Linear Regulator ENABLE - Page 1
Forum section: electronics / projects

author: Mark IV
author_rank: Contributor
timestamp: July 22, 2015, 07:02:16 am
content: Hi all!!What is the use of the ENABLE pin in some regulators like this one:http://www.ti.com/lit/ds/slvsag6c/slvsag6c.pdf?I mean, I know how it works but I don't know where to applying it!I'm trying to get some tips for reduce power consumption.Thanks!!

author: BravoV
author_rank: Super Contributor
timestamp: July 22, 2015, 07:08:53 am
content: Connect the EN to Vin (pull high) to enable, or ground it to disable the regulator.

author: Deathwish
author_rank: Unknown
timestamp: July 22, 2015, 07:11:11 am
content: Not sure what you mean but from what I am reading it seems to mean you apply a voltage of over 0.9v to a max of 6V on Pin 3 to switch it on , under 0.4v turns it off.

author: Kjelt
author_rank: Super Contributor
timestamp: July 22, 2015, 07:15:34 am
content: Just as you already mention to save power.Ofcourse you need multiple powersources, which can be a battery or a secondary more efficient low current supply.If you want to do the same thing with a single power supply you would use a p-fet to switch the voltage off to the circuit.So the usage can be multiple but usually when the circuit that consumes more power just has to be run in certain intervals, in between those intervals all power can be shut down as long as some circuit awakes it in time. There are special ic's from TI for that purpose, forgot their specific name though.

author: Mark IV
author_rank: Contributor
timestamp: July 22, 2015, 07:42:44 am
content: Quote from: Deathwish on July 22, 2015, 07:11:11 amQuote from: BravoV on July 22, 2015, 07:08:53 amThanks. Yes, as I said, I know how it works!Quote from: Kjelt on July 22, 2015, 07:15:34 amThanks! Yes, I can control it with the mcu of the board, but...What if this regulator is supplying power to an IC that is connected with the MCU?

author: krish2487
author_rank: Frequent Contributor
timestamp: July 22, 2015, 08:23:25 am
content: You cant bootstrap the MCU to switch on and off the supply to itself, if thats what you are asking!!Well it can be done but is kinda meh!!!Think of it like this, the ENABLE pin controls the power being supplied to a MCU but using a soft latching switch instead of inceptionizing it..No secondary sources.. no bootstraping chicken-and-egg problem.

author: Mark IV
author_rank: Contributor
timestamp: July 22, 2015, 08:41:56 am
content: POWER1 -------> REGULATOR-----------> GPIO EXPANDER (for example)| Enable || |POWER1 --------> MCU ------------------------------ I2C BusIt's horrible, but I think It's enough to imagine what I'm talking about.

author: Kjelt
author_rank: Super Contributor
timestamp: July 22, 2015, 02:34:50 pm
content: Quote from: Mark IV on July 22, 2015, 08:41:56 amIn your example you can better use a small p-fet to cut power to the gpio expander. Not that it makes much sense since the expander does not consume much power only if it has active outputs it will consume but you can also shut those down with software.No, shutting down the regulator and thus entire power supply only makes sense if multiple devices are being powered by it, so you save a lot of power.Take for instance this example from TI, now the TPL device is a timer device that just waits for a preprogrammed time and then again wakes up a microcontroller or as in this example enables the LDO that supplies the power to the microcontroller.This device consumes 26nA so can be fed by a battery for a very long time. Now instead of a low power microcontroller fed by a battery you can also imagine the LDO being fed by a power supply that will power a more hungry microcontroller and even more hardware that will consume hundred(s) of mA's but only has to run occasionally.So for instance you have an application with a display and user interaction blabla that has to run if someone is walking along.The microcontroller would normally poll (or through irq) a PIR sensor and do absolutely nothing until eventually someone is detected, then it can go to work.In a stupid application this consumes 24/7 that hundreds of mA's.In a smart application the microcontroller disables all other hardware and goes to sleep for an x amount of time then wakes up and polls the PIR. But with heavy microcontrollers even in sleep they will consume multipe mA's.Now instead you can use this application, you can "program" the TPL time with the resistor for lets say 1 second and then the microcontroller is powered up every second, polls shortly the PIR sensor (that probably does need to be powered 24/7 but it is an example) and if nothing is detected signals the TPL with the done signal and the TPL shuts the LDO (power) down and waits another second.If the polling routine takes 10ms you save 10/1000 = 99% of power that is otherwise thrown away. Just an example, probably better examples can be found.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 22, 2015, 04:13:33 pm
content: An example where I found the enable pin useful:In a 5V microcontroller project, I use an SD card for data logging. The card requires a 3.3V regulator. For low power use, I want to switch the power to the card off, so it's powered only occasionally. That would require an extra P MOSFET or PNP transistor as a switch, but since the 3.3V regulator already internally has this kind of transistor (to do the regulation), they have designed the enable pin, which I can drive directly from the 5V microcontroller, to switch off the regulator and the SD card powered from the regulator.