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ltc2917/ltc2918 1 29178fb typical application features applications description voltage supervisor with 27 selectable thresholds and watchdog timer the ltc ? 2917-a/ltc2917-b and ltc2918-a/ltc2918-b are low voltage single-supply monitors with selectable thresholds and an adjustable watchdog timer. the parts operate from 1.5v to 5.5v and consume a quiescent cur- rent of only 30a. two three state inputs select one of nine internally pro- grammed thresholds without the need for external resistors. for the ltc2917, an additional three state input determines the tolerance (C5%, C10%, C15%). the tolerance for the ltc2918 is ? xed at C5%. threshold accuracy is guaranteed at 1.5% over the entire operating temperature range. glitch ? ltering ensures reliable reset operation without false triggering. the reset timeout and the watchdog timeout may be set with no external components, or adjusted using an exter- nal capacitor. a windowed watchdog feature is available for high-reliability applications (b1 versions). a separate manual reset input on the ltc2918-a/ltc2918-b allows a simple push button interface. operation to 125c makes the ltc2917-a/ltc2917-b and ltc2918-a/ltc2918-b suitable for automotive applications. 1.8v supply monitor with manual reset and internal timers selected 9 selectable supply voltages 12v, 5v, 3.3v, 2.5v, 1.8v 1.5v, 1.2v, 1v, +adj (0.5v) 3 selectable tolerances C5%, C10%, C15% (ltc2917) manual reset input (ltc2918) 1.5v to 5.5v supply operation adjustable watchdog timeout windowed watchdog timeout for higher reliability applications (ltc2917-b, ltc2918-b) 6.2v shunt regulator for high voltage operation guaranteed operation to 125c guaranteed threshold accuracy: 1.5% low quiescent current: 30a typical power supply glitch immunity guaranteed rst for v cc 0.8v 10-lead msop packages and (3mm 2mm) dfn packages handheld devices cell phone base stations automotive control systems network servers optical networking systems nominal voltage sel1 sel2 12v v cc v cc 5v v cc open 3.3v v cc gnd 2.5v open v cc 1.8v open open 1.5v open gnd 1.2v gnd v cc 1v gnd open adj (0.5v) gnd gnd , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. 29178 ta01 vm wdi rt wt sel1 sel2 mr gnd v cc ltc2918-a p rst rst i/o 10k 0.1f 1.8v t wdu = 1.6s t rst = 200ms monitor selection table
ltc2917/ltc2918 2 29178fb absolute maximum ratings (note 1, 2) terminal voltages v cc (note 3) .......................................... C0.3v to 5.7v sel1, sel2, tol, wdi, mr , rst ......... C0.3v to 7.5v vm ......................................................... C0.3v to 15v rt, wt ....................................... C0.3v to (v cc + 0.3)v terminal currents v cc (note 3) .......................................................5ma operating temperature range ltc2917c/ltc2918c ............................... 0c to 70c ltc2917i/ltc2918i .............................. C40c to 85c ltc2917h/ltc2918h ......................... C40c to 125c storage temperature range ................... C65c to 150c lead temperature (soldering, 10 sec) msop ............................................................... 300c 1 2 3 4 5 gnd tol sel2 sel1 vm 10 9 8 7 6 rst rt wt wdi v cc top view ms package 10-lead plastic msop t jmax = 125c, ja = 200c/w ltc2917 top view 11 ddb package 10-lead (3mm s 2mm) plastic dfn gnd tol sel2 sel1 vm rst rt wt wdi v cc 6 8 7 9 10 5 4 2 3 1 t jmax = 125c, ja = 43c/w exposed pad (pin 11) pcb gnd connection optional ltc2917 1 2 3 4 5 gnd mr sel2 sel1 vm 10 9 8 7 6 rst rt wt wdi v cc top view ms package 10-lead plastic msop t jmax = 125c, ja = 200c/w ltc2918 top view 11 ddb package 10-lead (3mm s 2mm) plastic dfn gnd mr sel2 sel1 vm rst rt wt wdi v cc 6 8 7 9 10 5 4 2 3 1 t jmax = 125c, ja = 43c/w exposed pad (pin 11) pcb gnd connection optional ltc2918 pin configuration ltc2917 ltc2918 ltc2918 ltc2917
ltc2917/ltc2918 3 29178fb order information lead free finish tape and reel part marking* package description temperature range ltc2917cms-b1#pbf ltc2917cms-b1#trpbf ltcqp 10-lead plastic msop 0c to 70c ltc2917ims-b1#pbf ltc2917ims-b1#trpbf ltcqp 10-lead plastic msop ?40c to 85c ltc2917hms-b1#pbf ltc2917hms-b1#trpbf ltcqp 10-lead plastic msop ?40c to 125c ltc2917cms-a1#pbf ltc2917cms-a1#trpbf ltdgd 10-lead plastic msop 0c to 70c ltc2917ims-a1#pbf ltc2917ims-a1#trpbf ltdgd 10-lead plastic msop ?40c to 85c ltc2917hms-a1#pbf ltc2917hms-a1#trpbf ltdgd 10-lead plastic msop ?40c to 125c ltc2918cms-b1#pbf ltc2918cms-b1#trpbf ltdct 10-lead plastic msop 0c to 70c ltc2918ims-b1#pbf ltc2918ims-b1#trpbf ltdct 10-lead plastic msop ?40c to 85c ltc2918hms-b1#pbf ltc2918hms-b1#trpbf ltdct 10-lead plastic msop ?40c to 125c ltc2918cms-a1#pbf ltc2918cms-a1#trpbf ltdgg 10-lead plastic msop 0c to 70c ltc2918ims-a1#pbf ltc2918ims-a1#trpbf ltdgg 10-lead plastic msop ?40c to 85c ltc2918hms-a1#pbf ltc2918hms-a1#trpbf ltdgg 10-lead plastic msop ?40c to 125c tape and reel (mini) tape and reel part marking* package description temperature range ltc2917cddb-b1#trmpbf ltc2917cddb-b1#trpbf lcqr 10-lead (3mm 2mm) plastic dfn 0c to 70c ltc2917iddb-b1#trmpbf ltc2917iddb-b1#trpbf lcqr 10-lead (3mm 2mm) plastic dfn ?40c to 85c ltc2917hddb-b1#trmpbf ltc2917hddb-b1#trpbf lcqr 10-lead (3mm 2mm) plastic dfn ?40c to 125c ltc2917cddb-a1#trmpbf ltc2917cddb-a1#trpbf ldgf 10-lead (3mm 2mm) plastic dfn 0c to 70c ltc2917iddb-a1#trmpbf ltc2917iddb-a1#trpbf ldgf 10-lead (3mm 2mm) plastic dfn ?40c to 85c ltc2917hddb-a1#trmpbf ltc2917hddb-a1#trpbf ldgf 10-lead (3mm 2mm) plastic dfn ?40c to 125c ltc2918cddb-b1#trmpbf ltc2918cddb-b1#trpbf ldcv 10-lead (3mm 2mm) plastic dfn 0c to 70c ltc2918iddb-b1#trmpbf ltc2918iddb-b1#trpbf ldcv 10-lead (3mm 2mm) plastic dfn ?40c to 85c ltc2918hddb-b1#trmpbf ltc2918hddb-b1#trpbf ldcv 10-lead (3mm 2mm) plastic dfn ?40c to 125c ltc2918cddb-a1#trmpbf ltc2918cddb-a1#trpbf ldgh 10-lead (3mm 2mm) plastic dfn 0c to 70c ltc2918iddb-a1#trmpbf ltc2918iddb-a1#trpbf ldgh 10-lead (3mm 2mm) plastic dfn ?40c to 85c ltc2918hddb-a1#trmpbf ltc2918hddb-a1#trpbf ldgh 10-lead (3mm 2mm) plastic dfn ?40c to 125c trm = 500 pieces. *temperature grades are identi? ed by a label on the shipping container. consult ltc marketing for information on non-standard lead based ? nish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/
ltc2917/ltc2918 4 29178fb electrical characteristics symbol parameter conditions min typ max units v cc(min) minimum supply voltage rst in correct logic state 0.8 v v cc(uvlo) supply undervoltage lockout 1.5 v v cc(shunt) shunt regulation voltage i vcc = 0.5ma 5.7 6.2 7.0 v i cc v cc pin current sel1, sel2, tol, mr = open sel1, sel2, tol = gnd (ltc2917) mr = v cc (ltc2918) 30 45 50 80 a a monitor input (vm) v mt120 12v, 5% reset threshold 12v, 10% reset threshold 12v, 15% reset threshold 11.04 10.44 9.84 11.22 10.62 10.02 11.40 10.80 10.20 v v v v mt50 5v, 5% reset threshold 5v, 10% reset threshold 5v, 15% reset threshold 4.600 4.350 4.100 4.675 4.425 4.175 4.750 4.500 4.250 v v v v mt33 3.3v, 5% reset threshold 3.3v, 10% reset threshold 3.3v, 15% reset threshold 3.036 2.871 2.706 3.086 2.921 2.756 3.135 2.970 2.805 v v v v mt25 2.5v, 5% reset threshold 2.5v, 10% reset threshold 2.5v, 15% reset threshold 2.300 2.175 2.050 2.338 2.213 2.088 2.375 2.250 2.125 v v v v mt18 1.8v, 5% reset threshold 1.8v, 10% reset threshold 1.8v, 15% reset threshold 1.656 1.566 1.476 1.683 1.593 1.503 1.710 1.620 1.530 v v v v mt15 1.5v, 5% reset threshold 1.5v, 10% reset threshold 1.5v, 15% reset threshold 1.380 1.305 1.230 1.403 1.328 1.253 1.425 1.350 1.275 v v v v mt12 1.2v, 5% reset threshold 1.2v, 10% reset threshold 1.2v, 15% reset threshold 1.104 1.044 0.984 1.122 1.062 1.002 1.140 1.080 1.020 v v v v mt10 1v, 5% reset threshold 1v, 10% reset threshold 1v, 15% reset threshold 0.920 0.870 0.820 0.935 0.885 0.835 0.950 0.900 0.850 v v v v mtadj adj (0.5v), 5% reset threshold adj (0.5v), 10% reset threshold adj (0.5v), 15% reset threshold 460.0 435.0 410.0 467.5 442.5 417.5 475.0 450.0 425.0 mv mv mv r vm vm input impedance (note 4) fixed threshold modes 0.5 8 m i vm(adj) adj input current vm = 0.5v 15 na three-state inputs (sel1, sel2), (tol, ltc2917) v tpin,low low level input voltage 0.5 v v tpin,high high level input voltage 1.4 v v tpin,z pin voltage when open i = 0a 0.9 v i tpin,z allowable leakage in open state 5 a i tpin,h/l pin input current v tpin = 0v, v cc 20 a reset timer control (rt) i rt(up) rt pull-up current v rt = 0.25v C2 C3 C4 a i rt(down) rt pull-down current v rt = 1.1v 234a i rt(int) internal rt v cc detect current v rt = v cc 18a v rt(int, lh) rt internal timer threshold v rt rising, referenced to v cc C100 C160 C300 mv the denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v cc = 2.5v, unless otherwise noted. (note 2)
ltc2917/ltc2918 5 29178fb symbol parameter conditions min typ max units reset output ( rst ) t rst(int) internal reset timeout period v rt = v cc 150 200 260 ms t rst(ext) adjustable reset timeout period c rt = 2.2nf 16 20 25 ms t uv vm undervoltage detect to rst asserted vm less than reset threshold v mtx by more than 5% 10 80 150 s v ol output voltage low rst v cc = 3.3v, i rst = 2.5ma v cc = 1v, i rst = 100a v cc = 0.8v, i rst = 15a 0.15 0.15 0.05 0.4 0.3 0.2 v v v i oh(rst) rst output voltage high leakage rst = v cc 1 a watchdog timer control (wt) i wt(up) wt pull-up current v wt = 0.25v C2 C3 C4 a i wt(down) wt pull-down current v wt = 1.1v 234a v wt(int, lh) wt internal timer threshold v wt rising, referenced to v cc C100 C160 C300 mv i wt(int) internal wt v cc detect current v wt = v cc 18a i wt(dis) watchdog disable hold current v wt = 0v C3.5 a watchdog input (wdi) t wdu(int) internal watchdog upper boundary v wt = v cc 1.3 1.6 2 s t wdl(int) internal watchdog lower boundary (note 5) b versions, v wt = v cc 37.5 50 62.5 ms t wdu(ext) external watchdog upper boundary c wt = 2.2nf 130 160 200 ms t wdl(ext) external watchdog lower boundary (note 5) b versions, c wt = 2.2nf t wdu(ext) /32 ms v il(wdi) input low voltage 0.4 v v ih(wdi) input high voltage 1.1 v t pw(wdi) input pulsewidth 400 ns wdi leakage current 1 a manual reset input (ltc2918) v il(mr) input low voltage 0.2 ? v cc v v ih(mr) input high voltage 0.8 ? v cc v r pu pull-up resistance 50 100 150 k t pw(mr) pulsewidth 250 ns note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into pins are positive; all voltages are referenced to gnd unless otherwise noted. note 3: v cc maximum pin voltage is limited by input current. since the v cc pin has an internal 6.2v shunt regulator, a low impedance supply which exceeds 5.7v may exceed the rated terminal current. operation electrical characteristics the denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v cc = 2.5v, unless otherwise noted. (note 2) from higher voltage supplies requires a series dropping resistor. see applications information. note 4: input impedance is dependent on the con? guration of the sel pins. note 5: in the ltc2917-b/ltc2918-b, edges must occur on wdi with a period between the lower and upper boundary or rst is invoked. for the ltc2917-a/ltc2918-a, the edges must simply occur before the upper boundary. see applications information.
ltc2917/ltc2918 6 29178fb temperature (c) C50 normalized v mtnn (%) 0.5 1.0 1.5 25 75 29178 g01 0 C0.5 C25 0 50 100 125 C1.0 C1.5 v mt120 v mtadj v mt25 temperature (c) C50 20 quiescent supply current, i cc (a) 25 30 35 40 C25 0 25 50 29178 g02 75 100 125 sel1 = 0v sel2 = 2.5v tol = open v cc = 5.5v v cc = 2.5v v cc = 1.5v glitch percentage past threshold (%) 0.1 0 maximum allowable glitch duration (s) 200 250 300 1 10 100 29178 g03 150 100 50 reset occurs above curve temperature (c) C50 C25 150 reset timeout period, t rst(int) (ms) 190 250 0 50 75 29178 g05 170 230 210 25 100 125 rt = v cc temperature (c) C50 C25 1.0 watchdog timeout period, t wdu(int) (ms) 1.4 2.0 0 50 75 29178 g06 1.2 1.8 1.6 25 100 125 wt = v cc wt pin capacitance, c wt (nf) 0.001 1 watchdog timeout period, t wdu(ext) (ms) 100 10000 110 0.1 0.01 100 29178 g07 10 1000 supply current, i cc (ma) 0.01 shunt regulation voltage, v cc(shunt) (v) 6.4 6.6 100 29178 g09 6.2 6.0 0.1 1 10 7.0 6.8 typical performance characteristics threshold voltage vs temperature quiescent supply current vs temperature allowable glitch duration vs magnitude reset timeout period vs rt capacitance internal reset timeout period vs temperature internal watchdog timeout period vs temperature watchdog timeout period vs capacitance shunt regulation voltage vs temperature shunt regulation voltage vs supply current rt pin capacitance, c rt (nf) 0.001 0.1 reset timeout period, t rst(ext) (ms) 10 10000 0.1 0.01 1 10 100 1000 29178 g04 1 100 1000 temperature (c) C50 6.1 shunt regulation voltage, v cc(shunt) (v) 6.2 6.3 6.4 C25 0 25 50 29178 g08 75 100 125 i cc = 5ma i cc = 1ma i cc = 100a
ltc2917/ltc2918 7 29178fb gnd: device ground. mr (ltc2918 only) : manual reset input (active low). a low level on the mr input causes the part to issue a reset, which is released one reset timeout after the input goes high. the pin has an internal 100k pull-up to v cc , and thus may interface directly to a momentary pushbutton. leave open if unused. rst : open drain rst output. asserts low when vm is below the threshold selected by sel1, sel2 and tol input pins. held low for an adjustable timeout after vm input is above threshold. rt: reset timeout control pin. attach an external capacitor (c rt ) to gnd to set a reset timeout of 9ms/nf. leave rt open to generate a reset timeout of approximately 400s. tie rt to v cc to generate a reset timeout of approximately 200ms. sel1, sel2: monitor voltage select three-state input. sel1, and sel2 control the nominal threshold voltage that vm is set to monitor. connect to v cc , gnd or leave unconnected in open state. (see table 1). tol (ltc2917 only): three-state input for supply tolerance selection (C5%, C10% or C15%). controls the tolerance band at which the vm supply is monitored. connect to v cc , gnd, or leave unconnected in open state. (see table 2) v cc : power supply input. bypass this pin to ground with a 0.1f ceramic capacitor. a minimum of 1.5v on v cc ensures that the part is out of under voltage lockout and that the voltage thresholds are accurate. operates as a direct supply input for voltages up to 5.5v. operates as a shunt regulator for supply voltages greater than 5.7v and should have a resistor between this pin and the supply to limit v cc input current to no greater than 5ma. when used without a cur- rent-limiting resistor, pin voltage must not exceed 5.7v. vm: voltage monitor input to rst comparator. sel1, sel2 and tol inputs select the exact threshold that asserts the rst output. wdi: watchdog input. this pin must be driven to change state within a time less than the watchdog upper bound- ary time, or rst will be asserted low. on the ltc2917-b, ltc2918-b, the period must also be greater than the watchdog lower boundary time, and only falling edges are considered. tie wt and wdi to gnd to disable the watchdog timer. wt: watchdog timer control pin. attach an external capacitor (c wt ) to gnd to set a watchdog upper bound- ary timeout time of 72ms/nf. tie wt to v cc to generate a timeout of approximately 1.6s. leave wt open to generate a timeout of approximately 3.2ms. tie wt and wdi to gnd to disable the watchdog timer. exposed pad (dfn only): exposed pad may be left open or connected to device ground. pin functions supply voltage, v cc (v) 0 0 rst voltage (v) 1 2 3 4 5 6 1234 29178 g10 5 10k pull-up r to v cc sel1 = sel2 = tol = 0v vm = 0.5v supply voltage, v cc (v) 0 0 pull-down current, i rst (ma) 1 2 3 4 5 6 1234 29178 g11 5 rst at 150mv rst at 50mv i rst (ma) 0 rst voltage (v) 0.6 0.8 1.0 8 29178 g12 0.4 0.2 0 2 4 6 10 t a = 125c t a = 25c t a = C40c no pull-up r v cc = 2.5v typical performance characteristics rst output voltage vs v cc rst pull-down current vs v cc rst v ol vs i rst
ltc2917/ltc2918 8 29178fb block diagram + C gnd rst v cc v cc v cc 29178 bd vm sel1 mr sel2 rt 3 state decode monitor divider matrix reference divider matrix internal 200ms timer adjustable reset timer reset driver logic v cc detect tol 6.2v 100k 0.5v + C wt wdi v cc detect internal 1.6 second timer adjustable watchdog timer watchdog logic ltc2918 ltc2917 timing diagrams vm rst v mtx 1v t uv t rst 29178 td01 monitor input timing wdi rst t wdu t rst 29178 td01 watchdog timing (ltc2917-a, ltc2918-a) wdi rst t wdu t > t wdl t rst 29178 td03 t rst t < t wdl watchdog timing (ltc2917-b, ltc2918-b)
ltc2917/ltc2918 9 29178fb applications information supply monitoring the ltc2917/ltc2918 are low voltage single supply monitors with selectable thresholds. two three-state inputs select one of nine internally programmed thresholds. for the ltc2917, a third three-state input selects the tolerance at which the supply connected to the vm pin is monitored (C5%, C10%, C15%). the tolerance for the ltc2918 is ? xed at C5%. threshold accuracy is guaranteed at 1.5% over the entire operating temperature range. the ltc2917/ltc2918 asserts the rst output low when vm is below the programmed threshold, and for a reset timeout period (t rst ) after vm goes above the threshold. the reset timeout can be con? gured to use one of two internal timers with no external components, or an ad- justed timer programmed by placing an external capacitor from rt to ground. glitch ? ltering ensures reliable reset operation without false triggering. power-up v cc powers the drive circuits for the rst pin. therefore, as soon as v cc reaches 0.8v during power up, the rst output asserts low. until v cc reaches the undervoltage lockout threshold (guaranteed less than 1.5v), rst is held low regardless of the state of vm. once v cc is above the undervoltage lockout threshold and vm is above the programmed threshold, the reset timer is started. after the reset timeout, the open drain pull-down releases rst and the external pull-up resistor pulls high. power-down on power-down, once vm drops below its threshold or v cc drops below the undervoltage lockout, rst asserts logic low. monitor threshold control the monitor threshold on the vm pin is controlled by the sel1, sel2 and tol three-state pins. the sel1 and sel2 pins select one of nine preset nominal voltages (including one externally adjustable threshold) as shown in table 1. the sel1 and sel2 three-state input pins should be con- nected to gnd, v cc or left unconnected during normal operation. note that when left unconnected, the maximum leakage allowable from the pin to either gnd or v cc is 5a. the tolerance at which the monitored supply is measured is set by the tol pin (ltc2917 only) as shown in table 2. if desired (e.g. for margining purposes), the tol pin may be driven by a three-state buffer. that three-state buffer must have a v ol and v oh which meet the v il and v ih of the tol pin speci? ed in the electrical characteristics, and maintain less than 5a of leakage in the open state. table 1. voltage threshold settings nominal voltage sel1 sel2 12v v cc v cc 5v v cc open 3.3v v cc gnd 2.5v open v cc 1.8v open open *1.5v open gnd *1.2v gnd v cc *1v gnd open *adj (0.5v) gnd gnd *require a separate supply for v cc table 2. system voltage tolerance settings tolerance tol C5% v cc C10% open C15% gnd
ltc2917/ltc2918 10 29178fb applications information threshold accuracy the trip threshold for the supplies monitored is selected by con? guring the three-state input pins. when using the adjustable input, a external resistive divider sets the trip threshold, allowing the user complete control over the trip point. selection of this trip voltage is crucial to the reliability of the system. any power supply has some tolerance band within which it is expected to operate (e.g. 5v10%). it is generally undesirable that a supervisor issue a reset when the power supply is inside this tolerance band. such a nuisance reset reduces reliability by preventing the system from functioning under normal conditions. to prevent nuisance resets, the supervisor threshold must be guaranteed to lie outside the power supply tolerance band. to ensure that the threshold lies outside the power supply tolerance range, the nominal threshold must lie out- side that range by the monitors accuracy speci? cation. all 27 of the selectable thresholds have the same relative threshold accuracy of 1.5% of the programmed nominal input voltage (over the full operating temperature range). consider the example of monitoring a 5v supply with a 10% tolerance. the nominal threshold internal to the ltc2917 is 11.5% below the 5v input at 4.425v. with 1.5% ac- curacy, the trip threshold range is 4.425v75mv over temperature (i.e. 10% to 13% below 5v). the monitored system must thus operate reliably down to 4.35v or 13% below 5v over temperature. glitch immunity the above discussion is concerned only with the dc value of the monitored supply. real supplies also have relatively high-frequency variation, from sources such as load transients, noise, and pickup. these variations should not be considered by the monitor in determining whether a supply voltage is valid or not. the variations may cause spurious outputs at rst , particularly if the supply voltage is near its trip threshold. two techniques are used to combat spurious reset without sacri? cing threshold accuracy. first, the timeout period helps prevent high-frequency variation whose frequency is above 1/ t rst from appearing at the rst output. when the voltage at vm goes below the threshold, the rst pin asserts low. when the supply recovers past the threshold, the reset timer starts (assuming it is not disabled), and rst does not go high until it ? nishes. if the supply becomes invalid any time during the timeout period, the timer resets and starts a fresh when the supply next becomes valid. while the reset timeout is useful at preventing toggling of the reset output in most cases, it is not effective at preventing nuisance resets due to short glitches (due to load transients or other effects) on a valid supply. to reduce sensitivity to these short glitches, the comparator has additional anti-glitch circuitry. any transient at the input of the comparator needs to be of suf? cient magnitude and duration t uv before it can change the monitor state. the combination of the reset timeout and anti-glitch cir- cuitry prevents spurious changes in output state without sacri? cing threshold accuracy. adjustable input when the monitor threshold is con? gured as adj, the internal comparator input is connected to the pin without a resistive divider, and the pin is high-impedance. thus, any desired threshold may be chosen by attaching vm to a tap point on an external resistive divider between the monitored supply and ground, as shown in figure 1. figure 1. setting the trip point using the adjustable threshold. C + + C 0.5v vm r2 r1 29178 f01 v mon
ltc2917/ltc2918 11 29178fb the reference input of the comparator is controlled by the tolerance pin. the external resistive divider should make the voltage at vm = 0.5v when the supply is at nominal value. the actual threshold of vm accounts for the sup- ply tolerance of 1.5% guaranteed over the full operating temperature range. the resulting tolerances are C6.5%, C11.5%, C16.5% which correspond to 0.468v, 0.443v, 0.418v respectively. typically, the user will pick a value of r1 based on accept- able current draw. current used by the resistor divider will be approximately: r v i 1 05 = ? ? ? ? ? ? . recommended range of r1 is 1k1m. higher values of resistance exacerbate the degradation of threshold ac- curacy due to leakage currents. if the nominal value of the supply being monitored is v nom , then r2 = r1(2v nom C 1) resistor tolerances must be taken into account when determining the overall accuracy. selecting the reset timing capacitor the reset timeout period can be set to one of two ? xed internal timers or set with a capacitor in order to accom- modate a variety of applications. connecting a capacitor, c rt , between the rt pin and ground sets the reset timeout period, t rst . the following formula approximates the value of capacitor needed for a particular timeout: c rt = t rst ? 110 [pf/ms] for example, using a standard capacitor value of 2.2nf would give a 20ms timeout. figure 2 shows the desired reset timeout period as a function of the value of the timer capacitor. leaving rt open with no external capacitor generates a reset timeout of approximately 400s. shorting rt to v cc generates a reset timeout of approximately 200ms. rst output characteristics the dc characteristics of the rst pull-down strength are shown in the typical performance characteristics section. rst is an open-drain pin and thus requires an external pull-up resistor to the logic supply. rst may be pulled above v cc , providing the voltage limits of the pin are observed. the open-drain of the rst pin allows for wired-or con- nection of several ltc2917/ltc2918s. watchdog ltc2917-a/ltc2918-a a standard watchdog function is used to ensure that the system is in a valid state by continuously monitoring the microprocessors activity. the microprocessor must toggle the logic state of the wdi pin periodically (within upper boundary) in order to clear the watchdog timer. if timeout occurs, the ltc2917-a/ltc2918-a asserts rst low for the reset timeout period, issuing a system reset. once the reset timeout completes, rst is released to go high and the watchdog timer starts again. during power-up, the watchdog timer remains cleared while rst is asserted low. as soon as the reset timer times out, rst goes high and the watchdog timer is started. applications information figure 2. reset timeout period vs rt capacitance rt pin capacitance, c rt (nf) 0.001 0.1 reset timeout period, t rst (ext) (ms) 10 10000 0.1 0.01 1 10 100 1000 29178 f02 1 100 1000
ltc2917/ltc2918 12 29178fb ltc2917-b/ltc2918-b for applications in which reliability is even more critical, the ltc2917-b/ltc2918-b implements a windowed watch- dog function by adding a lower boundary condition to the standard watchdog function. if the wdi input receives a falling edge prior to the watchdog lower boundary, the part considers this a watchdog failure, and asserts rst low (releasing again after the reset timeout period as described above). the ltc2917-b/ltc2918-b wdi input only responds to falling edges. setting the watchdog timeout period the watchdog timeout period is adjustable and can be optimized for software execution. the watchdog timeout period is adjusted by connecting a capacitor between wt and ground. given a speci? ed watchdog timeout period, the capacitor is determined by: c wt = t wd ? 13.8 [nf/s] for example, using a standard capacitor value of 0.047f would give a 3.4s watchdog timeout period. leaving wt open with no external capacitor generates a timeout of approximately 3.2ms. shorting wt to v cc generates a timeout of approximately 1.6s. connecting wt to gnd disables the watchdog function. applications information manual reset (ltc2918 only) the ltc2918 includes the mr pin for applications where a manual reset is desired. mr is internally pulled up, making it ready to interface with a push button with no external components required. asserting mr low when rst is high initiates a reset, resulting in rst being asserted low for the reset timeout time. shunt regulator the ltc2917 and ltc2918 contain an internal 6.2v shunt regulator on the v cc pin to allow operation from a high voltage supply. to operate the part from a supply higher than 5.7v, the v cc pin must have a series resistor, r cc , to the supply. see figure 3. this resistor should be sized according to the following equation: vv ma r vv a smax cc smin () () . ? ? ? 57 5 7 250 where v s(min) and v s(max) are the operating minimum and maximum of the supply. as an example, consider operation from an automobile battery which might dip as low as 10v or spike to 60v. we must then pick a resistance between 10.86k and 12k. figure 3. 12v supply monitor powered from 12v, utilizing the internal shunt regulator with 3.3v logic out r cc 11k 12v 3.3v c rt c bypass 0.1f r pu 10k 29178 f03 vm sel1 gnd sel2 rt tol v cc (v trip = 10.64v) v cc ltc2917 p rst rst wdi i/o gnd r2 1.15m r1 49.9k c wt wt
ltc2917/ltc2918 13 29178fb typical applications 1v supply monitor with windowed watchdog timeout and internal timers selected 12v supply monitor with 20ms reset timeout and 3.4s watchdog timeout, with 3.3v logic out 9v, C15% tolerance supply monitor ith 1.8v logic out 3.3v 3.3v 1v c bypass 0.1 f r pu 10k 29178 ta02 vm sel1 gnd sel2 gnd rt wt tol v cc v cc ltc2917-b p rst rst wdi i/o t wdu = 1.6s t wdl = 50ms t rst = 200ms 3.3v 12v c bypass 0.1 f r pu 10k 29178 ta03 vm sel1 gnd sel2 gnd rt wt tol v cc v cc ltc2917-a p rst rst wdi i/o c wt 0.047 f c rt 0.0022f 1.8v 9v c bypass 0.1 f r pu 10k 29178 ta04 vm sel1 gnd sel2 tol v cc v cc ltc2917-a p rst rst wdi i/o gnd r2 866k r1 51.1k c rt rt c wt wt
ltc2917/ltc2918 14 29178fb typical applications 3.3v, C10% tolerance supply monitor with disabled watchdog 1.8v, C5% supply monitor with manual reset 1.5v supply monitor with tolerance control for margining, C5% operation with C15% margining 3.3v c bypass 0.1 f r pu 10k 29178 ta06 vm sel1 gnd sel2 tol v cc v cc ltc2917 p rst wdi rst gnd rt wt c rt 1.8v c bypass 0.1 f r pu 10k 29178 ta07 vm sel1 gnd sel2 mr rt v cc v cc ltc2918 p rst rst wdi i/o gnd 10k* *optional resistor recommended to extend esd tolerance c rt manual reset pushbutton wt c wt 3.3v 1.5v c bypass 0.1 f r pu 10k 29178 ta08 vm sel1 gnd sel2 rt v cc v cc ltc2917 p rst rst wdi i/o tol i/o gnd c rt wt c wt C5% C15%
ltc2917/ltc2918 15 29178fb information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description 2.00 p 0.10 (2 sides) note: 1. drawing conforms to version (wecd-1) in jedec package outline m0-229 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 p 0.10 bottom viewexposed pad 0.64 p 0.05 (2 sides) 0.75 p 0.05 r = 0.115 typ r = 0.05 typ 2.39 p 0.05 (2 sides) 3.00 p 0.10 (2 sides) 1 5 10 6 pin 1 bar top mark (see note 6) 0.200 ref 0 C 0.05 (ddb10) dfn 0905 rev ? 0.25 p 0.05 2.39 p 0.05 (2 sides) recommended solder pad pitch and dimensions 0.64 p 0.05 (2 sides) 1.15 p 0.05 0.70 p 0.05 2.55 p 0.05 package outline 0.25 p 0.05 0.50 bsc pin 1 r = 0.20 or 0.25 s 45 chamfer 0.50 bsc msop (ms) 0307 rev e 0.53 p 0.152 (.021 p .006) seating plane 0.18 (.007) 1.10 (.043) max 0.17 C?0.27 (.007 C .011) typ 0.86 (.034) ref 0.50 (.0197) bsc 12 3 45 4.90 p 0.152 (.193 p .006) 0.497 p 0.076 (.0196 p .003) ref 8 9 10 7 6 3.00 p 0.102 (.118 p .004) (note 3) 3.00 p 0.102 (.118 p .004) (note 4) note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 0.254 (.010) 0 C 6 typ detail a detail a gauge plane 5.23 (.206) min 3.20 C 3.45 (.126 C .136) 0.889 p 0.127 (.035 p .005) recommended solder pad layout 0.305 p 0.038 (.0120 p .0015) typ 0.50 (.0197) bsc 0.1016 p 0.0508 (.004 p .002) ms package 10-lead plastic msop (reference ltc dwg # 05-08-1661) ddb package 10-lead plastic dfn (3mm 2mm) (reference ltc dwg # 05-08-1722 rev ?)
ltc2917/ltc2918 16 29178fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2007 lt 0208 rev b ? printed in usa related parts part number description comments ltc690 5v supply monitor, watchdog timer and battery backup 4.65v threshold ltc694-3.3 3.3v supply monitor, watchdog timer and battery backup 2.9v threshold ltc1232 5v supply monitor, watchdog timer and push-button reset 4.37v/4.62v threshold ltc1326 micro power precision triple supply monitor 4.725v, 3.118v, 1v threshold (0.75%) ltc1536 precision triple supply monitor for pci applications meets pci tfall timing speci? cations ltc1726 micro power triple supply monitor for 2.5v/5v, 3.3v and adj adjustable reset and watchdog time-outs ltc1727 micro power triple supply monitor with open-drain reset individual monitor outputs in msop ltc1728 micro power triple supply monitor with open-drain reset 5-lead sot-23 package ltc2900 programmable quad supply monitor adjustable reset , 10-lead msop and 3mm 3mm 10-lead dfn ltc2901 programmable quad supply monitor adjustable reset and watchdog timer, 16-lead ssop package ltc2902 programmable quad supply monitor adjustable reset and tolerance, 16-lead ssop package, margining ltc2903 precision quad supply monitor 6-lead sot-23 package, ultra low voltage reset ltc2904 3-state programmable precision dual supply monitor adjustable tolerance, 8-lead sot-23 package ltc2905 3-state programmable precision dual supply monitor adjustable reset and tolerance, 8-lead sot-23 package ltc2906 precision dual supply monitor 1 selectable and 1 adjustable separate v cc pin, rst/ rst outputs ltc2907 precision dual supply monitor 1 selectable and 1 adjustable separate v cc pin, adjustable reset timer ltc2908 precision six supply monitor (four fixed and 2 adjustable) 8-lead sot-23 and ddb packages ltc2909 precision triple/dual input uv, ov 2 adj inputs ltc2910 octal positive/negative voltage monitor 16-lead ssop and 5mm 3mm dfn packages ltc2912 single uv/ov voltage monitor, adjustable uv and ov 8-lead tsot and 3mm 2mm dfn packages ltc2913 dual uv/ov voltage monitor 10-lead msop and 3mm 3mm dfn packages ltc2914 qual uv/ov positive/negative voltage monitor 16-lead ssop and 5mm 3mm dfn packages ltc2915 single supervisor with 27 selectable thresholds 10-lead msop and 3mm 2mm dfn-10 packages ltc2916 single supervisor with 9 selectable thresholds manual reset, 10-lead msop and 3mm 2mm dfn-10 packages 1.8v c bypass 0.1 f vm sel1 sel2 mr gnd rt v cc ltc2916 rst manual reset push button 1.8v 1.8v 12v c1 0.1 f r pu 10k 29178 ta10 vm sel1 gnd sel2 gnd wt rt tol v cc v cc ltc2917-b p rst rst wdi i/o typical application dual supply monitor (1.8v and 12v) with manual reset

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