january 2006 1 mic2779 mic2779 micrel, inc. mic2779 voltage monitor with adjustable hysteresis general description the mic2779 is a voltage monitoruniquely designed to detect two separate voltage thresholdscombined with a delay generator and logic. it is designed for monitoring the battery supply of portable digital systems, particularly pdas, pagers, and cellular telephones. high- and low-voltage thresholds can be adjusted inde- pendently, allowing for wide hysteresis. voltage detection thresholds are accurate to 2%. if the battery voltage falls below the low-voltage threshold, the output /rst or rst is asserted and latched, preventing system operation until the battery is replaced or recharged. internal logic prevents the output from chattering due to battery recovery or load removal. the output is asserted for 140ms (minimum) when a fresh battery is inserted. for applications requiring open-drain output, see mic2778/mic833. the ics power supply input is separate from the detector inputs, allowing the mic2779 to be powered from a down- stream supply, such a boost converter. supply current is extremely low (1a, typical), making it ideal for portable applications. a high-precision 1% grade is available. the mic2779 is sup- plied in micrels ittybitty? 5-pin sot-23-5 package. typical application hth / r s t vdd lth gnd mic2779l 604k 1% 56k 1% 340k 1% e n out in b y p gnd mic5207-3.0bm5 li-ion cell 470pf v ou t 3.0v 4.7f v bat(hi) = 3.6v v bat(lo) = 3.1v cellular telephone battery monitor features ? optimized for pdas, cellular telephones, pagers, and other battery-powered devices ? independently adjustable high- and low-voltage thresholds ? internal logic prevents battery-voltage-?uctuation chatter ? high 2% voltage threshold accuracy; 1% available ? built in 140ms (minimum) delay deglitches output ? extremely low 1a typical supply current ? for applications requiring open-drain output, see mic2778/mic833 ? immune to brief power supply transients ? 5-pin sot-23 package applications ? pdas ? pagers ? cordless phones ? consumer electronics ? embedded controllers ? personal electronics micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408 ) 474-1000 ? http://www.micrel.com ittybitty? is a trademark of micrel, inc. downloaded from: http:///
mic2779 micrel, inc. mic2779 2 january 2006 pin con?guration hth vdd rst lth 1 3 4 5 2 gnd sot-23-5 (m5) h version ordering information part number output polarity accuracy temperature range package standard marking pb-free marking mic2779h-2bm5 upa2 mic2779h-2ym5 upa2 active-high rst 2% C40oc to +85oc sot-23-5 mic2779h-1bm5 upa1 mic2779h-1ym5 upa1 active-high rst 1% C40oc to +85oc sot-23-5 mic2779l-2bm5 upb2 mic2779l-2ym5 upb2 active-low /rst 2% C40oc to +85oc sot-23-5 mic2779l-1bm5 upb1 mic2779l-1ym5 upb1 active-low /rst 1% C40oc to +85oc sot-23-5 hth vdd /rst lth 1 3 4 5 2 gnd sot-23-5 (m5) l version pin description pin number pin number pin name pin function mic2779h mic2779l 1 1 hth high-voltage theshold (input): analog input to a comparator. when the level on this pin initially rises above v ref , the delay generator cycles and the /rst remains low or rst remains high for a minimum of 140ms. 2 2 gnd ground 3 3 lth low-voltage threshold (input): analog input to a comparator. this is the voltage monitor input assigned to detect a low voltage condition. when the level on this pin falls below v ref , /rst or rst is asserted and the condition is latched until v hth > v ref . 4 rst reset (output): push-pull output. this output is asserted and latched when v lth v ref . the polarity of this signal (active-high or low) is deter mined by the part number suf?x. see ordering information. 4 /rst reset (output): push-pull output. this output is asserted and latched when v lth v ref . the polarity of this signal (active-high or low) is deter mined by the part number suf?x. see ordering information. 5 5 vdd power supply (input): independent supply input for internal circuitry. downloaded from: http:///
january 2006 3 mic2779 mic2779 micrel, inc. absolute maximum ratings (note 1) supply voltage (v dd ) .......................................C0.3v to +7v input voltages (v lth , v hth , v /rst , v rst ) ........C0.3v to +7v /rst, rst output current (i /rst ), (i rst ) .................... 20ma storage temperature (t s ) ........................ C65c to +150c esd rating, note 3 ....................................................... 2kv operating ratings (note 2) supply voltage (v dd ) .................................. +1.5v to +5.5v input voltages (v lth , v hth , v /rst , v rst ) .....C0.3v to +6.0v ambient temperature range (t a ) .............. C40c to +85c package thermal resistance ................................ 256c/w electrical characteristics1.5v v dd 5.5v; t a = +25c, bold values indicate C40c t a +85c; unless noted symbol parameter condition min typ max units i dd supply current /rst, rst not asserted 1 2 a i lth, i hth input leakage current 5 pa 10 na v ref reference voltage 1.240 v mic2779h/l-2 1.215 1.265 v mic2779h/l-1 1.228 1.252 v t d propagation delay v lth = v ref(max) +100mv to 5 s v ref(min) C 100mv t reset reset pulse width 140 420 ms v ol reset output low voltage /rst asserted or rst not asserted, i sink = 1.6ma, v dd 1.6v 0.3 v /rst asserted or rst not asserted, i sink = 100a, v dd 1.2v, 0.4 v v oh reset output high voltage /rst not asserted or rst asserted, i source = 500a, v dd 1.6v 0.8v dd v /rst not asserted or rst asserted, i source = 50a, v dd 1.2v, 0.8v dd v note 1. exceeding the absolute maximum rating may damage the device. note 2. the device is not guaranteed to function outside its operating rating. note 3. devices are esd sensitive. handling precautions recommended. human body model, 1.5k in series with 1 00pf. note 4. v dd operating range is 1.5v to 5.5v. output is guaranteed to be held low down to v dd = 1.2v. timing diagram v hth v batt v lth 0v v oh v ol t rst t rst a a v /rst v oh v ol v rst propagation delays not shown for clarity. note a. the mic2779 ignores very brief transients. see applications information for details. downloaded from: http:///
mic2779 micrel, inc. mic2779 4 january 2006 functional description the mic2779 monitors the voltage of a battery and detects when it is discharged below a programmed level. upon be- ing replaced, or being recharged above a second higher programmed trip point, the output remains low (mic2779l) or high (mic2779h) for a minimum of 140ms and then sends a reset signal to a microprocessor or other downstream component. see timing diagram. /rst, rst low output the output is a push-pull logic signal which is asserted when the mic2779 detects a low input voltage. the mic2779ls /rst output is active-low; the mic2779hs rst output is active-high. functional diagram gnd v batt r s t * 1.24v bandgap reference low-voltage detect high-voltage detect r s q q delay line lth hth v lo v hi mic2779 v dd * pinout and polarity vary by device type. see ordering information table. /rst* one shot trip points battery voltage is monitored by a comparator via a voltage divider network. the divided voltage is compared to an in- ternal reference voltage. when the voltage at the lth input pin drops below the internal reference voltage, the output is asserted. at this point, the voltage at hth is assumed to be below the reference voltage. delay at power-on or when the battery is replaced or recharged, and the voltage at hth exceeds the reference voltage, the output is deasserted after a minimum delay of 140ms. downloaded from: http:///
january 2006 5 mic2779 mic2779 micrel, inc. applications informationprogramming the thresholds the low-voltage threshold is calculated using: v v r1 r2 r3 r2 r3 bat(lo) ref = + + + ?? ? ?? ? the high-voltage threshold is calculated using: v v r1 r2 r3 r3 bat(hi) ref = + + ?? ? ?? ? where, for both equations: v 1.240v ref = in order to provide the additional criteria needed to solve for the resistor values, the resistors can be selected such that they have a given total value, that is, r1 + r2 + r3 = r total . a value such as 1m for r total is a reasonable value because it draws minimum battery current but has no measurable effect on accuracy. when working with large resistors, a small amount of leak- age current can cause voltage offsets that degrade system accuracy. the maximum recommended total resistance from v bat to ground is 3m. hth / r s t vdd lth gnd mic2779 604k 1% 56k 1% 340k 1% v batt r 1 r 2 r 3 r st figure 1. example circuit once the desired trip points are determined, set the v bat(hi) threshold ?rst. for example, use a total of 1m = r1 + r2 + r3. for a typical single-cell lithium ion battery, 3.6v is a good high threshold because at 3.6v the battery is moderately charged. solving for r3: v 1.24 1m r3 bat(hi) = ? ?? ? ?? ? r3 344k = ? once r3 is determined, the equation for v bat(lo) can be used to determine r2. a single lithium-ion cell should not be discharged below 2.5v. many applications limit the drain to 3.1v. using 3.1v for the v bat(lo) threshold allows calculation of the two remaining resistor values. v 3.1v 1.24 1m r2 344k bat(lo) = = ? + ?? ? ?? ? r2 56k = ? r1 1m r2 r3 = ? ? ? r1 600k = ? the accuracy of the resistors can be chosen based upon the accuracy required by the system. input transients the mic2779 is inherently immune to very short negative- going glitches. very brief transients may exceed the v bat(lo) threshold without tripping the output. as shown in figure 2, the narrower the transient, the deeper the threshold overdrive that will be ignored by the mic2779. the graph represents the typical allowable transient dura- tion for a given amount of threshold overdrive that will not generate a reset. 0 20 40 60 80 100 120 140 1 10 100 1000 max. transient duration (s) reset comp. overdrive, v ref Cv lth (mv) input transient response figure 2. input transient response downloaded from: http:///
mic2779 micrel, inc. mic2779 6 january 2006 package information 0.20 (0.008)0.09 (0.004) 0.60 (0.024)0.10 (0.004) 3.02 (0.119)2.80 (0.110) 10 0 3.00 (0.118)2.60 (0.102) 1.75 (0.069)1.50 (0.059) 0.95 (0.037) ref 1.30 (0.051)0.90 (0.035) 0.15 (0.006)0.00 (0.000) dimensions: mm (inch) 0.50 (0.020)0.35 (0.014) 1.90 (0.075) ref 5-pin sot-23 (m5) micrel inc. 2180 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 web http://www.micrel.com this information furnished by micrel in this data sheet is believed to be accurate and reliable. however no responsibility is assumed by micrel for its use. micrel reserves the right to change circuitry and speci?cations at any time without noti?cation to t he customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a signi?cant injury to the user. a purchaser's use or sale of micrel products for use in life support appliances, devices or systems is a purchaser's own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2000 micrel, inc. downloaded from: http:///
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