TIDUEM8B March   2019  – February 2021

 

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2.2.3 TPS3840

The TPS3840 family of voltage supervisors or reset ICs can operate at high voltage levels while maintaining very low quiescent current across the whole VDD and temperature range. The TPS3840 device offers best combination of low power consumption, high accuracy and low propagation delay.

The reset output signal of the device is asserted when the voltage at VDD drops below the negative voltage threshold (VIT-) or when manual reset is pulled to a low logic (VMR_L). The reset signal is cleared when VDD rises above VIT- plus hysteresis (VIT+) and manual reset ( MR) is floating or above VMR_H and the reset time delay (tD) expires. Reset time delay can be programmed by connecting a capacitor to ground in the CT pin, for a fast reset CT pin can be left floating. Additional features include low power on reset voltage (VPOR), built in glitch immunity protection for MR and VDD, build in hysteresis and low open drain output leakage current (ILKG(OD)).

For electricity meters, some manufacturers prefer to have external SVS devices to reset any microcontrollers in the system, even if the microcontrollers already have an internal SVS. External SVS devices are sometimes preferred over using the SVS within a microcontroller because the external option can be more secure than the internal option, since the external devices function independently of the microcontroller. Although the SVS of the MSP432 MCU suffices for this application, the TPS3840 external SVS device is added to this design for an additional level of security. External SVS devices may sometimes also be used for early detection of a Mains blackout condition by monitoring one of the rails of an AC/DC powered from Mains.

In this design, the TPS3840DL20 variant is specifically used, which has a 2-V threshold and an open drain, active low output.