TIDUF25 june 2023 ADS131M08 , MSPM0G1507
The TPS3840 device is an external supply voltage supervisor (SVS) that is used to externally reset the MSPM0+ MCU. The TPS3840 maintains very low quiescent current, which enables this device to still be used if there is a power outage and the meter is running from a backup battery. The MSPM0+ MCU has internal POR and BOR supply monitors which cannot be disabled and suffices for this application; however, using the optional external SVS adds redundancy to SVS, in case some issue has affected the MCU itself.
In this design, the TPS3840DL20 device variant is specifically used, which has a negative-voltage threshold voltage of 1.72 ±1% V. When the voltage rail that powers the MSPM0+ MCU drops below 1.74 V, the TPS3840 device resets the MSPM0+ MCU. When the monitored voltage rises above the undervoltage threshold plus hysteresis voltage value (approximately equal to 1.85 V total), the RESET pin of the TPS3840 is pulled back high after a user-defined reset delay time, tD, elapses. The tD is determined based on the value of the capacitor connected to the CT pin of the TPS3840 device.
The TPS3840 device is available with both push-pull and open-drain outputs. The open-drain output version TPS3840DL20 is specifically selected for this design since a 47-kΩ pullup resistor is recommended in the JTAG circuitry of the MSPM0+ MCU.