I have a need to sequence off the power rail from lowest voltage to the highest when a fault condition occurs.
The current implementation I have is I am sequencing ON 7 power rails as follows: 12V -> 5V -> 3.3V -> 1.8V -> 1.8V_g2 -> 1.5V -> 1.1V
This is power ON sequence is what I want. For the power OFF sequence I would like to power OFF in the reverse order of the power ON:
1.1V -> 1.5V -> 1.8V_g2 -> 1.8V -> 3.3V -> 5V
In addition whenever a UV or OV fault occurs to also power OFF from the lowest rail first to the highest rail.
Any design guidance or documentation explaining how to implement this power OFF sequence requirement would be greatly appreciated.
This can be done by setting Seq On and Seq Off dependancies on TI Fusion GUI.
Power On Sequencing :
For Rail2: In the "Rail seq on dependencies" in the Vout config tab, check Rail1 so that it turns on after rail1 turns on.
For Rail3 check Rail2 and so on for all the other rails.
Power Off Sequencing :
For Rail6(1.5V) : In the "Rail seq off dependancies" check Rail7(1.1V). For rail5, check rail6 and so on for other rails. You can verify your sequencing on the GUI main window
For the Fault Response: You can configure how you want your rail to respond on OV and UV conditions in the "Fault Response and limits" tab under Fault responses.
More detail can be found page21 of the UCD9090 Datasheet.
Let me know if you have problems setting this up.
The power ON sequencing in my implementation is good, no problem. For the power OFF sequencing on the other hand is not quite functioning as I want. The implementation for the power OFF sequencing you have suggested does not work at all. First is does not shut all the rails down and in addition the shutdown sequencing does not go from the lowest voltage rail to the highest voltage rail. Below is what happens when simulating this UV fault.
UV Fault on 1.8V (following rails do not shutdown)
12V Rail (This rail is OK, will never shutdown unless input power is lost)
5V Rail (ON)
3.3V Rail (ON)
1.8V Rail (OFF)
1.18V_G2 Rail (OFF)
1.5V Rail (OFF)
1.1V Rail (OFF)
Power OFF Sequencing order observed on a UV Fault from 1.8V Rail.
1.8V -> 1.8V_G2 -> 1.5V -> 1.1V
Here are the conditions and the power OFF sequencing order that I would prefer to happen and implement:
-- 12V Input power is lost or UV/OV fault then the rails should shutdown as follows:
12V -> 1.1V -> 1.5V -> 1.8V_G2 -> 1.8V -> 3.3V -> 5V
-- 5V Rail is lost or UV/OV fault then the rails should shutdown as follows:
5V -> 1.1V -> 1.5V -> 1.8V_G2 -> 1.8V -> 3.3V
-- 3.3V Rail is lost or UV/OV fault then the rails should shutdown as follows:
3.3V -> 1.1V -> 1.5V -> 1.8V_G2 -> 1.8V -> 5V
-- 1.8V Rail is lost or UV/OV fault then the rails should shutdown as follows:
1.8V -> 1.1V -> 1.5V -> 1.8V_G2 -> 3.3V -> 5V
-- 1.8V_G2 Rail is lost or UV/OV fault then the rails should shutdown as follows:
1.8V_G2 -> 1.1V -> 1.5V -> 1.8V -> 3.3V -> 5V
-- 1.5V Rail is lost or UV/OV fault then the rails should shutdown as follows:
1.5V -> 1.1V -> 1.8V_G2 -> 1.8V -> 3.3V -> 5V
-- 1.1V Rail is lost or UV/OV fault then the rails should shutdown as follows:
1.1V -> 1.5V -> 1.8V_G2 -> 1.8V -> 3.3V -> 5V
So as you can see the 1.1V rail (lowest voltage rail) should either be the first or the second rail to shutdown. Let me know if you wish for me to explain in more detail or need more clarity in what I am trying to accomplish.
Please attach your project file(.xml) and it would be easy for me to look at your implementation.
Attached is the .xml file of the design.
Here is the problem with your sequence off event.
Take two instances of your requirement:
1) -- 12V Input power is lost or UV/OV fault then the rails should shutdown as follows:
2)-- 1.8V Rail is lost or UV/OV fault then the rails should shutdown as follows:
Suppose I setup the sequence off for event1
Rail 12V goes off followed by 1.1V, 1.5V, 1.8V_G2, 1.8V. But here you wanted a different sequence when 1.8V is shut off, but if you notice in that sequence 1.1V and 1.5V have already been off because of the event of 12V being shut off. So that contradicts the implementation of Event2. In the event2 only 3.3V and 5V can be dependent on the 1.8V as the other rails were already off because they were dependant on 12V.
Event1 says 1.8V_G2 followed by 1.8V and Event2 says 1.8V followed by 1.8V_G2. Likewise the sequencing you intended has different allignment of the rails in each event.
So you can follow only one pattern of turnoff dependency but can vary how your rails are dependant on each other to shutdown.
Let me know if this is clear or if you feel you have a workaround.
Could you resolve setting your sequence off event? Can I close this post.
Let me know if you need more help.
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