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STM1817SW7F

Low power reset circuit

STMicroelectronics 

STM1810/1811/1812/1813/1815/1816/1817/1818

1

Description

Description

STM181x devices are low power reset devices used to monitor power supplies for

microcontrollers. They perform a single function: asserting a reset signal whenever VCC

supply voltage drops below a preset value and keeping it asserted until VCC has risen above

the preset threshold for a minimum period of time (trec). They provide excellent circuit

reliability without additional external components when used with +3.0 V / +3.3 V

(STM1815–STM1818), and +5 V (STM1810–STM1813) power supply systems.

A precision voltage reference and comparator monitors the VCC input for an out-of-tolerance

condition. When an invalid VCC condition occurs, the reset output (RST) is forced low (or

high in the case of RST) and remains asserted for trec after VCC rises above the reset

threshold. The STM1813/1818 also keep reset asserted for trec after the output is

momentarily pulled to ground by an external push-button switch.

The STM1812 and STM1817 have an active-high, push-pull output. The STM1810 and

STM1815 (push-pull) and STM1811, STM1813, STM1816, and STM1818 (Open Drain)

have an active-low RST output. The open drain devices

(STM1811/STM1813/STM1816/STM1818) also have an internal pull-up resistor to VCC. The

STM1813 and STM1818 feature a debounced manual reset feature that asserts a reset if

the RST pin is pulled low for more than 1.5 µs. When used to initiate manual reset, RST

debounces signals from devices such as mechanical switches. For devices with this feature,

the release of the external switch triggers the reset period.

The STM181x devices are guaranteed to output the correct logic state for VCC down to 1.0 V

(0 °C to +105 °C). They also provide a reset comparator designed to ignore fast transients

on VCC.

Reset thresholds are available between +2.55 V and +4.62 V. These small, low power

devices are ideal for use in portable equipment. All are available in the space-saving 3-pin

SOT23 package, and are specified from –40 °C to +105 °C. Figure 4 shows a typical

hardware hookup for STM181x devices to a Microcontroller.

Figure 2. Logic diagram

VCC

STM181x

RST (RST)(1)

VSS

1. For STM1812, STM1817.

AI09648

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