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LP-MSPM0G3507: MSPM0G is drawing significant current if UART RX pin is pull-down

Tiger Wang
Prodigy 145 points
Part Number: LP-MSPM0G3507
Other Parts Discussed in Thread: MSPM0G1507, , ENERGYTRACE, SYSCONFIG

Hi there,

Recently we are working on low power mode for MSPM0G. On our customized board (which is using MSPM0G1507), we are seeing that if we add external pull-down resistor with 100K Ohm value, the MCU is drawing more power than expected, if the UART puerperal is enabled.

This is reproducible on LP-MSPM0G3507 EVAL board. To reproduce:

  1. use example project uart_echo_interrupts_standby
  2. use EnergyTrace to measure the power, disconnect J4 (LED), and J13 (A-PWR)
  3. Uses 3 following sysconfig:
    1. default ("Enable pin configuration" isn't checked, disabled)
    2. Set related UART pins to pull-up resistor
    3. Set related UART pins to pull-down resistor
  4. Do following external wire-up action:
    1. Attach 100K Ohm resistor to Tx pin
    2. Attach 100K Ohm resistor to Rx pin
  5. J21/J22 connection:
    1. When attach external resistor, XDS UART is still connected (1-2)
    2. When attach external resistor, XDS UART is disconnected (2-3, or floating)

I observed following result, summarize as below:

Baseline (3a+5a): MCU 10~30uA

If Rx pin is "pull-down" by any combination, (3a+4b+5b, or 3c+5b or 3c+4b+5b), MCU is drawing significant power, ~1.2mA

  • 0
    TI__Mastermind 22805 points

    Hi Tiger

    May I confirn if the power consuption is measured w/o debug (free run mode)?

    and could you please explain why the pull-down resister will be added on the UART RX pin.

    Could you please share the UART information, baud rate, the the RX data?

    Thanks

  • 0 in reply to Xiaodong LI
    Prodigy 145 points

    Yes, we are running the EnergyTrace without starting the debug session.

    1. Debug, download the code, run. Stop debugging.
    2. Turn on EnergyTrace, start logging.
    3. Apply pull-down and remove it, if the test is focus on that difference.
  • 0 in reply to Tiger Wang
    TI__Mastermind 39255 points

    Hi,

    I have run some tests on the LP-MSPM0G3507 EVM board. And I get the same conclusion as yours. If there is any pull down resistor on the RX pin. MCU will consume more power in this situation. 

    And actually, the idle state of the UART TX and RX pin is logic high. Adding pull down resistor on the TX/RX pin will indeed consume more power. It does not make sense to add this pull down resistor from my side. 

    About adding the pull-up resistor on the UART TX/RX pin, there is some use cases which may need it. While the microcontroller is in reset, its I/O pins will be configured as high-impedance inputs. So the pin used for a UART serial Transmit Data (TXD) will be floating during this time. This can lead to noise causing rubbish to be transmitted. A pull up resistor can avoid this this. I also tested using the internal pull up resistor, it will not cause extra current consumption to the MCU. Customer can add this feature if they need it. 

    Best regards,

    Cash Hao