Search FAQs on the left to see if your question has been answered. Click on the dropdown to view all of the documents associated with the product. If you can't find your question, click on Ask a Question.
I am currently working on a design requirement that needs to create an output of +10V and -10V at up to 20mA continuous (implies a 500ohm load). The device I have been considering for this application is the AD713. TPC3 on the datasheet implies that the AD713 should meet this requirement (500ohm load). However, TPC3 also states that the curve applies for +/-15V supplies, where my application will be working from +/-12V supplies (could go as low as +/-11.6V). How would TPC3 be modified to reflect this?
Operating from +/-11.6V minimum supply, you are going to run into output head room problems even with the output unloaded. Referring to page 2, the output swing from a +/-15V supply with a 2k load is +13V to –12.5V at 25degC and +/-12V over temperature. This implies output head room of between 2 and 3 volts to either supply. Output headroom is fairly constant as the supply voltage is reduced as you can see from TPC 2. Assuming +/-11.6V supply and a 2k load, the output will swing close to +10V but falls short of –10V. If you then factor in a 500ohm load and variations over temperature, you can be fairly confident that the output will not swing +/-10V. Is there any possibility of increasing the supply voltages? I presume you have selected the AD713 for availability in military grade and it’s biFET input (low voltage offset and input bias current). If you really need the output to swing +/-10V from +/-11.6V supply, I would suggest using the AD713 as the input stage and using a second opamp with rail to rail output stage to provide the required output swing. IF you close the feedback loop from the output of the rail to rail back to the input of the AD713, you get a compound amplifier with the input characteristics of the AD713 and a rail to rail output ( by rail to rail output, I simply mean output head room of less than 100mV unloaded).