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MIC811/812 Micrel, Inc. MIC811/812 Microprocessor Reset Circuits Final Information General Description Features The MIC811 and MIC812 are inexpensive microprocessor supervisory circuit that monitors power supplies in microprocessor based systems. The function of this device is to assert a reset if either the power supply drops below a designated reset threshold level or /MR is forced low. Several different reset threshold levels are available to accommodate 3V, 3.3V or 5V powered systems. The MIC811 has an active low /RESET output, while the MIC812 offers an active high RESET output. The reset output is guaranteed to remain asserted for a minimum of 140ms after VCC has risen above the designed reset threshold level. Having a push-pull output stage, MIC811/812 does not require a pull-up resistor at the output. The MIC811/812 comes in a 4-pin SOT-143 package. If a microprocessor voltage supervisor with an open-drain output stage is needed, see MIC6315. • Precision voltage monitor for 3V, 3.3V or 5V power supplies • /RESET remains valid with VCC as low as 1.4V • 1.4V, ISINK = 50µA, TA = 0°C to +70°C 0.3 V VCC > 1.6V, ISINK = 50µA, TA = –40° to +85°C 0.3 V VOH RESET Output Voltage 1.8V < VCC < VTH min., ISOURCE = 150µA VOL RESET Output Voltage ISINK = 3.2mA, MIC812L/M/J 0.4 V ISINK = 1.2mA, MIC812R/S/T 0.3 V /MR Minimum Pulse Width 0.8× ×VCC 10 /MR to Reset Delay VIH /MR Input Threshold /MR Input Threshold µs 0.5 VCC > VTH max., MIC81_L/M/J MIC81_R/S/T VIL V 2.3 V 0.7× ×VCC V VCC . VTH max., MIC81-L/M/_ 0.8 MIC81_R/S/T V 0.25× ×VCC /MR Pull-Up Resistance 10 /MR Glitch Immunity Note 1. Note 2. Note 3. µs 20 100 30 kΩ ns Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. February 2005 3 MIC811/812 MIC811/812 Micrel, Inc. Timing Diagram VCC VTH /MR tRST tRST /RESET Reset Timing Diagram Functional Diagram       
           MIC811/812 4 February 2005 MIC811/812 Micrel, Inc. /RESET Valid at Low Voltage A resistor can be added from the /RESET pin to ground to ensure the /RESET output remains low with VCC down to 0V. A 100kΩ resistor connected from the /RESET to ground is recommended. The size of the resistor should be large enough not to load the output excessively and small enough to pull-down any stray leakage currents. Applications Information Microprocessor Reset The /RESET (or RESET) pin is asserted whenever VCC falls below the reset threshold voltage. The /RESET pin remains asserted for a period of 140ms after VCC has risen above the reset threshold voltage. The reset function ensures the microprocessor is properly reset and powers up in a known condition after a power failure. /RESET will remain valid with VCC as low as 1.4V. VCC Transients The MIC811/812 are relatively immune to negative-going VCC glitches below the reset threshold. Typically, a negativegoing transient 125mV below the reset threshold with a duration of 50µs (25µs for MIC8_R/S/T) or less will not cause a reset. Interfacing to Bidirectional Reset Pins The MIC811/812 can interface with µPs with bidirectional reset pins by connecting a 4.7kΩ resistor in series with the MIC811/812 output and the µP reset pin. February 2005 VCC VCC VCC MIC811 µP RESET RESET 100K Reset Valid to VCC = 0V 5 MIC811/812 MIC811/812 Micrel, Inc. Package Information 0.950 (0.0374) TYP 1.40 (0.055) 2.50 (0.098) 1.20 (0.047) 2.10 (0.083) CL CL DIMENSIONS: MM (INCH) 1.12 (0.044) 0.81 (0.032) 3.05 (0.120) 2.67 (0.105) 0.800 (0.031) TYP 0.400 (0.016) TYP 3 PLACES 8° 0° 0.10 (0.004) 0.013 (0.0005) 0.150 (0.0059) 0.089 (0.0035) 0.41 (0.016) 0.13 (0.005) 4-lead SOT-143 (M3) MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2003 Micrel, Incorporated. MIC811/812 6 February 2005