in hand, which does not include the XLR connectors to optimally connect the device, and have one OPA1637EVM on order which will take a few days to arrive.  Nevertheless, a quick test on the THP210EVM performs well up to 20Vrms with the 2kOhm load with THD+N < 0.001%.

Thank you and Best Regards,

Luis

Based on your findings, I drew a quick application. Correct me if I’m wrong (please!), but is the THP210 sourcing and sinking 19.8mA here? 14Vrms = 19.8Vpk, into 1K differential. Dual 15V supplies FWIW, but with the near-RRIO aspect of both ICs, one might look at dual 12V supplies as an option. I’m sure there would be a THD increase, but the source/sink plots appear to support the concept even at 125deg C.

The termination is just shorthand for the inputs to another FDA. This is a differential line receiver with a T-bias scheme, and the noise from the 1M bias Rs cancels in the THP210. OPA2210 + THP210, two great tastes that could taste great together…

HI Jonah,

This should work.  You are correct, if the signal is 14Vrms or 19.8Vpk differential, the load seen by the THP210 is the parallel combination of the load and feedback resistance, resulting into ~19.8mA pk.  See below:

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8737.THP210_march28_2023_forum.TSC

Thank you and Regards,

Luis