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general description the max16033?ax16040 supervisory circuits reduce the complexity and number of components required for power-supply monitoring and battery control functions in microprocessor (?) systems. the devices signifi- cantly improve system reliability and accuracy com- pared to other ics or discrete components. the max16033?ax16040 provide ? reset, backup-bat- tery switchover, power-fail warning, watchdog, and chip-enable gating features. the max16033?ax16040 operate from supply volt- ages up to 5.5v. the factory-set reset threshold voltage ranges from 2.32v to 4.63v. the devices feature a man- ual-reset input (max16033/max16037), a watchdog timer input (max16034/max16038), a battery-on output (max16035/max16039), an auxiliary adjustable reset input (max16036/max16040), and chip-enable gating (max16033?ax16036). each device includes a power-fail comparator and offers an active-low push- pull reset or an active-low open-drain reset. the max16033?ax16040 are available in 2mm x 2mm, 8-pin or 10-pin ?fn packages and are fully specified from -40? to +85?. applications features low 1.2v operating supply voltage precision monitoring of 5.0v, 3.3v, 3.0v, and 2.5v power-supply voltages independent power-fail comparator debounced manual-reset input watchdog timer, 1.6s timeout battery-on output indicator auxiliary user-adjustable resetin low 13 a quiescent supply current two available output structures: active-low push-pull reset active-low open-drain reset active-low reset valid down to 1.2v power-supply transient immunity 140ms (min) reset timeout period small 2mm x 2mm, 8-pin and 10-pin dfn packages max16033?ax16040 low-power battery backup circuits in small ?fn packages ________________________________________________________________ maxim integrated products 1 19-0882; rev 0; 7/07 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information continued on last page. * these parts offer a choice of reset threshold voltages. from the reset threshold ranges table, insert the desired threshold volt- age code in the blank to complete the part number. see selector guide for a listing of device features. + denotes a lead-free package. t = tape and reel. pin configurations and typical operating circuit appear at end of data sheet. ordering information part * temp range pin- package pkg code max16033 llb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16033plb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16034 llb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16034plb_ _+t -40? to +85? 10 ?fn-10 l1022-1 note: replace ??with l for push-pull or p for open-drain reset and pfo outputs. selector guide part mr watchdog batton resetin ce in/ ce out pfi, pfo pin-package max16033_ ??? 10 ?fn-10 max16034_ ??? 10 ?fn-10 max16035_ ??? 10 ?fn-10 max16036_ ?? ? 10 ?fn-10 max16037_ ? ? 8 ?fn-8 max16038_ ?? 8 ?fn-8 max16039_ ?? 8 ?fn-8 max16040_ ?? 8 ?fn-8 portable/battery- powered equipment pos equipment critical ?/? power monitoring set-top boxes controllers computers fax machines industrial control real-time clocks intelligent instrument
max16033?ax16040 low-power battery backup circuits in small ?fn packages 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = 2.25v to 5.5v, v batt = 3v, reset not asserted, t a = -40? to +85?, 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 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 voltages (with respect to gnd) v cc, batt, out .......................................................-0.3v to +6v reset (open drain), pfo (open drain) ....................-0.3v to +6v reset (push-pull), pfo (push-pull), batton, resetin, wdi mr , ce in, ce out, pfi ............................-0.3v to (v out + 0.3v) input current v cc peak..............................................................................1a v cc continuous ............................................................250ma batt peak ....................................................................250ma batt continuous ............................................................40ma gnd ................................................................................75ma output current out ..................................short-circuit protected for up to 5s reset , batton .............................................................20ma continuous power dissipation (t a = +70?) 8-pin ?fn (derate 4.8mw/? above +70?) ..........380.6mw 10-pin ?fn (derate 5mw/? above +70?) ...........402.8mw operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units operating voltage range v cc , v batt no load (note 2) 0 5.5 v v cc = 2.8v 13 30 v cc = 3.6v 16 35 supply current i cc no load, v cc > v th v cc = 5.5v 22 50 ? t a = +25? 1 supply current in battery backup mode v batt = 2.8v, v cc = 0v, excluding i out t a = -40? to +85? 2 ? t a = +25? -0.1 +0.02 batt standby current (note 3) i batt (v batt + 0.2v) < v cc < 5.5v t a = -40? to +85? -0.3 +0.02 ? v cc = 4.75v, v cc > v th , i out = 150ma 3.1 v cc = 3.15v, v cc > v th , i out = 65ma 3.7 v cc to out on-resistance r on v cc = 2.5v, v cc > v th , i out = 25ma 4.6 ? v batt = 4.50v, v cc = 0v, i out = 20ma v batt - 0.2 v batt = 3.15v, v cc = 0v, i out = 10ma v batt - 0.15 output voltage in battery backup mode v out v batt = 2.5v, v cc = 0v, i out = 5ma v batt - 0.15 v v cc rising 0 battery-switchover threshold v sw v cc - v batt , v cc < v th v cc falling -40 mv
max16033?ax16040 low-power battery backup circuits in small ?fn packages _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = 2.25v to 5.5v, v batt = 3v, reset not asserted, t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units reset output max160_ _ _l_46 4.50 4.63 4.75 max160_ _ _l_44 4.25 4.38 4.50 max160_ _ _l_31 3.00 3.08 3.15 max160_ _ _l_29 2.85 2.93 3.00 max160_ _ _l_26 2.55 2.63 2.70 reset threshold v th max160_ _ _l_23 2.25 2.32 2.38 v v cc falling reset delay v cc falling at 10v/ms 25 ? reset active timeout period t rp 140 280 ms i sink = 1.6ma, v cc > 2.1v 0.3 reset output low voltage v ol reset asserted i sink = 100?, v cc > 1.2v 0.4 v reset output high voltage v oh max160_ _l only (push-pull), reset not asserted, i source = 500?, v cc > v th ( max ) 0.8 x v cc v reset output leakage current i lkg max160_ _p only (open drain), not asserted 1 a power-fail comparator pfi input threshold v pfi v pfi falling 1.185 1.235 1.285 v pfi hysteresis 1% pfi input current v pfi = 0v or v cc -100 +100 na v cc > 2.1v, i sink = 1.6ma 0.3 pfo output low voltage v ol o utp ut asser ted v cc > 1.2v, i sink = 100? 0.4 v pfo output high voltage v oh max160_ _l only (push-pull), v cc > v th(max) , i source = 500?, output not asserted 0.8 x v cc v pfo leakage current max160_ _p only (open drain), v pfo = 5.5v, not asserted 1a pfo delay time v pfi + 100mv to v pfi - 100mv 4 ? manual reset (max16033/max16037) v il 0.3 x v cc mr input voltage v ih 0.7 x v cc v pullup resistance to v cc 20 165 k ? minimum pulse width 1s glitch immunity v cc = 3.3v 100 ns mr to reset delay 120 ns
max16033?ax16040 low-power battery backup circuits in small ?fn packages 4 _______________________________________________________________________________________ note 1: all devices are 100% production tested at t a = +25?. all overtemperature limits are guaranteed by design. note 2: v batt can be 0v any time, or v cc can go down to 0v if v batt is active (except at startup). note 3: positive current flows into batt. note 4: guaranteed by design. electrical characteristics (continued) (v cc = 2.25v to 5.5v, v batt = 3v, reset not asserted, t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units watchdog (max16034/max16038) watchdog timeout period t wd 1.00 1.65 2.25 s m i ni m um wd i inp ut p ul se w i d th t wdi (note 4) 100 ns v il 0.3 x v cc wdi input voltage v ih 0.7 x v cc v wdi input current -1.0 +1.0 a batton (max16035/max16039) output voltage v ol i sink = 3.2ma, v batt = 2.1v 0.4 v sink current, v cc = 5v 60 ma output short-circuit current source current, v batt > 2v 10 30 120 ? resetin (max16036/max16040) resetin threshold v rth 1.185 1.235 1.285 v resetin input current 0.01 25 na resetin to reset delay (v rth + 100mv) to (v rth - 100mv) 1.5 ? chip-enable gating (max16033?ax16036) ce in leakage current reset asserted ? ? ce in to ce out resistance reset not asserted, v cc = v th(max), v ce in = v cc / 2, i sink = 10ma 100 ? ce out short-circuit current reset asserted, v ce out = 0v 1 2.0 ma v cc = 4.75v 1.5 7 ce in to ce out propagation delay (note 4) 50 ? source impedance driver, c load = 50pf v cc = 3.15v 2 9 ns v cc = 5v, v cc > v batt , i source = 100? 0.7 x v cc ce out output-voltage high v cc = 0v, v batt > 2.2v, i source = 1? v batt - 0.1 v reset to ce out delay 1s
max16033?ax16040 low-power battery backup circuits in small ?fn packages _______________________________________________________________________________________ 5 supply current vs. temperature max16033 toc01 temperature ( c) supply current ( a) 60 35 10 -15 11 12 13 14 15 16 17 18 19 20 10 -40 85 v cc = 5v battery supply current (backup mode) vs. temperature max16033 toc02 temperature ( c) battery supply current ( a) 60 35 10 -15 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 -40 85 v batt = 3v v cc = 0v batt-to-out on-resistance vs. temperature max16033 toc03 temperature ( c) battery-to-out on-resistance ( ? ) 60 35 10 -15 1 2 3 4 5 6 7 8 9 1.0 0 -40 85 v cc = 0v v batt = 2v v batt = 3v v batt = 5v v cc -to-out on-resistance vs. temperature max16033 toc04 temperature ( c) v cc -to-out on-resistance ( ? ) 65 50 -25 -10 5 20 35 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 -40 80 v cc = 2.5v i out = 25ma v cc = 4.5v i out = 150ma v cc = 3v i out = 65ma reset timeout period vs. temperature max16033 toc05 temperature ( c) reset timeout period (ms) 60 35 10 -15 185 190 195 200 205 210 215 220 225 230 180 -40 85 v cc = 5v v cc -to-reset propagation delay vs. temperature max16033 toc06 temperature ( c) v cc -to-reset propagation delay ( s) 60 40 -20 0 20 15 30 45 60 75 90 105 120 0 -40 80 v cc falling 0.25v/ms 1v/ms 10v/ms normalized reset threshold vs. temperature max16033 toc07 temperature ( c) normalized reset threshold 60 40 20 0 -20 0.991 0.992 0.993 0.994 0.995 0.996 0.997 0.998 0.999 1.000 1.001 1.002 1.003 0.990 -40 80 maximum transient duration vs. reset threshold overdrive max16033 toc08 reset threshold overdrive (v th - v cc ) (mv) maximum transient duration ( s) 1000 100 10 50 100 150 200 250 300 0 1 10,000 max160_ _-29 (v th = 2.93v) max160_ _-46 (v th = 4.63v) reset occurs above curve typical operating characteristics (t a = +25?, unless otherwise noted.)
max16033?ax16040 low-power battery backup circuits in small ?fn packages 6 _______________________________________________________________________________________ typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) battery supply current vs. supply voltage max16033 toc09 supply voltage (v) battery supply current ( a) 4.5 4.0 3.0 3.5 1.0 1.5 2.0 2.5 0.5 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 -0.25 0 5.0 v batt = 2.8v v th = 2.93v v batt = 2.5v v batt = 2.3v resetin threshold vs. temperature max16033 toc10 temperature ( c) resetin threshold (v) 60 35 -15 10 1.215 1.220 1.225 1.230 1.235 1.240 1.245 1.250 1.210 -40 85 max16036/ max16040 resetin-to-reset propagation delay vs. temperature max16033 toc11 temperature ( c) resetin-to-reset propagation delay ( s) 60 35 -15 10 1.3 1.5 1.8 2.0 2.3 2.5 2.8 3.0 1.0 -40 85 max16036/ max16040 v od = 50mv cein propagation delay vs. ceout load capacitance max16033 toc12 ceout load capacitance (pf) cein propagation delay (ns) 150 125 100 75 50 25 0.5 1.0 1.5 2.0 2.5 3.0 0 0175 v cc = 3v v cc = 5v cein to ceout on-resistance vs. temperature max16033 toc13 temperature ( c) cein to ceout on-resistance ( ? ) 60 35 10 -15 5 10 15 20 25 30 35 0 -40 85 v cc = 3v v cc = 5v pfi-to-pfo delay vs. temperature max16033 toc15 temperature ( c) pfi-to-pfo delay ( s) 60 35 10 -15 3.25 3.50 4.00 3.75 4.25 4.50 2.25 2.75 2.50 3.00 4.75 5.00 2.00 -40 85 v od = 30mv falling edge pfi threshold vs. temperature max16033 toc16 temperature ( c) pfi threshold (v) 60 35 -15 10 1.215 1.220 1.225 1.230 1.235 1.240 1.245 1.250 1.210 -40 85 watchdog timeout period vs. temperature max16033 toc14 temperature ( c) watchdog timeout period (s) 60 35 10 -15 1.4 1.5 1.6 1.7 1.8 1.1 1.2 1.3 1.9 2.0 1.0 -40 85 v cc = 5v
max16033?ax16040 low-power battery backup circuits in small ?fn packages _______________________________________________________________________________________ 7 pin description pin max16033 max16036 (10-pin ?fn) max16037 max16040 (8-pin ?fn) name function 11 reset active-low reset output. reset remains low when v cc is below the reset threshold (v th ), the manual-reset input is low, or resetin is low. it asserts low in pulses when the internal watchdog times out. reset remains low for the reset timeout period (t rp ) after v cc rises above the reset threshold, after the manual-reset input goes from low to high, after resetin goes high, or after the watchdog triggers a reset event. the max160_ _l is an active-low push-pull output, while the max160_ _p is an active-low open-drain output. 2 ce in chip-enable input. the input to the chip-enable gating circuit. connect to gnd or out if not used. 3 2 pfi power-fail input. pfo goes low when v pfi falls below 1.235v. 4 3 gnd ground mr manual-reset input (max16033/max16037). driving mr low asserts reset . reset remains asserted as long as mr is low and for the reset timeout period (t rp ) after mr transitions from low to high. leave unconnected, or connect to v cc if not used. mr has an internal 20k ? pullup to v cc . wdi watchdog input (max16034/max16038 ) . if wdi remains high or low for longer than the watchdog timeout period (t wd ), the internal watchdog timer runs out and a reset pulse is triggered for the reset timeout period (t rp ). the internal watchdog clears whenever reset asserts or whenever wdi sees a rising or falling edge (figure 2). batton battery-on output (max16035/max16039). batton goes high during battery backup mode. 54 resetin reset input (max16036/max16040). when resetin falls below 1.235v, reset asserts. reset remains asserted as long as resetin is low and for at least t rp after resetin goes high. 65 pfo active-low power-fail output. pfo goes low when v pfi falls below 1.235v. pfo stays low until v pfi goes above 1.235v. pfo also goes low when v cc falls below the reset threshold voltage. 76v cc supply voltage, 1.2v to 5.5v 8 7 out output. out sources from v cc when reset is not asserted and from the greater of v cc or batt when v cc is below the reset threshold voltage. 9 8 batt backup battery input. when v cc falls below the reset threshold, out switches to batt if v batt is 40mv greater than v cc . when v cc rises above v batt , out switches to v cc . the 40mv hysteresis prevents repeated switching if v cc falls slowly. 10 ce out chip-enable output. ce out goes low only when ce in is low and reset is not asserted. when ce out is disconnected from ce in, ce out is actively pulled up to out.
max16033?ax16040 low-power battery backup circuits in small ?fn packages 8 _______________________________________________________________________________________ reset generator watchdog timer watchdog transition detector 1.235v chip-enable output control out ceout pfo reset batton (max16035/max16039 only) v cc batt cein (max16033?ax16036 only) mr (max16033/max16037 only) wdi (max16034/max16038 only) resetin (max16036/max16040 only) pfi gnd max16033 max16040 1.235v 1.235v functional diagram
max16033?ax16040 low-power battery backup circuits in small ?fn packages _______________________________________________________________________________________ 9 detailed description the typical operating circuit shows a typical connec- tion for the max16033?ax16040. out powers the static random-access memory (sram). if v cc is greater than the reset threshold (v th ), or if v cc is lower than v th but higher than v batt , v cc is connected to out. if v cc is lower than v th and v cc is less than v batt , batt is connected to out. out supplies up to 200ma from v cc . in battery-backup mode, an internal mosfet connects the backup battery to out. the on- resistance of the mosfet is a function of the backup- battery voltage and temperature and is shown in the batt-to-out on-resistance vs. temperature graph in the typical operating characteristics . chip-enable signal gating (max16033?ax16036 only) the max16033max16036 provide internal gating of chip-enable ( ce ) signals to prevent erroneous data from being written to cmos ram in the event of a power failure or brownout condition. during normal operation, the ce gate is enabled and passes all ce transitions. when reset asserts, this path becomes disabled, preventing erroneous data from corrupting the cmos ram. the max16033?ax16036 provide a series transmission gate from ce in to ce out. a 2ns (typ) propagation delay from ce in to ce out allows these devices to be used with most ?s and high- speed dsps. when reset is deasserted, ce in is connected to ce out through a low on-resistance transmission gate. if ce in is high when reset is asserted, ce out remains high regardless of any subsequent transitions on ce in during the reset event. if ce in is low when reset is asserted, ce out is held low for 1? to allow completion of the read/write opera- tion (figure 1). after the 1? delay expires, ce out goes high and stays high regardless of any subsequent transitions on ce in during the reset event. when ce out is disconnected from ce in, ce out is actively pulled up to out. the propagation delay through the chip-enable circuit- ry depends on both the source impedance of the drive to ce in and the capacitive loading at ce out. the chip-enable propagation delay is specified from the 50% point of ce in to the 50% point of ce out, using a 50 ? driver and 50pf load capacitance. minimize the capacitive load at ce out and use a low output-imped- ance driver to minimize propagation delay. in high-impedance mode, the leakage current at ce in is ?? (max) over temperature. in low-impedance mode, the impedance of ce in appears as a 75 ? resis- tor in series with the load at ce out. v cc v th t rd t rd t rp t rp cein ceout reset pfo pfi > v pfi reset-to-ceout delay * * if cein goes high before reset asserts, ceout goes high without delay as cein goes high. figure 1. reset and chip-enable timing
max16033?ax16040 low-power battery backup circuits in small ?fn packages 10 ______________________________________________________________________________________ backup battery switchover to preserve the contents of the ram in a brownout or power failure, the max16033?ax16040 automatically switch to back up the battery installed at batt when the following two conditions are met: 1) v cc falls below the reset threshold voltage. 2) v cc is below v batt . table 1 lists the status of the inputs and outputs in bat- tery-backup mode. the devices do not power-up if the only voltage source is v batt . out only powers up from v cc at startup. manual-reset input (max16033/max16037 only) many ?-based products require manual-reset capabil- ity, allowing the user or external logic circuitry to initiate a reset. for the max16033/max16037, a logic-low on mr asserts reset . reset remains asserted while mr is low and for a minimum of 140ms (t rp ) after it returns high. mr has an internal 20k ? (min) pullup resistor to v cc . this input can be driven from ttl/cmos logic outputs or with open-drain/collector outputs. connect a normally-open momentary switch from mr to gnd to create a manual-reset function; external debounce cir- cuitry is not required. when driving mr from long cables or when using the device in a noisy environ- ment, connect a 0.1? capacitor from mr to gnd to provide additional noise immunity. watchdog input (max16034/max16038 only) the watchdog monitors ? activity through the watch- dog input (wdi). reset asserts when the ? fails to toggle wdi. connect wdi to a bus line or ? i/o line. a change of state (high to low, low to high, or a minimum 100ns pulse) resets the watchdog timer. if wdi remains high or low for longer than the watchdog timeout period (t wd ), the internal watchdog timer runs out and triggers a reset pulse for the reset timeout period (t rp ). the internal watchdog timer clears whenever reset is asserted or whenever wdi sees a rising or falling edge. if wdi remains in either a high or low state, a reset pulse periodically asserts after every watchdog timeout period (t wd ); see figure 2. table 1. input and output status in battery-backup mode pin status v cc disconnected from out out connected to batt batt connected to out. current drawn from the battery is less than 1? (at v batt = 2.8v, excluding i out ) when v cc = 0v. reset asserted batton high state mr , resetin, ce in, and wdi inputs ignored ce out connected to out pfo asserted t wd = watchdog timeout period t rp = reset timeout period wdi reset t wd t wd t rp t rp figure 2. max16034/max16038 watchdog timeout period and reset active time
max16033?ax16040 low-power battery backup circuits in small ?fn packages ______________________________________________________________________________________ 11 batton indicator (max16035/max16039 only) batton is a push-pull output that asserts high when in battery-backup mode. batton typically sinks 3.2ma at a 0.4v saturation voltage. in battery-backup mode, this terminal sources approximately 10? from out. use batton to indicate battery-switchover status or to supply base drive to an external pass transistor for higher current applications (see figure 3). resetin comparator (max16036/max16040 only) an internal 1.235v reference sets the resetin thresh- old voltage. reset asserts when the voltage at resetin is below 1.235v. use the resetin function to monitor a secondary power supply. use the following equations to set the reset threshold voltage (v rth ) of the secondary power supply (see figure 4): v rth = v ref (r1 / r2 + 1) where v ref = 1.235v. to simplify the resistor selection, choose a value for r2 and calculate r1. r1 = r2 [(v rth / v ref ) - 1] since the input current at resetin is 25na (max), large values (up to 1m ? ) can be used for r2 with no signifi- cant loss in accuracy. power-fail comparator the max16033?ax16040 issue an interrupt (nonmask- able or regular) to the ? when a power failure occurs. the power line is monitored by two external resistors con- nected to the power-fail input (pfi). when the voltage at pfi falls below 1.235v, the power-fail output ( pfo ) drives the processor? nmi input low. an earlier power-fail warn- ing can be generated if the unregulated dc input of the regulator is available for monitoring. the max16033 max16040 turn off the power-fail comparator and force pfo low when v cc falls below the reset threshold volt- age (see figure 1). the max160_ _l devices provide push-pull pfo outputs. the max160_ _p devices provide open-drain pfo outputs. 2.4v to 5.5v ce (cein) ( ) for max16035 only a0?15 p cmos ram batton v cc batt (ceout) gnd reset out 0.1 f address decode max16035 max16039 reset figure 3. max16035/max16039 batton driving an external pass transistor max16036 max16040 r1 resetin v in v cc r2 figure 4. setting resetin voltage for the max16036/max16040
max16033?ax16040 low-power battery backup circuits in small ?fn packages 12 ______________________________________________________________________________________ reset a ?? reset input puts the ? in a known state. the max16033?ax16040 ? supervisory circuits assert a reset to prevent code-execution errors during power- up, power-down, and brownout conditions. reset asserts when v cc is below the reset threshold voltage and for at least 140ms (t rp ) after v cc rises above the reset threshold. reset also asserts when mr is low (max16033/max16037) or when resetin is below 1.235v (max16036/max16040). the max16034/ max16038 watchdog function causes reset to assert in pulses following a watchdog timeout (figure 2). the max160_ _l devices provide push-pull reset outputs. the max160_ _p devices provide open-drain reset outputs. applications information operation without a backup power source the max16033?ax16040 provide a battery backup function. if a backup power source is not used, connect batt to gnd and out to v cc . using a super cap as a backup power source super caps are capacitors with extremely high capaci- tance, such as 0.47f. figure 5 shows two methods to use a super cap as a backup power source. connect the super cap through a diode to the 3v input (figure 5a) or connect the super cap through a diode to 5v (figure 5b) if a 5v supply is available. the 5v supply charges the super cap to a voltage close to 5v, allow- ing a longer backup period. since v batt can be higher than v cc while v cc is above the reset threshold volt- age, there are no special precautions required when using these ? supervisors with a super cap. (a) 3v or 3.3v 0.47f 1n4148 v cc batt max16033 max16040 (b) 3v or 3.3v 5v 0.47f 1n4148 v cc batt max16033 max16040 figure 5. using a super cap as a backup source
max16033?ax16040 low-power battery backup circuits in small ?fn packages ______________________________________________________________________________________ 13 watchdog software considerations one way to help the watchdog timer to monitor soft- ware execution more closely is to set and reset the watchdog at different points in the program, rather than pulsing the watchdog input periodically. figure 6 shows a flow diagram where the i/o driving the watch- dog is set low in the beginning of the program, set high at the beginning of every subroutine or loop, and set low again when the program returns to the beginning. if the program should hang in any subroutine, the watch- dog would timeout and reset the ?. replacing the backup battery decouple batt to gnd with a 0.1? capacitor. the backup power source may be removed while v cc remains valid without the danger of triggering a reset pulse. the device does not enter battery-backup mode when v cc stays above the reset threshold voltage. power-fail comparator monitoring an additional power supply monitor another voltage by connecting a resistive divider to pfi as shown in figure 7. the threshold voltage is: v th(pfi) = 1.235 (r1 / r2 + 1) where v th(pfi) is the threshold at which the monitored voltage will trip pfo . to simplify the resistor selection, choose a value for r2 and calculate r1. r1 = r2 [(v th(pfi) / 1.235) - 1] connect pfo to mr in applications that require reset to assert when the second voltage falls below its threshold. reset remains asserted as long as pfo holds mr low, and for 140ms (min) after pfo goes high. adding hysteresis to the power-fail comparator the power-fail comparator provides a typical hysteresis of 12mv, which is sufficient for most applications where a power-supply line is being monitored through an external voltage-divider. connect a voltage-divider between pfi and pfo as shown in figure 8a to provide additional noise immunity. select the ratio of r1 and r2 such that v pfi falls to 1.235v when v in drops to its trip point, v trip . r3 adds hysteresis and is typically more than 10 times the value of r1 or r2. the hysteresis win- dow extends above (v h ) and below (v l ) the original trip point, v trip . connecting an ordinary signal diode in series with r3 as shown in figure 8b causes the lower trip point (v l ) to coincide with the trip point without hys- teresis (v trip ). this method provides additional noise margin without compromising the accuracy of the power-fail threshold when the monitored voltage is falling. set the current through r1 and r2 to be at least 10? to ensure that the 100na (max) pfi input current does not shift the trip point. set r3 to be higher than 10k ? to reduce the load at pfo . capacitor c1 adds additional noise rejection. set wdi low subroutine or program loop set wdi high return end start gnd v cc v+ v cc reset to p pfi r1 r2 max16033 max16040 mr pfo figure 6. watchdog flow diagram figure 7. monitoring an additional power supply
max16033?ax16040 low-power battery backup circuits in small ?fn packages 14 ______________________________________________________________________________________ gnd to p pfi r2 c1 c1 r3 r3 r1 pfo (push-pull) max16033 max16040 v cc v in pfo gnd to p pfi r2 r1 pfo (push-pull) max16033 max16040 v cc v in 0v v l v h v h v in v trip v trip pfo 0v v in (a) (b) figure 8. (a) adding additional hysteresis to the power-fail comparator. (b) shifting the additional hysteresis above v trip vv r r vv v r r r r vv r r r r r r v vv vmv trip pft h pft pfh l pft cc pft pfh ( ) . =+ ? ? ? ? ? ? =+ ++ ? ? ? ? ? ? =++ ? ? ? ? ? ? ? = = 1 1 2 1 1 2 1 3 1 1 2 1 3 1 3 1 235 12 vv r r vv v r r r r r r v vv vv vmv v diode forward voltage trip pft h pft pfh d l trip pft pfh d ( ) . =+ ? ? ? ? ? ? =+ ++ ? ? ? ? ? ? ? = = = = 1 1 2 1 1 2 1 3 1 3 1 235 12
monitoring a negative voltage connect the circuit as shown in figure 9 to use the power-fail comparator to monitor a negative supply rail. pfo stays low when v- is good. when v- rises to cause pfi to be above +1.235v, pfo goes high. ensure v cc comes up before the negative supply. negative-going v cc transients the max16033?ax16040 are relatively immune to short-duration, negative-going v cc transients. resetting the ? when v cc experiences only small glitches is not usually desired. the typical operating characteristics section contains a maximum transient duration vs. reset threshold overdrive graph. the graph shows the maximum pulse width of a negative-going v cc transient that would not trigger a reset pulse. as the amplitude of the transient increases (i.e., goes further below the reset threshold voltage), the maximum allowable pulse width decreas- es. typically, a v cc transient that goes 100mv below the reset threshold and lasts for 25? does not trigger a reset pulse. a 0.1? bypass capacitor mounted close to v cc pro- vides additional transient immunity. max16033?ax16040 low-power battery backup circuits in small ?fn packages ______________________________________________________________________________________ 15 gnd pfi r2 r1 v- max16033 max16040 3.0v or 3.3v v cc pfo pfo 0v v l v- v trip figure 9. monitoring a negative voltage vrvv rr v r vrv rr v r vv vmv trip pft pfh cc l pft cc pft pfh . =+ () + ? ? ? ? ? ? ? ? ? ? ? ? ? = () + ? ? ? ? ? ? ? ? ? ? ? ? ? = = 2 1 1 1 21 2 1 1 1 21 1 235 12
max16033?ax16040 low-power battery backup circuits in small ?fn packages 16 ______________________________________________________________________________________ device marking codes part top mark part top mark part top mark part top mark max16033llb23+t +abe max16035llb23+t +acc max16037lla23+t +abx max16039lla23+t +acv max16033llb26+t +abf max16035llb26+t +acd max16037lla26+t +aby max16039lla26+t +acw max16033llb29+t +abg max16035llb29+ +ace max16037lla29+ +abz max16039lla29+t +acx max16033llb31+t +abh max16035llb31+ +acf max16037lla31+ +aca max16039lla31+t +acy max16033llb44+t +abi max16035llb44+t +acg max16037lla44+t +acb max16039lla44+t +acz max16033llb46+t +abj max16035llb46+ +ach max16037lla46+ +acc max16039lla46+t +ada max16033plb23+t +abk max16035plb23+t +aci max16037pla23+t +acd max16039pla23+t +adb max16033plb26+t +abl max16035plb26+t +acj max16037pla26+t +ace max16039pla26+t +adc max16033plb29+ +abm max16035plb29+ +ack max16037pla29+ +acf max16039pla29+ +add max16033plb31+ +abn max16035plb31+ +acl max16037pla31+ +acg max16039pla31+ +ade max16033plb44+t +abo max16035plb44+t +acm max16037pla44+t +ach max16039pla44+t +adf max16033plb46+ +abp max16035plb46+ +acn max16037pla46+ +aci max16039pla46+ +adg max16034llb23+t +abq max16036llb23+t +aco max16038lla23+t +acj max16040lla23+t +adh max16034llb26+t +abr max16036llb26+t +acp max16038lla26+t +ack max16040lla26+t +adi max16034llb29+t +abs max16036llb29+ +acq max16038lla29+ +acl max16040lla29+t +adj max16034llb31+t +abt max16036llb31+ +acr max16038lla31+ +acm max16040lla31+t +adk max16034llb44+t +abu max16036llb44+t +acs max16038lla44+t +acn max16040lla44+t +adl max16034llb46+t +abv max16036llb46+ +act max16038lla46+ +aco max16040lla46+t +adm max16034plb23+t +abw max16036plb23+t +acu max16038pla23+t +acp max16040pla23+t +adn max16034plb26+t +abx max16036plb26+t +acv max16038pla26+t +acq max16040pla26+t +ado max16034plb29+ +aby max16036plb29+ +acw max16038pla29+ +acr max16040pla29+ +adp max16034plb31+ abz max16036plb31+ +acx max16038pla31+ +acs max16040pal31+ +adq max16034plb44+t +aca max16036plb44+t +acy max16038pla44+t +act max16040pla44+t +adr max16034plb46+ +acb max16036plb46+ +acz max16038pla46+ +acu max16040pla46+ +ads note: 48 standard versions shown in bold are available. sample stock is generally held on standard versions only. contact factory for nonstandard versions availability.
max16033?ax16040 low-power battery backup circuits in small ?fn packages ______________________________________________________________________________________ 17 123 10 9 8 45 76 reset cein pfi gnd mr (wdi) ceout batt out v cc pfo max16033 max16034 10- dfn ( ) for max16034 only top view + 123 10 9 8 45 76 reset cein pfi gnd batton (resetin) batton (resetin) ceout batt out v cc pfo max16035 max16036 10- dfn ( ) for max16036 only + 123 87 4 65 max16037 max16038 8- dfn ( ) for max16038 only batt out v cc + reset pfi gnd + denotes a lead-free package. mr (wdi) pfo 123 87 4 65 max16039 max16040 8- dfn ( ) for max16040 only batt out v cc + reset pfi gnd pfo pin configurations
max16033?ax16040 low-power battery backup circuits in small ?fn packages 18 ______________________________________________________________________________________ gnd cein** pfi ceout** wdi*** pfo out a0?15 i/o i/o real- time clock resetin* r4 r3 additional dc voltage * resetin applies to max16035/max16039 only. **cein and ceout apply to max16033?ax16036 only. ***wdi applies to max16034/max16038 only. batt 2.4v to 5.5v p cmos ram v cc 0.1 f address decode max16033 max16040 reset reset ce r2 r1 additional dc voltage 0.1 f typical operating circuit
max16033?ax16040 low-power battery backup circuits in small ?fn packages ______________________________________________________________________________________ 19 chip information process: bicmos * these parts offer a choice of reset threshold voltages. from the reset threshold ranges table, insert the desired threshold volt- age code in the blank to complete the part number. see selector guide for a listing of device features. + denotes a lead-free package. t = tape and reel. ordering information (continued) part * temp range pin- package pkg code max16035 llb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16035plb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16036 llb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16036plb_ _+t -40? to +85? 10 ?fn-10 l1022-1 max16037 lla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16037pla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16038 lla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16038pla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16039 lla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16039pla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16040 lla_ _+t -40? to +85? 8 ?fn-8 l822-1 max16040pla_ _+t -40? to +85? 8 ?fn-8 l822-1 reset threshold ranges reset threshold voltage (v) suffix min typ max 46 4.50 4.63 4.75 44 4.25 4.38 4.50 31 3.00 3.08 3.15 29 2.85 2.93 3.00 26 2.55 2.63 2.70 23 2.25 2.32 2.38
max16033?ax16040 low-power battery backup circuits in small ?fn packages 20 ______________________________________________________________________________________ package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) 6, 8, 10l udfn.eps even terminal l c odd terminal l c l e l a e e d pin 1 index area b e a b n solder mask coverage a a 1 pin 1 0.10x45 l l1 (n/2 -1) x e) xxxx xxxx xxxx sample marking a1 a2 7 a 1 2 21-0164 package outline, 6, 8, 10l udfn, 2x2x0.80 mm -drawing not to scale-
max16033?ax16040 low-power battery backup circuits in small ?fn packages 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 21 2007 maxim integrated products is a registered trademark of maxim integrated products, inc. heaney package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) common dimensions symbol min. nom. a 0.70 0.75 a1 d 1.95 2.00 e 1.95 2.00 l 0.30 0.40 pkg. code n e b package variations l1 6 l622-1 0.65 bsc 0.300.05 0.250.05 0.50 bsc 8 l822-1 0.200.03 0.40 bsc 10 l1022-1 2.05 0.80 max. 0.50 2.05 0.10 ref. (n/2 -1) x e 1.60 ref. 1.50 ref. 1.30 ref. a2 - -drawing not to scale- a 2 2 21-0164 package outline, 6, 8, 10l udfn, 2x2x0.80 mm 0.15 0.20 0.25 0.020 0.025 0.035

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