AD8397 : Clarification regarding output swing range

Question

Hi Analog, I hope you are having a pleasant day !! 
 Description of the issue: 
 The reason I am here is to get some clarification regarding the output swing range of AD8397 full-swing Opamp. I have simulated a simple Voltage follower circuit in LTspice to check the maximum and minimum Voltage at the output. Below mentioned are the configuration and observations made. 
 
 I have used " ad8397.cir " model for simulation. I got this model from the product info page of AD8397 
 Supply of +5V and - 5V are given to VCC and VEE respectively 
 Input is a 1000Hz sine wave with 0 DC offset and 10VPP 
 During the positive half cycle the output clips at 4.57 V 
 During the negative half cycle the output clips at -3.64 V 
 
 Query: 
 
 In datasheet , it is mentioned " Output swing to within 0.5 V of supply rails " 
 But in simulation the observations made were different. 
 Please let me know if the simulation result is wrong Or if is there something more I need to know. 
 I have attached screenshots of the simulation result for your reference.

Thanks, 
 Sameep Pai K S

PaulCA · Accepted Answer

Hello Champ7374 , 
 I have run some tests in the lab using your setup and here are the results: 
 Dual Supply: Vs = +/- 5 V 
 Input = 1kHz, 10Vpp 
 
 Output:

Single Supply: Vs = + 5 V 
 Input = 1kHz, 5Vpp, 2.5 V DC offset 
 Output:

Based on the results above, at gain of 1, the part is still able to provide an output within 0.5 V of Supply Rails. The statement " When operating the AD8397 in a unity-gain configuration, the output does not swing to the rails and is constrained by the H-bridge input", I think this is the reason why there is 0.5 V output head room/foot room from the supply stated on the data sheet. At gain of 1, the output should be still within 0.5 V of the Supply rails as can be seen on the results above. I do agree with ZoltanDTI that in order " To avoid overdriving the input and to realize the full swing afforded by the rail-to-rail output stage, use the amplifier in a gain of two or greater. " 
 ​ 
 At gain of 2, the part should be able to provide a rail-to-rail output. Please see the simulation below: 
 In conclusion, there seems to be a problem with the spice model when configured in Unity Gain (Gain = 1). I will be reporting this issue to the LTSpice Service Desk in order for it to get fixed. Regards, Paul

Electronic Design Services - PartnerZone

Products In This Thread

AD8397 : Clarification regarding output swing range

Top Replies