Better op-amp selection and power requirements recommendation

[pavjayt]

We are in process of updating our FPGA daughter board and would like to have some suggestions.

- The current board has 2x DAC5672 generating four analog single ended outputs utilizing 4x LT1227(running at dual supply voltage) for each channel outputting approximately 0-4V signal full scale. LT1227 has offset adjustment which is helpful for us to adjust the DC offset slightly (but the range is not much) and we are needing of few more -mV of offset so the output offset is at max -30mV which we are not able to right now. The signal itself is a positive going analog waveform (no negative output other than the offset).
Q) Is there a simple way to add adjustable offset +/-30mV without using another op-amp?

- In our updated design, we are adding another DAC5672 for two more output channels which will be bipolar outputs generated using THS3091. In the current setup, we have a +12V supply from FPGA that is run though an Inverting Charge Pump regulator (LT3261 - max 100mA) to output -12V and then both are fed into a LT3032 (Dual 150mA regulator) to generate +/-5V.
Q) With 4x LT1227 and 2x THS3091 on the board, will the above power supply setup suffice the needs? LT1227 states a maximum supply current of 15mA, but nothing in the datasheet for THS3091.

thanks in advance

 

[tumbleweed]

As far as your second question goes re: the THS3091, I think you can just use the ICC for the 3095 on that datasheet, which is shown as 10.5mA.

However, that's a high output current opamp (310mA max), so the actual supply requirement depends on the load you're driving.

 

[pavjayt]

As far as your second question goes re: the THS3091, I think you can just use the ICC for the 3095 on that datasheet, which is shown as 10.5mA.

However, that's a high output current opamp (310mA max), so the actual supply requirement depends on the load you're driving.

Good point, will be driving the outputs of THS into a 50Ohm load at max

Still not sure about the power supply setup though, since the inverting charge pump is rated at max 100mA and we are planning to update the power supply on the new design to +/-10V using adjustable LT3032. In the current setup of +/-5V, we are not able to drive the LT1227 outputs to close to 4V at full scale.

 

[tumbleweed]

In the current setup of +/-5V, we are not able to drive the LT1227 outputs to close to 4V at full scale.

That sort of makes sense since the LT1227 datasheet states "Outputs Swing Within 0.8V of Supplies"

Good point, will be driving the outputs of THS into a 50Ohm load at max

Not quite sure I get the whole setup, but if the THS is running with +/-10V supplies then each one will need about 160mA driving a 50ohm load.

and we are planning to update the power supply on the new design to +/-10V using adjustable LT3032

Maybe I'm missing something, but I don't see how all this is going to work with a charge pump that's rated for 100mA output.