general description the MAX821/max822 microprocessor (?) supervisory circuits monitor power supplies in ? and digital sys- tems. they provide excellent circuit reliability and low cost by eliminating external components and adjust- ments when used with 5v-powered or 3v-powered cir- cuits. the MAX821/max822 also provide a power-on reset timeout delay that is pin selectable to 1ms (max), 20ms (min), or 100ms (min). these devices perform a single function: they assert a reset signal whenever the v cc supply voltage falls below a preset threshold, and they keep reset asserted for the pin-selected reset timeout delay after v cc has risen above the reset threshold. the only difference between the two devices is that the MAX821 has an active-low reset output (which is guaranteed to be in the correct state for v cc down to 1v), while the max822 has an active-high reset output. the reset comparator is designed to ignore fast transients on v cc . reset thresholds suitable for operation with a vari- ety of supply voltages are available. low supply current makes the MAX821/max822 ideal for use in portable equipment. these devices come in a 4-pin sot143 package. ________________________applications bar-code scanners computers controllers intelligent instruments critical p and c power monitoring portable/battery-powered equipment features pin-selectable, precision power-on reset delay: 1ms (max), 20ms (min), or 100ms (min) precision monitoring of +3v to +5v power-supply voltages 2.5 a supply current guaranteed over temperature (-40? to +125?) guaranteed reset valid to v cc = 1v (MAX821) power-supply transient immunity no external components sot143 package MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay ________________________________________________________________ maxim integrated products 1 1 2 4 3 v cc srt (reset) reset gnd MAX821 max822 sot143 top view ( ) are for max822 pin configuration MAX821 max822 v cc reset (reset) reset input gnd v cc gnd p ( ) are for max822 srt 20ms 100ms 1ms __________typical operating circuit 19-1122; rev 2; 5/00 part MAX821 lus-t MAX821mus-t 4.38 4.63 nominal v th (v) top mark* az_ _ ba_ _ ordering information * the first two letters in the package top mark identify the part, while the remaining two letters are the lot-tracking code. for free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. for small orders, phone 1-800-835-8769. MAX821pus-t 4.00 bm_ _ MAX821tus-t 3.08 bb_ _ MAX821sus-t 2.93 bc_ _ MAX821uus-t 2.78 bl_ _ MAX821rus-t 2.63 bd_ _ max822 lus-t 4.63 bf_ _ max822mus-t 4.38 bg_ _ max822tus-t 3.08 bh_ _ max822sus-t 2.93 bj_ _ max822rus-t 2.63 bk_ _
MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = full range, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. terminal voltage (with respect to gnd) v cc ......................................................................-0.3v to 6.0v all other inputs.......................................-0.3v to (v cc + 0.3v) input current, v cc , srt......................................................20ma output current, reset or reset .......................................20ma continuous power dissipation (t a = +70?) sot143-4 (derate 4mw/? above +70?)...................320mw operating temperature range .........................-40? to +125? storage temperature range .............................-65? to +160? lead temperature (soldering, 10sec) .............................+300? srt = unconnected v 0.5v cc v open srt input threshold 0.9v cc v ih 0.07v cc v il ms 100 160 200 t rp reset active timeout period 20 32 40 2.5 7.0 v 1.2 5.5 1.0 5.5 v cc range 0.5 0.8 1 ? 50 v cc to reset delay (note 1) ppm/? 30 reset threshold tempco v 2.55 2.70 v th reset threshold (note 1) 12 1.8 5.5 ? 9 i cc supply current 2.59 2.63 2.66 units min typ max symbol parameter t a = -40? to +85? t a = 0? to +70? v cc falling at 1mv/? reset = low for MAX821, reset = high for max822 max82_r max82_l/m/p, v cc = 5.5v, i out = 0 max82_r/s/t/u, v cc = 5.5v, i out = 0 conditions 4.56 4.63 4.70 4.50 4.75 4.31 4.38 4.45 4.25 4.50 max82_l max82_m 3.97 4.00 4.04 3.91 4.09 2.89 2.93 2.96 3.04 3.08 3.11 2.85 3.00 3.00 3.15 max82_p 2.74 2.78 2.81 2.70 2.85 max82_s max82_u ? -1 1 srt input current (note 2) 100 -100 reset = low for MAX821, reset = high for max822 srt = gnd srt = v cc t a = +25? t a = +25? t a = +25? t a = +25? t a = +25? max82_t t a = +25? t a = +25? t a = +25? t a = +25? srt = gnd srt = unconnected srt = v cc t a = -40? to +125? t a = -40? to +125? t a = -40? to +125? t a = -40? to +125? t a = -40? to +125? t a = -40? to +125? t a = -40? to +125? t a = t min to t max t a = t min to t max
MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay _______________________________________________________________________________________ 3 note 1: reset output for MAX821; reset output for max822. note 2: during reset active timeout period only. note 3: guaranteed by design. electrical characteristics (continued) (v cc = full range, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) 0.3 0.4 pf 20 srt input capacitance (note 3) (see setting the reset timeout delay section) units min typ max symbol parameter MAX821r/s/t/u only, i sink = 1.2ma, v cc = v th(min) MAX821l/m/p only, i sink = 3.2ma, v cc = v th(min) internal conditions 0.3 v ol 0.3 i sink = 50? 0.3 0.4 max822r/s/t only, i sink = 1.2ma, v cc = v th(max) max822l/m only, i sink = 3.2ma, v cc = v th(max) v 0.8v cc v oh reset output voltage (MAX821) v cc -1.5 MAX821r/s/t/u only, i source = 500?, v cc v th(max) MAX821l/m/p only, i source = 800?, v cc v th(max) 0.6 -40 reset timeout period vs. temperature 0.7 max 821/822 toc-04 temperature (?) reset timeout period (ms) 40 60 80 0.9 0.8 -20 20 100 1.0 0 srt = gnd 30 -40 reset timeout period vs. temperature 32 31 max 821/822 toc-05 temperature ( c) reset timeout period (ms) 40 60 80 35 34 33 -20 20 100 36 0 srt = v cc 150 -40 reset timeout period vs. temperature 160 155 max 821/822 toc-06 temperature ( c) reset timeout period (ms) 40 60 80 175 170 165 -20 20 100 180 0 srt = unconnected v ol v v oh reset output voltage (max822) 0.8v cc i source = 150?, 1.4v v cc v th(min) __________________________________________typical operating characteristics (t a = +25?, unless otherwise noted.) t a = 0? to +70?, v cc 1v t a = -40? to +85?, v cc 1.2v
MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay 4 _______________________________________________________________________________________ ____________________________typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) 0.997 -40 normalized reset threshold vs. temperature 0.999 0.998 max 821/822 toc-07 temperature ( c) normalized reset threshold (v) 40 60 80 1.002 1.001 1.000 -20 20 100 1.003 0 ______________________________________________________________pin description 1 gnd ground 2 reset active-low reset output. reset is low while v cc is below the reset threshold. it remains low for the reset timeout period after the reset condition is terminated. the reset timeout period is determined by the srt input. reset active-high reset output. reset is high while v cc is below the reset threshold. it remains high for the reset timeout period after the reset condition is terminated. the reset timeout period is determined by the srt input. 3 srt set reset timeout input. connect to gnd for 1ms (max) delay; connect to v cc for 20ms (min) delay; leave unconnected for 100ms (min) delay. 4 v cc supply voltage 1 pin 2 3 4 name function MAX821 max822 0 -40 max82_r/s/t power-down reset delay vs. temperature 10 5 max 821/822 toc-02 temperature ( c) power-down reset delay ( s) 40 60 80 40 35 30 25 20 15 -20 20 100 45 0 v cc falling at 1mv/ s v cc falling at 10mv/ s 0 -40 max82_l/m power-down reset delay vs. temperature 20 10 max 821/822 toc-03 temperature ( c) power-down reset delay ( s) 40 60 80 50 40 30 -20 20 100 60 0 v cc falling at 1mv/ s v cc falling at 10mv/ s 0.90 -40 normalized supply current vs. temperature 0.95 max 821/822 toc-01 temperature ( c) normalized supply current ( a) 40 60 80 1.05 1.00 -20 20 100 1.10 0
_______________detailed description reset output a microprocessor? (??) reset input starts the ? in a known state. these p supervisory circuits assert reset to prevent code-execution errors during power-up, power-down, or brownout conditions. they also provide a reset timeout delay that is pin programmable to 1ms (max), 20ms (min), or 100ms (min). this feature allows flexibility in designing bar-code scanners, hand-held devices, and other applications that require quick or nonstandard power-up times. the MAX821? reset output is guaranteed to be a logic low for v cc > 1v. once v cc exceeds the reset threshold, an internal timer keeps reset low for the reset timeout period, as determined by the set reset timeout (srt) input. see the setting the reset timeout delay section. if a brownout condition occurs (v cc dips below the reset threshold), reset goes low. any time v cc goes below the reset threshold, the internal timer resets to zero, and reset goes low. the internal timer begins counting after v cc returns above the reset threshold, and reset remains low for the reset timeout period. the max822 has an active-high reset output that is the inverse of the MAX821? reset output. setting the reset timeout delay use the three-level set reset timeout (srt) input to set the reset timeout delay. connect srt to gnd for a 1ms (max) delay; connect it to v cc for a 20ms (min) delay; or leave it unconnected for a 100ms (min) delay. if you choose to drive the srt pin with an external sig- nal, make sure the signal source can charge/discharge the capacitance on srt quickly enough (<500?) to avert an unintended reset timeout delay. to ensure proper operation when selecting the 100ms timeout (srt = unconnected), minimize capacitive loading on the srt pin (< 200pf). excessive capacitive loading can select an unintended faster timeout mode. reset threshold accuracy the MAX821/max822 are designed to meet their worst- case specifications over their entire operating tempera- ture range. choose a reset threshold guaranteed to assert at a voltage below the power supply? regulation range and above the minimum specified operating volt- age range for the system? ics. __________applications information negative-going v cc transients while designed to issue a reset to the microprocessor (?) during power-up, power-down, and brownout con- ditions, the MAX821/max822 are relatively immune to short-duration, negative-going v cc transients (glitches). figure 1 shows the maximum transient duration vs. reset comparator overdrive for which the MAX821/max822 typically do not generate a reset pulse. this graph was generated using a negative-going pulse applied to v cc , starting above the actual reset threshold and ending below it by the magnitude indicated (reset comparator overdrive). the graph indicates the typical maximum pulse width a negative-going v cc transient may have without causing a reset pulse to be issued. as the mag- nitude of the transient increases (goes farther below the reset threshold), the maximum allowable pulse width decreases. typically, for the MAX821/max822, a v cc transient that goes 100mv below the reset threshold and lasts 12? or less will not cause a reset pulse to be issued. a 0.1? capacitor mounted as close as possible to v cc can provide additional transient immunity, if desired. MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay _______________________________________________________________________________________ 5 300 250 0 1 10 100 1000 50 MAX821/822 fig-01 reset comparator overdrive, v th -v cc (mv) maximum transient duration ( s) 100 150 200 t a = +25 c figure 1. maximum transient duration without causing a reset pulse vs. comparator overdrive
MAX821/max822 ensuring a valid reset output down to v cc = 0v when v cc falls below 1v, the MAX821 reset output no longer sinks current?t becomes an open circuit. therefore, high-impedance cmos logic inputs con- nected to the reset output can drift to undetermined voltages. this presents no problem in most applica- tions, since most p and other circuitry is inoperative with v cc below 1v. however, in applications where the reset output must be valid down to 0v, adding a pull- down resistor to the reset pin will cause any stray leakage currents to flow to ground, holding reset low (figure 2a). r1? value is not critical; 100k ? is large enough not to load reset , and small enough to pull reset to ground. a 100k ? pull-up resistor to v cc is also recommended for the max822 if reset is required to remain valid for v cc < 1v (figure 2b). interfacing to ps with bidirectional reset pins ?s with bidirectional reset pins (such as the motorola 68hc11 series) can contend with the MAX821 reset output. for example, if the MAX821 reset output is asserted high and the ? wants to pull it low, indetermi- nate logic levels may result. to correct such cases, connect a 4.7k ? resistor between the MAX821 reset output and the ? reset i/o (figure 3). buffer the reset output to other system components. ___________________chip information transistor count: 492 4-pin p voltage monitors with pin-selectable power-on reset timeout delay 6 _______________________________________________________________________________________ 4.7k v cc gnd reset MAX821 reset v cc gnd p buffer buffered reset to other system components figure 3. interfacing to ?s with bidirectional reset i/o r1 v cc v cc gnd MAX821 reset r1 v cc v cc gnd max822 reset a) b) figure 2. reset/ reset valid to v cc = ground circuit
MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay _______________________________________________________________________________________ 7 ________________________________________________________package information sot1434.eps
MAX821/max822 4-pin p voltage monitors with pin-selectable power-on reset timeout delay notes maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 8 _____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2000 maxim integrated products printed usa is a registered trademark of maxim integrated products.
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