ADC3644: DC Offset temination loading

Felipe Sandoval

Part Number: ADC3644

Tool/software:

Hello, I have designed a fully differential amplifier that has an output termination equivalent to that as seen in section 8.3.1.2.3.1 (AC-coupled) of the datasheet. Disconnected, Vcm is ~900mV, however, once connected as shown in figure 8.7 of the datasheet the voltage appears to drop to ~525mV. Is this a problem with a solution? Thanks.

6 months ago

0 Rob Reeder 6 months ago

TI__Mastermind 45220 points

Hi Felipe,

There must be a short or bad solder joint somewhere in the circuit. The VCM should not drop to 525mV from 900mV.

If you have a schematic you can share, that might be helpful.

Regards,

rob

0 Felipe Sandoval 6 months ago in reply to Rob Reeder

Prodigy 110 points

Hey Rob,

Thanks for your help. The problem appears to arise when I probe the output of the amplifier with my scope. Do you know if this problem will persist when I connect directly to the ADC3644? Here is the schematic of my amplifier, where VOCMB_ADC is the Vcm output from the ADC.

Thank you,

Felipe

0 Rob Reeder 5 months ago in reply to Felipe Sandoval

TI__Mastermind 45220 points

Hi Felipe,

Sorry for the delay.

There should be 0.9VDC between R3/R4. The VOCM connection on the amp should be +Vs/2.

Regards,

Rob

0 Felipe Sandoval 5 months ago in reply to Rob Reeder

Prodigy 110 points

Hey Rob,

Yes the voltage between R3/R4 is the output from the ADC at 0.95V after decoupling the 2.5V from the amp. My concern was that when I probed the outputs the DC voltage from the ADC dropped significantly than the 0.95V.

Thanks!,

Felipe

Data converters

Data converters forum

ADC3644: DC Offset temination loading