Other Parts Discussed in Thread: TINA-TI, TEST
Our customer is simulated LMP7721 in TINA-TI for an electrometer application and would like to confirm if the simulation result is correct. According to our customer,
I am using the Spice simulator to build the design and have observed a wide variation in input currents. I want to know if this is correct.
The device is being used in a transimpedance configuration. The input current is from 0 -10pA. The feedback resistor is 10G Ohms.
The positive input to the device is set to 1.25V by a voltage reference - in the simulator I am just using a Voltage source.
With Vcc = 2.5V and VSS = 0V, the input current is 58fA. But by making slight changes to either the supply Voltage (3.3 or 5V) the changes in input current are huge. Also if I adjust the reference Voltage on the positive input I likewise get huge variations in input current which I don't understand.
Is this behaviour correct or is the real-life part better (more stable/predictable)...?
By increasing the supply Voltage to the LMP7721 from 2.0V to 5V the change in input current is significant.
Does the real part behave this way..?