Other Parts Discussed in Thread: LM2902, TS321, OPA2131
Hi Team,
The customer is using LM2904. VCC is 5V. The schematic is in the attach. The level 1 circuit is magnified by 19 times the differential circuit.
The level 2 circuit is magnified by 11 times phase circuit. When a 2V common voltage is both input the 2 pin and the 3 pin of LM2904, the output voltage of
U100A is about 0.6V and the output voltage of U100B is about 1.2V.
My understanding: For the level 1 differential circuit, if a 2V common voltage is both input the 2 pin and the 3 pin, since the offset voltage exists, the output
voltage is 3mV offset voltage *19 =57mV. This value is closed to 0.6V.
But for the level 2 circuit, 0.6V is the common voltage, the output voltage should be 0.6V*11=6.6V. Since VCC is 5V, so the output voltage cannot reach 6.6V.
I use TINA to simulate his circuit. But the output voltage of the level circuit is 98.57mV.
Q1: For the customer's output voltages, would you explain the reason?
Q2: Is my understanding correct? If my understanding correct, why is the test result different from the simulation result for the level 1
differential circuit?
Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments
