The TPS3420, TPS3421, and TPS3422 (TPS342x) are low-current, ultrasmall, push-button reset timers. These devices use a long timing setup delay to provide the intended system reset, and avoid resets from short push-button closures or key presses. This reset configuration also allows for differentiation between software interrupts and hard system resets.
The TPS3420 and TPS3421 monitor two inputs (PB1 and PB2) and output an active-low reset pulse signal (RST) when both inputs are low for the selected time delay. For the TPS3421, RST remains low for a factory-programmed fixed time. For the TPS3420, RST remains low until one of the PBx inputs is released. The need for a dedicated reset button is eliminated because two inputs are used to ensure reset. The TPS3422 monitors one input (PB1) and outputs an active-low reset pulse signal (RST) when PB1 is low for the selected time delay.
The TPS342x have an open-drain output that can be wire-ORed with other open-drain devices. The TPS342x operate from 1.6 V to 6.5 V over the –40°C to +125°C temperature range, and provide a precise, space-conscious micropower solution for system resetting needs.
PART NUMBER | PACKAGE | BODY SIZE (NOM) |
---|---|---|
TPS342x | USON (6) | 1.45 mm × 1.00 mm |
Changes from A Revision (December 2012) to B Revision
Changes from * Revision (August 2012) to A Revision
PIN | I/O | DESCRIPTION | ||
---|---|---|---|---|
NAME | TPS3420/21 | TPS3422 | ||
GND | 2 | 2 | — | Ground. |
PB1 | 3 | 3 | I | Push-button input. PB1 and PB2 must be held low for greater than tTIMER time to assert the reset output. |
PB2 | 6 | — | I | Second push-button input. PB1 and PB2 must be held low for greater than tTIMER time to assert the reset output. |
RST | 1 | 1 | O | Active low, open-drain output. Reset is asserted (goes low) when both PB1 and PB2 are held low for longer than tTIMER time (only PB1 for TPS3422). For TPS3420: Reset is deasserted when either PBx input goes high. For TPS3421,TPS3422: Reset is deasserted after fixed time of tRST. |
TS | 5 | 5 | I | Time delay selection input. Connect to VCC or GND for different tTIMER selections. In normal operation, the TS pin state should not be changed because it is intended to be permanently connected to either GND or VCC. If switching the TS pin is required, it should be done during power off, or when either PBx input is high. |
TST | — | 6 | — | Connect this pin to GND or VCC during normal device operation. |
VCC | 4 | 4 | I | Supply voltage input. Connect a 1.6-V to 6.5-V supply to VCC to power the device. It is good analog design practice to place a 0.1-µF ceramic capacitor close to this pin. |