Power Up Sequencing using Enable Pin


For our application we want to use yours ADP5024 and generate delay Between BUCK1 and BUCK2 Enable pin's.

As mentioned in the data sheet those pins are active logic level high  with Vih of min 1.1v.

Your ADP5134 has the feature of precision enable that controls the Enable pin voltage level using Hysteresis.

We want to know the behaviour of the power supply in the range of 1.1 to the high logic level apply on yours ADP5024 Enable pins.

This will direct us to delay the Enable pins using RC circuit.


  • 0
    •  Analog Employees 
    on Jan 20, 2014 11:29 AM

    Hi Itamar,

    For the ADP5024, at some test conditions such as at 25C ambient temperature only and 3.6Vin for example, you could see the regulators turn ON even at lower than 1.1V EN voltages. But to ensure that the regulators turn ON across different Vin and temperature settings, you should set the Logic HI voltage at the EN pin to be a minimum of 1.1V. On the other hand, to ensure the regulators turn OFF across the whole range, you should set the Logic LO voltage at the EN pin to be at 400mV max. Adding an RC circuit at the Buck's En pins will work, although the computed delays to trip the rising and falling thresholds are not very precise due to the fact that the threshold varies over different test conditions.

    Sequencing is easier using the ADP5134, since the Precision Enable turn-ON threshold is set to a typical of 0.97V with a tighter deviation over the whole Vin and temp range. So if you compute for the RC circuit that will give you a 1us delay for example to trip the precision enable rising threshold of 0.97V, it's easier to match the actual results with your computations. Aside from using an RC circuit, I would suggest that you also try a sequencing method in which you use the output of one of the regulators, let's say Buck1 to go through a resistor divider network for example and tie it to the Enable pin of Buck2. This will allow you to delay the activation of Buck2, until a time that the EN2 voltage gets enough charge from Buck1 output to trip the 0.97V EN rising threshold. You can view the ADP5134 User Guide for more information on this technique: http://www.analog.com/en/power-management/multi-output-regulators/adp5134/products/product.html

    Let me know if these answer your questions, hope this helps!