Push-button reset controllers for portable applications

June 12, 2013 // By Graham Prophet
Texas Instruments has introduced a new family of low-power, dual-channel, low quiescent current timers featuring flexible time selection and tiny package

The two push-button reset controllers are for space-constrained, power-sensitive applications such as pedometers, fitness bands, cell phones and tablets. The dual-channel TPS3420 and TPS3421 feature low power consumption and a selectable reset time delay to improve system stability.

Push-button reset controllers are required for portable electronics with an embedded battery. In practice, the user presses and holds one or two external keys for a specific period of time, which turns the portable device off or generates a reset. The TPS3420 and TPS3421 use a long input delay to provide the intended system reset and avoid reset from short push-button or key presses. This reset configuration enables differentiation between software interrupts and hard system resets. The timers are the first in a family of new push-button controllers from TI to ensure a hard and full system reset when needed to increase efficiency.

They feature; selectable input delay of 7.5 or 12.5 seconds to eliminate unintended resets; low 250-nA quiescent current to conserve power; selectable reset pulse of 400 or 800 msec to allow for flexible initialising; and come in a 1.45 x 1.0 xy 0.55-mm SON package using 70% less board space than competitive devices.

Although TI’s MSP430 MCUs are already equipped with a push-button interrupt, an external push-button reset controller, such as the TPS3420 or TPS3421, along with a voltage supervisor such as the TPS3839, can serve as an extra line of security. The controller and supervisor remain isolated from the MSP430 MCU, ensuring reset as long as they are connected to a power supply. The TPS3420 and TPS3421 also relieve the MSP430 MCU of the processing power required to monitor a push-button interrupt. They are priced at $0.40 (1,000).

TI, www.ti.com