TPS3760: I need help designing a circuit that can turn on a sub-circuit when the input supply goes above voltage threshold

We will respond shortly. Thank you.

Hi Jonathan,

Thank you for your question. For the TPS3760, we do have the adjustable under voltage active low TPS3760A012DYYR and the adjustable over voltage active low TPS3760E012DYYR. For the adjustable variant, you will need to have a voltage divider to drop the 20V threshold to 800mV. If you are going to stick with the DN1509, Nmos, the under voltage TPS3760A012DYYR will do the trick. I can provide an example schematic with the proper values, I just have a few questions.

• Is the rail going to be noisy? What is the pulse duration of transients you would want to filter out.
• Needed reset delay for the system?

Jesse    

Thanks for the info.
we are not at all married to the DN1509, it was just in there from a schematic I found online.  We could use a P-channel on the high side, N-chan on the low side, or any other combination. I'm happy to look at recommendations on any other parts that you think could do a better job than the TPS3760 series we started with, including FETs or high-side switcher all-in-one chips you might know of.

We have our 20V classification voltage that is the max we should ever see during the initial up/down voltage levels.
I am not sure the timing on this as it can be variable based on other system parameters, but our worst case scenario probably has ~750ms max before the voltage rail ever goes above 20V.

The top dotted line is the 20V max voltage level.  This graph is one example of possible voltage input levels. As some point after this we will turn the "power on" and bring the voltage up to ~48V.  

I am really looking for something like this over-simplified drawing:

We have Vrail that does the up and down thing and some circuitry that looks like >2MOhm (infinite-ish) impedance for any Vrail <21V.
Then once we have gone thru our start-up voltage dance and raise the Vrail over 21V** our black box will pass through the Vrail to Vo with minimal loss. 
**(or some other voltage we can set using a voltage divider, zener, Power-on reset, supply monitor, etc.)

Ideally we'll have some hysteresis where we'd be safe from any kind of droop on Vrail below that 20V, and this would be shorter blips less than 1ms.  In other words, Vout needs to always track Vrail any time after we've first crossed that 20V line even if the voltage drops down to 15V (or some other voltage we can set.)

I hope this helps clarify better our scenario.

If you provide an example schematic would you be able to provide guidance on any easy adjustments we can make for things like reset-delay times or easy transient filtering.

THANK YOU!

That's great, thank you so much!

is that M1 FET in your schematic meant to be the DN1509?  (I am assuming yes as it's an N-chan depletion mode doing high-side switching)  If I were to want to use a P-channel I would just swap to the TPS37 overvoltage version.  I think using that essentially inverts the logic, right?

I saw that there is an eval board available for the TPS3760.    Would that be something that would allow me to try different R and C values before doing my PCB?
Is there another eval board that has a few different products that allows a side-by-side comparison of the functionality of a few different chips similar to this? (a long-shot, i know, but worth asking)

Thanks.