LMH6629SDEVAL: Channel IN- is not functioning

Hi

Can you check if the "RGB" resistor is populated on your board for the inverting connection? That resistor is left unpopulated for the inverting configuration and the board will not show an output if it is left unpopulated.

Regards,

Also, just to clarify, I want to use it as a difference amplifier.

Edit: 

I take my previous reply back. After looking at the schematic again, I don't think it's as simple as I said. So my question now is: is it possible to modify the board so that I can use the amp for differential amplification? 

Hi,

My apologies for the response delay over the US holiday. For a difference amplifier you can follow the standard configuration shown in the following image.

upload.wikimedia.org/.../300px-Op-Amp_Differential_Amplifier.svg.png

You will need to make sure that you match the source impedances correctly and will also need to configure the device with enough gain so that it is stable (10 V/V in the default mode of the LMH6629).

Regards,

Hi,

Thanks for your reply and hope you had a happy Thanksgiving.

I'm familiar with differential amps. My question was more about the eval board itself and not about using the LMH to design a new circuit. The inputs will be 50-ohm terminated. Are there standard component values you could tell me and connections that I can make/change on the board? I could just simulate the circuit but I wanted to check here first if: a) modifying the board as such is possible (no caveats that I wasn't aware of). and b) if there was a BOM and an available differential design made for this specific board that I could follow. Alternatively, Is there an eval board for the same amp but setup for differential input?

Thanks.

Hi,

Unfortunately the board by default does not have a configuration as a difference amplifier because there is no space for a series resistor on the non-inverting input. It is possible to cut the trace on the non-inverting input and manually insert a series resistor. I would only suggest trying that option if you are comfortable making manual PCB modifications because it is possible to render the board useless in the process. You could also try to shift the SMA connector for IN+ so that it's input is not connected to any traces. You can then solder and jumper a series resistor to the top of the Rin resistor connection. If this is not clear, I can send you a diagram showing what I mean.

Regards,
Jacob

Thanks. No need for a diagram this was helpful enough actually.

One last question just to confirm, I will need to populate RGB and put a series resistor in IN+ befor RIN. Correct? Anything else I'm missing? Shouldn't I disconnect RGA? 

Thanks,

Mohamed