View MIC2571-2BMM_3375410.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1997 1 mic2571 mic2571 micrel mic2571 single-cell switching regulator final information general description micrel? mic2571 is a micropower boost switching regulator that operates from one alkaline, nickel-metal-hydride cell, or lithium cell. the mic2571 accepts a positive input voltage between 0.9v and 15v. its typical no-load supply current is 120 a. the mic2571 is available in selectable fixed output or adjust- able output versions. the mic2571-1 can be configured for 2.85v, 3.3v, or 5v by connecting one of three separate feedback pins to the output. the mic2571-2 can be config- ured for an output voltage ranging between its input voltage and 36v, using an external resistor network. the mic2571 has a fixed switching frequency of 20khz. an external sync connection allows the switching frequency to be synchronized to an external signal. the mic2571 requires only four components (diode, induc- tor, input capacitor and output capacitor) to implement a boost regulator. a complete regulator can be constructed in a 0.3 in 2 area. all versions are available in an 8-lead msop with an operat- ing range from ?0 c to +85 . typical applications features operates from a single-cell supply 0.9v to 15v operation 120 a typical quiescent current complete regulator fits 0.3 in 2 area 2.85v/3.3v/5v selectable output voltage (mic2571-1) adjustable output up to 36v (mic2571-2) 1a current limited pass element frequency synchronization input 8-lead msop package applications pagers lcd bias generator battery-powered, hand-held instruments palmtop computers remote controls detectors battery backup supplies single-cell to 5v dc-to-dc converter in sw gnd mic2571-1 c2 47f 16v 5v/5ma c1* 47f 16v 1v to1.5v 1 cell 2.85v 3.3v 5v 2 4 5 6 1 7 8 l1 150h sync d1 mbr0530 * needed if battery is 4" from mic2571 circuit size < 0.3 in 2 excluding c1 single-cell to 3.3v dc-to-dc converter in sw gnd mic2571-1 c2 47f 16v 3.3v/8ma c1* 47f 16v 1v to1.5v 1 cell 2.85v 3.3v 5v 2 4 5 6 1 7 8 l1 150h sync d1 mbr0530 * needed if battery is 4" from mic2571 circuit size < 0.3 in 2 excluding c1 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
mic2571 micrel mic2571 2 1997 ordering information part number temperature range voltage frequency package mic2571-1bmm 40 c to +85 c selectable* 20khz 8-lead msop MIC2571-2BMM 40 c to +85 c adjustable 20khz 8-lead msop * externally selectable for 2.85v, 3.3v, or 5v pin configuration 1 2 3 4 8 7 6 5 sw gnd nc 5v in sync 2.85v 3.3v mic2571-1 selectable voltage 20khz frequency 1 2 3 4 8 7 6 5 in sync fb nc sw gnd nc nc mic2571-2 adjustable voltage 20khz frequency 8-lead msop (mm) pin description pin no. (version ? ) pin name pin function 1 sw switch: npn output switch transistor collector. 2 gnd power ground: npn output switch transistor emitter. 3 nc not internally connected. 4 (-1) 5v 5v feedback (input): fixed 5v feedback to internal resistive divider. 4 (-2) nc not internally connected. 5 (-1) 3.3v 3.3v feedback (input): fixed 3.3v feedback to internal resistive divider. 5 (-2) nc not internally connected. 6 (-1) 2.85v 2.85v feedback (input): fixed 2.85v feedback to internal resistive divider. 6 (-2) fb feedback (input): 0.22v feedback from external voltage divider network. 7 sync synchronization (input): oscillator start timing. oscillator synchronizes to falling edge of sync signal. 8 in supply (input): positive supply voltage input. ? example: (-1) indicates the pin description is applicable to the mic2571 -1 only.
199 7 3 mic2571 mic2571 micrel electrical characteristics v in = 1.5v; t a = 25 c, bold indicates C 40 c t a 85 c; unless noted paramete r conditio n mi n ty p ma x units input voltag e startup guaranteed, i sw = 100ma 15 v 0. 9 v 2.7 3.14 4.75 3.0 3.47 5.25 208 232 quiescent curren t output switch of f 120 a fixed feedback voltag e mic2571-1; v 2.85v pin = v out , i sw = 100m a 2.8 5 v mic2571-1; v 3.3v pin = v out , i sw = 100m a 3.3 0 v mic2571-1; v 5v pin = v out , i sw = 100m a 5.0 0 v reference voltag e mic2571-2, [adj. voltage versions], i sw = 100ma, note 1 22 0 mv comparator hysteresi s mic2571-2, [adj. voltage versions ] 6 mv output hysteresi s mic2571-1; v 2.85v pin = v out , i sw = 100m a 6 5 mv mic2571-1; v 3.3v pin = v out , i sw = 100m a 7 5 mv mic2571-1; v 5v pin = v out , i sw = 100m a 12 0 mv feedback curren t mic2571-1; v 2.85v pin = v out 4.5 a mic2571-1; v 3.3v pin = v out 4.5 a mic2571-1; v 5v pin = v out 4.5 a mic2571-2, [adj. voltage versions]; v fb = 0 v 2 5 na reference line regulatio n 1.0v v in 12 v 0.3 5 %/v switch saturation voltag e v in = 1.0v, i sw = 200m a 20 0 mv v in = 1.2v, i sw = 600m a 40 0 mv v in = 1.5v, i sw = 800m a 50 0 mv switch leakage curren t output switch off, v sw = 36 v 1 a oscillator frequenc y mic2571-1, -2; i sw = 100m a 2 0 khz maximum output voltage 3 6 v sync threshold voltage 0. 7 v switch on time 35 s currrent limit 1. 1 a duty cycl e v fb < v ref , i sw = 100m a 6 7 % general note: devices are esd protected; however, handling precautions are recommended. note 1: measured using comparator trip point. absolute maximum ratings supply voltage (v in ) .................................................... . 18v switch voltage (v sw ) ................................................... . 36v switch current (i sw ) ...................................................... . 1a sync voltage (v sync ) .................................... C 0.3v to 15v storage temperature (t a ) ....................... C 65 c to +150 c msop power dissipation (p d ) ............................... . 250mw operating ratings supply voltage (v in ) ................................... . +0.9v to +15v ambient operating temperature (t a ) ........ C 40 c to +85 c junction temperature (t j ) ....................... C 40 c to +125 c msop thermal resistance ( ja ) ......................... . 240 c/w
mic2571 micrel mic2571 4 1997 typical characteristics 0 0.2 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 1.0 switch current (a) switch voltage (v) switch saturation voltage t a = 40 c 1.4v 1.3v 1.1v 1.2v v in = 1.0v 0 0.2 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 1.0 switch current (a) switch voltage (v) switch saturation voltage t a = 25 c v in = 0.9v 1.0v 1.1v 1.2v 1.3v 1.4v 0 0.2 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 1.0 switch current (a) switch voltage (v) switch saturation voltage t a = 85 c 1.2v 1.0v 1.1v v in = 0.9v 1.4v 1.3v 15 20 25 30 -60 -30 0 30 60 90 120 150 osc. frequency (khz) temperature ( c) oscillator frequency vs. temperature v in = 1.5v i sw = 100ma 50 55 60 65 70 75 -60 -30 0 30 60 90 120 150 duty cycle (%) temperature ( c) oscillator duty cycle vs. temperature v in = 1.5v i sw = 100ma 50 75 100 125 150 175 200 -60 -30 0 30 60 90 120 150 quiescent current ( a) temperature ( c) quiescent current vs. temperature v in = 1.5v 0 2 4 6 8 10 -60 -30 0 30 60 90 120 150 feedback current ( a) temperature ( c) feedback current vs. temperature v in = 1.5v mic2571-1 0 10 20 30 40 50 -60 -30 0 30 60 90 120 150 feedback current (na) temperature ( c) feedback current vs. temperature v in = 2.5v mic2571-2 0 25 50 75 100 125 150 175 200 0246810 quiescent current ( a) supply voltage (v) quiescent current vs. supply voltage 40 c +85 c +25 c 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 -60 -30 0 30 60 90 120 150 current limit (a) temperature ( c) output current limit vs. temperature 0.01 0.1 1 10 100 1000 -60 -30 0 30 60 90 120 150 switch leakage current (na) temperature ( c) switch leakage current vs. temperature 0 25 50 75 100 125 150 -60 -30 0 30 60 90 120 150 output hysteresis (mv) temperature ( c) output hysteresis vs. temperature v out = 2.85v 3.3v 5v
1997 5 mic2571 mic2571 micrel block diagrams oscillator 0.22v reference driver in v batt 2.85v gnd sw sync 3.3v 5v v out mic2571-1 selectable voltage version with external components oscillator 0.22v reference driver in v batt gnd sw sync mic2571-2 v out fb adjustable voltage version with external components
mic2571 micrel mic2571 6 1997 functional description the mic2571 switch-mode power supply (smps) is a gated oscillator architecture designed to operate from an input voltage as low as 0.9v and provide a high-efficiency fixed or adjustable regulated output voltage. one advantage of this architecture is that the output switch is disabled whenever the output voltage is above the feedback comparator threshold thereby greatly reducing quiescent current and improving efficiency, especially at low output currents. refer to the block diagrams for the following discription of typical gated oscillator boost regulator function. the bandgap reference provides a constant 0.22v over a wide range of input voltage and junction temperature. the comparator senses the output voltage through an internal or external resistor divider and compares it to the bandgap reference voltage. when the voltage at the inverting input of the comparator is below 0.22v, the comparator output is high and the output of the oscillator is allowed to pass through the and gate to the output driver and output switch. the output switch then turns on and off storing energy in the inductor. when the output switch is on (low) energy is stored in the inductor; when the switch is off (high) the stored energy is dumped into the output capacitor which causes the output voltage to rise. when the output voltage is high enough to cause the com- parator output to be low (inverting input voltage is above 0.22v) the and gate is disabled and the output switch remains off (high). the output switch remains disabled until the output voltage falls low enough to cause the comparator output to go high. there is about 6mv of hysteresis built into the comparator to prevent jitter about the switch point. due to the gain of the feedback resistor divider the voltage at v out experiences about 120mv of hysteresis for a 5v output. appications information oscillator duty cycle and frequency the oscillator duty cycle is set to 67% which is optimized to provide maximum load current for output voltages approxi- mately 3 larger than the input voltage. other output voltages are also easily generated but at a small cost in efficiency. the fixed oscillator frequency (options -1 and -2) is set to 20khz. output waveforms the voltage waveform seen at the collector of the output switch (sw pin) is either a continuous value equal to v in or a switching waveform running at a frequency and duty cycle set by the oscillator. the continuous voltage equal to v in happens when the voltage at the output (v out ) is high enough to cause the comparator to disable the and gate. in this state the output switch is off and no switching of the inductor occurs. when v out drops low enough to cause the comparator output to change to the high state the output switch is driven by the oscillator. see figure 1 for typical voltage waveforms in a boost application. 5v 0v 5v 0ma i peak v in supply voltage peak current output voltage time figure 1. typical boost regulator waveforms synchronization the sync pin is used to synchronize the mic2571 to an external oscillator or clock signal. this can reduce system noise by correlating switching noise with a known system frequency. when not in use, the sync pin should be grounded to prevent spurious circuit operation. a falling edge at the sync input triggers a one-shot pulse which resets the oscillator. it is possible to use the sync pin to generate oscillator duty cycles from approximately 20% up to the nominal duty cycle. current limit current limit for the mic2571 is internally set with a resistor. it functions by modifying the oscillator duty cycle and fre- quency. when current exceeds 1.2a, the duty cycle is reduced (switch on-time is reduced, off-time is unaffected) and the corresponding frequency is increased. in this way less time is available for the inductor current to build up while maintaining the same discharge time. the onset of current limit is soft rather than abrupt but sufficient to protect the inductor and output switch from damage. certain combina- tions of input voltage, output voltage and load current can cause the inductor to go into a continuous mode of operation. this is what happens when the inductor current can not fall to zero and occurs when: duty cycle v + v v v + v v out diode in out diode sat time inductor current current "ratchet" without current limit current limit threshold continuous current discontinuous current figure 2. current limit behavior
1997 7 mic2571 mic2571 micrel figure 2 shows an example of inductor current in the continu- ous mode with its associated change in oscillator frequency and duty cycle. this situation is most likely to occur with relatively small inductor values, large input voltage variations and output voltages which are less than ~3 the input voltage. selection of an inductor with a saturation threshold above 1.2a will insure that the system can withstand these condi- tions. inductors, capacitors and diodes the importance of choosing correct inductors, capacitors and diodes can not be ignored. poor choices for these compo- nents can cause problems as severe as circuit failure or as subtle as poorer than expected efficiency. a. b. c. inductor current time figure 3. inductor current: a. normal, b. saturating and c. excessive esr inductors inductors must be selected such that they do not saturate under maximum current conditions. when an inductor satu- rates, its effective inductance drops rapidly and the current can suddenly jump to very high and destructive values. figure 3 compares inductors with currents that are correct and unacceptable due to core saturation. the inductors have the same nominal inductance but figure 3b has a lower saturation threshold. another consideration in the selection of inductors is the radiated energy. in general, toroids have the best radiation characteristics while bobbins have the worst. some bobbins have caps or enclosures which signifi- cantly reduce stray radiation. the last electrical characteristic of the inductor that must be considered is esr (equivalent series resistance). figure 3c shows the current waveform when esr is excessive. the normal symptom of excessive esr is reduced power transfer efficiency. note that inductor esr can be used to the designers advantage as reverse battery protection (current limit) for the case of relatively low output power one-cell designs. the potential for very large and destructive currents exits if a battery in a one-cell application is inserted back- wards into the circuit. in some applications it is possible to limit the current to a nondestructive (but still battery draining) level by choosing a relatively high inductor esr value which does not affect normal circuit performance. capacitors it is important to select high-quality, low esr, filter capacitors for the output of the regulator circuit. high esr in the output capacitor causes excessive ripple due to the voltage drop across the esr. a triangular current pulse with a peak of 500ma into a 200m ? esr can cause 100mv of ripple at the output due the capacitor only. acceptable values of esr are typically in the 50m ? range. inexpensive aluminum electro- lytic capacitors usually are the worst choice while tantalum capacitors are typically better. figure 4 demonstrates the effect of capacitor esr on output ripple voltage. 4.75 5.00 5.25 0 500 1000 1500 output voltage (v) time ( s) figure 4. output ripple output diode finally, the output diode must be selected to have adequate reverse breakdown voltage and low forward voltage at the application current. schottky diodes typically meet these requirements. standard silicon diodes have forward voltages which are too large except in extremely low power applications. they can also be very slow, especially those suited to power rectifica- tion such as the 1n400x series, which affects efficiency. inductor behavior the inductor is an energy storage and transfer device. its behavior (neglecting series resistance) is described by the following equation: i = v l t where: v = inductor voltage (v) l = inductor value (h) t = time (s) i = inductor current (a) if a voltage is applied across an inductor (initial current is zero) for a known time, the current flowing through the inductor is a linear ramp starting at zero, reaching a maximum value at the end of the period. when the output switch is on, the voltage across the inductor is: v = v v 1in sat
mic2571 micrel mic2571 8 1997 when the output switch turns off, the voltage across the inductor changes sign and flies high in an attempt to maintain a constant current. the inductor voltage will eventually be clamped to a diode drop above v out . therefore, when the output switch is off, the voltage across the inductor is: v = v + v v 2 out diode in for normal operation the inductor current is a triangular waveform which returns to zero current (discontinuous mode) at each cycle. at the threshold between continuous and discontinuous operation we can use the fact that i 1 = i 2 to get: v t = v t 11 2 2 v v = t t 1 2 2 1 this relationship is useful for finding the desired oscillator duty cycle based on input and output voltages. since input voltages typically vary widely over the life of the battery, care must be taken to consider the worst case voltage for each parameter. for example, the worst case for t 1 is when v in is at its minimum value and the worst case for t 2 is when v in is at its maximum value (assuming that v out , v diode and v sat do not change much). to select an inductor for a particular application, the worst case input and output conditions must be determined. based on the worst case output current we can estimate efficiency and therefore the required input current. remember that this is power conversion, so the worst case average input current will occur at maximum output current and minimum input voltage. average i = v i v efficiency in(max) out out(max) in(min) referring to figure 1, it can be seen the peak input current will be twice the average input current. rearranging the inductor equation to solve for l: l = v i t 1 l = v 2 average i t in(min) in(max) 1 where t = duty cycle f 1 osc to illustrate the use of these equations a design example will be given: assume: mic2571-1 (fixed oscillator) v out = 5v i out(max) =5ma v in(min) = 1.0v efficiency = 75%. average i = 5v 5ma 1.0v 0.75 = 33.3ma in(max) l = 1.0v 0.7 2 33.3ma 20khz l = 525 h use the next lowest standard value of inductor and verify that it does not saturate at a current below about 75ma (< 2 33.3ma).
1997 9 mic2571 mic2571 micrel gnd 5v sw mic2571 sync u1 micrel mic2571-1bmm c1 sprague 594d476x0016c2t tantalum esr = 0.11 ? c2 sprague 594d476x0016c2t tantalum esr = 0.11 ? d1 motorola mbr0530t1 l1 coilcraft do1608c-154 dcr = 1.7 ? 7 4 1 2 8 in c2 47f 16v v out 5v/5ma 1v to 1.5v 1 cell c1* 47f 16v d1 mbr0530 l1 150h * needed if battery is more than 4" away from mic2571 example 1. 5v/5ma regulator gnd 3.3v sw mic2571 sync u1 micrel mic2571-1bmm c1 sprague 594d476x0016c2t tantalum esr = 0.11 ? c2 sprague 594d476x0016c2t tantalum esr = 0.11 ? d1 motorola mbr0530t1 l1 coilcraft do1608c-154 dcr = 1.7 ? 7 5 1 2 8 in c2 47f 16v v out 3.3v/8ma 1v to 1.5v 1 cell c1* 47f 16v d1 mbr0530 l1 150h * needed if battery is more than 4" away from mic2571 example 2. 3.3v/8ma regulator gnd fb sw mic2571 sync u1 micrel mic2570-2bmm c1 sprague 594d476x0016c2t tantalum esr = 0.11 ? c2 sprague 594d156x0025c2t tantalum esr = 0.22 ? d1 motorola mbra0530t1 l1 coilcraft do1608c-154 dcr = 1.7 ? 7 6 1 2 8 in c2 15f 25v v out 12v/2ma 1.0v to 1.5v 1 cell c1* 47f 16v d1 mbr0530 l1 150h r2 1m 1% r1 20k 1% * needed if battery is more than 4" away from mic2571 v out = 0.22v (1 + r2/r1) example 3. 12v/40ma regulator application examples
mic2571 micrel mic2571 10 1997 gnd 5v sw mic2571 sync u1 micrel mic2571-1bmm c1 sprague 594d476x0016c2t tantalum esr = 0.11 ? c2 sprague 594d476x0016c2t tantalum esr = 0.11 ? c3 sprague 594d476x0016c2t tantalum esr = 0.11 ? c4 sprague 594d476x0016c2t tantalum esr = 0.11 ? d1 motorola mbr0530t1 d2 motorola mbr0530t1 d3 motorola mbr0530t1 l1 coilcraft do1608c-154 dcr = 1.7 ? 7 4 1 2 8 in c2 47f 16v v out /+i out 5v/2ma 1v to 1.5v 1 cell c1* 47f 16v d1 mbr0530 l1 150h * needed if battery is more than 4" away from mic2571 c3 47f 16v d2 mbr0530 d3 mbr0530 r1 220k c4 47f 16v v out / i out 5v/2ma i out +i out example 4. 5v/2ma regulator gnd 5v sw mic2571 sync u1 micrel mic2571-1bmm c1 avx tpsd107m010r0100 tantalum esr = 0.1 ? c2 avx tpsd107m010r0100 tantalum esr = 0.1 ? d1 motorola mbra140t3 l1 coilcraft do3308p-473 dcr = 0.32 ? 7 4 1 2 8 in c2 100f 10v v out 5v/15ma 1v to 1.5v 1 cell c1 100f 10v d1 mbra140 l1 47h r1 51k q1 2n3906 minimum start-up supply voltage v in = 1v, i load = 0a v in = 1.2v, i load = 15ma example 5. 5v/15ma regulator gnd fb sw mic2571 sync u1 micrel mic2571-2bm c1 sprague 594d476x0016c2t tantalum esr = 0.11 ? c2 sprague 594d156x0025c2t tantalum esr = 0.22 ? c3 sprague 594d156x0025c2t tantalum esr = 0.22 ? d1 motorola mbr0530t1 d2 motorola mbr0530t1 l1 coilcraft do1608c-154 dcr = 1.7 ? 7 6 1 2 8 in c2 0.1f c1 47f 16v d3 1n4148 l1 150h r2 1.1m 1.1% r1 20k 1% 1v to 1.5v 1 cell r3 220k c2 15f 25v v out 12v/2ma d2 mbr0530 d1 mbr0530 c1 15f 25v v out = 0.22v (1+r2/r1) + 0.6v example 6. 12v/2ma regulator
1997 11 mic2571 mic2571 micrel suggested manufacturers list inductors capacitors diodes coilcraft avx corp. general instruments (gi) 1102 silver lake rd. 801 17th ave. south 10 melville park rd. cary, il 60013 myrtle beach, sc 29577 melville, ny 11747 ph (708) 639-2361 ph (803) 448-9411 ph (516) 847-3222 fx (708) 639-1469 fx (803) 448-1943 fx (516) 847-3150 coiltronics sanyo video components corp. international rectifier corp. 6000 park of commerce blvd. 2001 sanyo ave. 233 kansas st. boca raton, fl 33487 san diego, ca 92173 el segundo, ca 90245 ph (407) 241-7876 ph (619) 661-6835 ph (310) 322-3331 fx (407) 241-9339 fx (619) 661-1055 fx (310) 322-3332 sumida sprague electric motorola inc. 637 e. golf road, suite 209 lower main street 3102 north 56th st. arlington heights, il 60005sanford, me 04073 ms 56-126 ph (708) 956-0666 ph (207) 324-4140 phoenix, az 85018 fx (708) 956-0702 ph (602) 244-3576 fx (602) 244-4015 component side and silk screen (not actual size) solder side and silk screen (not actual size) evaluation board layout
mic2571 micrel mic2571 12 1997 package information 0.008 (0.20) 0.004 (0.10) 0.039 (0.99) 0.035 (0.89) 0.021 (0.53) 0.012 (0.03) r 0.0256 (0.65) typ 0.012 (0.30) r 5 max 0 min 0.122 (3.10) 0.112 (2.84) 0.120 (3.05) 0.116 (2.95) 0.012 (0.03) 0.007 (0.18) 0.005 (0.13) 0.043 (1.09) 0.038 (0.97) 0.036 (0.90) 0.032 (0.81) dimensions: inch (mm) 0.199 (5.05) 0.187 (4.74) 8-pin msop (mm) 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. ? 1997 micrel incorporated

▲Up To Search▲

Price & Availability of MIC2571-2BMM

	To Download MIC2571-2BMM Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .