STMicroelectronics

The Smart Reset™ devices provide a useful feature that ensures that inadvertent short reset push-button closures do not cause system resets as the extended Smart Reset™ delay setup periods are implemented. Once the valid Smart Reset™ input levels and setup delay are met, the device generates an output reset pulse for a fixed timeout period (tREC). The typical application hookup shows that either a single Smart Reset™ input, or both reset inputs can be connected to the applications interrupt and control both the interrupt pin and the hard reset functions. If the push-button is closed for a short time, the processor is only interrupted. If the system still does not respond properly, holding the push-button(s) for the extended setup time (tSRC) causes a hard reset of the processor. The Smart Reset™ feature helps significantly increase system stability and eliminates the need for a dedicated reset button. The STM65xx family of Smart Reset™ devices consists of low-current microprocessor reset circuits targeted at applications such as MP3 players, portable navigation or mobile phones, generally any application that requires delayed reset push-button(s) response for improved system stability. The devices in the STM65xx Smart Reset™ family include various combinations of useful features for the targeted applications. The STM6522 has two combined Smart Reset™ inputs (SR0andSR1) with delayed reset setup time (tSRC) programmed by an external capacitor on the SRC pin.

The STM6600-01 devices monitor the state of connected push-button(s) as well as sufficient supply voltage. An enable output controls power for the application through the MOSFET transistor, DC-DC converter, regulator, etc. If the supply voltage is above a precise voltage threshold, the enable output can be asserted by a simple press of the button. Factory-selectable supply voltage thresholds are determined by highly accurate and temperature-compensated references. An interrupt is asserted by pressing the push-button during normal operation and can be used to request a system power-down. The interrupt is also asserted if undervoltage is detected. By a long push of one button (PB) or two buttons (PBandSR) either a reset is asserted or power for the application is disabled depending on the option used. The device also offers additional features such as precise 1.5 V voltage reference with very tight accuracy of 1%, separate output indicating undervoltage detection and separate output for distinguishing between interrupt by push-button or undervoltage. The device consumes very low current of 6 μA during normal operation and only 0.6 μA current during standby. The STM6600-01 is available in the TDFN12 package and is offered in several options among features such as selectable threshold, hysteresis, timeouts, output types, etc.

The STM6717/18/19/20 and STM6777/78/79/80 supervisors are a family of low-voltage/low-supply current processor (micro or DSP) supervisors, designed to monitor two (or three) system power supply voltages. They are targeted at applications such as set-top boxes (STBs), portable, battery-powered systems, networking, and communication systems. All device options have a push-button-type manual reset input (MR). The STM6777/78/79/80 also includes an option which enables the user to delay the start of the manual reset process from 6 μs (MRC pin left open) or more with external capacitor. The delay is implemented by connecting the appropriately sized capacitor between the MRC pin and VSS(typical 4 s delay with a 3.3 μF capacitor). Two of the three supplies monitored (VCC1and VCC2) have fixed (customer-selectable, factory-trimmed) thresholds (VRST1and VRST2). The third voltage is monitored using an externally adjustable RSTIN threshold (0.626 V internal reference). If any of the three monitored voltages drop below its factory-trimmed or adjustable thresholds, or ifMRis asserted to logic low, aRSTis asserted (driven low). Once asserted,RSTis maintained at low for a minimum delay period (trec) after ALL supplies rise above their respective thresholds andMRreturns to high. These devices are guaranteed to be in the correct reset output logic state when VCC1and/or VCC2is greater than 0.8 V. These devices are available in standard 5-pin or 6-pin SOT23 packages.