________________general description the max823/max824/max825* microprocessor (?) supervisory circuits combine reset output, watchdog, and manual reset input functions in 5-pin sot23 and sc70 packages. they significantly improve system relia- bility and accuracy compared to separate ics or discrete components. the max823/max824/max825 are specifi- cally designed to ignore fast transients on v cc . seven preprogrammed reset threshold voltages are available (see reset threshold table ). 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 max823 also offers a watchdog input and manual reset input. the max824 offers a watchdog input and a comple- mentary active-high reset. the max825 offers a manual reset input and a complementary active-high reset. the selector guide explains the functions offered in this series of parts. ________________________applications computers and controllers embedded controllers intelligent instruments automotive systems critical ? monitoring portable/battery-powered equipment features ? precision monitoring of +2.5v, +3v, +3.3v, and +5v power supplies ? operating current: 6a (max823l/m) (sc70) 2a (max825t/s/r/z/y) (sc70) ? fully specified over temperature ? 140ms min power-on reset ? guaranteed reset valid to v cc = 1v ? power-supply transient immunity ? watchdog timer with 1.6s timeout (max823/max824) ? manual reset input (max823/max825) ? no external components max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset ________________________________________________________________ maxim integrated products 1 1 5 2 3 4 1 5 2 3 4 1 5 2 3 4 gnd wdi v cc max823 sot23/sc70 top view mr reset gnd wdi reset v cc max824 sot23/sc70 reset gnd mr reset v cc max825 sot23/sc70 reset ______________________selector guide 19-0487; rev 5; 12/05 ? insert the desired suffix letter (from the reset threshold table) into the blank to complete the part number. all devices are available in tape-and-reel only. there is a 2500 piece minimum order increment. devices are available in both leaded and lead-free packaging. specify lead-free by replacing ?t?with ?t?when ordering. max823 active-low reset ? active-high reset function watchdog input ? max824 ? ? ? max825 ? ? manual reset input ? ? 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. ordering information part ? temp. range pin-package max823 _exk-t -40? to +85? 5 sc70-5 max823_euk-t -40? to +125? 5 sot23-5 max824 _exk-t -40? to +85? 5 sc70-5 ordering information continued at end of data sheet. reset threshold table z (sc70 only) 2.32 y (sc70 only) 2.19 pin configurations *pg for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset 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, v cc = +2.38v to +2.75v for max82_z, v cc = +2.25v to +2.75v for max82_y, t a = t min to t max , t a = -40 c to +85 c (sc70), t a = -40c to +125 c (sot23), unless otherwise noted. typical values are at t a = +25 c.) (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 continuous power dissipation (t a = +70c) 5-pin sc70 (derate 3.1mw/c above +70 c) ...............247mw 5-pin sot23 (derate 7.1mw/c above +70 c).............571mw operating temperature range max82_exk......................................................-40 c to +85c max82_euk ...................................................-40 c to +125c storage temperature range .............................-65 c to +150c lead temperature (soldering, 10s) .................................+300 c max825t/s/r/z/y parameter symbol min typ max units 4.56 4.63 4.70 supply current (sot23 only) i supply 38 ? 4.5 12 10 24 4.50 4.75 operating voltage range max825l/m max823l/m max824l/m 1.0 5.5 v cc 1.2 v 512 max823t/s/r/z/y max824t/s/r/z/y 2.59 2.63 2.66 2.55 2.70 t a = t min to t max t a = +25? max82_r 3.04 3.08 3.11 3.00 3.15 t a = t min to t max t a = +25? max82_t 2.89 2.93 2.96 2.85 3.00 t a = t min to t max t a = +25? conditions max82_s mr unconnected t a = t min to t max t a = +25? max82_l 4.31 4.38 4.45 t a = 0? to +70? t a = t min to t max 4.25 4.50 wdi and mr unconnected t a = t min to t max t a = +25? max82_m max825t/s/r/z/y supply current (sc70 only) i supply 26 ? 38 617 max825l/m max823l/m max824l/m 412 max823t/s/r/z/y max824t/s/r/z/y mr unconnected wdi and mr unconnected 2.28 2.32 2.35 2.25 2.38 reset threshold v t a = t min to t max t a = +25? max82_z (sc70 only) 2.16 2.19 2.22 2.13 2.25 t a = t min to t max t a = +25? max82_y (sc70 only) v rst
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset _______________________________________________________________________________________ 3 parameter symbol conditions min typ max units max82_l/m 10 reset threshold hysteresis max82_t/s/r/z/y 5 mv reset threshold temperature coefficient 40 ppm/ c reset timeout period t rp 140 200 280 ms v cc to reset delay v rst - v cc = 100mv 20 s max82_l/m, v cc = v rst max, i source = 120 a v cc - 1.5 v oh max82_t/s/r/z/y, v cc = v rst max, i source = 30 a 0.8 ? v cc max82_l/m, v cc = v rst min, i sink = 3.2ma 0.4 max82_t/s/r/z/y v cc = v rst min, i sink = 1.2ma 0.3 t a = 0 c to +70 c, v cc = 1v, v cc falling, i sink = 50 a 0.3 reset output voltage v ol t a = t min to t max , v cc = 1.2v, v cc falling, v batt = 0v, i sink = 100 a v max82_l/m, reset = 0v, v cc = 5.5v 800 reset output short-circuit current (note 2) i source max82_t/s/r/z/y, reset = 0v, v cc = 3.6v 400 a v oh v cc > 1.8v, i source = 150 a 0.8 ? v cc max824l/m, max825l/m, v cc = v rst max, i sink = 3.2ma 0.4 reset output voltage v ol max824t/s/r/z/y, max825t/s/r/z/y, v cc = v rst max, i sink = 1.2ma 0.3 v watchdog input (max823/max824) watchdog timeout period t wd 1.12 1.60 2.40 s wdi pulse width t wdi v il = 0.4v, v ih = 0.8 ? v cc 50 ns v il 0.3 ? v cc wdi input voltage (note 3) v ih 0.7 ? v cc v wdi = v cc , time average 120 160 wdi input current (note 4) wdi = 0, time average -20 -15 a 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, v cc = +2.38v to +2.75v for max82_z, v cc = +2.25v to +2.75v for max82_y, t a = t min to t max , t a = -40 c to +85 c (sc70), t a = -40 c to +125 c (sot23), unless otherwise noted. typical values are at t a = +25 c.) (note 1)
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset 4 _______________________________________________________________________________________ note 1: over-temperature limits are guaranteed by design and not production tested. note 2: the reset short-circuit current is the maximum pullup 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. parameter symbol conditions min typ max u n it s manual reset input (max823/max825) v il 0.3 ? v cc mr input voltage v ih 0.7 ? v cc v mr pulse width 1.0 s mr noise immunity (pulse width with no reset) 100 ns mr to reset delay 500 ns mr pullup resistance (internal) 35 52 75 k ? 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, v cc = +2.38v to +2.75v for max82_z, v cc = +2.25v to +2.75v for max82_y, t a = t min to t max , t a = -40 c to +85 c (sc70), t a = -40c to +125 c (sot23), unless otherwise noted. typical values are at t a = +25c.) (note 1)
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset _______________________________________________________________________________________ 5 __________________________________________typical operating characteristics max823_, v cc = +5v, t a = +25?, unless otherwise noted.) 1 3 2 6 5 4 8 7 9 -40 20 40 -20 0 60 80 100 120 max823/4/5 toc01 temperature ( c) supply current ( a) v cc supply current vs. temperature max823l (sc70 only) max824y max825r 250 150 -40 -20 40 100 reset timeout period vs. temperature 170 160 180 230 240 max823/4/5 toc02 temperature ( c) 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 toc03 temperature ( c) propagation delay ( 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 toc04 temperature ( c) watchdog timeout period (s) 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 toc05 temperature ( c) normalized reset threshold (v) 020 80 60 0 10 5 20 15 30 25 35 45 40 50 0406 080 20 100 120 140 180160 200 max823/4/5 toc06 reset threshold overdrive (mv), v rst - v cc transient duration ( s) (sc70 only) maximum v cc transient duration vs. reset threshold overdrive reset occurs above curve max82_y max82_r max82_l
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset 6 _______________________________________________________________________________________ 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 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 ? pullup 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 with wa tchdog timer and manual reset _______________________________________________________________________________________ 7 _______________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 ? pullup 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 (1.6s), reset asserts. the internal 1.6s timer is cleared by either a reset pulse or by tog- gling 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 1.6s timer every 1.4s. 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
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset 8 _______________________________________________________________________________________ interfacing to ps with bidirectional reset pins the reset output maximum pullup current is 800? for l/m versions (400? for t/s/r/z/y 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 max823_? 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. 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 p v cc v cc v cc v cc gnd gnd reset i source max = 800 a l, m 400 a t, s, r, z, y 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
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset _______________________________________________________________________________________ 9 t ypical operating circuit ____________________chip information transistor count: 607 process technology: bicmos max823 p v cc v cc v cc gnd gnd manual reset reset i/o reset mr wdi ordering information (continued) part ? temp. range pin-package max824_euk-t -40? to +125? 5 sot23-5 max825 _exk-t -40? to +85? 5 sc70-5 max825_euk-t -40? to +125? 5 sot23-5 ? insert the desired suffix letter (from the reset threshold table) into the blank to complete the part number. all devices are available in tape-and-reel only. there is a 2,500 piece minimum order increment. devices are available in both leaded and lead-free packaging. specify lead-free by replacing ?t?with ?t?when ordering. 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 (sot only) marking information (top) xxxx (sc70 only) aal = max823l aam = max823m aap = max823r aao = max823s aan = max823t aar = max823y aaq = max823z aas = max824l aat = max824m aaw = max824r aav = max824s aau = max824t aay = max824y aax = max824z aaz = max825l aba = max825m abd = max825r abc = max825s abb = max825t abf = max825y abe = max825z marking information
max823/max824/max825 5-pin microprocessor supervisory circuits with wa tchdog timer and manual reset 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. 10 __________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 (408) 737-7600 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. sot-23 5l .eps e 1 1 21-0057 package outline, sot-23, 5l package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .)
|
