THS4524: unity gain differential amplifier offset?

Mani Kandan Devarasu

Part Number: THS4524
Other Parts Discussed in Thread: THS4551, TPS54521, ADS1278

In my design i have added THS 4524 Differential Amplifier for driving single ended input signal to differential output with feedback gain set to unity.

below is an sample reading from the DSO.

Single ended input signal (V) to THS452X	Diff. output(V)	offset for unit gain(mV)
1.26	0.89	370
1.31	0.929	381
1.34	0.954	386
1.39	1.01	380
1.43	1.04	390
1.47	1.08	390

Why is the THS4524 differential output is not converting my single ended input to expected differential output?

For example 1.25V single ended to 1.25V differential output

thanks

Mani

over 5 years ago

0 Jacob Freet over 5 years ago

TI__Expert 8650 points

Hi Mani,

Are you able to share your circuit schematic? What power supplies are you using and what is the common mode of your input signal?

Regards,

0 Michael Steffes over 5 years ago in reply to Jacob Freet

Guru 48395 points

Yea Mani, that question is way to open ended to close up.

1. Full schematic would be required.

2. DSO? be careful about adding any measurement C to the I/O pins - oscillation hazard.

3. The layers of output differential DC offset are a little deeper than basic op amps, this attached article tried to step through that - actually found a term I was mistreating in earlier FDA datasheets like the THS4551.

This was originally a Planet Analog article, but they broke the figure expand links in an Aug. 2019 platform migration -

https://www.planetanalog.com/dc-precision-considerations-for-high-speed-current-feedback-and-fully-differential-amplifiers-insight-4/

Here is the pdf original,

DC error considerations for High Speed CFA and FDA's article Dec25 update.pdf

0 Mani Kandan Devarasu over 5 years ago in reply to Jacob Freet

Prodigy 140 points

snip of the schematics

Power supply for the THS4524 here is from an 12V buck to 5V using TPS54521.

Reference is 2.5V from ADS1278(VCOM)

thank you,

0 Michael Steffes over 5 years ago in reply to Mani Kandan Devarasu

Guru 48395 points

Thanks Mani,

Without running any sims, that 10nF feedback is hazardous from a stability standpoint - if you removed those temporarily, and probed differentially at C467 does the gain look right?

Also, does the sensor have a DC output impedance we need to include in the analysis?

0 Mani Kandan Devarasu over 5 years ago in reply to Michael Steffes

Prodigy 140 points

removed both feedback caps ,seeing offset again-also high frequency noise (3.8 MHz)

For Dc output impedance : its a pressure sensor and it does not have an specs on datasheet.

thanks

0 Sima Jalaleddine over 5 years ago in reply to Mani Kandan Devarasu

TI__Mastermind 27465 points

Hello Mani,

Sorry for the delay in response, would you be able to send us scope shots for two circuit setups: without the feedback caps and with feedback caps lowered to 1.5n?

Thank you!

Sima

0 Mani Kandan Devarasu over 5 years ago in reply to Sima Jalaleddine

Prodigy 140 points

found this issue in particular to one board only.

same design is working in other boards.

not sure if this is an component malfunction.

thanks

Mani

0 Sima Jalaleddine over 5 years ago in reply to Mani Kandan Devarasu

TI__Mastermind 27465 points

Hello Mani,

Thank you for the quick reply! Would you be able to test the device on the boards that work? Or have you already done that and it seems to be the device itself rather than the board?

Thank you,

Sima

0 Sima Jalaleddine over 5 years ago in reply to Sima Jalaleddine

TI__Mastermind 27465 points

Hello Mani,

Were you able to determine the root of the problem?

Thank you,

Sima

0 Mani Kandan Devarasu over 5 years ago in reply to Sima Jalaleddine

Prodigy 140 points

Its particular to that part.

I had replaced with new one and found to work satisfactory.

Thanks

0 Sima Jalaleddine over 5 years ago in reply to Mani Kandan Devarasu

TI__Mastermind 27465 points

Hello Mani,

Thank you for the update. I will be closing this thread; if this situation occurs again let us know by either replying to this thread or starting a new thread.

Thank you!

Sima

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THS4524: unity gain differential amplifier offset?