VCC OUT

[ofer 0]

Hi all,

 

I have an msp-exp430g2, my power supply is from USB and i have another unit (LMR61428) that convert 3.3 volt to 5 volt.

 

I need this conversion unit to work only when I need. if i connect it to the VCC pin, it works all the time. Ive tried to connect it to an I/O pin that I can program to be on and off but the current output from the I/O pins is to low.

 

Is there anyway to program the VCC pins on and off? or to increase the current output of the I/O ports?

 

P.S. i tried to build an electronic switch with a bi-poler transistor but i couldnt make it work

 

Thanks,

 

Ofer.

[SixSixSevenSeven 23]

If you are not confident with using a transistor (the perfect solution in this case) then you could use a relay. Some smaller relays can be driven from an I/O pin and used for switching VCC to your 5v booster on/off, bigger relays sadly need a transistor anyway such as those commonly used in automotive electrical systems.

 

Decent guide on using a transistor here though: https://learn.adafruit.com/adafruit-arduino-lesson-13-dc-motors/transistors
That is in the context of a DC motor connected to an arduino uno but could just as easily be your LMR61428 connected to the launchpad.

[ofer 0]

thanks @@SixSixSevenSeven i will try it, although i would have prefer a software based solution.  

[roadrunner84 466]

Your LMR61428 has an enable pin (pin 2 on the IC), why not use that to turn it on and off?

[ofer 0]

hi @@roadrunner84, I tried using the enable pin but i see that it only stops the conversion from 3.3 to 5 volts so the output to the load is 3.3 volts. maybe im using it wrong, do you know of a way to connect it so the enable pin would shut down the output voltage?

 

thanks,

Ofer. 

[roadrunner84 466]

According to the datasheet you have to be above 0.7 times Vdd. And I guess Vdd is 5 volts.

You could use a transistor to open/close that connection, or you could try using the pin in open-collector mode with a pull-up from Vdd.

[SixSixSevenSeven 23]

thanks @@SixSixSevenSeven i will try it, although i would have prefer a software based solution.  

Not possible to do in software, the VCC pin on the launchpad is linked to the VCC pin of the MSP430 and the onboard regulator. There is no on/off for it.

 

You're either going to have to look into the enable pin on your stepup converter or deal with the transistor.

[ofer 0]

Thanks to all

 

ill try and post back.

[ofer 0]

@@SixSixSevenSeven method worked   but is there a better way to do this? maybe a buffer or a CMOS transistor?

 

Thanks,

 

Ofer.