View LTC2908IDDB-B1_3908419.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1 ltc2908 sn2908 2908fs precision six supply monitor ultralow voltage reset: v cc = 0.5v guaranteed* monitors six inputs simultaneously: 5v, 3.3v, 2.5v, 1.8v, adj1, adj2 (ltc2908-a1) 3.3v, 2.5v, 1.8v, 1.5v, adj1, adj2 (ltc2908-b1) guaranteed threshold accuracy: 1.5% of monitored voltage over temperature internal v cc auto select power supply glitch immunity 200ms reset time delay active low open-drain rst output low profile (1mm) sot-23 (thinsot tm ) and plastic (2mm 3mm) dfn packages six supply monitor with 5% tolerance (12v, 3.3v, 2.5v, 1.8v, 1.5v, 1.2v) network servers wireless base stations optical networking systems mulitvoltage systems desktop and notebook computers handheld devices features descriptio u applicatio s u typical applicatio u the ltc ? 2908 is a six supply monitor for systems with a large number of supply voltages that require a precise and compact solution. the common reset output remains low until all six inputs have been in compliance for 200ms. the ltc2908 features a tight 1.5% threshold accuracy over the entire operating temperature range (C 40 c to 85 c) and glitch immunity to ensure reliable reset opera- tion without false triggering. the open-drain rst output state is guaranteed to be in the correct state as long as v1 and/or v2 is 0.5v or greater. the ltc2908 also features two adjustable inputs with a nominal threshold level at 0.5v. this product provides a precise, space-conscious, micropower and general pur- pose solution for any kind of system requiring supply monitors. , ltc and lt are registered trademarks of linear technology corporation. rst 2.15m 0.1 f v1 v2 v3 v4 gnd ltc2908-b1 v adj1 12v 3.3v 2.5v 1.8v 1.5v 1.2v 2908 ta01a 0.1 f 100k dc/dc dc/dc dc/dc dc/dc dc/dc system 124k v adj2 100k v1 (v) 0 rst output voltage (v) 0.2 v2 = gnd v2 = v1 0.3 0.8 2908 ta01b 0.1 0 0.2 0.4 0.6 0.4 v3 = v4 = v adj1 = v adj2 = gnd rst output voltage vs v1 with 10k pull-up resistor to v1 thinsot is a trademark of linear technology corporation. *patent pending.
2 ltc2908 sn2908 2908fs terminal voltages v1, v2, v3, v4 ........................................ C 0.3v to 7v v adj1 , v adj2 ........................... C 0.3v to (v cc + 0.3v) rst ........................................................ C 0.3v to 7v operating temperature range ltc2908c-a1/ltc2908c-b1 .................. 0 c to 70 c ltc2908i-a1/ltc2908i-b1 ................ C40 c to 85 c absolute axi u rati gs w ww u symbol parameter conditions min typ max units v rt50 5v, 5% reset threshold v1 input threshold 4.600 4.675 4.750 v v rt33 3.3v, 5% reset threshold v2 input threshold 3.036 3.086 3.135 v v rt25 2.5v, 5% reset threshold v3 input threshold 2.300 2.338 2.375 v v rt18 1.8v, 5% reset threshold v4 input threshold 1.656 1.683 1.710 v v rtadj adj, 5% reset threshold v adj1 , v adj2 input threshold 0.492 0.500 0.508 v (ltc2908-a1) the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c. v cc = 5v, unless otherwise noted. (note 2) electrical characteristics (notes 1, 2) consult factory for parts specified with wider operating temperature ranges. package/order i for atio uu w ltc2908cts8-a1 ltc2908its8-a1 ltc2908cts8-b1 ltc2908its8-b1 order part number t jmax = 125 c, ja = 250 c/ w storage temperature range dfn package .....................................C65 c to 125 c tsot-23 package ..............................C65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c ltbfj ltbfk ltbfm ltbfn ts8 part marking ltc2908cddb-a1 ltc2908iddb-a1 ltc2908cddb-b1 LTC2908IDDB-B1 order part number lbfd lbff lbfg lbfh ddb8 part marking t jmax = 125 c, ja = 76 c/ w exposed pad (pin 9) (pcb connection optional) v2 1 v4 2 rst 3 gnd 4 8 v1 7 v adj1 6 v3 5 v adj2 top view ts8 package 8-lead plastic tsot-23 top view 9 ddb8 package 8-lead (3mm 2mm) plastic dfn 5 6 7 8 4 3 2 1 gnd rst v4 v2 v adj2 v3 v adj1 v1 symbol parameter conditions min typ max units v rt33 3.3v, 5% reset threshold v1 input threshold 3.036 3.086 3.135 v v rt25 2.5v, 5% reset threshold v2 input threshold 2.300 2.338 2.375 v v rt18 1.8v, 5% reset threshold v3 input threshold 1.656 1.683 1.710 v v rt15 1.5v, 5% reset threshold v4 input threshold 1.380 1.403 1.425 v v rtadj adj, 5% reset threshold v adj1 , v adj2 input threshold 0.492 0.500 0.508 v (ltc2908-b1) the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c. v cc = 3.3v, unless otherwise noted. (note 2)
3 ltc2908 sn2908 2908fs symbol parameter conditions min typ max units v cc internal operating voltage rst in correct logic state 0.5 6 v i v1 v1 input current v1 = 5.0v (ltc2908-a1) (note 4) 26 50 a v1 = 3.3v (ltc2908-b1) 24 50 a i v2 v2 input current v2 = 3.3v (ltc2908-a1) (note 4) 10 20 a v2 = 2.5v (ltc2908-b1) 820 a i v3 v3 input current v3 = 2.5v (ltc2908-a1) 25 a v3 = 1.8v (ltc2908-b1) 25 a i v4 v4 input current v4 = 1.8v (ltc2908-a1) 25 a v4 = 1.5v (ltc2908-b1) 25 a i vadj v adj1 , v adj2 input current v adj1 = v adj2 = 0.55v 15 na t rst reset time-out period 160 200 260 ms t uv v x undervoltage detect to rst or rst v x less than reset threshold v rtx by 250 s more than 1% v oh output voltage high rst (note 5) i rst = C1 a, v cc = 5v (ltc2908-a1) v cc C 1.5 v i rst = C1 a, v cc = 3.3v (ltc2908-b1) v cc C 1.0 v v ol output voltage low rst v cc = 0.5v, i rst = 5 a 0.01 0.15 v v cc = 1.0v, i rst = 100 a 0.01 0.15 v v cc = 3.0v, i rst = 2500 a 0.10 0.30 v the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c. v cc = 5v for the lt2908-a1 and v cc = 3.3v for the ltc2908-b1, unless otherwise noted. (notes 2, 3) electrical characteristics note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the greater of v1, v2 is the internal supply voltage (v cc ). note 3: all currents into pins are positive; all voltages are referenced to gnd unless otherwise noted. note 4: under typical operating conditions, most of the quiescent current is drawn from the v1 input. when v2 exceeds v1, v2 supplies most of the quiescent current. note 5: the output pin rst has an internal pull-up to v cc of typically 6 a. however, an external pull-up resistor may be used when a faster rise time is required or for v oh voltages greater than v cc . typical perfor a ce characteristics uw 5v threshold voltage vs temperature 3.3v threshold voltage vs temperature 2.5v threshold voltage vs temperature temperature ( c) C50 4.750 4.725 4.700 4.675 4.650 4.625 4.600 25 75 2908 g01 C25 0 50 100 threshold voltage, v rt50 (v) temperature ( c) C50 3.135 3.115 3.095 3.075 3.055 3.035 25 75 2908 g02 C25 0 50 100 threshold voltage, v rt33 (v) temperature ( c) C50 2.375 2.360 2.345 2.330 2.315 2.300 25 75 2908 g03 C25 0 50 100 threshold voltage, v rt25 (v) specifications are at t a = 25 c unless otherwise noted.
4 ltc2908 sn2908 2908fs 1.8v threshold voltage vs temperature 1.5v threshold voltage vs temperature adj threshold voltage vs temperature i v1 vs temperature i v2 vs temperature i v3 vs temperature i v4 vs temperature typical transient duration vs comparator overdrive reset time-out period (t rst ) vs temperature temperature ( c) C50 1.710 1.700 1.690 1.680 1.670 1.660 25 75 2908 g04 C25 0 50 100 threshold voltage, v rt18 (v) temperature ( c) C50 threshold voltage, v rt15 (v) 50 1.425 2908 g05 0 C25 75 25 100 1.410 1.405 1.400 1.395 1.390 1.385 1.380 1.415 1.420 temperature ( c) C50 threshold voltage, v rtadj (v) 0.4980 0.5000 0.5020 25 75 2908 g06 0.4960 0.4940 0.4920 C25 0 50 0.5040 0.5060 0.5080 100 temperature ( c) C50 i v1 ( a) 17 19 21 23 29 31 33 27 C25 02550 2908 g07 75 100 25 a1 b1 v1 = 5.0v (a1)/v1 = 3.3v (b1) v2 = 3.3v (a1)/v2 = 2.5v (b1) v3 = 2.5v (a1)/v3 = 1.8v (b1) v4 = 1.8v (a1)/v4 = 1.5v (b1) v adj1 = v adj2 = 0.55v temperature ( c) C50 i v2 ( a) 8 9 a1 b1 10 25 75 2908 g08 7 6 4 5 C25 0 50 11 12 14 13 100 v1 = 5.0v (a1)/v1 = 3.3v (b1) v2 = 3.3v (a1)/v2 = 2.5v (b1) v3 = 2.5v (a1)/v3 = 1.8v (b1) v4 = 1.8v (a1)/v4 = 1.5v (b1) v adj1 = v adj2 = 0.55v temperature ( c) C50 i v3 ( a) 1.7 1.8 1.9 25 75 2908 g09 1.6 1.5 1.4 C25 0 50 2.0 2.1 2.2 100 v1 = 5.0v (a1)/v1 = 3.3v (b1) v2 = 3.3v (a1)/v2 = 2.5v (b1) v3 = 2.5v (a1)/v3 = 1.8v (b1) v4 = 1.8v (a1)/v4 = 1.5v (b1) v adj1 = v adj2 = 0.55v temperature ( c) C50 i v4 ( a) 1.7 1.8 1.9 25 75 2908 g10 1.6 1.5 1.4 C25 0 50 2.0 2.1 2.2 100 v1 = 5.0v (a1)/v1 = 3.3v (b1) v2 = 3.3v (a1)/v2 = 2.5v (b1) v3 = 2.5v (a1)/v3 = 1.8v (b1) v4 = 1.8v (a1)/v4 = 1.5v (b1) v adj1 = v adj2 = 0.55v comparator overdrive voltage (% of v rtx ) 0.1 400 typical transient duration ( s) 500 600 700 1 10 100 2908 g11 300 200 100 0 reset occurs above curve t a = 25 c temperature ( c) C50 reset time-out period, t rst (ms) 190 200 210 25 75 2908 g12 180 170 150 160 C25 0 50 220 230 250 240 100 typical perfor a ce characteristics uw specifications are at t a = 25 c unless otherwise noted.
5 ltc2908 sn2908 2908fs rst output voltage vs v1 with 10k pull-up resistor to v1 rst pull-down current (i rst ) vs supply voltage (v cc ) rst pull-down current (i rst ) vs supply voltage (v cc ) with dual channel supply rst pull-up current (i rst ) vs supply voltage (v cc ) rst output voltage vs v1 with 10k pull-up resistor to v1 rst output voltage low (v ol ) vs rst pull-down current (i rst ) ltc2908-a1 v1 (v) 0 rst output voltage (v) 3.0 4.0 5.0 4 2908 g13 2.0 1.0 0 1 2 3 5 v1 = v2 v3 = 2.5v (a1)/v3 = 1.8v (b1) v4 = 1.8v (a1)/v4 = 1.5v (b1) v adj1 = v adj2 = 0.55v v rt33 ltc2908-b1 v rt50 ltc2908-a1 v1 (v) 0 rst output voltage (v) 0.2 v2 = gnd v2 = v1 0.3 0.8 2908 g14 0.1 0 0.2 0.4 0.6 0.4 v3 = v4 = v adj1 = v adj2 = gnd supply voltage, v cc (v) 0 rst pull-down current, i rst (ma) 2 4 1 3 5 6 1234 2908 g15 5 0 rst at 150mv rst at 50mv v cc = v1 = v2 v3 = v4 = v adj1 = v adj2 = gnd v rt33 ltc2908-b1 v rt50 ltc2908-a1 supply voltage, v cc (v) 0.01 rst pull-down current, i rst (ma) 0.1 1 10 0 0.4 0.6 0.8 0.001 0.2 1 2908 g16 v cc = v1 = v2 v3 = v4 = v adj1 = v adj2 = gnd rst at 150mv rst at 50mv rst pull-down current (i rst ) vs supply voltage (v cc ) with single channel supply supply voltage, v cc (v) 0.01 rst pull-down current, i rst (ma) 0.1 1 10 0 0.4 0.6 0.8 0.001 0.2 1 2908 g17 v cc = v1 v2 = v3 = v4 = v adj1 = v adj2 = gnd rst at 150mv rst at 50mv rst pull-down current, i rst (ma) 0 rst output voltage low, v ol (v) 0.7 15 2908 g18 0.4 0.2 510 20 0.1 0 0.8 0.6 0.5 0.3 25 30 35 v1 = 5.0v v2 = 3.3v v3 = 2.5v v4 = 1.8v v adj1 = v adj2 = 0.4v 85 c C40 c 25 c rst output voltage low (v ol ) vs rst pull-down current (i rst ) ltc2908-b1 rst pull-down current, i rst (ma) 0 rst output voltage low, v ol (v) 0.7 15 2908 g19 0.4 0.2 510 20 0.1 0 0.8 0.6 0.5 0.3 25 v1 = 3.3v v2 = 2.5v v3 = 1.8v v4 = 1.5v v adj1 = v adj2 = 0.4v 85 c C40 c 25 c supply voltage, v cc (v) 2 0 rst pull-up current, i rst ( a) C5 C10 C15 C20 C30 2.5 3 3.5 4 2908 g20 4.5 5 C25 v cc = v1 = v2 v3 = 2.5v (a1)/v3 = 1.8v (b1) v4 = 1.8v (a1)/v4 = 1.5v (b1) v adj1 = v adj2 = 0.55v rst held at 0v v rt33 ltc2908-b1 v rt50 ltc2908-a1 typical perfor a ce characteristics uw specifications are at t a = 25 c unless otherwise noted.
6 ltc2908 sn2908 2908fs rst output voltage high (v oh ) vs rst output source current (i rst ) ltc2908-a1 typical perfor a ce characteristics uw output source current, i rst ( a) 0 rst output voltage high, v oh (v) 3 4 C16 2908 g21 2 1 C4 C8 C12 C20 85 c C40 c 5 25 c v1 = 5.0v v2 = 3.3v v3 = 2.5v v4 = 1.8v v adj1 = v adj2 = 0.55v rst output voltage high (v oh ) vs rst output source current (i rst ) ltc2908-b1 output source current, i rst ( a) 0 0.5 rst output voltage high, v oh (v) 1.0 1.5 2.0 2.5 3.0 C2 C4 C6 C8 2908 g22 C10 C12 85 c C40 c 25 c v1 = 3.3v v2 = 2.5v v3 = 1.8v v4 = 1.5v v adj1 = v adj2 = 0.55v uu u pi fu ctio s v2 (pin 1/pin 4): voltage input 2. the greater of v1, v2 is also the internal v cc . the operating voltage on this pin shall not exceed 6v. when in normal operation (v1 > v2), this pin draws approximately 8 a. when this pin is acting as the v cc (v2 > v1), this pin draws an additional 15 a. bypass this pin to ground with a 0.1 f (or greater) capacitor. v4 (pin 2/pin 3): voltage input 4. rst (pin 3/pin 2): reset logic output. pulls low when any voltage input is below the reset threshold and is held low for 200ms after all voltage inputs are above threshold. this pin has a weak pull-up to v cc and may be pulled above v cc using an external pull-up. gnd (pin 4/pin 1): device ground. (ts8 package/ddb8 package) v adj2 (pin 5/pin 8): adjustable voltage input 2. see table 1 for recommended adj resistors values. v3 (pin 6/pin 7): voltage input 3. v adj1 (pin 7/pin 6): adjustable voltage input 1. see table 1 for recommended adj resistors values. v1 (pin 8/pin 5): voltage input 1. the greater of v1, v2 is also the internal v cc . the operating voltage on this pin shall not exceed 6v. when in normal operation (v1 > v2), this pin draws approximately 21 a. when this pin is not acting as the v cc (v2 > v1), this pin draws approximately 8 a. bypass this pin to ground with a 0.1 f (or greater) capacitor. exposed pad (pin 9, ddb8 only): exposed pad may be left open or connected to device ground.
7 ltc2908 sn2908 2908fs block diagra w C + C + C + C + C + C + power detect v cc v1 c1 c2 c3 c4 c5 c6 v2 v3 v4 v adj1 v adj2 2908 bd gnd bandgap reference v cc ltc2908-a1/ltc2908-b1 200ms reset pulse generator rst 6 a ti i g diagra u ww t uv t rst 1v v rtx v x 2908 td rst v x monitor timing
8 ltc2908 sn2908 2908fs applicatio s i for atio wu uu supply monitoring the ltc2908 is a low power, high accuracy, six input supply monitoring circuit with two adjustable inputs. the reset delay is set to a nominal of 200ms with an internal capacitor, eliminating the need for an external timing capacitor. all input voltages must be above predetermined thresh- olds for the reset not to be invoked. the ltc2908 asserts the reset output during power-up, power-down and brown- out conditions on any one of the voltage inputs. ultralow voltage pull-down on rst the ltc2908 issues a logic low on the rst output when any one of the inputs falls below its threshold. ideally, the rst logic output would remain low with the input supply voltage down to zero volts. most supervisors lack pull- down capability below 1v. the ltc2908 power supply supervisor incorporates a novel low voltage pull-down circuit that can hold the rst line low with as little as 200mv of input supply voltage on v1 and/or v2 (see figures 1 and 2). the pull-down circuit helps maintain a low impedance path to ground, reducing the risk of the rst node from floating to an indeterminate voltage. such an indeterminate voltage may trigger external logic causing erroneous reset operation(s). furthermore, a mid-scale voltage level could cause external circuits to operate in the middle of their voltage transfer character- istic, consuming more quiescent current than normal. these conditions could cause serious system reliability problems. power-up during power-up, rst starts asserting low as soon as there is at least 200mv on v1 and/or v2. the rst pull- down capability is a function of v1 and v2 as shown in the typical performance characteristics. the greater of v1, v2 is the internal supply voltage (v cc ) that powers the other internal circuitry. once all the v x inputs rise above their thresholds, an internal timer is started. after the internal timer counts a 200ms delay time, rst weakly pulls high to v cc . power-down on power-down, once any of the v x inputs drop below their threshold, rst asserts logic low. v cc of at least 0.5v guarantees a logic low of 0.15v at rst. supply voltage, v cc (v) 0.01 rst pull-down current, i rst (ma) 0.1 1 10 0 0.4 0.6 0.8 0.001 0.2 1 2908 g16 v cc = v1 = v2 v3 = v4 = v adj1 = v adj2 = gnd rst at 150mv rst at 50mv supply voltage, v cc (v) 0.01 rst pull-down current, i rst (ma) 0.1 1 10 0 0.4 0.6 0.8 0.001 0.2 1 2908 g17 v cc = v1 v2 = v3 = v4 = v adj1 = v adj2 = gnd rst at 150mv rst at 50mv figure 1. rst pull-down current (i rst ) vs supply voltage (v cc ) with dual channel supply figure 2. rst pull-down current (i rst ) vs supply voltage (v cc ) with single channel supply
9 ltc2908 sn2908 2908fs adjustable input the noninverting input on the v adj comparator is set to 0.5v. and the high impedance inverting input directly ties to the v adj pin. in a typical application, this pin connects to a tap point on an external resistive divider between the positive voltage being monitored and ground. the following formula de- rives the value of the r1 resistor in the divider from a particular value of r2 and the desired trip voltage: r v v trip 1 05 1 = ? ? ? ? ? ? . Cr2 r2 = 100k is recommended. table 1 shows suggested 1% resistor values for various adjustable applications and their corresponding trip thresholds. table 1. suggested 1% resistor values for the v adj inputs v supply (v) v trip (v) r1 (k ? ) r2 (k ? ) 12 11.25 2150 100 10 9.4 1780 100 8 7.5 1400 100 7.5 7 1300 100 6 5.6 1020 100 5 4.725 845 100 3.3 3.055 511 100 3 2.82 464 100 2.5 2.325 365 100 1.8 1.685 237 100 1.5 1.410 182 100 1.2 1.120 124 100 1.0 0.933 86.6 100 0.9 0.840 68.1 100 0.8 0.750 49.9 100 0.7 0.655 30.9 100 0.6 0.561 12.1 100 if an application has less than six supply voltages, the unused supervisor inputs should be tied to the closest higher supply voltage available. applicatio s i for atio wu uu figure 3. setting the adjustable trip point C + + C r1 1% r2 1% 0.5v ltc2908-a1/ltc2908-b1 v adj 2908 f03 v trip threshold accuracy specifying system voltage margin for worst-case operation requires the consideration of three factors: power supply tolerance, ic supply voltage tolerance and supervisor re- set threshold accuracy. highly accurate supervisors ease the design challenge by decreasing the overall voltage margin required for reliable system operation. consider a 5v system with a 5% power supply tolerance band. system ics powered by this supply must operate reliably within this band (and a little more, as explained below). the bottom of the supply tolerance band, at 4.75v (5% below 5v), is the exact voltage at which a perfectly accurate supervisor generates a reset (see figure 4). such a perfectly accurate supervisor does not existthe actual reset threshold may vary over a specified band ( 1.5% for the ltc2908 supervisors). figure 5 shows the typical relative threshold accuracy for all six inputs over temperature. region of potential malfunction with 2.5% monitor minimum reliable system voltage supply tolerance ideal supervisor threshold 5.000v 1.5% threshold band 2.5% threshold band nominal supply voltage 4.750v 4.675v 4.600v 4.500v C5.0% C6.5% C8.0% C10% 2908 f04 figure 4. threshold band diagram
10 ltc2908 sn2908 2908fs with this variation of reset threshold in mind, the nominal reset threshold of the supervisor resides below the minimum supply voltage; just enough so that the reset threshold band and the power supply tolerance bands do not overlap. if the two bands overlap, the supervisor could generate a false or nuisance reset when the power supply remains within its specified tolerance band (for example at 4.8v). adding half of the reset threshold accuracy spread (1.5%) to the ideal 5% thresholds puts the ltc2908 thresholds at 6.5% (typ) below the nominal input voltage. for example, the 5v typical threshold is 4.675v, or 75mv below the ideal threshold of 4.750v. the guaranteed threshold lies in the band between 4.600v (8% below 5v) and 4.750v (5% below 5v) over temperature. the powered system must work reliably down to the lowest voltage in the threshold band or risk malfunction before the reset line falls. in the 5v example, using the 1.5% accurate supervisor, the system ics must work down to 4.60v (8% below 5v). system ics working with a 2.5% accurate supervisor must operate down to 4.50v (10% below 5v), increasing the required system voltage margin and the probability of system malfunction. in any supervisory application, supply noise riding on the monitored dc voltage can cause spurious resets, particu- larly when the monitored voltage is near the reset thresh- old. a less desirable but common solution to this problem is to introduce hysteresis around the nominal threshold. notice however, this hysteresis introduces an error term in the threshold accuracy. therefore, a 2.5% accurate monitor with 1% hysteresis is equivalent to a 3.5% monitor with no hysteresis. therefore, the ltc2908 takes a different approach to solving this problem of supply noise causing spurious reset. the first line of defense against this spurious reset is a first order lowpass filter at the output of the compara- tors. therefore, each comparator output is integrated over time before triggering the output logic. therefore, any kind of transient at the input of the comparator needs to be of sufficient magnitude and duration before it can trigger a change in the output logic. the second line of defense is the 200ms delay time t rst . this delay eliminates the effect of any supply noise, whose frequency is above 1/200ms = 5hz, on the rst output. when any one of the supply voltages drops below its threshold, the rst pin asserts low. when the supply recovers above its threshold, the reset-pulse-generator timer starts counting. if all the supplies remain above their corresponding thresh- old when the timer finishes counting, the rst pin weakly pulls high. however, if any of the supplies falls below its threshold any time during the period when the timer is still counting, the timer resets and it starts fresh when all the supplies rise above their corresponding threshold. note that this second line of defense is only effective for a rising supply and does not affect the sensitivity of the system to a falling supply. therefore, the first line of defense that works for both cases of rising and falling is necessary. these two approaches prevent spurious reset caused by supply noise without sacrificing the threshold accuracy. although all six comparators for the six inputs have built- in glitch filtering, use bypass capacitors on the v1 and v2 inputs because the greater of v1 or v2 supplies the v cc for the part (a 0.1 f ceramic capacitor satisfies most applica- tions). apply filter capacitors on the v3, v4, v adj1 and v adj2 inputs in extremely noisy situations. applicatio s i for atio wu uu figure 5. typical threshold accuracy vs temperature temperature ( c) C50 C1.5 typical threshold accuracy (%) C1.0 C0.5 0 0.5 1.5 C25 02550 2908 f05 75 100 1.0
11 ltc2908 sn2908 2908fs applicatio s i for atio wu uu rst output characteristics the dc characteristics of the rst pull-up and pull-down strength are shown in the typical performance character- istics section. the rst output has a weak internal pull-up to v cc = max(v1, v2) and a strong pull-down to ground. the weak pull-up and strong pull-down arrangement allows this pin to have open-drain behavior while possess- ing several other beneficial characteristics. the weak pull-up eliminates the need for external pull-up resistors when the rise time on these pins is not critical. on the other hand, the open-drain rst configuration allows for wired-or connections and can be useful when more than one signal needs to pull down on the rst line. as noted in the discussion of power-up and power-down, the circuits that drive rst are powered by v cc . during fault condition, v cc of at least 0.5v guarantees a maxi- mum v ol = 0.15v at rst. output rise and fall time estimation the following formula estimates the output fall time (90% to 10%) for a particular external load capacitance (c load ): t fall 2.2 ? r pd ? c load where r pd is the on-resistance of the internal pull-down transistor estimated to be typically 40 ? at room tempera- ture (25 c) and c load is the external load capacitance on the pin. assuming a 150pf load capacitance, the fall time is about 13ns. the rise time on the rst pin is limited by a weak internal pull-up current source to v cc . the following formula esti- mates the output rise time (10% to 90%) at the rst pin: t rise 2.2 ? r pu ? c load where r pu is the on-resistance of the pull-up transistor. notice that this pull-up transistor is modeled as a 6 a current source in the block diagram as a typical representation. the on-resistance as a function of the v cc = max(v1, v2) voltage (for v cc > 1v) at room temperature is estimated as follows: r max v v v pu = () ? 610 12 1 5 ? ,C at v cc = 3.3v, r pu is about 260k. using 150pf for load capacitance, the rise time is 86 s. a smaller external pull- up resistor may be used if the output needs to pull up faster and/or to a higher voltage. for example, the rise time reduces to 3.3 s for a 150pf load capacitance when using a 10k pull-up resistor.
12 ltc2908 sn2908 2908fs typical applicatio s u six supply monitor, 5% tolerance, 12v, 5v, 3.3v, 2.5v, 1.8v, 1v rst r1 2.15m c1 0.1 f c2 0.1 f v1 v2 v3 v4 gnd ltc2908-a1 v adj1 12v 5v 3.3v 2.5v 1.8v 1.0v 2908 ta02 r2 100k dc/dc dc/dc dc/dc dc/dc dc/dc system r3 86.6k v adj2 r4 100k
13 ltc2908 sn2908 2908fs rst c1 0.1 f c2 0.1 f v1 v2 v3 v4 gnd ltc2908-b1 v adj1 3.3v 2.5v 1.8v 1.2v 2908 ta03 dc/dc dc/dc dc/dc system r3 124k v adj2 r4 100k quad supply monitor with one adjustable input, 5% tolerance, 3.3v, 2.5v, 1.8v, 1.2v typical applicatio s u
14 ltc2908 sn2908 2908fs ddb package 8-lead plastic dfn (3mm 2mm) (reference ltc dwg # 05-08-1702) 2.00 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 0.38 0.10 bottom viewexposed pad 0.56 0.05 (2 sides) 0.75 0.05 r = 0.115 typ 2.15 0.05 (2 sides) 3.00 0.10 (2 sides) 1 4 8 5 pin 1 bar top mark (see note 6) 0.200 ref 0 C 0.05 (ddb8) dfn 1103 0.25 0.05 0.50 bsc pin 1 chamfer of exposed pad 0.25 0.05 2.20 0.05 (2 sides) recommended solder pad pitch and dimensions 0.61 0.05 (2 sides) 1.15 0.05 0.675 0.05 2.50 0.05 package outline 0.50 bsc u package descriptio
15 ltc2908 sn2908 2908fs u package descriptio ts8 package 8-lead plastic tsot-23 (reference ltc dwg # 05-08-1637) 1.50 C 1.75 (note 4) 2.80 bsc 0.22 C 0.36 8 plcs (note 3) datum a 0.09 C 0.20 (note 3) ts8 tsot-23 0802 2.90 bsc (note 4) 0.65 bsc 1.95 bsc 0.80 C 0.90 1.00 max 0.01 C 0.10 0.20 bsc 0.30 C 0.50 ref pin one id note: 1. dimensions are in millimeters 2. drawing not to scale 3. dimensions are inclusive of plating 4. dimensions are exclusive of mold flash and metal burr 5. mold flash shall not exceed 0.254mm 6. jedec package reference is mo-193 3.85 max 0.52 max 0.65 ref recommended solder pad layout per ipc calculator 1.4 min 2.62 ref 1.22 ref 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
16 ltc2908 sn2908 2908fs lt/tp 0504 1k ? printed in usa ? linear technology corporation 2004 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com related parts u typical applicatio six supply monitor with manual reset button, 5% tolerance, 12v, 5v, 3.3v, 2.5v, 1.8v, 1.5v part number description comments ltc690 5v supply monitor, watchdog timer and battery backup 4.65 threshold ltc694-3.3 3.3v supply monitor, watchdog timer and battery backup 2.9v threshold ltc699 5v supply monitor and watchdog timer 4.65 threshold ltc1232 5v supply monitor, watchdog timer and pushbutton reset 4.37v/4.62v threshold ltc1326/ltc1326-2.5 micropower precision triple supply monitor for 5v/2.5v, 3.3v 4.725v, 3.118v, 1v threshold ( 0.75%) and adj ltc1536 precision triple supply monitor for pci applications meets pci t fail timing specifications ltc1726-2.5/ltc1726-5 micropower triple supply monitor for 2.5v/5v, 3.3v and adj adjustable reset and watchdog time-outs ltc1727-2.5/ltc1727-5 micropower triple supply monitor with open-drain reset individual monitor outputs in msop ltc1728-1.8/ltc1728-3.3 micropower triple supply monitor with open-drain reset 5-lead sot-23 package ltc1728-2.5/ltc1728-5 micropower triple supply monitor with open-drain reset 5-lead sot-23 package ltc1985-1.8 micropower triple supply monitor with push-pull reset output 5-lead sot-23 package ltc2900 programmable quad supply monitor adjustable reset, 10-lead msop and dfn packages 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 ltc2903 precision quad supply monitor 6-lead sot-23 package ltc2904 three-state programmable precision dual supply monitor adjustable tolerance, 8-lead sot-23 and dfn packages ltc2905 three-state programmable precision dual supply monitor adjustable reset and tolerance, 8-lead sot-23 and dfn packages ltc2906 dual supply monitor with one pin selectable threshold and 0.5v adjustable threshold and three supply one adjustable input tolerances, 8-lead sot-23 and dfn packages ltc2907 dual supply monitor with one pin selectable threshold and 0.5v adjustable threshold, reset and three supply one adjustable input tolerances, 8-lead sot-23 and dfn packages rst r1 182k c1 0.1 f c2 0.1 f v1 v2 v3 v4 gnd ltc2908-a1 v adj1 12v 5v 3.3v 2.5v 1.8v 1.5v 2908 ta04 r2 100k dc/dc dc/dc dc/dc dc/dc dc/dc system manual reset button (normally open) r3 2.15m v adj2 r5 10k r4 100k

▲Up To Search▲

Price & Availability of LTC2908IDDB-B1

	To Download LTC2908IDDB-B1 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .