Original question:
need a programmable gain amplifier to get output from 0 to +/- 10V.
Other Parts Discussed in Thread: DAC11001A, PGA202, PGA103, PGA280, PGA281, OPA4182, OPA4191, OPA1604
I am looking for a PGA for the output from DAC11001A to be able to output up to +/-10V, but also take a 5V output down to 0.5V. Do you have any devices that would do this? Or another suggestion on how to accomplish this? Thank you
Hi KB,
Unfortunately we do not have a PGA that can output +/-10V with your desired gains. PGA103 and PGA202 have 36V supplies but their gain settings are somewhat limited and they cannot attenuate. PGA280/PGA281 have more flexible gain settings but will require an additional gain stage at the output to achieve the +/-10V output swing.
Kai's suggestion to attenuate up front is likely the best option, however with your unbuffered DAC output this will require an additional buffer stage as well. How flexible are your gain settings? What is your bandwidth requirement? I can see a solution using a quad amp and making use of the PGA280 internal multiplexer that will meet the specified gain and output requirements. Below I included a simplified TINA simulation for proof of this concept using the PGA281 TINA spice model and the OPA4182.
Regards,
Zach
Hi KB,
The PGA280 does have the SPI interface as well as an internal multiplexer. The PGA281 is essentially the same device, but using a digital interface and no multiplexer. I used the PGA281 model in the simulation as the AC and DC performance is functionally equivalent to the PGA280. See the PGA280 block diagram below.
If size is a concern, I recommend the OPA4191 as your quad amp as this is available in the 4mm x 4mm WQFN package.
The PGA280 has binary gains from 1/8 V/V to 128 V/V, as well as an optional gain factor of 1.375. Depending on how tight your gain requirements are and/or if you can slightly adjust your gain through the DAC reference voltage, you may be able to omit one of the input attenuating amps and reduce to a 3 amp + PGA solution.
Regards,
Zach
KB,
As you only require four specific gain settings, the simplest and smallest solution here may be to simply use a buffer along with a quad amp and an output multiplexer to select the gain. This will simplify the design and give you more options to select small package devices.
Regards,
Zach
Zach,
I really like that idea--my only problem is that the output will be inverted, so I'd have to add another device between the gain stage and the mux. The other thing I like about using the PGA is that the gain is more flexible. The system I'm working on is relatively experimental and frequently requirements change. That being said, I can only predict the future so much 
. You have given me food for thought and I very much appreciate your help.
Hi KB,
Have you considered resolving the inversion digitally? You may be able to use processing to invert the polarity of your digital code before sending it to your DAC.
The PGA solution will likely be larger and more complex, although it does provide the most flexible gain options. Do consider that the PGA280 requires multiple power supplies with decoupling capacitors, Schottky protection diodes, and current-limiting resistors that will add to the overall solution size.
Let me know if you have any further questions and good luck with your design.
Regards,
Zach
Hi KB,
The settling time is a function of the slew rate and the small-signal bandwidth. A lot of older parts do not have a specification for settling time, although the OPA1604 datasheet does show small-signal and large-signal step response in the typical characteristics section. There is also a TINA model for the OPA160x which can be used to simulate settling time based on the slew rate and bandwidth parameters.
Regards,
Zach
