Hi Guys
Our customer is using our opa192 for 12Vout high side current sample. Please see below the schematic:
But when test the load transient sample, we found that 12_Iout non-linear phenomenon. Please see below the waveform:
CH1: 12Vout; CH2: Io; CH4: OP_OUTPUT;
So why are there non-linear section at the transient up-going?
Thanks
-Pengfei
Pengfei,
Since your customer references the output to ground and output cannot swing all the way to negative rail, in a single supply application there must be enough differential voltage to drive the output into a linear range - in case of OPA192, Vout must be driven to 5mV or higher.
Since the gain of the customer's application is G=-200, Vin=0V would result in Vout=0V (however, Vout shown below is 1.1mV because of Vos=-5.5uV).
Under the same conditions but in a single supply application, the output swing limitation to negative rail forces the output to be at 3.6mV.
Applying 10mV differential input signal should result in Vout=-2V but in a single supply application output swing to negative rail forces the output to be at 3.5mV
It is difficult to follow all of the above waveforms so if your customer needs additional help we need more details of the application. I assume the input common-mode voltage is 12V but what is the voltage range and frequency of the input differential voltage?
Hi Pengfei,
I think the ringing is the result of the finite symmetry and finite common mode rejection of difference amplifier caused by the resistor and capacitance tolerances:
You should consider replacing the self built difference amplifier by a TI's INA. Due to the monolithic construction these chips offer an unbeatable symmetry and common mode rejection which cannot be achieved by using discrete components.
Kai
