july 2005 1 mic1815 mic1815 micrel mic1815 microprocessor reset circuit general description the mic1815 is an inexpensive microprocessor supervisory circuit that monitors power supplies in microprocessor based systems. the function of these devices is to assert a reset if the power supply drops below a designated reset threshold lev el. several different reset threshold levels are available to accommodate 10% or 20% drop in 3.3v powered systems. the mic1815 has an active low /reset output. the reset output is guaranteed to remain asserted for a minimum of 100ms after v cc has risen above the designated reset thresh- old level. the mic1815 comes in a 3-pin sot-23 package. typical application v ccreset p reset v cc mic1815 v cc features ? precision voltage monitor for 10% or 20% drop in 3.3v power supplies ? /reset remains valid with v cc as low as 1v ? 5a supply current ? 100ms minimum reset pulse width ? no external components required ? available in 3-pin sot-23 package applications ? portable equipment ? intelligent instruments ? critical microprocessor power monitoring ? printers/computers ? embedded controllers micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 474-1000 ? fax + 1 (408 ) 944-0970 ? http://www.micrel.com ordering information threshold part number marking voltage operating temp. range package pb-free mic1815-10u nd 2.88v C40c to +85c sot-23 no mic1815-20u ne 2.55v C40c to +85c sot-23 no mic1815-10uy nd 2.88v C40c to +85c sot-23 yes mic1815-20uy ne 2.55v C40c to +85c sot-23 yes downloaded from: http:///
mic1815 micrel mic1815 2 july 2005 pin description pin number pin name pin function 1 /reset /reset goes low if v cc falls below the reset threshold and remains as- serted for one reset timeout period (100ms min) after v cc exceeds the reset threshold. 2 vcc power supply input. 3 gnd ic ground pin pin con?guration 12 3 v cc gnd mic1815 reset 3-lead sot23 downloaded from: http:///
july 2005 3 mic1815 mic1815 micrel absolute maximum ratings (note 1) terminal voltage (v cc ) ....................................C0.3v to +6v input current (v cc ) ..................................................... 20ma output current (/reset) ........................................... 20ma rate of rise (v cc ) .................................................. 100v/s lead temperature (soldering, 10 sec.) ...................... 300c storage temperature (t s ) .......................... C65c to 150c esd rating, note 3 ....................................................... 3kv operating ratings (note 2) operating temperature range mic1815-10u ......................................... C40c to +85c mic1815-20u ......................................... C40c to +85c power dissipation (t a = +70c) .............................. 320mw electrical characteristicsfor typical values, v cc = 3.3v, t a = 25c; bold values indicate C40c t a +85c; unless noted symbol parameter condition min typ max units v cc operating temperature range t a = C40c to +85c 1 5.5 v i cc supply current 5 20 a v th reset voltage threshold mic1815-10u 2.80 2.88 2.97 v mic1815-20u 2.47 2.55 2.64 v t rst reset timeout period 100 150 250 ms v oh /reset output voltage i source = 800a 1.5 v v ol /reset output voltage v cc = v th min., i sink = 10ma 0.4 v v cc > 1v, i sink = 50a 0.3 v 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 1 00pf. timing diagram /reset v cc t rst t rst v th v th reset timing diagram downloaded from: http:///
mic1815 micrel mic1815 4 july 2005 functional diagram v cc (2) gnd (3) reset (1) reset threshold (v th ) reset generator downloaded from: http:///
july 2005 5 mic1815 mic1815 micrel applications informationmicroprocessor reset the /reset pin is asserted whenever v cc falls below the reset threshold voltage. the reset pin remains asserted for a period of t rst after v cc has risen above the reset threshold voltage. the reset function ensures the microprocessor is properly reset and powers up into a known condition after a power failure. /reset will remain valid with v cc as low as 1v. v cc transients the mic1815 is relatively immune to negative-going v cc glitches below the reset threshold. typically, a negative-going transient 125mv below the reset threshold with a duration of 20s or less will not cause an unwanted reset. /reset valid at low voltage a resistor can be added from the /reset pin-to-ground to ensure the /reset output remains low with v cc down to 0v. a 100k resistor connected from /reset-to-ground is recommended. the resistor should be large enough not to load the /reset output and small enough to pull-down any stray leakage currents. see figure below. v cc reset p reset v cc mic1815 v cc 100k /reset valid to v cc = 0v downloaded from: http:///
mic1815 micrel mic1815 6 july 2005 package information ???????????? ?????????????? ???????????? ???????????? ???????????? ???????????? ? ? ? ? ??????????????????????????? ???????????? ???????????? ???????????? ???????????? ???????????? ?????????????? ???????????? ???????????? ??????????? ????????? ???????????? ???????????? ? ? ? ? 3-pin sot-23 small outline transistor 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 the information furnished by micrel in this datasheet is believed to be accurate and reliable. howev er, no responsibility is assumed by micrel for its use. micrel reserves the right to change circuitry and speci?cations at any time without noti?cation to t he customer. micrel products are noth 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 signi?cant injury to the user. a purchasers use or sale of micrel products for use in life support appliances, devices or systems is at purchase rs own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2005 micrel, incorporated. downloaded from: http:///
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