september 29, 2000 1 MIC2774 MIC2774 micrel MIC2774 dual micro-power low voltage supervisor final information general description the MIC2774 is a dual power supply supervisor that provides under-voltage monitoring, manual reset capability, and power- on reset generation in a compact 5-pin sot package. fea- tures include two under-voltage detectors, one fixed and one adjustable, and a choice of reset outputs. one under-voltage detector compares v dd against a fixed threshold. ten fac- tory-programmed thresholds are available. the second, user- adjustable input is compared against a 300mv reference. this low reference voltage allows monitoring voltages lower than those supported by previous supervisor ics. the reset outputs are asserted at power-on and any time either voltage drops below the programmed threshold volt- ages and remains asserted for 140ms (min.) after they subsequently rise back above the threshold boundaries. manual reset functionality can be provided by a switch connected between ground and the /mr input. a wide choice of voltage thresholds provides for a variety of supply voltages and tolerances. hysteresis is included to prevent chattering due to noise. typical supply current is a low 3.5 a. typical application in /rst vdd /mr gnd MIC2774l-23 r1 r2 /reset vcore gnd power_good v core 1.0v manual reset microprocessor vi/o v i/o 2.5v features monitors two independent power supplies for under- voltage conditions one fixed and one user adjustable input choice of factory-programmed thresholds adjustable input can monitor supplies as low as 0.3v generates 140ms (minimum) power-on reset pulse manual reset input choice of active-high, active-low, or open-drain active- low reset outputs inputs may be pulled above v dd (7v abs. max.) open-drain output can be pulled above v dd (7v abs max.) /rst output valid down to 1.2v ultra-low supply current, 3.5 a typical rejects brief input transients ittybitty 5-lead sot-23 package pin compatible upgrade for max6306/09/12 applications monitoring processor asic, or faga core and i/o voltages pdas, hand-held pcs embedded controllers telecommunications systems power supplies wireless / cellular systems networking hardware micrel, inc. ?1849 fortune drive ?san jose, ca 95131 ?usa ?tel + 1 (408) 944-0800 ?fax + 1 (408) 944-0970 ?http://www.mic rel.com ittybitty is a trademark of micrel, inc. ordering information part number marking reset output temperature range package MIC2774n-xxbm5 ugxx open-drain, active-low (/rst) ?0 c to +85 c sot-23-5 MIC2774h-xxbm5 uhxx active-high, complementary (rst) ?0 c to +85 c sot-23-5 MIC2774l-xxbm5 uixx active-low, complementary (/rst) ?0 c to +85 c sot-23-5
MIC2774 micrel MIC2774 2 september 29, 2000 pin configuration rst vdd in /mr 1 3 45 2 gnd sot-23-5 (m5) ??version /rst vdd in /mr 1 3 45 2 gnd sot-23-5 (m5) ??and ??version standard voltage options* voltage typical nominal threshold code application (v dd ) voltage (v th ) 46 5.0v 5% 4.68 44 5.0v 10% 4.43 31 3.3v 5% 3.09 29 3.3v 10% 2.93 28 3.0v 5% 2.81 26 2.85v 5% 2.67 25 2.70v 5% 2.53 23 2.5v 5% 2.34 22 2.4v 5% 2.25 17 1.8v 5% 1.69 *there are ten standard versions available with an order increment of 3000 pieces. samples of standard versions are normally available from stock. contact factory for information on non-standard versions. available in tape-and-reel only. pin description pin number pin number pin name pin function MIC2774h MIC2774l MIC2774n 1 rst digital (output): asserted high whenever v in or v dd falls below the thresh- old voltage. it will remain asserted for no less than 140ms after v in and v dd return above the threshold limits. 1 /rst digital (output): asserted low whenever v in or v dd falls below the threshold voltage. it will remain asserted for no less than 140ms after v in and v dd return above the threshold limits. (open-drain for n version) 2 2 gnd ground 3 3 /mr digital (input): driving this pin low initiates immediate and unconditional reset. assuming v in and v dd are above the thresholds when /mr is released (returns high), the reset output will be de-asserted no less than 140ms later. /mr may be driven by a logic signal or a mechanical switch. /mr has an internal pull-up to v dd and may be left open if unused. 4 4 in analog (input): the voltage on this pin is compared to the internal 300mv reference. an under-voltage condition will trigger a reset sequence. 5 5 vdd analog (input): power supply input for internal circuitry and input to the fixed voltage monitor. the voltage on this pin is compared against the internal reference. an undervoltage condition will trigger a reset sequence.
september 29, 2000 3 MIC2774 MIC2774 micrel absolute maximum ratings (note 1) supply voltage (v dd ) ..................................... 0.3v to +7v input voltages (v in , v /mr ) .............................. 0.3v to +7v output voltages (v /rst , v rst ) ....................... 0.3v to +7v rst, (/rst) current .................................................. 20ma storage temperature (t s ) ....................... 65 c to +150 c esd rating, note 3 ................................................... 1.5kv operating ratings (note 2) supply voltage (v dd ) .................................. +1.5v to +5.5v input voltages (v in , v /mr ) ........................... 0.3v to +6.0v output voltages v /rst (n version), .................................... 0.3v to +6.0v v /rst , v rst (h and l versions) ......... 0.3v to v dd +0.3v ambient temperature range (t a ) ............. 40 c to +85 c package thermal resistance ( ja ) ...................... 256 c/w electrical characteristics note 5 ; t a = +25 c, bold values indicate 40 c t a +85 c; unless noted symbol parameter condition min typ max units i dd supply current v dd = v in = v th +1.6%, 3.5 a note 5 ; /mr, rst, /rst open vdd voltage threshold under-voltage threshold on v dd v th ?.5% v th v th +1.5% v (see standard voltage options table) v hyst hysteresis voltage 1% in, under-voltage detector input v ref under-voltage threshold note 5 295 300 305 mv v hyst hysteresis voltage 3mv i in input current 5pa t min t a t max 10 na rst, /rst outputs t prop propagation delay v in = (v ref(max) + 100mv) to 20 s v in = (v ref(min) 100mv), /mr = open; t rst reset pulse width t min t a t max 140 280 ms v ol rst or /rst output voltage low i sink = 1.6ma; 0.3 v v dd 1.6v i sink = 100 a; 0.3 v v dd 1.2v; note 4 v oh rst or /rst output voltage high i source = 500 a; 0.8v dd v v dd 1.5v (h and l version only) i source = 10 a; 0.8v dd v v dd 1.2v; note 4 /mr inputs v ih input high voltage note 5 0.7v dd v v il input low voltage note 5 0.3v dd v t prop propagation delay v /mr < (v il 100mv); note 5 5 s t min minimum input pulse width reset occurs, v /mr < v il 33 ns i pu internal pull-up current 100 na i in input current, /mr v /mr < v il 100 na 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 100pf. note 4. v dd operating range is 1.5v to 5.5v. output is guaranteed to be asserted down to v dd = 1.2v. note 5. v dd equals nominal typical application (v dd ) as shown in standard voltage options table.
MIC2774 micrel MIC2774 4 september 29, 2000 timing diagram v /mr v ih v il v in 0v v th v dd 0v v /rst (active low) v oh v ol v rst (active high) v oh v ol t rst t rst > t min t rst v hyst a a a v ref v hyst propagation delays not shown for clarity. note a. the MIC2774 ignores very brief transients. see applications information for details.
september 29, 2000 5 MIC2774 MIC2774 micrel functional diagram gnd v dd /mr in MIC2774 * pinout and polarity vary by device type. see ordering information table. v ref v v dd ref rst* r s q /q /rst* delay line one shot i pu functional description in, under-voltage detector input the voltage present at the in pin is compared to the internal 300mv reference voltage. a reset is triggered if and when v in falls below v ref . typically, a resistor divider is used to scale the input voltage to be monitored such that v in will fall below v ref as the voltage being monitored falls below the desired trip-point. hysteresis is employed to prevent chattering due to noise. the comparator on the in pin is relatively immune to very brief negative-going transients. v dd input the v dd pin is both the power supply terminal and a moni- tored input voltage. the voltage at this pin is continually compared against the internal reference. the trip-point at which a reset occurs is factory programmed. a reset is triggered if and when v dd falls below the trip-point. hyster- esis is employed to prevent chattering due to noise. the comparator on the v dd input is relatively immune to very brief negative-going transients. rst, /rst reset output typically, the MIC2774 is used to monitor the power supplies of intelligent circuits such as microcontrollers and micropro- cessors. by connecting the appropriate reset output of a MIC2774 to the reset input of a c or p, the processor will be properly reset at power-on and during power-down and brown-out conditions. in addition, asserting /mr, the manual reset input, will activate the reset function. the reset output is asserted any time /mr is asserted or if v in or v dd drops below the corresponding threshold voltage. the reset output remains asserted for t rst (min) after v in and/or v dd subsequently return above the threshold boundaries and/or /mr is released. a reset pulse is also generated at power-on. hysteresis is included in the comparators to pre- vent chattering of the output due to noise. /mr, manual reset input the ability to initiate a reset via external logic or a manual switch is provided in addition to the MIC2774 s automatic supervisory functions. driving the /mr input to a logic low causes an immediate and unconditional reset to occur. assuming v in and v dd are within tolerance when /mr is released (returns high), the reset output will be de-asserted no less than t rst later. /mr may be driven by a logic signal, or mechanical switch. typically, a momentary push-button switch is connected such that /mr is shorted to ground when the switch contacts close. switch de-bouncing is performed internally; the switch may be connected directly between /mr and gnd. /mr is internally pulled-up to v dd and may be left open if unused.
MIC2774 micrel MIC2774 6 september 29, 2000 application information programming the voltage threshold referring to the typical application circuit , the voltage threshold on the in pin is calculated as follows: vv r1 r2 r2 th ref = + () where v ref = 0.300v in order to provide the additional criteria needed to solve for the resistor values, the resistors can be selected such that the two resistors have a given total value, that is, r1 + r2 = r total . imposing this condition on the resistor values pro- vides two equations that can be solved for the two unknown resistor values. a value such as 1m ? for r total is a reasonable choice since it keeps quiescent current to a generally acceptable level while not causing any measurable errors due to input bias currents. the larger the resistors, the larger the potential errors due to input bias current (i in ). the maximum recommended value of r total is 3m ? . applying this criteria and rearranging the v th expression to solve for the resistor values gives: r2 rv v total ref th = () () r1 r r2 total =? application example figure 1 below illustrates a hypothetical MIC2774l-23 appli- cation in which the MIC2774l-23 is used to monitor the core and i/o supplies of a high-performance cpu or dsp. the core supply, v core , in the example is 1.0v 5%. the main power rail and i/o voltage, v i/o , is 2.5v 5%. as shown in figure 1, the MIC2774 is powered by v i/o . the minimum value of v i/o is 2.5v 5% = 2.375v; the maximum is 2.5v +5% = 2.625v. this is well within the device s supply range of 1.5v to 5.5v. resistors r1 and r2 must be selected to correspond to the v core supply of 1.0v. the goal is to insure that the core supply voltage is adequate to insure proper operation, i.e., v core (1.0v 5%) = 0.950v. because there is always a small degree of uncertainty due to the accuracy of the resistors, variations in the devices voltage reference, etc., the threshold will be set slightly below this value. the poten- tial variation in the MIC2774 s voltage reference (v ref ) is specified as 1.5%. the resistors chosen will have their own tolerance specification. this example will assume the use of 1% accurate resistors. the potential worst-case error contri- bution due to input bias current can be calculated once the resistor values are chosen. if the guidelines above regarding the maximum total value of r1+r2 are followed, this error contribution will be very small thanks to the MIC2774 s very low input bias current. to summarize, the various potential error sources are: variation in v ref : specified at 1.5% resistor tolerance: chosen by designer (typically 1%) input bias current, i in : calculated once resistor values are known, typically very small taking the various potential error sources into account, the threshold voltage will be set slightly below the minimum v core specification of 0.950v so that when the actual thresh- old voltage is at its maximum, it will not intrude into the normal operating range of v core . the target threshold voltage will be set as follows: given that the total tolerance on v th for the in pin is [v ref tolerance] + [resistor tolerance] = 1.5% + 1% = 2.5%, and v th(max) = v core(min) , then v core(min) = v th + 2.5% v th = 1.025 v th , therefore, solving for v th results in v= v 1.025 = 0.950 1.025 = 0.9268v th core(min) solving for r1 and r2 using this value for v th and the equations above yields: r1 = 676.3k ? 673k ? r2 = 323.7k ? 324k ? the resulting circuit is shown in figure 1. input bias current effects now that the resistor values are known, it is possible to calculate the maximum potential error due to input bias current, i in . as shown in the electrical characteristics table, the maximum value of i in is 10na. (note that the typical value is a much smaller 5pa!) the magnitude of the offset caused by i in is given by: v i r1|| r2 error in(max) = () = v 1 10 a 2.189 10 = error 5 = ? 8 ? v 2.189 10 v = error 3 = ? v 2.189mv error = the typical error is about three orders of magnitude lower than this - close to one microvolt ! generally, the error due to input bias can be discounted. if it is to be taken into account, simply adjust the target threshold voltage downward by this amount and recalculate r1 and r2. the resulting value will be very close to optimum. if accuracy is more important than the quiescent current in the resistors, simply reduce the value of r total to minimize offset errors.
september 29, 2000 7 MIC2774 MIC2774 micrel in /rst vdd /mr gnd MIC2774l-23 r1 676k 1% r2 324k 1% /reset vcore gnd v core 1.0v 5% manual reset microprocessor vi/o v i/o 2.5v 5% figure 1. MIC2774 example design interfacing to processors with bidirectional reset pins some microprocessors have reset signal pins that are bidi- rectional, rather than input only. the motorola 68hc11 family is one example. because the MIC2774n s output is open- drain, it can be connected directly to the processor s reset pin using only the pull-up resistor normally required. see figure 2. in /rst vdd /mr gnd MIC2774n-xx r1 r2 /reset vcc gnd v cc microprocessor 100k figure 2. interfacing to bidirectional reset pin transient response the MIC2774 is inherently immune to very short negative- going glitches. very brief transients may exceed the voltage thresholds without tripping the output. as shown in figure 3a and 3b, in general the narrower the transient, the deeper the threshold overdrive that will be ignored by the MIC2774. the graphs represent the typical allowable transient duration for a given amount of threshold overdrive that will not generate a reset. 0 5 10 15 20 25 30 35 40 0 100 200 300 max. transient duration ( s) reset comp. overdrive, v ref v in (mv) typical in transient response figure 3a. typical input transient response 0 20 40 60 80 100 0 500 1000 1500 2000 max. transient duration ( s) reset comp. overdrive, v ref v dd (mv) typical v dd transient response figure 3b. typical v dd transient response ensuring proper operation at low supply at levels of v dd below 1.2v, the MIC2774 s reset output cannot turn on sufficiently to produce a valid logic-low on /rst. in this situation, circuits driven by /rst could be allowed to float, causing undesired operation. (in most cases, however, it is expected that the circuits driven by the MIC2774l will be similarly inoperative at v dd 1.2v.) if a given application requires that /rst be valid below v dd = 1.2v, this can be accomplished by adding a pull-down resistor to the /rst output. a value of 100k ? is recom- mended as this is usually an acceptable compromise of quiescent current and pull-down current. the resistor s value is not critical, however. see figure 4. the statements above also apply to the MIC2774h s rst output. that is, to ensure valid rst signal levels at v dd < 1.2v, a pull-up resistor (as opposed to a pull-down) should be added to the rst output. a value of 100k ? is typical for this application as well. see figure 5. in /rst vdd /mr gnd MIC2774l-xx r1 r2 /reset vcc gnd v cc manual reset microprocessor 100k rpull-down figure 4. MIC2774l valid /rst below 1.2v in rst vdd /mr gnd MIC2774h-xx r1 r2 reset vcc gnd v cc manual reset microprocessor 100k rpull-up figure 5. MIC2774h valid rst below 1.2v
MIC2774 micrel MIC2774 8 september 29, 2000 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 sot-23-5 (m5) micrel inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 web http://www.micrel.com this information is believed to be accurate and reliable, however no responsibility is assumed by micrel for its use nor for an y infringement of patents or other rights of third parties resulting from its use. no license is granted by implication or otherwise under any patent or pat ent right of micrel inc. ? 2000 micrel incorporated
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