MIC809-5 Micrel MIC809-5 Microprocessor Reset Circuit General Description Features The MIC809-5 is a power supply supervisor that provides under-voltage monitoring and power-on reset generation in an industry standard 3-pin SOT package and SC-70 package. The reset output is asserted at power-on and any time the input voltage drops below the programmed threshold. It remains asserted for 30ms (min.) after the input subsequently rises back above the threshold boundary. The MIC809-5 has an active-low reset output. The MIC809-5 is inherently immune to brief power supply transients. Typical supply current is a low 5µA. For those applications that require a manual reset function, see the MIC811/812. For those applications that require a longer reset timeout, see the MIC809/810. (The MIC809-5 is identical to the industry-standard MIC809 with the exception of a shorter reset timeout). • • • • • • • • Ordering Information Under-voltage monitor Power-on reset generation (30ms minimum) Choice of threshold voltages Active-low reset output No external components required Rejects brief input transients Industry standard package and pinout 3-pin IttyBitty™ SOT23-3 package and SC-70 package Applications • • • • • • PDAs, hand-held PCs Embedded controllers Telecommunications systems Power supplies Wireless/cellular systems Networking hardware Part Number Marking Typical Application Voltage* Nominal Threshold Voltage tRST (ms) Operating Temp. Range Package Pb-Free MIC809-5SU IX 3.3V±5% 2.93 30 –40°C to +85°C SOT23-3 No MIC809-5SBC3 IX 3.3V±5% 2.93 30 –40°C to +85°C SC70-3 No MIC809-5SUY IX 3.3V±5% 2.93 30 –40°C to +85°C SOT23-3 Yes MIC809-5SYC3 IX 3.3V±5% 2.93 30 –40°C to +85°C SC70-3 Yes *Other voltages available. Contact Micrel for details. Minimum order may apply. Typical Application VCC VCC VCC MIC809-5 µP /RESET /RESET IttyBitty is a trademark of Micrel, Inc. Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com July 2005 1 M9999-071305 MIC809-5 Micrel Pin Configuration MIC809-5 GND 1 3 VCC /RESET 2 3-Lead SOT23 3-Lead SC-70 Pin Description Pin Number Pin Name 1 GND 2 /RESET 3 VCC M9999-071305 Pin Function Ground return for all IC functions. Digital Output. Active-low. Asserted whenever VCC falls below the threshold voltage. It will remain asserted for no less than 30ms and be de-asserted after VCC returns above the threshold. Analog Input. Power supply input to the IC. 2 July 2005 MIC809-5 Micrel Absolute Maximum Ratings(1) Operating Ratings(2) Terminal Voltage (VCC) .................................–0.3V to +6.0V Input Current (VCC)..................................................... 20mA Output Current (/RESET, RESET) .............................. 20mA Lead Temperature (soldering, 10 sec.) ...................... 300°C Storage Temperature (TS) .......................... –65°C to 150°C Rate of Rise (VCC) .................................................. 100V/µs ESD Rating(3) ................................................................ 3kV Ambient Temperature (TA) .......................... –40°C to +85°C Power Dissipation (TA = +70°C) .............................. 320mW Electrical Characteristics For typical values, VCC = 3.3V, TA = 25°C; bold are for –40°C to +85°C; unless otherwise noted Symbol Parameter Condition VCC Operating Voltage Range TA = –40°C to 85°C 1 S Voltage Options 2.85 ICC Supply Current VHYST Typical hysteresis tPROP Propogation delay VOL /RESET Output Voltage Low VTH VCC < 3.6V Reset Voltage Threshold tRST Typ Max 5.5 V 10 µA 2.93 3.00 30 /RESET < VOL, 100mV Overdrive /RESET Output Voltage High 0.8×VCC ISOURCE = 500µA VCC > 1V, ISINK = 50µA Note 1. Exceeding the absolute maximum rating may damage the device. Note 2. The device is not guaranteed to function outside its operating rating. Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. V mV 66 14.5 VCC = VTH min., ISINK = 1.2mA Units 5 5 Reset Timeout Period VOH Min ms µs V 0.3 V 0.3 V Timing Diagram VCC VTH VTH tRST tRST /RESET Reset Timing Diagram July 2005 3 M9999-071305 MIC809-5 Micrel Functional Diagram + VCC (3) Reset Threshold (V) RESET GENERATOR - RESET (2) RESET (MIC810) GND (1) M9999-071305 4 July 2005 MIC809-5 Micrel Applications Information VCC MAX. TRANSIENT DURATION (µs) Microprocessor Reset The /RESET pin is asserted whenever VCC falls below the reset threshold voltage. The /RESET pin remains asserted for a period of 30ms 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 1V. Transients on VCC The MIC809-5 is inherently immune to very short “glitches” on VCC. In the case of very brief transients, VCC may drop below the reset-voltage threshold without triggering a reset. As shown in the graph, the MIC809-5 is relatively immune to transients with typical duration of 20µs. The lines on the graph of Figure 1 represent the typical allowable transient duration for a given amount of threshold overdrive that will not generate a reset. The data was taken by adding negative-going square-wave pulse to a DC input voltage set at 0.5V above actual measured threshold for the part being characterized. 25 MIC809 TH /RESET INPUT GND Microcontroller or Microprocessor GND Figure 2. Ensuring a Valid /RESET Signal at Low Voltage Interfacing to Processors with Bidirectional Reset Pins Some microprocessors have reset signal pins that are bidirectional, rather than input only. The Motorola 68HC11 family is one example. To prevent excessive current flow when the processor asserts its reset output, a series resistor is employed between the MIC809-5’s output and the reset pin. This limits the current that will flow between the MIC809-5 and the reset pin to a theoretical maximum of VCC/RSERIES. Because this resistor also limits the drive capability of the supervisor’s output, a buffer may be required to drive additional circuitry. See Figure 3. = 2.932 20 15 BUFFER 10 5 RESET SIGNAL to OTHER CIRCUITS VCC 0 0 200 400 600 800 1000 RESET COMP. OVERDRIVE, V TH –VCC (mV) VCC VIN MIC809 Figure 1. Comparator Overdrive vs. Duration /RESET Ensuring Proper Operation at Low VCC At levels of VCC below 1V, the MIC809-5’s output driver cannot always turn on sufficiently to produce a valid logic-low. In this situation, other circuits driven by /RESET could be allowed to float, causing undesired operation. (In most cases, however, it is expected that the circuits driven by the MIC809-5 will be similarly inoperative at VCC =1V.) If a given application requires that /RESET be valid below VCC = 1V, this can be accomplished by adding a pull-down resistor to the output. A value of 100kΩ is recommended, as this is usually an acceptable compromise of leakage current and pull-down current. The resistor’s value is not critical, however. See Figure 2. July 2005 /RESET RPULL-DOWN 100k Typical Transient Response V VCC VIN GND 4.7k RESET I/O Microcontroller or Microprocessor GND Figure 3. Interfacing to Processors with Bidirectional Reset Pins 5 M9999-071305 MIC809-5 Micrel Package Information 1.40 (0.055) 2.50 (0.098) 1.19 (0.047) 2.10 (0.083) CL 2.36 (0.093) 2.28 (0.090) CL DIMENSIONS : MM (INCH) 1.15 (0.045) 0.76 (0.030) 3.05 (0.120) 2.67 (0.105) 0.445 (0.0175) TYP 3 PLACES 8 0 0.10 (0.004) 0.013 (0.0005) 0.15 (0.006) 0.076 (0.0030) 0.41 (0.016) 0.13 (0.005) 3-lead SOT-23 (M3) 3-Lead SC-70 (C3) MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com The information furnished by Micrel in this datasheet 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 Prod 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 imp cant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2004 Micrel, Incorporated. M9999-071305 6 July 2005