DS1818 3.3v econoreset with pushbutton DS1818 050798 1/5 features ? automatically restarts a microprocessor after power failure ? monitors pushbutton for external override ? maintains reset for 150 ms after v cc returns to an in tolerance condition ? reduces need for discrete components ? precision temperaturecompensated voltage reference and voltage sensor ? accurate 5%, 10% or 20% power monitoring ? lowcost to92 or space saving surface mount sot23 packages available ? efficient opendrain output with internal 5.5k w pullup resistor ? operating temperature 40 c to +85 c pin assignment 1 23 to92 package see mech. drawings section 12 3 sot23 package 123 pin descriptions to92 1 rst active low reset output 2v cc power supply 3 gnd ground sot23 1 rst active low reset output 2v cc power supply 3 gnd ground description the DS1818 econoreset uses a precision temperature compensated reference and comparator circuit to moni- tor the status of the power supply (v cc ). when an out oftolerance condition is detected, an internal power fail signal is generated which forces reset to the active state. when v cc returns to an intolerance condition, the reset signal is kept in the active state for approxi- mately 150 ms to allow the power supply and processor to stabilize.
DS1818 050798 2/5 the DS1818 also monitors a pushbutton on the reset output. if the reset line is pulled low, a reset is generated upon release and the DS1818 output will be held in reset output low for typically 150 ms. operation power monitor the DS1818 provides the functions of detecting outof tolerance power supply conditions and warning a pro- cessorbased system of impending power failures. when v cc is detected as outoftolerance, the rst signal is asserted. on powerup, rst is kept active for approximately 150 ms after the power supply has reached the selected tolerance. this allows the power supply and microprocessor to stabilize before rst is re- leased. block diagram (opendrain output) figure 1 + v cc ground v cc tolerance bias t.c. reference 150 ms delay rst reset monitor 5.5k w application example figure 2 DS1818 v cc microprocessor rst reset
DS1818 050798 3/5 operation pushbutton reset the DS1818 provides a pushbutton switch for manual reset control. when the DS1818 is not in a reset cycle, a pushbutton reset can be generated by pulling the rst pin low for at least 1 m s. when the pushbutton is held low, the rst is forced active low and will remain active low for about 150 ms after the pushbutton is released. see figure 2 for an application example and figure 3 for the timing diagram. timing diagram: pushbutton reset figure 3 rst v ih t rst v il t pb timing diagram: power up figure 4 t r t rpu v oh v cc rst v cctp v cctp (max) v cctp (min) timing diagram: power down figure 5 v ol t rpd t f v cctp v cc rst v cctp (max) v cctp (min)
DS1818 050798 4/5 absolute maximum ratings* voltage on v cc pin relative to ground 0.5v to +7.0v voltage on rst relative to ground 0.5v to v cc +0.5v operating temperature 40 c to +85 c storage temperature 55 c to +125 c soldering temperature 260 c for 10 seconds * this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. recommended dc operating conditions ( 40 c to +85 c ) parameter symbol min typ max units notes supply voltage v cc 1.0 5.5 v 1 dc electrical characteristics ( 40 c to +85 c ; v cc = 1.2v to 5.5v) parameter symbol min typ max units notes output current @ 0.4v i ol +10 ma 2, 3 voltage input low v il 0.4 v 1 voltage input high v ih 0.7*v cc v 1 operating current v cc <5.5v i cc 28 35 m a 4 v cc trip point (DS18185) v cctp 2.98 3.06 3.15 v 1 v cc trip point (DS181810) v cctp 2.80 2.88 2.97 v 1 v cc trip point (DS181820) v cctp 2.47 2.55 2.64 v 1 internal pullup resistor r p 3.50 5.5 7.5 k w 7 output capacitance c out 10 pf ac electrical characteristics ( 40 c to +85 c ; v cc = 1.2v to 5.5v) parameter symbol min typ max units notes reset active time t rst 100 150 250 ms 5 v cc detect to rst t rpd 2 5 m s v cc slew rate (v cctp (max) to v cctp (min)) t f 300 m s 8 v cc slew rate (v cctp (min) to v cctp (max)) t r 0 ns v cc detect to rst t rpu 100 150 250 ms 5, 6 pushbutton detect to rst t pb 1 m s pushbutton reset t pbrst 100 150 250 ms 5 notes: 1. all voltages are referenced to ground. 2. measured with v cc > 2.7v. 3. a 1k w external pullup resistor may be required in some applications for proper operation of the microprocessor reset control circuit.
DS1818 050798 5/5 4. measured with rst output open. 5. measured with 2.7v < v cc < 3.3v. 6. t r = 5 m s. 7. v oh and i oh are a function of the value of r p and the associated output load conditions. 8. the t f value is for reference in defining values for t rpd and should not be considered a requirement for proper operation or use of the device. part marking codes 12 3 abcd aao, abo, & aco represents the device type. 810 ds1810 811 ds1811 812 ds1812 813 ds1813 815 ds1815 816 ds1816 817 ds1817 818 DS1818 ado represents the device tolerance. a5% b 10% c 15% d 20%
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