THS4531: ADC Signal conditioning for 28377D

Jongwan Kim

Part Number: THS4531
Other Parts Discussed in Thread: TMS320F28377D, , TLV9004

HI,

I have a question using THS4531 as a signal conditioning circuit for TMS320F28377D.

Currently, I am using a differential signaling mode (16 bit) ADC with 3 V VREFHI, and 1.5V VOCM. The circuit diagram follows the figure below (from tidu569)

I am wondering if I can use the circuit for a single-ended signaling mode (12 bit) adc only with single output (AINP1P) as shown in the figure below.

Best Regards,

Jongwan

over 4 years ago

0 Michael Steffes over 4 years ago

Guru 47485 points

Hello Jongwan,

Their are not very many single input ADC's input - almost all are differential. The point of the FDA is to deliver the differential signal they need centered on the required Vcom voltage. You could use one side, but dummy load the other to match - the single sided signal is not going to be as good as differential in DC precision and distortion - also,

1. If you care about DC precision, use the improved THS4531A
2. When you think you are done, make sure to check phase margin using the approach described here.

www.planetanalog.com/author.asp

0 Jongwan Kim over 4 years ago in reply to Michael Steffes

Prodigy 50 points

I need 16 ADC channels which can't be configurable with differential signaling mode and decide to go with single-ended signaling mode.

Can you please explain some more details about dummy load for the unused output of FDA? Do I need to connect a simple resistor to the unused output?

Thanks

0 Michael Steffes over 4 years ago in reply to Jongwan Kim

Guru 47485 points

Maybe you should use a quad op amp then - are you AC coupled or DC coupled.

0 Jongwan Kim over 4 years ago in reply to Michael Steffes

Prodigy 50 points

It is ac coupled.

0 Michael Steffes over 4 years ago in reply to Jongwan Kim

Guru 47485 points

Your filter caps indicate no more than 20kHz signal, Say you wanted 200kHz in the op amp at your low gain just over 1. Perhaps you should look for a low power quad like the TLV9004 and use a standard diff to single op amp structure for the input differencing, then AC couple the output resetting the ADC input DC CM level on the other side of that at the ADC input.

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THS4531: ADC Signal conditioning for 28377D