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STM1812：Low Power Reset Circuit

STM181x devices are low power reset devices used to monitor power supplies for microcontrollers. They perform a single function: asserting a reset signal whenever V_CCsupply voltage drops below a preset value and keeping it asserted until V_CChas risen above the preset threshold for a minimum period of time (t_rec). 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 V_CCinput for an out-of-tolerance condition. When an invalid V_CCcondition occurs, the reset output (RST) is forced low (or high in the case of RST) and remains asserted for t_recafter V_CCrises above the reset threshold. The STM1813/1818 also keep reset asserted for t_recafter 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 RSToutput. The open-drain devices (STM1811 / STM1813 / STM1816 / STM1818) also have an internal pull-up resistor to V_CC. The STM1813 and STM1818 feature a debounced manual reset feature that asserts a reset if the RSTpin is pulled low for more than 1.5 μs. When used to initiate manual reset, RSTdebounces 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 V_CCdown to 1.0 V (0 °C to +105 °C). They also provide a reset comparator designed to ignore fast transients on V_CC.

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.

Key Features

• Precision monitoring of 3 V, 3.3 V, and 5 V supply voltages
• Four output configurations:
  • Push-pull, active-high (STM1812,1817)
  • Push-pull, active-low (STM1810,1815)
  • Open-drain, active-low (STM1811,1816)
  • Open-drain, active-low with push-button detect (STM1813,1818)
• Reset pulse width - 100 ms (min.)
• Low supply current - 4 μA (typ.)
• Guaranteed assertion down to VCC = 1.0 V (0 °C to 105 °C)
• Factory-trimmed reset thresholds of 2.55 V, 2.88 V, 3.06 V, 4.37 V, and 4.62 V (typ.)
• Power supply transient immunity
• Push-button/manual reset detect (STM1813/1818)
• Operating temperature: –40 °C to 105 °C
• ± 2.5% reset threshold accuracy:(–40 °C to 105 °C)
• Available in the SOT23-3 package
• Fully compatible with DS181x and MXD181x products.

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