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Hi,
I'm designing a power supply for an automotive controller that has sensors, some high power contactors (to drive air compressors) and a remote touchscreen display.
The raw 12V is going through a protection circuit based around a LT4356HMS-1PBF "Surge Stopper" which clamps at 27V to take care of surges, load dumps, etc.
The 12 "clean" power then feeds three 1A, 5V R-615.0P packaged switching regulators. One for the microcontroller and associated circuits (350mA), one for off-board sensors (70mA), and a third (not shown) in the remote dash display module (800 mA). The remote display pulls power and CAN buss data from the main module.
The filtered 12V also powers three large 12V contactors (driven by the microcontroller via MOSFETS) that total about 1A.
The caps currently shown are per the application notes for the respective controllers. C4 and C6 end up being in parallel in close proximity.
My question is: do I need to add additional caps for filtering, and to prevent the inrush (load step) of the 25 ohm coils on the contactors from dragging down the 12V supply? They will be staged to close one at a time and will have flyback diodes.
It's not shown in the application diagram, but later in the datasheet for the surge stopper it states: "A total bulk capacitance of at least 22µF low ESR is required close to the source pin of MOSFET Q1 (Q7 here). In addition, the bulk capacitance should be at least 10 times larger than the total ceramic bypassing capacitor on the input of the DC/DC converter."
Based on that, I think I need a 22UP capacitor just after Q7, correct?
Also, any thing else that looks foolish in this design.
Thanks.
I'm designing a power supply for an automotive controller that has sensors, some high power contactors (to drive air compressors) and a remote touchscreen display.
The raw 12V is going through a protection circuit based around a LT4356HMS-1PBF "Surge Stopper" which clamps at 27V to take care of surges, load dumps, etc.
The 12 "clean" power then feeds three 1A, 5V R-615.0P packaged switching regulators. One for the microcontroller and associated circuits (350mA), one for off-board sensors (70mA), and a third (not shown) in the remote dash display module (800 mA). The remote display pulls power and CAN buss data from the main module.
The filtered 12V also powers three large 12V contactors (driven by the microcontroller via MOSFETS) that total about 1A.
The caps currently shown are per the application notes for the respective controllers. C4 and C6 end up being in parallel in close proximity.
My question is: do I need to add additional caps for filtering, and to prevent the inrush (load step) of the 25 ohm coils on the contactors from dragging down the 12V supply? They will be staged to close one at a time and will have flyback diodes.
It's not shown in the application diagram, but later in the datasheet for the surge stopper it states: "A total bulk capacitance of at least 22µF low ESR is required close to the source pin of MOSFET Q1 (Q7 here). In addition, the bulk capacitance should be at least 10 times larger than the total ceramic bypassing capacitor on the input of the DC/DC converter."
Based on that, I think I need a 22UP capacitor just after Q7, correct?
Also, any thing else that looks foolish in this design.
Thanks.
