This is the circuit of the mentioned two op-amps which are basically only current buffers;
They are both supplied with 12 V and GND. They share the VCOM_x reference voltage as input which is around 7 V. When I ran them without any load connected to them I noticed they are thermally terrible, up to 130°:
It is because they are drawing 850 mA when there is no load! The source of the heat must be inside the chip somewhere, not the output transistors, because when I connect the loads (i.e. 750 Ω for a 10 mA load current) I see that the input follows the output and the op-amps can withstand 1 A. As I said, they are designed to be current buffers. So this 850 mA must be heating something inside the chip. After a while this triggers thermal shutdown and the output becomes low, then an on again, off again, situation. The bottom line is I came to notice this strange thing. Look at the configs below:
12 V supply, both A+ and B+ inputs of one buffer tied together to GND in buffer mode, it is OK!
12 V supply, both A+ and B+ inputs of one buffer tied together to 12 V in buffer mode, it is OK!
12 V same supply to each, A+ and B+ inputs of IC1103 and A+ input of IC1102 are tied together to GND, it starts heating abnormally, I saw 60° without a load.
12 V same supply to each, A+ and B+ inputs of IC1103 and A+ input of IC1102 are tied together to 12 V, it blows up the power switch transistor whose current rating is 3.9 A.
When I run the single op-amp separately, I see that the output follows the input from 0 to 12 V, but when I connect their inputs together, they will almost explode. What might be the reason for this?
Best Answer
You generally cannot drive capacitive loads directly with high speed opamps. I would try first removing R1165, R1184, R1194 and R1197 and see if this solves your problem. If it doesn't you likely have a circuit error somewhere.
Next, experiment with resistor values until you find a value that reduces the no-load current draw.
Finally, remember that you are dropping 5 volts (12 -7) across the op amp. If you run 1 amp, you will be dissipating 5 watts in the opamp. You can see this is out of range for the part from the chart below, taken from the data sheet.
Good Luck!