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Can I connect switching regulator's EN pin directly to the car's ACC?
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sidlauskas:
I am developing an electronic circuit that will be installed in a car and I'm wondering how I should properly turn the regulator on from the car's ignition (ACC) using ENABLE pin. I'm planning to use BD9778F switching regulator (link to datasheet). Can I connect it directly? If not, how this should be implemented then?

By the way, someone suggested me to power my project directly from ACC, but I want to highlight that I can not do this because the ACC I get from the car's radio the max load is 150mA and my circuit could drain up to 500mA, so I need a proper schematic for enabling/disabling regulator using ACC.
Psi:
ACC can provide much more than 150mA.

ACC doesn't come from the car radio, it comes from the car ignition.
Mechatrommer:
ACC comes from when you put car key in ON position, regardless if ignition is on or off... somesort of relay will just connect it to fuse and battery. so basically the current limit is the fuse limit. almost every car's appliances will use ACC line to turn themselves ON.
Ian.M:
A typical automotive battery supply is really hostile to electronics with transients of either polarity that can peak at an order of magnitude higher than the supply voltage, and the possibility of significant overvoltage for long enough that the power rating of clamping networks can be a significant issue, and supply dropouts of significant duration.


--- Quote from: sidlauskas on October 09, 2018, 08:36:54 am ---I am developing an electronic circuit that will be installed in a car and I'm wondering how I should properly turn the regulator on from the car's ignition (ACC) using ENABLE pin. I'm planning to use BD9778F switching regulator (link to datasheet). Can I connect it directly?
--- End quote ---

That would be disastrous if the main Vbatt supply to Vin was ever interrupted, even momentarily, while ACC was on. 

--- Quote ---If not, how this should be implemented then?
--- End quote ---
Assuming a nominally 12V vehicle,  I would suggest  a potential divider, 1K lower arm, 1.8K upper arm, to feed about 5V to EN while drawing 5mA from ACC (enough to prevent stray voltages turning it on), with 10nF to Gnd and Schottky diode clamping to Vin and Gnd at the EN pin. 

Don't forget you also need to adequately protect the regulator Vin, and any other signals to your circuit from the rest of the car's electrical and electronic systems . . .


--- Quote from: Psi on October 09, 2018, 08:53:24 am ---ACC can provide much more than 150mA.

ACC doesn't come from the car radio, it comes from the car ignition.

--- End quote ---
OTOH if ACC is tapped from the car radio rather than the supply to it, it may well be limited by the current capability of tracks on the radio PCB, or may even be a switched output from the radio after its power control circuit (which is fairly common to support electrically operated antennae, CD changers etc.)   Ignoring any warnings about a 150mA limit would be foolish . . .
Mechatrommer:
i've opened and repaired a few car electronics equipments such as player and power amp i dont see any over complicated overvoltage protection other than reverse polarity diode protection and fuse similar to what usually available in other non-automotive products. i rechecked my log, for example there is TL494 connected directly to the Vbatt (car battery), granted its a 40V max chip but in other is PT2313, 10V max chip, so it must be fed from some jellybean regulator or simply emitter follower bjt by a voltage divider directly from battery, since i dont see any fancy regulator in there. if there is high transient reaching ACC, i will be more worry on the car's battery health life.
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