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TMS320F28035: Low-power mode power consumption questions

Brian Wang0
Expert 5190 points
Part Number: TMS320F28035

Hi team,

My customer is evaluating F28035 in a power consumption sensitive OBC system. I have the following questions needing your support.

1. What is the correct way to measure the power consumption of MCU?

Currently we are using a series resistors to measure the current flowing into Vddio and Vdda. But a mA class current can be measured in halt mode, which is obvious not right. So, what is the right way to measure the MCU power consumption? Do we need any special operation to achieve the uA class power consumption claimed on the datasheet?

2. How to make sure the MCU has entered halt mode?

Some MCU has a Pin indicating the state of the MCU by showing different voltage level, but I was not able to find this pin on F28035. When we enable halt mode, we did noticed lower power consumption. But how can we verify the state of the MCU or indicating the state to other devices?

3. What is the states of GPIO when MCU is in halt mode?

Are the configured direction and pull-up still available in halt mode? If not, what is the GPIO state? Will be power consumption influenced by external circuit?

Thanks,

Brian 

  • 0
    Guru 30330 points

    Brian,

    1. Are you attempting to measure the current during the application or during bench tests for evaluation? If it is just the bench, you can use a simple DMM in ammeter mode. Another option, though using dedicated HW, would be to use a current sense resistor and instrumentation amplifier to measure the current into the system. You should not need to do anything special to acheive the uA power, just ensure that all things that can be powered down by SW are - including the analog domain, and Flash.
    2. No C2000 device has an LPM indicator pin. But you can use a GPIO or PWM to indicate that the system is operational or in LPM as needed.
    3. GPIOs remain in their configuration and will remain in their state during LPM. And yes, Power consumption can be influenced by external devices. Generally, if the MCU is entering LPM, you should absolutely prepare the system to handle this. For example, The application should halt communications with the MCU or allow the current transactions to complete, the PWMs should be drive to a safe state.

    Please let me know if you have additional questions.

    -Mark

  • 0 in reply to Mark Labbato
    TI__Expert 5190 points

    Hi Mark,

    1. You mentioned :

    You should not need to do anything special to acheive the uA power, just ensure that all things that can be powered down by SW are - including the analog domain, and Flash


    Currently, we only write LPMCR0 to 1x to enable the halt mode, but we are observing a mA power. According to your explanation, we still need to manually power off the Flash and analog domain, is that correct?

    1) To power off the Flash, I believe we need to write 00 to PWR mode of FPWR register, do we need any other operation?

    2) How to power off the analog domain? In F28035 we have to power up several peripherals (ADC, LIN and CAN and etc.). Do we have to power them down one by one, or there is a general control register in general? Could you please share a list of what need to be powered off manually? 

    So, in general, write 1x to LPMCR0 mode only put clock module in halt mode. We still need to power off all the other modules in S/W. Is that correct?

    Since low power mode is seldom used in my customer, I am not familiar with this application. Sorry about the tons of questions. 

    Regards,

    Brian

  • 0 in reply to Brian Wang0
    Guru 30330 points

    Brain,

    Basically, yes, chances are that not everything is powered down. 

    1. See the Flash and OTP Power Modes section of the TRM (SPRUI10) Ensure that the procedure is executed from RAM and that no accesses are made to memory locations within flash until after LPM is exited.
    2. For the Analog domain, see this thread - https://e2e.ti.com/support/microcontrollers/c2000/f/171/t/697177. The ADC and Flash are the only things needed to be powered down manually. The rest of the Peripheral Clocks are halted when the SYSCLK halts after the asm("IDLE") instruction is called. The Flash and ADC have their own circuitry, so it is necessary to power them down independently.

    Regards,

    Mark

  • 0 in reply to Mark Labbato
    Guru 30330 points
    Brian,

    Do you have additional questions or can I close this thread?

    Thanks,
    Mark
  • 0 in reply to Mark Labbato
    TI__Expert 5190 points
    Sorry about the late confirmation.