How to manage a power-on/off sequence

Hi Maciej,

I don't know if this will help but I searched my inventory for Power Management ICs and came up with these three part numbers. TL 7705,  DS 1232, and MAX813L. These are parts that I have salvaged from circuit boards and I have not used one myself. They are designed to monitor voltage on a microprocessor and to reset it if voltage drops or if other anomalous situations occur. If these aren't what you are looking for they may at least give you a place to start. The Data Sheets for each number is available at   https://octopart.com/  .

John

Maciej,

The class of parts that you are looking for are Power Management Supervisors.  These parts are available with 1 to 10+ inputs that can be monitored and used to sequence the enable on each of the different supply voltages to provide a controlled turn on and/or turn off process.

Good Luck.

Gene

Sorry but those are not what I'm looking for. They seem to reset circuits when the conditions are not stable rather than provide ordering.

Depending on the type of regulators your using and the order in which the supplies need to turn on you might be able to just use the individual regulators.  if the highest voltage supply needs to be on before the lower ones then you can just drive the lower voltage supplies from the higher ones.  ie 5v reg/source -> 3.3v LDO -> 1.8v LDO

It looks like I found such system under name of Power Manage IC (PMIC). I'm still not clear about the difference between DCDC output and LDO though...

DCDC includes a lot of possible devices, but typically it refers to a device that used high speed switching and a storage element (inductor or capacitor) to more efficiently generate a DC voltage.  This can be used to either generate a higher or lower voltage than the input to the device.  LDO (Low Drop Out) regulators are a specialized form of regulator that is designed to have a low inline voltage drop (across the device), usually < 1.0V.  As with any linear regulator, the difference between the input and the output is drop across the device.  This voltage drop times the current flow, equal the power dissipated in the device.  DCDC do not suffer from this same power dissipation, as the duty cycle of the switching lowers the power dissipation as current is only flowing through the device for very short periods of the switching frequency.

Gene

Regulators require a minimum amount of voltage overhead to operate correctly.  An LDO typically (always check the documentation for the IC) have a voltage drop out of roughly 0.3-0.5 of volt where as a typical voltage regulator may have somewhere between 1.5-1.7 voltage drop out (again not necessarily, so always check the chips documentation).  Say you had a 5v source (like a wall wart) and you wanted to power a 3.3 volt device, this would be a great application for an LDO as after you subtract your 0.5v from the 5v, you still have 4.5v, plenty of head room to regulate down to 3.3v.  Where as if you used a regular dcdc converter that might have a voltage drop out much greater and may not get the regulated voltage that you want.  I guess what im trying to say is pay attention to the voltage drop out spec, this value is also relative to current draw as well; again you should look at the documentation and check for a graph that shows how the voltage drop out is effect by current draw.

Like this one for TI TPS7A91, found on page 8 http://www.ti.com/lit/ds/symlink/tps7a91.pdf

Hope this helps