Kingbor Technology Co.,Ltd KB809 TEL:(86)0755-83095458 FAX:(86)0755-88364052 Microprocessor Reset circuits General Description Features The KB809 is a power supply supervisor that provides under-voltage monitoring and power-on reset generation in an industry standard 3-pin SOT package and pinout. The reset output is asserted at power-on and any time the input voltage drops below the programmed threshold. It remains asserted for 180ms (typ.) after the input subsequently rises back above the threshold boundary. The KB809 has an active-low reset output. Hysteresis is included to prevent chattering due to noise, and the KB809 is inherently immune to brief power supply transients. Typical supply current is a low 3µA. For those applications that require a manual reset function, see the KB811/812. For those applications that require a longer reset timeout, see the KB809. (The KB809 is identical to the industrystandard KB809 with the exception of a shorter reset timout.) • Under-voltage monitor • Power-on reset generation (180ms Typ) • Choice of threshold voltages (contact Kingbor regarding availability) • Active-low reset output • No external components required • Rejects brief input transients • Industry standard package and pinout • 3-pin SOT23-3 package Applications • Monitoring processor, ASIC, or FPGA core and I/O voltages • PDAs, hand-held PCs • Embedded controllers • Telecommunications systems • Power supplies • Wireless / Cellular systems • Networking hardware Ordering Information Part Number KB809-293 Part Number KB809-263 Top Marking: Marking** Typical Application Voltage* Nominal Threshold Voltage TRST (ms) Junction Temperature Range Package ADAA C956 3.3V ±5% 2.93 180 –40°C to +85°C SOT23-3 Marking** Typical Application Voltage* Nominal Threshold Voltage TRST (ms) Junction Temperature Range Package AFAA C756 3.3V ±10% 2.63 180 –40 °C to +85°C SOT23-3 ADAA & AFAA: To manufacture marking after 2007-3-15 C956 & C756: Before 2007-3-15 Typical Application Block Diagrams VCC VCC VCC KB809 µP /RESET /RESET Typical Operating Circuit March 2007 1 KB809 Kingbor Technology Co.,Ltd KB809 TEL:(86)0755-83095458 FAX:(86)0755-88364052 Pin Configuration KB809 GND 1 3 VCC /RESET 2 3-Lead SOT23 Pin Description Pin Number Pin Name 1 GND 2 /RESET 3 VCC 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 180ms and be de-asserted after VCC returns above the threshold. Analog Input. Power supply input to the IC. 2 March 2007 Kingbor Technology Co.,Ltd KB809 TEL:(86)0755-83095458 FAX:(86)0755-88364052 Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Terminal Voltage (VCC) ................................. –0.3V to 10V Lead Temperature (soldering, 10 sec.) ..................... 300°C Storage Temperature (TS) ......................... –65°C to 150°C Rate of Rise (VCC) ................................................. 100V/µs ESD Rating, Note 3 Ambient Temperature (TA) ......................... –40°C to +85°C Power Dissipation (TA = +70°C) .............................. 320mW Electrical Characteristics TA = 25°C; VCC = 3.3V for KB809 unless otherwise noted. Values in bold are for –40 °C to +85 °C; unless otherwise noted Symbol Parameter Condition Min VCC Operating Voltage Range TA = 0°C to 70°C TA = –40°C to 85°C Typ Max Units 0.95 8 V 0.95 8 V 1 3 µA ICC Supply Current VCC = 3.3V VTH Reset Voltage Threshold S Voltage Options (KB809-293) 2.85 2.93 3.00 V Reset Voltage Threshold S Voltage Options (KB809-263) 2.55 2.63 2.70 V VHYST Typical hysteresis 5 TRST Reset Timeout Period TPROP Propogation delay /RESET < VOL, 100mV Overdrive VOH /RESET Output Voltage High ISOURCE = 500µA VOL /RESET Output Voltage Low VCC = VTH min., ISINK = 1.2mA 0.3 V VCC > 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 140 Exceeding the absolute maximum rating may damage the device. 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. Timing Diagrams VTH TRST TRST RESET Reset Timing Diagram March 2007 3 ms µs 0.8·VCC Note 2. VTH 300 9.3 Note 1. VCC 180 mV V Kingbor Technology Co.,Ltd KB809 TEL:(86)0755-83095458 FAX:(86)0755-88364052 Functional Diagram + VCC (3) VTH RESET GENERATOR - RESET (2) GND (1) KB809 Block Diagram Standard Circuits 4 March 2007 Kingbor Technology Co.,Ltd KB809 TEL:(86)0755-83095458 FAX:(86)0755-88364052 Applications Information VCC Microprocessor Reset The /RESET pin is asserted whenever VCC falls below the reset threshold voltage. The /RESET pin remains asserted for a period of 180ms 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 0.95V. Transients on VCC The KB809 is inherently immune to very short “glitches” on VCC. In the case of very brief transients, VCC may drop below the under-voltage threshold without triggering a reset. As shown in the graph of Figure 1, the narrower the transient, the deeper the threshold overdrive that will be ignored. The line on the graph represents the typical allowable transient duration for a given amount of threshold overdrive that will not generate a reset. The data from which Figure 1 is derived was taken by adding negative-going square-wave pulses to a DC input voltage set at 0.5V above the actual measured threshold for the part being characterized. MAX. TRANSIENT DURATION (µs) Typical Transient Response 20 VTH = 2.932 15 KB809 /RESET /RESET INPUT GND Microcontroller or Microprocessor RPULL-DOWN 100k 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 KB809’s output and the reset pin. This limits the current that will flow between the KB809 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. BUFFER 10 RESET SIGNAL to OTHER CIRCUITS VCC 5 0 0 200 400 600 RESET COMP. OVERDRIVE, VTH –VCC (mV) VCC VIN KB809 Figure 1. Comparator Overdrive vs. Duration /RESET Ensuring Proper Operation at Low VCC At levels of VCC below 1.4V, the KB809’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 KB809 will be similarly inoperative at V CC =0.95V.) If a given application requires that /RESET be valid below VCC =1.4V, 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. March 2007 VCC VIN 5 GND 4.7k RESET I/O Microcontroller or Microprocessor GND Figure 3. Interfacing to Processors with Bidirectional Reset Pins Kingbor Technology Co.,Ltd KB809 TEL:(86)0755-83095458 FAX:(86)0755-88364052 PACAGE DESCRIPTION 0.021 0.015 0.055 0.047 0.098 0.083 0.120 0.105 0.040 0.031 0.079 0.071 0.004 0.001 0.0059 0.0035 0-8¼ 0.010 0.005 3-lead SOT-23 Kingbor Technology TEL:(86) 0755-83095458 FAX: (86) 0755-88364052 www.kingbor.com 6 March 2007