I have a simple circuit that pumps 5A for 100uSec. (Constant current circuit with Opamp).
This circuit is on a different board. 20V is generated locally on this board from the 4V supply (not shown, using a switcher). uP gives a 3.3V pulse and I observe 5A pass through the LED. The 5A pulse is occasional so, I charge the cap and when I need the 5A, the cap provides the current.
Occasionally, I have seen that the 5A return current destroys the CPU and some other components on my mother board. What am I doing wrong?
The GND of this board is connected to the mother board ground via the connector at a single point, I was expecting the current (5A) comes back to the Cap and hardly any current flows back the the motherboard ground. Apparently, something wrong.
Opamp is TLV2465
Cap is 2x 1.5mF (UHE1V152MHD Nichicon)
Schematic above has a mistake, the -/+ are swapped, the CPU goes to the + terminal and feedback from the sense resistor is to the -.
The board receives 4V which is boosted to 20V. Board has only 4 inputs, GND, 3.3V pulse from CPU (hidden behind a buffer), and blank. Opamp is run from the 4V before it is boosted to 20V. I also have a PTC to avoid inrush current between the 20V and the + end of the Cap.