Hello,
What function would you like to achieve with this device?
If you connect the device in single supply configuration, these are your limitations:
INPUT:
VCM or average voltage seen at inputs must be greater than -.1V when V- = GND. VCM must also be less than V+-3V for linear operation.
This means if you supply the device with +30V for V+, and GND for V-, your worst case valid VCM range would be -.1V to 27V.
OUTPUT
Output swing depends on output current, but we can use this table to estimate swing to rail performance:
If you can provide more details for what you would like to accomplish, I can help with designing a circuit for you.
Remember also, most all applications using the OPA549 will require a relatively large external heatsink due to the high power dissipation of this device. I can help with picking a heatsink once we hash out the project requirements here.
Best,
Jacob
Hey, thanks for the additional details, this is very helpful to me.
Either the OPA549 or the OPA541 would be suitable to this application.
Something simple like this can work well:
Do you know your servo coil impedance? It will also be important to consider total power dissipation here. 10A will be lots of power dissipation in the output stage.
The OPA549 for example will only do 10A pulsed. Worst case, it may be beneficial to use two amplifiers.
Here is a curve which defines the output current relative to VDS across the output stage transistors:
Best,
Jacob
Hi Jacob,
The schematics of the circuit is on the below. There are two modules because of two motors . As you see, the amplifier has got characteristic of current control. Can we provide this feature with OPA549?
M. Bulent KAYA
You are correct regarding the schematic. This is a very strange device to me, but it does look like the datasheet recommends +28V+-4V for V+ and -15V+-2V for negative supply. This makes +27V and -15V a valid operating range for the part.
I am also interested in understanding how the current drive is functioning with just 1.5A limit on the V- rail.
I take it the motor has the negative terminal grounded since we have one motor driver per motor. Surely these motor drivers can rotate backwards, right? If we were only driving one direction, or there was only significant mechanical loading in one direction, then it would make sense for V+ to have higher current requirements than the V- rail.
Yeah, I think signals, especially being output and input signals will be helpful here.
The E1308 datasheet is a bit short, but it has offered some help in understanding how this driver may be operating.
Thanks,
Jacob
Yes, the OPA549 will run on an unbalanced supply rail without issue.
There are two effects here to think of.
1. output swing limits
2. current limiting (either from the rail or from the device hitting IOUT max)
If the impedance of the motor windings are excessively high, we would presumably run out of output drive. I can only imagine our OPA549 is a better performing device compared to the original amplifier used, but there is still some risk.
If the V- rail is truly limited to supplying just 1.5A, then we will likely see some non-desired performance in driving the servo if the motor load ever wanted more than 1.5A.
As I understand, the servo is a DC motor, which has speed correlate with motor voltage.
Here is a simple simulation which shows the performance with an impedance I may expect to see out of a motor:
Here, we are not having issues with output swing, though we are also using an ideal power rail.
Here is the same simulation with a power limit on the V- side.
I am not completely sure why the 1.5A limit would exist, this feels like it would limit functionality for this system. You are correct on the other way of interpreting, maybe this means that the servo driver on the positive side is way overkill for what is needed. Still a very strange design to me. Maybe signals will tell us more.
Thanks,
Jacob
