LTC1998 1 1998f applicatio s u features thinsot is a trademark of linear technology corporation. n lithium-ion battery-powered equipment pdas cell phones handheld instruments battery packs pagers palm top computers pos terminals n high accuracy trip voltage: 1% max error using external 1% resistors n adjustable threshold voltage and hysteresis n quiescent current: 2.5 m a typ n output swings rail-to-rail n thresholds programmable from 2.5v to 3.25v n output state guaranteed for v batt 3 1.5v n low profile (1mm) thinsot tm package 2.5 m a, 1% accurate sot-23 comparator and voltage reference for battery monitoring the ltc ? 1998 is a micropower comparator and a preci- sion adjustable reference in a 6-pin sot-23 package that is optimized for lithium-ion low battery detection circuits. the LTC1998 features a voltage detection circuit with an adjustable threshold voltage and hysteresis. the thresh- old voltage can be programmed from 2.5v to 3.25v with two external resistors. a 10mv to 750mv hysteresis can be added with a third external resistor. a proprietary internal architecture maintains 1% thresh- old voltage accuracy over temperature with low cost 1% external resistors. a separate power supply pin, v logic , allows the battery- low logic output to operate below the battery voltage, allowing compatibility with low voltage microprocessors without a pull-up resistor. power supply glitches are eliminated by preventing the cross-conducting current which occurs when the output changes state. the LTC1998 operates with battery or supply voltages up to 5.5v and its battery-low output is valid for battery voltages above 1.5v. , ltc and lt are registered trademarks of linear technology corporation. threshold voltage error vs temperature descriptio u 1998 bd threshold adjust v hyst.a v th.a batt v logic battlo 1.1r r 1.2v block diagra w temperature ( c) ?5 15 55 1998 g05 ?5 5 35 75 95 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 % error v th.a set by 1% external r, threshold = 3v v th.a = 1v threshold = 3v v th.a shorted to ground, threshold = 2.5v
LTC1998 2 1998f total supply voltage (batt or v logic to gnd) ......... 6v voltage v th.a , v h.a ........................... batt + 0.3v to gnd C 0.3v battlo ........................ v logic + 0.3v to gnd C 0.3v operating temperature range (note 3) ...C40 c to 85 c specified temperature range (note 4) LTC1998c ...........................................C40 c to 85 c LTC1998i .............................................C40 c to 85 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c order part number s6 part marking* t jmax = 150 c, q ja = 250 c/w ltty LTC1998cs6 LTC1998is6 absolute axi u rati gs w ww u package/order i for atio uu w (note 1) electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v gnd = 0v, unless otherwise noted. consult ltc marketing for parts specified with wider operating temperature ranges. 6 battlo 5 v logic 4 v h.a batt 1 top view s6 package 6-lead plastic sot-23 gnd 2 v th.a 3 *the temperature grades are indentified by a label on the shipping container. parameter conditions min typ max units power supply supply voltage range-batt l 1.5 5.5 v supply voltage range-v logic l 1v batt v supply current, v batt = 3v, t a = 25 c 2.5 3.5 m a v th.a = 1.5v LTC1998cs6 l 4.2 m a LTC1998is6 l 4.5 m a supply current, v batt = 5.5v, t a = 25 c 3 4.3 m a v th.a = 1.5v LTC1998cs6 l 5.2 m a LTC1998is6 l 5.5 m a monitor threshold accuracy v batt.th = 2.5v, pin 3 shorted to ground 0.6 0.85 % l 0.8 1 % v batt.th = 3v, pin 3 driven by precision LTC1998c l 0.5 0.61 % voltage source to 1v LTC1998i l 0.6 0.71 % v batt.th = 3v, v th.a = 1v (note 5) LTC1998c l 0.8 1 % programmed with 1% max external resistors LTC1998i l 0.9 1.1 % v batt.th = 3.25v, pin 3 diven by precision LTC1998c l 0.6 0.65 % voltage source to 1.5v LTC1998i l 0.7 0.85 % v batt.th = 3.25v, v th.a = 1.5v (note 5) LTC1998c l 0.9 1.1 % programmed with1% max external resistors LTC1998i l 1 1.3 % hysteresis accuracy v hyst 250mv l C5 5 mv 250mv v hyst 750mv l 5mv allowable hysteresis range (note 2) l 10 750 mv propagation delay c out = 100pf, overdrive = 10mv 350 m s overdrive = 100mv 150 m s threshold adjust pin leakage, i th.a v th.a 1.5v l 0.01 1 na hysteresis adjust pin leakage, i h.a v h.a 1.5v l 0.01 1 na output battlo high voltage i out = C1ma l v logic C 0.3 v battlo low voltage i out = 1ma, v batt 3 2v l 0.2 v battlo low voltage i out = 0.25ma, v batt = 1v l 0.3 v
LTC1998 3 1998f typical perfor a ce characteristics uw threshold adjust voltage (v) 0 threshold voltage (v) 3.5 3.0 2.5 1998 g03 0.5 1.0 1.5 low battery threshold voltage (v) 2.5 available hysteresis (mv) 750 500 250 0 1998 g04 2.75 3.0 3.25 quiescent supply current vs supply voltage quiescent supply current vs temperature threshold voltage vs threshold adjust voltage available hysteresis vs threshold voltage threshold voltage error vs temperature input current vs temperature supply voltage (v) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 supply current ( a) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 1998 g01 t a = 25 c v logic = v batt v th.a = 0v v th.a = 1.5v temperature ( c) 50 ?0 ?0 10 30 50 70 90 supply current ( a) 1998 g02 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 v batt = v logic = 3v v th.a = 1.5v temperature ( c) ?5 15 55 1998 g05 ?5 5 35 75 95 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 % error v th.a set by 1% external r, threshold = 3v v th.a = 1v threshold = 3v v th.a shorted to ground, threshold = 2.5v temperature ( c) 35 0.1 input current v th.a , v h.a (pa) 1 100 1000 10000 55 75 85 125 1998 g06 10 45 65 95 105 115 v in = 1.5v v in = 0.5v v in = 1v note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: maximum allowable hysteresis depends on desired trip voltages. see application notes for details. note 3: LTC1998c and LTC1998i are guaranteed functional over the operating temperature range of C 40 c to 85 c. note 4: the LTC1998c is guaranteed to meet specified performance from 0 c to 70 c. the LTC1998c is designed, characterized and expected to meet specified performance from C40 c to 85 c but is not tested or qa sampled at these temperatures. the LTC1998i is guaranteed to meet specified performance from C40 c to 85 c. note 5: this parameter is not 100% tested. electrical characteristics
LTC1998 4 1998f how to calculate the external resistor values the LTC1998 is a low battery warning indicator and is especially designed for monitoring the voltage of single- cell lithium-ion batteries. the LTC1998 compares its supply pin (batt) to an accurate internal reference; if the battery voltage falls below the programmed low battery quick desig guide u uu u pi fu ctio s batt (pin 1): battery voltage to be monitored. supply current is also drawn from this pin. board layout should connect this pin to the battery(+) terminal, through a trace that does not conduct load current. gnd (pin 2): ground should be connected to the battery (C) terminal through a trace that does not conduct load return current. v th.a (pin 3): threshold adjust pin. adjusts the low battery threshold voltage, v batt.th = 2.5v + (v th.a /2). v th.a can be supplied by a voltage source or a resistor divider. v h.a (pin 4): hysteresis adjust. hysteresis threshold voltage v th2 = 2.5v + (v h.a /2). v h.a can be supplied by a voltage source or resistor divider. v h.a must always be programmed to a higher potential than v th.a . hysteresis voltage, v hyst = v th2 C v batt.th . v logic (pin 5): positive supply voltage for output driver. this voltage can be driven from an external logic supply or tied to batt. battlo (pin 6): output of comparator. low for batt < v batt.th (low battery threshold voltage). output state guaranteed for v batt 3 1.5v. output low voltage vs load current output high voltage vs load current output short-circuit current vs supply voltage output sink current (ma) 1 output voltage (v) 1998 g07 234 5 0.6 0.4 0.2 0 t a = 25 c v logic = v batt = 3v t a = 40 c t a = 85 c t a = 25 c output source current (ma) 1 output voltage relative to v batt (mv) 1998 g08 234 5 0 ?0 ?00 ?50 200 250 t a = 25 c v logic = v batt t a = 85 c t a = 40 c batt = 3v batt = 5v t a = 25 c t a = 40 c t a = 85 c t a = 25 c supply voltage (v) 1.0 1.5 2.5 3.5 4.5 5.5 current (ma) 120 100 80 60 40 20 0 2.0 3.0 4.0 5.0 1998 g09 6.0 source current, battlo shorted to gnd sink current, battlo shorted to v logic t a = 25 c v batt = v logic typical perfor a ce characteristics uw threshold voltage of the LTC1998, the battery low pin (battlo) will change state, from high to low, to indicate a low battery condition. the low battery threshold voltage is programmed via the voltage threshold adjust pin (v th.a ). a hysteresis adjust pin (v h.a ) will add hysteresis to the programmed value of the low battery threshold voltage.
LTC1998 5 1998f 1998 f01 LTC1998 r1 1% r2 1% r3 1% v h.a v th.a batt v logic battlo 4 3 2 1 5 6 regulator p li-ion gnd 0.1 f 1.5v to 4.2v v logic + figure 1. low battery threshold detector with hysteresis example 1: a system using a 4.2v (fully charged) lithium- ion battery requires a low battery threshold of 2.7v, 100mv hysteresis and can allow up to 4.2 m a maximum resistor current. r total = 1m w , r1 = 786k, r2 = 66k and r3 = 148k choose standard 1% values. r1 = 787k, r2 = 66.5k, r3 = 147k quick desig guide u typical application table 1: design equations for r1, r2, r3, figure 1 choose desired values for: ? v batt.th : low battery threshold voltage ? v hyst : hysteresis voltage ? i r : max allowable resistor current solve: rrrr v i rr v vv rr v v r rr rr total r total batt th hyst total batt th total =+ + = = + ? ? ? ? = ? ? ? ? = 12 3 42 1 5 1 2 5 11 312 . . . low battery threshold voltage and hysteresis adjust low battery threshold voltage adjustment, pin 3 the low battery threshold voltage is the battery voltage which will trip the (battlo) pin high to low. it should be adjusted via the threshold adjust pin (v th.a ). this is a high input impedance pin that senses an externally applied voltage and programs the low battery threshold voltage (v batt.th ). the v th.a pin is designed to accommodate voltages from 0v to 1.5v with respect to ground. this allows the low battery threshold voltage to be set to any voltage between 2.5v and 3.25v, that is: vv v batt th th a . . . () =+ 25 2 applicatio s i for atio wu uu for instance, if the applied voltage at pin 3, v th.a , is 1v the LTC1998 will indicate a low battery condition when the battery voltage pin (batt) falls below 3v. the voltage at the threshold adjust pin (v th.a ) can be set with any voltage source. this pin allows a continuous time adjustment, that is, the low battery threshold voltage may be changed at any time. the high input impedance of the v th.a pin allows the use of a high valued resistive divider (to minimize current drain) from the battery to set the battery low threshold voltage, figure 2. figure 2. resistor divider sets threshold 1998 f02 LTC1998 r1 r2 v th.a batt + li-ion 1 2 3
LTC1998 6 1998f figure 3. combined resistor divider 1998 f03 LTC1998 r1 r2 r3 v h.a v th.a batt + li-ion 1 4 3 the simple calculations of resistor values r1 and r2 are illustrated below. set a value for r1 + r2. this value will affect the max amount of current drawn from the battery when fully charged. for instance if r1 + r2 = 1m the resistive divider will draw 4.1 m a when the battery voltage is 4.1v. set the desired value of v batt.th (this value should be between 2.5v and 3.25v) that is the value of the battery voltage that will trip the internal circuitry of the LTC1998 and change the state of the battery low pin (battlo). solve for r r r v v batt th 112 5 1 =+ ? ? ? ? () . example: a lithium-ion battery is monitored and a battery low signal should be issued when it discharges to 2.85v, that is, v batt.th = 2.85v; if (r1 + r2) = 1m, then r1 = 754.38k and r2 = 245.62k. choose the closest 1% value of r1 = 750k and r2 = 243k. calculate the practical value for v batt.th as it will be slightly different from 2.85v, due to the use of standard 1% resistor values. vv rr rrr v batt th . () . = + ++ = 5 12 112 2 849 the above low battery threshold of 2.849v is guaranteed to within 1% even though 1% resistors are used to program the v th.a voltage applied to pin 3. for sake of completeness, the voltage at pin 3 (v th.a ) can be easily calculated by v th.a = v batt.th (r2/(r1 + r2) = 0.6972v (when v battery = v batt.th ). hysteresis adjustment, pin 4. the LTC1998 has an adjustable hysteresis ranging from 10mv to 0.75v. a large hysteresis is useful in the event that a low battery signal at the LTC1998s battlo pin causes the system to shed some battery load, thus induc- ing system confusion as the partially loaded battery recov- ers and changes the status of pin 6 (battlo). the 2.5v to 3.25v programming window of low battery threshold voltage includes the hysteresis. if, for instance, the low battery threshold voltage is set to 2.5v, 750mv hysteresis can be added on top of the 2.5v. if the low battery threshold voltage is set to 3.15v, only 100mv hysteresis can be applied. the programming of the hysteresis threshold adjust pin (v h.a ) is similar to the programming of the voltage thresh- old adjust pin (v th.a ) already described in the previous paragraph. pin 4 effectively adjusts the threshold voltage at which the low battery pin (battlo) changes state from low to high. this threshold (v th2 ) is defined as: vv v th ha 2 25 2 =+ . () . the actual hysteresis voltage is: v hyst = v th2 C v batt.th it is imperative that the hysteresis threshold adjust voltage at pin 4 be set to a higher voltage than the low battery threshold adjust voltage at pin 3, at all times, to avoid oscillation at the battlo output pin. the hysteresis threshold adjust pin may be set with a voltage source or with a resistor divider, just as with the low battery thresh- old adjust pin. combined control of threshold and hysteresis if a resistor divider is desired, then both threshold adjust dividers can be combined in order to save current. this simple technique also guarantees that the hysteresis thresh- old adjust voltage at pin 4 is higher than the voltage at the v th.a pin, figure 3. the calculation of the resistor values r1, r2 and r3 is quite straightforward and similar to the procedure out- lined in the previous paragraph. choose a value for the sum of r1 + r2 + r3 as well as the values for low battery threshold and hysteresis. solve for resistor r1: applicatio s i for atio wu uu
LTC1998 7 1998f figure 4. LTC1998 function plot rrrr v v th 1123 5 1 2 =++ ? ? ? ? () solve for the sum of ()( ) . rr rr r v v batt th 12 12 3 5 1 +=++ ? ? ? ? then solve for r2 and r3. example: a system needs to detect a low battery voltage of 3v (v batt.th = 3v) with 250mv hysteresis (v th2 = 3.25v). set the value of the resistor divider (r1 + r2 + r3) = 1m. r1 = 539k, r1 + r2 = 667k, r2 = 128k, r3 = 333k. choose the closest 1% values, that is 536k, 332k, 127k. figure 4 graphically shows the function of the LTC1998 as described above. versatile output driver v logic , battlo (pins 5,6) the LTC1998 uses a cmos push-pull output stage to drive the low battery output signal. this output pin (battlo) applicatio s i for atio wu uu package descriptio u 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. s6 package 6-lead plastic tsot-23 (reference ltc dwg # 05-08-1636) 1.50 ?1.75 (note 4) 2.80 bsc 0.30 ?0.45 6 plcs (note 3) datum ? 0.09 ?0.20 (note 3)
LTC1998 8 1998f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear.com ? linear technology corporation 2001 lt/tp 0802 2k ? printed in usa related parts part number description comments ltc1440/ltc1540 micropower comparator with 1% reference 1.182v 1% reference, 10mv (max) input offset ltc1441/ltc1442 micropower dual comparator with 1% reference 1.182v 1% reference (ltc1442) ltc1443/ltc1444/ltc1445 micropower quad comparator with 1% reference ltc1443 has 1.182v reference, ltc1444/ltc1445 have 1.221v reference and adjustable hysteresis typical applicatio s u 1998 ta03 4 3 2 1 5 6 3.3v r1 715k 1% r2 9.09k 1% r3 274k 1% out LTC1998 v h.a v th.a batt v logic battlo gnd low threshold = 2.9v hysteresis = 15mv 1998 ta04 4 3 2 1 5 6 r1 787k 1% r4 1m r2 68.1k 1% r3 147k 1% + + 3v backup battery 2.5v to 4.2v bat54c bat54c si2301 si2301 LTC1998 v h.a v th.a batt v logic battlo gnd v out switches to backup battery when primary falls below 2.7v. switches back to primary when voltage recovers to 3 2.8v li-ion mbrm120 1998 ta05 LTC1998 v h.a v th.a batt v logic battlo 4 3 2 1 5 6 gnd r1 787k 1% r2 68.1k 1% r3 147k 1% + si2301 critical circuitry noncritical circuitry low threshold = 2.7v hysteresis = 100mv li-ion regulator 4 3 2 1 5 6 r4 909k 1% r5 6.98k 1% r6 76.8k 1% LTC1998 v h.a v th.a batt v logic battlo gnd 4 3 2 1 5 6 r1 619k 1% r2 6.04k 1% r3 383k 1% LTC1998 v h.a v th.a batt v logic battlo gnd v in nc v + r7 1m 2n7002 window low threshold = 2.6v hysteresis = 10mv window high threshold = 3.1v hysteresis = 10mv 1998 ta06 v out v out = v + when 2.6v v in 3.1v micropower 2.9v v cc threshold detector with 15mv hysteresis low battery load reduction circuit backup battery switchover circuit high accuracy window comparator with dual hysteresis 1998 ta01 LTC1998 r1 1% r2 1% r3 1% v h.a v th.a batt v logic battlo 4 3 2 1 5 6 p li-ion gnd 0.1 f v batt = 1.5v to 4.2v v logic = 1v to 5v + regulator single li-ion cell low battery detector
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