This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS709: TPS70930 EN Voltage?

Part Number: TPS709

I am using a TPS70930 to trip a switch when a charging capacitor reaches a certain voltage. From the datasheet I figured that the EN voltage was at 0.9V at a minimum but in practice I found it to be around 0.5V, is this correct?

My test circuit is applying 5V to the IN pin with a power supply and varying the voltage on the EN pin with another power supplies. There is a 1uF capacitor from IN to GND and a 2.2uF capacitor from OUT to GND. Then I'm probing the EN pin and OUT pin with an oscilloscope (typical 1Mohm probes) to determine the level. I find that the LDO turns on with EN=0.51V minimum.

  • Hi Erik,

    The specs for the EN threshold say that if VEN > 0.9V, all devices will be on, and if VEN < 0.4V, all devices will be off. There is a gray area between; the trip point varies between devices but what I've described is what is guaranteed. If you need a precise timing you will need to use something more accurate, like a comparator with the RC or something like that. 

    Regards,

    Nick

  • Hey Nick,

    Thanks for the quick reply. I think there shouldn't be a gray area there, and those voltages should be describing the hysteresis of the enable voltage: The 0.9V is the minimum voltage to turn it on and the 0.4V is the maximum voltage to turn it off. What I'm seeing is that at 0.5V EN the LDO turns on from an off state.

    My application is low power with voltages >15V, timing doesn't need to be precise, and this part is cheap and fills a very niche application where I've had trouble using a comparator circuit.

  • Hi Erik,

    Most of our LDOs with EN are spec'd this way. What you are describing is expected; most devices are going to turn on in the gray area and not exactly at the 0.9V limit. Only a small number of our devices are spec'd with hysteresis. This is not one of them. 

    Regards,

    Nick