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TM4C1290NCPDT: Peripheral operating in Vbat operation

Saisivarajagopal KS
Prodigy 50 points
Part Number: TM4C1290NCPDT
Other Parts Discussed in Thread: MSP432E401Y, MSP432E411Y

Hi Ti Team,

We have identified the below probable  MCU for our project.

TM4C1290NCPDT

MSP432E401Y

MSP432E411Y

We have one requirement to operate the Peripheral  (I2C) during battery operation to drive the LCD display when external wakeup is asserted. 

From the datasheet i found  that during hibernation mode (main power is absent and MCU  powered in vbat)  , even when external interrupt or wakeup signal is asserted (for eg push button) the MCU wont come out of hibernation untill vdd is present. could any one suggest or clarify wheather MCU peripheral section also can be powered by vbat when external wakeup signal is asserted?

Also suggest any TI MCU which can supports this function (operating the few peripherals on Battery operation) would be helpful.

  • 0
    TI__Guru**** 159445 points

    Hi,

      When you are in hibernation mode, the VDDC core power is turned off and there is no SYSCLK to the device. Therefore, no peripherals will operate during hibernation mode except the hibernation module (including the RTC) itself and a few battery-backed memory. In order to have the peripherals operating, the clock and VDDC will need to be active which will drain the battery quickly if they were allowed during hibernation mode. This is why they are turned off during hibernation mode. 

      I'm the device expert for TM4C12x MCU. I'm not sure which other MCUs can support peripherals operating on battery.  You might want to open a new forum post for our MSP430 MCU. The experts there will be able to assist if any of their products can support your application requirements. Here is link to the MSP430 product selection page. https://www.ti.com/microcontrollers-mcus-processors/microcontrollers/msp430-micrcontrollers/products.html

  • 0 in reply to Charles Tsai
    Prodigy 50 points

    Thanks Charles Tsai for your information. I would like to clarify one more query,  If we use external battery and Main power switching circuitry such as shown below   and connecting to VDD shall make the MCU to operate the peripherals? In this scenario whether MCU able to differentiate the Main and battery power? If so we can able to put in deep sleep mode during VDD powering from battery. 

  • +1 in reply to Saisivarajagopal KS
    TI__Guru**** 159445 points

    Hi,

      MCU will not be able to differentiate between battery or LDO supplying the VDD in your connection scheme. In this case, you can try to operate in deepsleep mode and only enable the peripheral(s) that you want to keep active. However, the current consumption will be much higher in deep sleep mode than hibernation mode. You need to check if your battery can hold enough charge for the duration of your application. Refer to the current consumption table in the datasheet. The lowest deepsleep current is about 166uA assuming all peripherals are off. If you have some peripherals turned on such as I2C, then the current will increase. Compared to 1.29uA as in the hibernation mode, the deepsleep mode current will be much higher. 

  • 0 in reply to Charles Tsai
    Prodigy 50 points

    Hi charles, Currently we are looking for the possible approach for  Switching between Main supply (LDO) and Vbat Operation. 

    We have Two backup supplies requirement , Battery and supercap. Either one of the backup supplies is selected but provision should be provided. (either one of the backup circuit component will be mounted) and other is made DNI(Do not populate)

    Super cap back supply is only for RTC and monitor and logging the tampering Events connected to Vbat pin  (if Super cap is selected as backup supply by enduser)

    we have also have one ADC monitoring 24V from which the 3.3V is derived.

    Also there is energy hold up circuit  for 3.3V upto 500ms (upto which LDO supplies powe to MCU) to shutdown the MCU as soon the Main power outage .

    Battery backup is for RTC , Event logging and also the Peripherals (I2C for LCD Display for vey short duration) and Core of the MCU  and it act as a alternate option for short duration when Main Supply (LDO Voltage) is not present

    If Battery backup is selected by enduser, then Vbat pin will not be connected.  Also Does VDD pins Power to Backup circuitry such as RTC? and Tamper GPIOS?

    We have considered some of below approaches and provided  thoughts  on MCU possible operation mode  for Battery and main Backup switching circuit, Whether controller can able to  detect and differentiate the power source based on 24V Monitoring ADC able to operate between the run mode and  Low power Mode to reduce the power consumption of vbat operation and again resume to run mode when main power is present or with external Interrupt or wakeup signal 

  • 0 in reply to Saisivarajagopal KS
    TI__Guru**** 159445 points

    Hi,

      I think the approach 3 is a better option. The switch from LDO to the backup battery is controlled by the Supervisor IC. I have some comments.

      - The ADC only takes up to 3.3V input. You cannot feed a 24V input to the ADC. Make sure you go through some type of voltage divider. 

      - When the MCU is running off the battery supply, it may quickly drain your battery. I don't know what type of battery you have and how much charge it can hold and how long it can supply the MCU in sleep mode and run mode. Datasheet provides the current for different power modes, run, sleep and deepsleep. You need to do your own calculation. 

      - When you get a wake up interrupt, will that signal the supervisor IC to switch back to the main supply? Again, if you plan to run LCD application off the battery supply only, you need to determine if your battery has enough charge and what duration can it supply the run mode operations.