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MIC809-5
Micrel
MIC809-5
Microprocessor Reset Circuit
General Description
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 5A. 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).
Features
* * * * * * * * * * * * * * 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 IttyBittyTM SOT23-3 package and SC-70 package PDAs, hand-held PCs Embedded controllers Telecommunications systems Power supplies Wireless/cellular systems Networking hardware
Applications
Ordering Information
Part Number MIC809-5SU MIC809-5SBC3 MIC809-5SUY MIC809-5SYC3 Marking IX IX IX IX
Typical Application Voltage* 3.3V5% 3.3V5% 3.3V5% 3.3V5%
Nominal Threshold Voltage 2.93 2.93 2.93 2.93
tRST (ms) 30 30 30 30
Operating Temp. Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package SOT23-3 SC70-3 SOT23-3 SC70-3
Pb-Free No No Yes Yes
*Other voltages available. Contact Micrel for details. Minimum order may apply.
Typical Application
VCC
VCC
VCC
P
MIC809-5
/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
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M9999-071305
MIC809-5
Micrel
MIC809-5
GND 1 3 VCC /RESET 2
Pin Configuration
3-Lead SOT23 3-Lead SC-70
Pin Description
Pin Number 1 2 Pin Name GND /RESET 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.
3
VCC
M9999-071305
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July 2005
MIC809-5
Micrel
Absolute Maximum Ratings(1)
Terminal Voltage (VCC) .................................-0.3V to +6.0V Input Current (VCC)..................................................... 20mA Output Current (/RESET, RESET) .............................. 20mA Lead Temperature (soldering, 10 sec.) ...................... 300C Storage Temperature (TS) .......................... -65C to 150C Rate of Rise (VCC) .................................................. 100V/s ESD Rating(3) ................................................................ 3kV
Operating Ratings(2)
Ambient Temperature (TA) .......................... -40C to +85C Power Dissipation (TA = +70C) .............................. 320mW
Electrical Characteristics
For typical values, VCC = 3.3V, TA = 25C; bold are for -40C to +85C; unless otherwise noted Symbol VCC ICC VTH Parameter Condition Operating Voltage Range Supply Current Reset Voltage Threshold Typical hysteresis Reset Timeout Period Propogation delay /RESET Output Voltage High /RESET Output Voltage Low ISOURCE = 500A /RESET < VOL, 100mV Overdrive 30 14.5 0.8xVCC 0.3 0.3 TA = -40C to 85C S Voltage Options VCC < 3.6V Min 1 5 2.85 2.93 5 66 Typ Max 5.5 10 3.00 Units V A V mV ms s V V V
VHYST tRST VOH VOL tPROP
VCC = VTH min., ISINK = 1.2mA VCC > 1V, ISINK = 50A
Note 1. Note 2. Note 3.
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.
Timing Diagram
VCC VTH tRST /RESET VTH tRST
Reset Timing Diagram
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MIC809-5
Micrel
Functional Diagram
VCC (3)
+
Reset Threshold (V)
-
RESET GENERATOR
RESET (2) RESET (MIC810)
GND (1)
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MIC809-5
Micrel
VCC
Applications Information
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 20s. 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.
Typical Transient Response
V
TH
VIN MIC809 /RESET GND RPULL-DOWN 100k
VCC
/RESET INPUT 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.
BUFFER RESET SIGNAL to OTHER CIRCUITS
MAX. TRANSIENT DURATION (s)
25 20 15 10 5
= 2.932
VCC
0 0 200 400 600 800 1000 RESET COMP. OVERDRIVE, V TH -VCC (mV)
VIN MIC809 /RESET GND
4.7k
VCC
Figure 1. Comparator Overdrive vs. Duration 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 100k 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.
RESET I/O Microcontroller or Microprocessor GND
Figure 3. Interfacing to Processors with Bidirectional Reset Pins
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Package Information
1.40 (0.055) 2.50 (0.098) 1.19 (0.047) 2.10 (0.083)
C L 2.36 (0.093) 2.28 (0.090) C L
3.05 (0.120) 2.67 (0.105)
1.15 (0.045) 0.76 (0.030)
DIMENSIONS : MM (INCH)
8 0
0.15 (0.006) 0.076 (0.0030)
0.445 (0.0175) TYP 3 PLACES
0.10 (0.004) 0.013 (0.0005)
0.41 (0.016) 0.13 (0.005)
3-lead SOT-23 (M3)
3-Lead SC-70 (C3)
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. (c) 2004 Micrel, Incorporated. M9999-071305
MICREL, INC.
1849 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
6
July 2005

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