_______________general description the max823/max824/max825* microprocessor ( p) supervisory circuits combine reset output, watchdog, and manual-reset input functions in a 5-pin sot23-5 package. they significantly improve system reliability and accuracy compared to separate ics or discrete components. the max823/max824/max825 are specifically designed to ignore fast transients on v cc . five preprogrammed reset threshold voltages are available, designated by the following package suffixes: l = 4.63v, m = 4.38v, t = 3.08v, s = 2.93v, and r = 2.63v. all three devices have an active-low reset output, which is guaranteed to be in the correct state for v cc down to 1v. the max824/max825 also have an active-high reset output. the following selector guide explains the functions offered in this series of parts. ________________________applications battery-powered computers and controllers embedded controllers intelligent instruments automotive systems critical ? monitoring portable/battery-powered equipment ____________________________features ? precision monitoring of +3v, +3.3v, and +5v power supplies ? operating current: 10? (max823l/m) 3? (max825t/s/r) ? fully specified over temperature ? 140ms min power-on reset ? guaranteed reset valid to v cc = 1v ? power-supply transient immunity ? watchdog timer with 1.6sec timeout (max823/max824) ? manual-reset input (max823/max825) ? no external components max823/max824/max825 5-pin microprocessor supervisory circuits ________________________________________________________________ maxim integrated products 1 1 5 2 3 4 1 5 2 3 4 1 5 2 3 4 gnd wdi mr v cc reset max823 sot23-5 top view gnd wdi reset v cc reset max824 sot23-5 gnd mr reset v cc reset max825 sot23-5 __________________________________________________________pin configurations _____________________selector guide 19-0487; rev 0; 3/96 part ? max823_euk max824_euk -40? to +85? -40? to +85? temp. range pin-package 5 sot23-5 5 sot23-5 ______________ordering information ? insert the desired suffix letter (from the table below) into the blank to complete the part number. future product?ontact factory for availability. for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 max825_euk -40? to +85? 5 sot23-5 max823 active-low reset 4 active-high reset function watchdog input 4 max824 4 4 4 max825 4 4 manual-reset input 4 4 suffix reset threshold (v) l 4.63 m 4.38 t 3.08 s 2.93 r 2.63 typical operating circuit appears at end of data sheet. marking information appears at end of data sheet. *patents pending
max823/max824/max825 5-pin microprocessor supervisory circuits 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +4.75v to +5.5v for max82_l, v cc = +4.5v to +5.5v for max82_m, v cc = +3.15v to +3.6v for max82_t, v cc = +3v to +3.6v for max82_s, v cc = +2.7v to +3.6v for max82_r, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v cc ........................................................................-0.3v to +6.0v all other pins..............................................-0.3v to (v cc + 0.3v) input current, all pins except reset and reset ..............20ma output current, reset, reset ..........................................20ma rate of rise, v cc ............................................................100v/? continuous power dissipation (t a = +70?) sot23-5 (derate 7.1mw/? above +70?)...................571mw operating temperature range max82_euk .....................................................-40? to +85? storage temperature range .............................-65? to +160? lead temperature (soldering, 10sec) .............................+300? max82_m t a = +25? t a = 0? to +70? wdi and mr unconnected 4.25 4.50 t a = -40? to +85? t a = 0? to +70? 4.31 4.38 4.45 max82_t/s/r max82_l/m max82_l t a = +25? t a = 0? to +70? mr unconnected max82_s conditions t a = +25? t a = 0? to +70? 2.85 3.00 2.89 2.93 2.96 max82_t t a = +25? t a = 0? to +70? 3.00 3.15 3.04 3.08 3.11 max82_l/m max82_t/s/r mv 5 reset threshold hysteresis 10 max82_r t a = +25? t a = 0? to +70? v 2.55 2.70 v rst reset threshold 2.59 2.63 2.66 max823t/s/r, max824t/s/r 512 v 1.2 v cc 1.0 5.5 max823l/m, MAX824L/m max825l/m operating voltage range ms 140 200 280 t rp reset timeout period 140 200 280 ppm/? 40 reset threshold temperature coefficient 4.50 4.75 10 24 4.5 12 ? 38 i supply supply current 4.56 4.63 4.70 units min typ max symbol parameter max825t/s/r
electrical characteristics (continued) (v cc = +4.75v to +5.5v for max82_l, v cc = +4.5v to +5.5v for max82_m, v cc = +3.15v to +3.6v for max82_t, v cc = +3v to +3.6v for max82_s, v cc = +2.7v to +3.6v for max82_r, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) note 1: over-temperature limits are guaranteed by design and not production tested. note 2: the reset short-circuit current is the maximum pull-up current when reset is driven low by a ? bidirectional reset pin. note 3: wdi is internally serviced within the watchdog period if wdi is left unconnected. note 4: the wdi input current is specified as the average input current when the wdi input is driven high or low. the wdi input is designed to drive a three-stated-output device with a 10? maximum leakage current and a maximum capacitive load of 200pf. this output device must be able to source and sink at least 200? when active. max823/max824/max825 5-pin microprocessor supervisory circuits _______________________________________________________________________________________ 3 v rst - v cc = 100mv max824t/s/r, max825t/s/r, v cc = v rst max, i sink = 1.2ma max82_l/m, v cc = v rst max, i source = 120? MAX824L/m, max825l/m, v cc = v rst max, i sink = 3.2ma v cc > 1.8v, i source = 150? max82_l/m, reset = 0v, v cc = 5.5v conditions ? 20 v cc to reset delay v 0.3 v ol reset output voltage v cc - 1.5 0.4 0.8v cc v oh 800 units min typ max symbol parameter max82_t/s/r, v cc = v rst max, i source = 30? 0.8v cc v oh max82_t/s/r, v cc = v rst min, i sink = 1.2ma max82_l/m, v cc = v rst min, i sink = 3.2ma 0.3 0.4 t a = 0? to +70?, v cc = 1.2v, v cc falling, v batt = 0v, i sink = 100? t a = 0? to +70?, v cc = 1v, v cc falling, i sink = 50? v 0.3 v ol reset output voltage 0.3 max82_t/s/r, reset = 0v, v cc = 3.6v ? 400 i source reset output short-circuit current (note 2) v il = 0.4v, v ih = 0.8v cc ns 50 t wdi wdi pulse width sec 1.12 1.60 2.40 t wd watchdog timeout period wdi = 0v, time average wdi = v cc , time average v cc = 5v ? -20 -15 wdi input current (note 4) 120 160 v 0.7v cc v ih wdi input threshold (note 3) 0.3v cc v il ? 1.0 mr pulse width v 0.7v cc v ih mr input threshold 0.3v cc v il k 35 52 75 mr pull-up resistance (internal) ns 500 mr to reset delay ns 100 mr noise immunity (pulse width with no reset) manual-reset input (max823/max825) watchdog input (max823/max824)
max823/max824/max825 5-pin microprocessor supervisory circuits 4 _______________________________________________________________________________________ __________________________________________typical operating characteristics (max823l, v cc = +5v, t a = +25?, unless otherwise noted.) 12.5 7.5 -40 -20 40 100 v cc supply current
vs. temperature 8.5 8.0 9.0 11.5 12.0 max823/4/5-01 temperature (?) supply current ( m a) 020 80 60 10.5 11.0 9.5 10.0 250 150 -40 -20 40 100 reset timeout period
vs. temperature 170 160 180 230 240 max823/4/5-02 temperature (?) reset timeout period (ms) 020 80 60 210 220 190 200 30 0 -40 -20 40 100 reset comparator propagation delay
vs. temperature 5 25 max823/4/5-03 temperature (?) propagation delay ( m s) 020 80 60 20 10 15 v cc falling 2.0 1.0 -40 -20 40 100 watchdog timeout period
vs. temperature 1.2 1.1 1.3 1.8 1.9 max823/4/5-04 temperature (?) watchdog timeout period (sec) 020 80 60 1.6 1.7 1.4 1.5 1.06 0.94 0.96 0.98 1.00 1.02 1.04 -40 -20 40 100 normalized reset threshold
voltage vs. temperature max823/4/5-05 temperature (?) normalized reset threshold (v) 020 80 60 0 20 40 60 80 100 120 140 160 40 100 200 180 120 140 160 maximum v cc transient duration
vs. reset threshold overdrive max823/4/5-06 reset threshold overdrive (mv), v rst - v cc transient duration ( m s) 020 80 60 reset occurs
above curve
max823/max824/max825 5-pin microprocessor supervisory circuits _______________________________________________________________________________________ 5 ______________________________________________________________pin description max823
max824
max825 v cc v cc wdi
(max823/max824
only) 1.25v gnd reset
(max824/max825
only)
reset mr
(max823/max825
only) reset
generator watchdog
timer watchdog
transition
detector function 1 1 active-low reset output. pulses low for 200ms when triggered, and remains low whenever v cc is below the reset threshold or when mr is a logic low. it remains low for 200ms after one of the following occurs: v cc rises above the reset threshold, the watchdog triggers a reset, or mr goes low to high. 2 2 ground. 0v reference for all signals. 3 manual-reset input. a logic low on mr asserts reset. reset remains asserted as long as mr is held low and for 200ms after mr returns high. the active-low input has an internal 52k pull-up resistor. it can be driven from a cmos-logic line or shorted to ground with a switch. leave open or connect to v cc if unused. 3 active-high reset output. inverse of reset . 5 5 supply voltage 4 4 watchdog input. if wdi remains either high or low for longer than the watch- dog timeout period, the internal watchdog timer runs out and a reset is trig- gered. the internal watchdog timer clears whenever reset is asserted, or whenever wdi sees a rising or falling edge. if wdi is left unconnected or is connected to a three-stated buffer output, the watchdog feature is disabled. name 1 reset 2 gnd 4 mr 3 reset 5 v cc wdi figure 1. functional diagram max824 max823 max825 pin
max823/max824/max825 5-pin microprocessor supervisory circuits 6 _______________________________________________________________________________________ _______________detailed description reset output a microprocessor? (??) reset input starts the ? in a known state. the max823/max824/max825 ? super- visory circuits assert a reset to prevent code-execution errors during power-up, power-down, and brownout conditions. reset is guaranteed to be a logic low for v cc down to 1v. once v cc exceeds the reset thresh- old, an internal timer keeps reset low for the specified reset timeout period (t rp ); after this interval, reset returns high (figure 2). if a brownout condition occurs (v cc dips below the reset threshold), reset goes low. each time reset is asserted it stays low for the reset timeout period. any time v cc goes below the reset threshold the internal timer restarts. reset both sources and sinks current. reset on the max824/max825 is the inverse of reset . manual-reset input (max823/max825) many ?-based products require manual-reset capabili- ty, allowing the operator, a test technician, or external logic circuitry to initiate a reset. on the max823/ max825, a logic low on mr asserts reset. reset remains asserted while mr is low, and for t rp (200ms nominal) after it returns high. mr has an internal 52k pull-up resistor, so it can be left open if not used. this input can be driven with cmos-logic levels or with open-drain/ collector outputs. connect a normally open momentary switch from mr to gnd to create a manual-reset func- tion; external debounce circuitry is not required. if mr is driven from long cables or the device is used in a noisy environment, connect a 0.1? capacitor from mr to gnd to provide additional noise immunity. watchdog input (max823/max824) in the max823/max824, the watchdog circuit monitors the ?? activity. if the ? does not toggle the watchdog input (wdi) within t wd (1.6sec), reset asserts. the inter- nal 1.6sec timer is cleared by either a reset pulse or by toggling wdi, which detects pulses as short as 50ns. while reset is asserted, the timer remains cleared and does not count. as soon as reset is released, the timer starts counting (figure 3). disable the watchdog function by leaving wdi uncon- nected or by three-stating the driver connected to wdi. the watchdog input is internally driven low during the first 7/8 of the watchdog timeout period and high for the last 1/8 of the watchdog timeout period. when wdi is left unconnected, this internal driver clears the 1.6sec timer every 1.4sec. when wdi is three-stated or uncon- nected, the maximum allowable leakage current is 10? and the maximum allowable load capacitance is 200pf. __________applications information watchdog input current the max823/max824 wdi inputs are internally driven through a buffer and series resistor from the watchdog counter (figure 1). when wdi is left unconnected, the watchdog timer is serviced within the watchdog timeout period by a low-high-low pulse from the counter chain. for minimum watchdog input current (minimum overall power consumption), leave wdi low for the majority of the watchdog timeout period, pulsing it low-high-low once within the first 7/8 of the watchdog timeout period to reset the watchdog timer. if wdi is externally driven high for the majority of the timeout period, up to 160? can flow into wdi. v cc 1v 1v t rd v rst v rst t rd reset gnd reset t rp t rp figure 2. reset timing diagram v cc t wd t rp t rp t rst wdi reset* *reset on the max824/max825 is the inverse of reset. figure 3. max823/max824 watchdog timing relationship
interfacing to ?s with bidirectional reset pins the reset output maximum pull-up current is 800? for l/m versions (400? for t/s/r versions). this allows ?s with bidirectional resets, such as the 68hc11, to force reset low when the max823/max824/max825 are pulling reset high (figure 4). negative-going v cc transients these supervisors are relatively immune to short- duration, negative-going v cc transients (glitches), which usually do not require the entire system to shut down. resets are issued to the ? during power-up, power- down, and brownout conditions. the typical operating characteristics show a graph of the max823l? maximum v cc transient duration vs. reset threshold overdrive, for which reset pulses are not generated. the graph was produced using nega- tive-going v cc pulses, starting at 5v and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). the graph shows the maximum pulse width that a negative-going v cc transient can typically have without triggering a reset pulse. as the amplitude of the transient increases (i.e., goes farther below the reset threshold), the maximum allowable pulse width decreases. typically, a v cc transient that goes 100mv below the reset threshold and lasts for 15? or less will not trigger a reset pulse. an optional 0.1? bypass capacitor mounted close to v cc provides additional transient immunity. watchdog software considerations (max823/max824) one way to help the watchdog timer monitor software execution more closely is to set and reset the watchdog input at different points in the program, rather than pulsing the watchdog input high-low-high or low-high- low. this technique avoids a stuck loop, in which the watchdog timer would continue to be reset inside the loop, keeping the watchdog from timing out. figure 5 shows an example of a flow diagram where the i/o driving the watchdog input is set high at the begin- ning of the program, set low at the beginning of every subroutine or loop, then set high again when the pro- gram returns to the beginning. if the program should hang in any subroutine, the problem would quickly be corrected, since the i/o is continually set low and the watchdog timer is allowed to time out, causing a reset or interrupt to be issued. as described in the watchdog input current section, this scheme results in higher time average wdi input current than does leaving wdi low for the majority of the timeout period and periodically pulsing it low-high-low. max823/max824/max825 5-pin microprocessor supervisory circuits _______________________________________________________________________________________ 7 max823
max824
max825 m p v cc v cc v cc gnd gnd reset i source max = 800 m a l, m
400 m a t, s, r reset
generator figure 4. interfacing to ?s with bidirectional resets start set wdi
high program
code subroutine or
program loop set wdi low return figure 5. watchdog flow diagram
maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit 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 1996 maxim integrated products printed usa is a registered trademark of maxim integrated products. max823/max824/max825 5-pin microprocessor supervisory circuits maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit 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 1996 maxim integrated products printed usa is a registered trademark of maxim integrated products. __________typical operating circuit ___________________chip information ______________package information transistor count: 607 max823 m p v cc v cc v cc gnd manual
reset reset i/o reset mr wdi l dim
a
a1
a2
b
c
d
e
e1
l
e
e1
a min
0.90
0.00
0.90
0.35
0.08
2.80
2.60
1.50
0.35
0 max
1.45
0.15
1.30
0.50
0.20
3.00
3.00
1.75
0.55
10 millimeters a 5-pin sot23-5
small-outline
transistor package d e1 a a2 a1 c b e e1 21-0057b e 0.95ref 1.90ref marking information (top)
aaai = max823l
aaaj = max823m
aaak = max823t
aaal = max823s
aaam = max823r
aaan = MAX824L
aaao = max824m
aaap = max824t
aaaq = max824s
aaar = max824r
aaas = max825l
aaat = max825m
aaau = max825t
aaav = max825s
aaaw = max825r xxxx
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