Other Parts Discussed in Thread: CONTROLSUITE, DRV8301, OPA365
Hi,
I am unable to simulate OPA365 opamp performance. OPA365 is used in DRV8301 EVM. Attached the TINA9 file and the DRV schematics (C:\ti\controlSUITE\development_kits\DRV830x-HC-C2-KIT_v103\~DRV830x-HC-EVM-HWdevPkg\DRV830x_RevC_HWDevPKG\Schematic).
Pl help me to simulate the opamp.
thx
To understand what is wrong with this circuit, take a look at voltage source VS4. For simplicy, we will consider the case when there is zero voltage drop across the shunt resistor:
In this case, the voltage from VS4 is divided by 2 from the resistor divider formed by R1 and R83. Therefore half the value of VS4 appears at the non-inverting input of the OPA365. We know that signals at the non-inverting input of an opamp are amplified by the equation 1 + RF/RG, and with the values shown above, this will give a gain of 11. In your simulation you have VS4 set to 1.65V, so the opamp wants to drive it's output to (1.65 / 2) * 11 = 9.075V. However, the opamp only has a 3.3V power supply and so its output is forced close to this power supply voltage. If you would like 1.65V with 0 current through the shunt than the voltage at the non-inverting input needs to be 1.65V / 11 = .15V and because of the voltage divider VS4 will need to be twice this value: .15V x 2 = .3V. Try setting VS4 to .3V and see if your circuit functions properly.
Looking at the circuit as a whole, from the goals you wrote in the tina file, you want a 3V span, centered around 1.65 for +/-60A of current in a 2mOhm shunt. This means that you need a gain of 12.5 ((span/2)/(/.12V). The voltage drop across the shunt will see the OPA365 as an inverting amplifier and will be amplified by the equation (-RF / RG), so the ratio of R5 to R4 must be 12.5. The gain applied to the non-inverting pin will be 1 + (R5/R4) and this means the ratio of R1 to R83 must also be 12.5 if you are to use a value of 1.65V for VS4. Standard 1% resistor values with these ratios are shown below, but any resistor values that have the proper ratio will work:
Performing a DC sweep of VG1 from -.12V to .12V to mimic the shunt voltage gives:
I previously had not seen the schematic because I do not support the DRV8301 part. Looking at the schematic, yes this is a differential summing amplifier that sums the voltages across the three shunt resistors. You should notice that the value you use for R1 in your TINA schematic does not match the schematic for the EVM, it is 49.9k not 4.99k. This circuit can be simulated in TINA using three current generators each with a specified phase shift (available for sinusoidal waveforms) and doing a transient simulation.
You may change the input waveform to sinusoidal by double clicking on the current generator to open this dialog:
The default signal is "unit step", click in this box to highlight unit step, and then click on the "..." button. This brings up the new window:
Click on the button for a sinusoidal waveform and enter the specifications for your desired waveform.
