Question about Regulator Enable & Termination

[Thundercat]

Hi, in some data sheets for small onboard regulators, they mention you must "terminate" the regulator enable pin either "actively or passively."

I'm wondering exactly what this means. I'm assuming some kind of resistor to ground?

I've got some Teensy projects where I used a Teensy digital pin directly to the regulator "enable" pin, just sending high or low. This seems to work fine to turn on or off the regulator. But I'm a little nervous maybe I'm missing something important that could have long term safety ramifications.

Is this a safe way to do it, or do I need some kind of resistor to ground from the Teensy digital pin to "terminate" the enable pin? If so, what kind of values, 10K? Just from Teensy digital pin to ground?

Thank you for your expertise. I'm sure this is a basic question, but I couldn't seem to find an answer in googling.

Mike

 

[WMXZ]

AFAIK, LDOs are enabled by either connecting to GND (disabled) of to VIN (enabled), whereby any voltage above a certain level is valid for enable. So Teensy 3V level is sufficient.

 

[Thundercat]

AFAIK, LDOs are enabled by either connecting to GND (disabled) of to VIN (enabled), whereby any voltage above a certain level is valid for enable. So Teensy 3V level is sufficient.

Thank you. My experience with them has been the same - I've connected the Teensy digital pin to the "enable" pin on the LDO, and turned on the digital pin, and it's worked fine in a PCB setting.

The reason for the question is, I want to make sure I'm doing it right. It's going into a product that other people will have out in the field, so if there's a "best practices" way to do this, that's what I'd like to know.

If sending HIGH directly from a Teensy digital pin to the LDO "enable" pin is fine, then great. If I need some kind of resistor on the enable pin to ground to "terminate" it, as one data sheet says, then that's what I need to know.

Or maybe different LDOs are different?

Thanks,

Mike

 

[PaulStoffregen]

This conversation would be much easier if you gave a specific voltage regulator part number and pointed to the specific words in its datasheet. Details matter. So does context.

But generally speaking, that sort of language usually means the enable pin is a high impedance input which could give more or less random results if not driven by a low impedance signal. That condition exists in the time before your program runs pinMode(). Normally a conservative (but power consuming) approach would involve a pull down (or perhaps pull up) resistor on the enable signal, so it is well defined before pinMode() and digitalWrite() are executed.

Again, this is only generic advice about voltage regulators in general. It may or may not apply to your specific part and circuitry.

 

[Thundercat]

This conversation would be much easier if you gave a specific voltage regulator part number and pointed to the specific words in its datasheet. Details matter. So does context.

But generally speaking, that sort of language usually means the enable pin is a high impedance input which could give more or less random results if not driven by a low impedance signal. That condition exists in the time before your program runs pinMode(). Normally a conservative (but power consuming) approach would involve a pull down (or perhaps pull up) resistor on the enable signal, so it is well defined before pinMode() and digitalWrite() are executed.

Again, this is only generic advice about voltage regulators in general. It may or may not apply to your specific part and circuitry.

Thank you Paul, fair enough.

The data sheet for the regulator is this one: Texas Instruments LP38692MP-3.3/NOPB

The wording is here:



I have used the one above, but at the time I was just connecting the enable pin to the VIN, so I was not turning it on with the Teensy.

But now I'd like to do that, so I'm wondering since this is so vaguely worded if just a 10K resistor to ground from the Enable pin would suffice?

Thanks kindly,

Mike