Tool/software:
Hello Team ,
Currently using LM2904 as the non-inverting gain amplifier . Planning to replace with LM2904B for better ESD protection . Kindly confirm what are the changes need to do in my schematic to adapt the LM2904B. In current schematic there is no Rin( input signal resistor ) . Kindly confirm is it mandatory to use the Rin with LM2904B , if yes what would be the value recommended .
Hi Vasu,
Kindly confirm is it mandatory to use the Rin with LM2904B , if yes what would be the value recommended .
The LM2904B's Vin+ input is not mandatory to match the input impedance of the op amp (in theory). If RF||RG is small, then Rin is not necessary. If RF||RG is large, then it is a good practice to have Rin ≈ RF||RG. Also Rin will limit the input current to the non-inverting input, though the part does not specify the max. input current limiting requirement (Rin may be used to limit the input overcurrent conditions under high voltage conditions).
If you have other questions, please let us know.
Best,
Raymond
Hi Vasu,
Rf and RG value is 10 KOhms and 20 KOhms respectively with gain factor of 1.5. Please confirm the need/mandatory of Rin resistor in the input
Here is the circuit that will work. The Rin is not necessary for this op amp. It is good to place Rin = 1 to 5 kohm as Rin in front Vin+ pin (20k||10k), which it will limit the input current. Per the datasheet, Rin at the non-inverting input node is not needed per your circuit.
In addition, it is good idea to improve the op amp's stability by parallel Cf or C1 on top of RF resistor.
If you have other questions, please let us know.
Best,
Raymond
