I just had a PCB made for a new project I'm working on. Essentially, a uC turns a load on or off through a P-channel FET. The circuit is powered by USB. The uC is powered directly from the USB 5V. There's a 100mΩ shunt resistor in line with the source to current sense. See the attached pseudo-circuit.
When the load is turned on, the initial capacitance of the load causes a transient drop in the 5V source. The shunt resistor doesn't help the situation, either. Unfortunately, the drop is enough to brown-out the uC. No other components in the circuit are sensitive to the voltage drop, just the uC.
I'm trying to think in terms of saving the PCB if I can. Would a large, low-ESR capacitor across the uC power pins be a practical solution here? If so, how do I choose the capacitor value (other than just going with the biggest one I can get)?
Is there another clever technique I should consider?
Thanks!
When the load is turned on, the initial capacitance of the load causes a transient drop in the 5V source. The shunt resistor doesn't help the situation, either. Unfortunately, the drop is enough to brown-out the uC. No other components in the circuit are sensitive to the voltage drop, just the uC.
I'm trying to think in terms of saving the PCB if I can. Would a large, low-ESR capacitor across the uC power pins be a practical solution here? If so, how do I choose the capacitor value (other than just going with the biggest one I can get)?
Is there another clever technique I should consider?
Thanks!
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