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MSP430F6736: Questions about new Auxiliary Power Systems

BasePointer
Expert 1570 points
Other Parts Discussed in Thread: MSP430F6736

Hi to all,

Soon we will start a new design using MSP430F6736. In this product simply we have three different power sources. 

DVCC is 3.3V which is sourced by AC power.

AUXVCC1 is connected to a battery which is 3.6V

AUXVCC2 is connected to another type battery which is 3.3V

AUXVCC3 is connected to VDSYS which is output of power switch inside MSP so that there will be always power on AUXVCC3 which is mandatory for external 32KHz crystal.

In this configuration, system always starts over AUXVCC1, because it is the biggest. But immediately code starts executing, I will check if DVCC is available, I will force MSP to use DVCC instead of AUXVCC1 which is 3.6V battery. So, this is question number one, is this possible?

2. Pull up resistor of Reset pin of MSP should be tied to VDSYS, correct?

3. JTAG programmer connector should sense the power from VDSYS instead of DVCC. So Pin 4 of JTAG header will be tied to VDSYS. (board powered application) Question, during flash programming, will VDSYS be available?

4. As I understand, all digital outputs will take their power from VDSYS while they are logic-1 (sourcing current to outside). Is there any current consumption limitation for VDSYS? If I have 10 digital outputs, which supplies 5mA to their peripherals each (like opto couplers), then total VDSYS current will be around 50mA + MCU internal consumption. Would it be a problem for internal switch or it is a just piece of cake for it?

Thank you.

  • 0
    TI__Intellectual 875 points

    Hi Basepointer,

    1. Yes, this software controlled mode is possible and  switching is triggered by changing values in AUX module registers, as described in Section 4.2.3 of the User's Guide (http://www.ti.com/lit/ug/slau208k/slau208k.pdf).
    2. The reset pin should be connected to the external power domain, i.e Vcc.
    3. Flash programming should not have an influence on VDSYS, so this should be available.
    4. As you are using AUXVCC1 and AUXVCC2, you are limited to 20mA total current for ICORE plus IIO  (see data sheet page 47, ILOAD,DVCDD), so no, this will not work for you.

    Regards,
    Richard

  • 0 in reply to Richard Oed
    Guru 227245 points

    Richard Oed said:
    The reset pin should be connected to the external power domain, i.e Vcc.

    Sure? This means if VCC fails, the device will be reset even if it is switched to aux power.
    Also, most 5x family devices have internal pullup active on RST pin by default, (and powered by whatever currently drivers the MSPs I/O), so there's no need for a pullup resistor at all.

  • 0 in reply to Jens-Michael Gross
    TI__Intellectual 875 points

    Jens-Michael Gross said:

    The reset pin should be connected to the external power domain, i.e Vcc.

    Sure? This means if VCC fails, the device will be reset even if it is switched to aux power.
    Also, most 5x family devices have internal pullup active on RST pin by default, (and powered by whatever currently drivers the MSPs I/O), so there's no need for a pullup resistor at all.

    [/quote]

    You are totally right on that! I mixed up some things. It is implemented that way on our EVM as well.

    Richard

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