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MSP430G2553: MCU Power Supply Switching with TPS2103?

William Stevers
Intellectual 350 points
Part Number: MSP430G2553
Other Parts Discussed in Thread: TPS2103, LM66100

I am currently working on an embedded design where the primary power source for the MSP430G2553 MCU is a CR2032 battery.  The MCU is being used to power cycle another system.  I was hoping to use the system to power the MCU via a 3V3 LDO (TLV70033) when it is switched on and then have the MCU powered from the battery when the system is powered off.  I thought that the TPS2103 would work for this application, but I am having an issue where the MCU resets during the switch between the power supplies. 

I have attached the current circuit here as well as the recommended circuit from the datasheet.  The current debug code on the MCU simply turns an LED on,  as this allows me to see if the MCU resets during the supply switch.  I have experimented with multiple output capacitors to no avail.  I used Figure 16 of the TPS2103 datasheet to select my capacitor values, but capacitors in the range of 1 uF to 220 uF seem to just force the MCU off when the supply switch happens.  In the current configuration without an output capacitor, the MCU flickers on and off when the supply switch happens.

Is there a better component for what I am trying to do here?  I think the issue is related to how sensitive the MCU is to a drop in the supply voltage, but I'm not 100% sure.  Measuring the output of the TPS2103 using the Peak mode on my Fluke 87V shows a minimum of between 1.2 and 1.5 V when the switch happens.  In the regular MaxMin mode, my meter reads a minimum of between 2.4 and 2.7 V (i.e. the voltage drop during the switch is very brief).

Current circuit:

Recommended circuit:

  • 0
    TI__Mastermind 28745 points

    Hey William,

    Sounds like this a question for the Power team.  I'm going to move this thread over to their forum so they can give a recommendation.  

    Thanks,

    JD

  • 0
    TI__Mastermind 32650 points

    Hi William,

    Does the MCU flicker when the switchover is from the LDO to the battery or when the switchover is from the battery to the LDO?

    If you look at Figure 16 in the datasheet, output capacitance is needed to maintain the voltage on the output pin during that switchover time. I don't think any Power MUX solution will help here as there will be some switchover time that will require an output capacitor.

    The ideal diode LM66100 can be used to mux power between two sources and the body diode of the fet will be able to pass voltage from input to output during the switchover time. Using 2 LM66100s might be a method to get around the inability to use any output capacitance.

  • 0 in reply to Shreyas Dmello
    TI__Mastermind 32650 points

    William,

    I would like to follow up on this post. Have you tried the Ideal Diode implementation or figure out a way to add output capacitance?

    I will close this thread for now but feel free to reply back and we will resume support.

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