Power supply - rus084

[rus084]

what do you think about this citcut?

[kb1gtt]

I'm not quite certain about the goal of that circuit, it appears it would provide a weak and dirty 3.3V and would allow the MCU to disconnect itself via a relay. There are 3.3V regulators that offer a shutdown option with far less components. I also think the diode isn't doing much. Here is one such chip that I found after a quick Google search for "3.3V regulator shutdown". http://www.linear.com/product/LT1129

[rus084]

Not so, this scheme must provide delay power off the ECU. it is necessary for properly shutting down some of the components and capabilities save fuel tables after power off.

[rus084]

I think the best point in front of the diode connected to the ADC input Vbatt, a resistor with a zener diode is unnecessary
I initially thought that they would want to limit the voltag to digital input on stm32, but we already have ADC with voltage divider

[UnaClocker]

This is why I've been saying to provide the ECU with constant power, provide it with a way of detecting ignition power being on, and use the uC's native ability to sleep. The micro amps it draws in sleep is WAY below the 30ma draw that lead acid batteries will tolerate.

[rus084]

stm32f4 can working with lt1129 ? how it will power on without power supply on stm? this is closed loop.
may be need use batt pin on stm?

[kb1gtt]

Generally you have bulk caps on your low voltage. I would expect that when the Bat Sense is noticed as 0V, that the MCU would preform a shut down procedure before the bulk caps discharge. As well, I would expect the bulk caps to store enough energy to allow for shutting down.

I would expect a regulator with a shut down option to be used on items more like dash gauges or other power hogging devices. As a way to extend the bulk storage, you can shut down other devices via the shutdown option. I'm not sure I'm seeing a need for shutting off the MCU's regulator via MCU signal. I guess as part of monitor circuit or watch dog processes. But other than that I'm not sure I see the need.