ADA4177-

Question

Hi 
 Can I use the opamp ADA4177-2 in single supply operation? 
 It is specified for +/- 15V. 
 Can I apply 28V dc to positive supply rail V+ and ground V- 
 I plan to bias the input to the chip at 14V dc. 
 Thanks 
 Sreelakshmi R

FormerMember · Accepted Answer

SR, 
 From an email to another customer: 
 " We get this type of question a lot with respect to op amps: --- Your op amp is spec'ed on +/V, will it work single supply?? OR --- Your op amp is spec'ed on ground and +V, can I operate it on +/- supplies? With respect to dual supplies vs. single supplies, ALL op amps can run on both. The little electrons inside the op amp don't know where ground is, because there are no ground pins on modern op amps. So an op amp that is spec'ed for +/-15V operation, can run on +100V and +130V PROVIDED you observe the input voltage range (IVR) and output swings. The first op amps did not have RR inputs or RR outputs, so when National introduced the LM324 in 1975, it had a PNP input stage, so the IVR included the V- pin. So you could run it on ground and +V. So the official definition of single supply is: "An op amp whose input range includes the V- pin". To stay with this example, can I say to a customer, "Yes, you can use the part at dual supply +110V/+130V ? Does the part work in this case like specified at +-15V? Do we guarantee this? "All specification data in the +-15V table, exclusive of input/output range are valid; in other words, CMRR, PSRR, Isy, etc. are the same. Although note that the CMRR test conditions might be -10V <Vin < +10V, so you would have to adjust for this. When I was talking my network analysis course, the professor said you could pick any node for ground and write your equations for the other nodes in terms of that reference point. He also said to pick a direction for current through a resistor. If the number came out negative, it was going in the other direction. Again, there is no ground pin on the op amp, so if we measure a Vos of 100 uV on an op amp with +/-15V supplies, and then move everything in the test circuit up by 115V, then you will have 100V on the V- pin and 130V on the V+ pin. But the silicon doesn't know this, so the Vos is still 100uV. You could operate any op amp that is specified at +/-15V at 100V/130V with one BIG caveat: You have to keep the inputs and output within the rails. If you have an op amp that is specified at +/-15V and the IVR is -14V to +13V, then on 100/130V, the IVR would be 101V to 127V. In real life, this is not practical, because of power up/power down. Let's say you have a cap on the output of the op amp, and it is charged to +110V. When you shut off the power and the V- pin and the V+ pin go to zero, the cap will discharge back into the output stage and blow up the part. So with the OP497, the IVR on +/-15V is +/-13V, so you have to keep the inputs at least 2V away from either rail. So on ground and +12V, the inputs should be between 2V and 10V. For the output, with a 2k load, returned to +6V, the swing will be within 2V of either rail; i.e. 2V to 10V. A side note: For unused sections, they should be connected as a voltage follower with the non-inverting input tied to any convenient voltage within the IVR. Harry")

EZAdministrator · Answer

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