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september 2005 1 m9999-083005 mic2588/mic2594 micrel mic2588/mic2594 single-chann el, negative high-voltage hot swap power controllers general description the mic2588 and the mic2594 are single-channel, nega - tive-voltage hot swap controllers designed to address the need for safe insertion and removal of circuit boards into live high-voltage system backplanes, while using very few external components. the mic2588 and the mic2594 are each available in an 8-pin soic package and work in con - junction with an external n-channel mosfet for which the gate drive is controlled to provide inrush current limiting and output voltage slew-rate control. overcurrent fault protection is also provided and includes a programmable overcurrent threshold. during an output overload condition, a constant- current regulation loop is engaged to ensure that the system power supply maintains regulation. if a fault condition exceeds a built-in 400s nuisance-trip delay, the mic2588 and the mic2594 will latch the circuit breakers output off and will remain in the off state until reset by cycling either the uv/off pin or the power to the ic. a master power-good signal is provided to indicate that the output voltage of the soft-start circuit is within its valid output range. this signal can be used to enable one or more dc-dc converter modules. all support documentation can be found on micrels web site at www.micrel.com. typical application /pwrg d drain uv ov vd d se ns e gate vee 1 8 7 6 5 4 3 2 r1 698k? 1% r3 12.4k? 1% r2 11.8 k? 1% c1 1u f r se ns e 0.01? 5% *d1 smat70 a 100v m1 sum1 10n 10-0 9 r fdb k 15 k? c3 0.22uf c fdb k 6.8n f 100v r4 10? -48v ou t -48v rt n c5 100u f c4 0. 1uf -48v in (long pin ) -48v rtn (long pin) *c6 0.33uf mic2588-2bm -48v rt n (short pin) dc-dc converte r in- in+ on/off # out+ ou t- +2.5v r tn +2.5v ou t vd d *c2 22nf n o m i n a l u n d e r v o l t a ge an d o v e r v o l ta g e t h r e s h o l ds : v u v = 36 . 5 v v o v = 7 1 . 2 v * o p tio n al co m p o n e n ts ( s e e a pplica t i o ns i n f o r m a t i o n f o r m o r e d e t a i l s ) # a n e x t e r n a l p u l l - u p r e s i st o r f o r t h e p o w e r - g oo d s i g n a l i s n e c e ss a ry f o r dc - dc s u p p li e s ( an d a ll o t he r l o ad m o du l e s ) n ot eq u i pp e d wi t h i nt e r n a l p u l l - u p i m pe d enc e features ? mic2588: pin-for-pin functional equivalent to the lt1640/lt1640a/lt4250 ? provides safe insertion and removal from live C48v (nominal) backplanes ? operates from C19v to C80v ? electronic circuit breaker function ? built-in 400s nuisance-trip delay (t flt ) ? regulated maximum output current into faults ? programmable inrush current limiting ? fast response to short circuit conditions (< 1s) ? programmable undervoltage and overvoltage lockouts (mic2588-xbm) ? programmable uvlo hysteresis (mic2594-xbm) ? fault reporting: active-high (-1bm) and active-low (-2bm) power-good output signal applications ? central of?ce switching ? C48v power distribution ? distributed power systems ? server networks micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com
mic2588/mic2594 micrel m9999-083005 2 september 2005 pin con?guration 1 pwrgd ov uv vee 8 vdd drain gate sense 7 6 5 2 3 4 8-pin soic (m) mic2588-1bm 1 pwrgd on off vee 8 vdd drain gate sense 7 6 5 2 3 4 8-pin soic (m) mic2594-1bm ordering information part number pwrgd polarity lockout functions circuit breaker function package standard pb-free mic2588-1bm mic2588-1ym active-high undervoltage and overvoltage latched off 8-pin soic mic2588-2bm mic2588-2ym active-low undervoltage and overvoltage latched off 8-pin soic mic2594-1bm MIC2594-1YM active-high programmable uvlo hysteresis latched off 8-pin soic mic2594-2bm mic2594-2ym active-low programmable uvlo hysteresis latched off 8-pin soic 1 /pwrgd ov uv vee 8 vdd drain gate sense 7 6 5 2 3 4 8-pin soic (m) mic2588-2bm 1 /pwrgd on off vee 8 vdd drain gate sense 7 6 5 2 3 4 8-pin soic (m) mic2594-2bm
september 2005 3 m9999-083005 mic2588/mic2594 micrel pin description pin number pin name pin function pwrgd power-good output: open-drain. asserted when the voltage on the drain 1 /pwrgd pin (v drain ) is within v pgth of vee, indicating that the output voltage is within proper speci?cations. mic25xx-1 mic2588-1 and mic2594-1: pwrgd will be high-impedance when 1 pwrgd v drain is less than v pgth , and will pull-down to v drain when v drain is active-high greater than v pgth . asserted state: open-drain. mic25xx-2 mic2588-2 and mic2594-2: /pwrgd will pull-down to v drain when 1 /pwrgd v drain is less than v pgth, and will be high impedance when v drain is active-low greater than v pgth . asserted state: active-low. ov mic2588: overvoltage threshold input. when the voltage at the ov pin is 2 threshold greater than the v ovh threshold, the gate pin is immediately pulled low by an internal 100a current pull-down. on mic2594: turn-on threshold. at initial system power-up or after the device 2 turn-on threshold has been shut off by the off pin, the voltage on the on pin must exceed the v onh threshold in order for the mic2594 to be enabled. uv mic2588: undervoltage threshold input. when the voltage at the uv pin is 3 threshold less than the v uvl threshold, the gate pin is immediately pulled low by an internal 100a current pull-down. the uv pin is also used to cycle the device off and on to reset the circuit breaker. taken together, the ov and uv pins form a window comparator which de?nes the limits of v ee within which the load may safely be powered. off mic2594: turn-off threshold. when the voltage at the off pin is less than 3 turn-off threshold the v offl threshold, the gate pin is immediately pulled low by an internal 100a current pull-down. the off pin is also used to cycle the device off and on to reset the circuit breaker. taken together, the on and off pins provide programmable hysteresis for the turn-on command voltage. 4 vee negative supply voltage input. connect to the negative, or low side, terminal of the input power supply. 5 sense circuit breaker sense input: the current-limit threshold is set by connecting a resistor between this pin and v ee . when the current-limit threshold of ir = 50mv is exceeded for an internal delay t flt (400s), the circuit breaker is tripped and the gate pin is immediately pulled low by i gateoff . toggling the uv/off pin will reset the circuit breaker. to disable the circuit breaker, externally connect sense and vee together. 6 gate gate drive output: connect to the gate of an external n-channel mosfet. 7 drain drain sense input: connect to the drain of an external n-channel mosfet. 8 vdd positive supply input. connect to the positive, or high side, terminal of the input power supply.
mic2588/mic2594 micrel m9999-083005 4 september 2005 absolute maximum ratings (1) (all voltages are referred to v ee ) supply voltage (v dd C v ee ) ........................... C0.3v to 100v drain, pwrgd pins .................................... C0.3v to 100v gate pin ...................................................... C0.3v to 12.5v sense, ov, uv, on, off pins ......................... C0.3v to 6v lead temperature (soldering) standard package (-xbm) (ir re?ow, peak temperature) ........ 240c +0c/C5c pb-free package-(xym) (ir re?ow, peak temperature) ........ 260c +0c/C5c esd ratings (3) human body model ................................................... 2kv machine model ........................................................ 100v operating ratings (2) supply voltage (v dd C v ee ) .......................... +19v to +80v ambient temperature range ( t a ) ................ C40c to 85c junction temperature ( t j ) ......................................... 125c package thermal resistance soic ( ja ) ........................................................ 152c/w dc electrical characteristics (4) v dd = 48v, v ee = 0v, t a = 25c, unless otherwise noted. bold indicates speci?cations apply over the full operating temperature range of C40c to +85c. symbol parameter condition min typ max units v dd C v ee supply voltage 19 80 v i dd supply current 3 5 ma v trip circuit breaker trip voltage v trip = v sense C v ee 40 50 60 mv i gateon gate pin pull-up current v gate = v ee to 8v 30 45 60 a 19v (v dd C v ee ) 80v i gateoff gate pin sink current (v sense C v ee ) = 100mv 100 230 ma v gate = 2v v gate gate drive voltage, (v gate C v ee ) 15v (v dd C v ee ) 80v 9 10 11 v i sense sense pin current v sense = 50mv 0.2 a v uvh uv pin high threshold voltage low-to-high transition 1.213 1.243 1.272 v v uvl uv pin low threshold voltage high-to-low transition 1.198 1.223 1.247 v v uvhys uv pin hysteresis 20 mv v ovh ov pin high threshold voltage low-to-high transition 1.198 1.223 1.247 v v ovl ov pin low threshold voltage high-to-low transition 1.165 1.203 1.232 v v ovhys ov pin hysteresis 20 mv v onh ansi on pin high threshold low-to-high transition 1.198 1.223 1.247 v voltage v offh ansi off pin low threshold high-to-low transition 1.198 1.223 1.247 v voltage i cntrl input bias current v uv = 1.25v 0.5 a (ov, uv, on, off pins) v pgth power-good threshold high-to-low transition 1.1 1.26 1.40 v (v drain C v ee ) v olpg pwrgd output voltage v olpg C v drain (relative to voltage at the drain pin) 0ma i pg(low) 1ma mic25xx-1 (v drain C v ee ) < v pgth C0.25 0.8 v mic25xx-2 (v drain C v ee ) > v pgth C0.25 0.8 v i lkg(pg) pwrgd output leakage current v pwrgd = v dd = 80v 1 a notes: 1. exceeding the absolute maximum ratings may damage the devices. 2. the devices are not guaranteed to function outside the speci?ed operating conditions. 3. devices are esd sensitive. handling precautions recommended. human body model: 1.5k in series with 100pf. machine model: 200pf, no series resistance. 4. speci?cation for packaged product only.
september 2005 5 m9999-083005 mic2588/mic2594 micrel ac electrical characteristics (5) symbol parameter condition min typ max units t flt built-in overcurrent nuisance trip 400 s time delay (6) (figure 1) t ocsense overcurrent sense to gate low v sense C v ee = 100mv 3.5 s (figure 2) t ovphl ov to gate low (6) (figure 3) 1 s t ovplh ov to gate high (6) (figure 3) 1 s t uvphl uv to gate low (6) (figure 4) 1 s t uvplh uv to gate high (6) (figure 4) 1 s t pgl(1) drain high to pwrgd output low (6) r pullup = 100k, c load on pwrgd = 50pf 1 s (-1 version parts only) t pgl(2) drain low to /pwrgd output low (6) r pullup = 100k, c load on /pwrgd = 50pf 1 s (-2 version parts only) t pgh(1) drain low to pwrgd output high (6) r pullup = 100k, c load on pwrgd = 50pf 2 s (-1 version parts only) t pgh(2) drain high to /pwrgd output high (6) r pullup = 100k, c load on /pwrgd = 50pf 2 s (-2 version parts only) notes: 5. speci?cation for packaged product only. 6. not 100% production tested. parameters are guaranteed by design. timing diagrams i limit i load 0a v drain v gate (v ee +10v) t < t flt t ? t flt (at v ee ) (at v ee ) (at v ee ) overcurrent event output off (at v dd ) load current is regulated at i limit = 50mv/r sense reduction in v drain to support i limit = 50mv/r sense figure 1. overcurrent response v sense - v ee 100mv 1v t ocsense v gate figure 2. sense to gate low timing response
september 2005 6 m9999-083005 mic2588/mic2594 micrel v ov 1.223v 1v 1.203v 1v t ovphl v gate t ovplh figure 3. overvoltage response v uv 1.223v 1v 1.243v 1v t uvphl v gate t uvplh figure 4. undervoltage response v drain mic2588/94-1 mic2588/94-2 v pgth v pgth v ee v ee v pwrgd e v drain = 0v v pwrgd e v drain = 0v t pgh1 v ee v ee pwrgd pwrgd not asserted pwrgd not asserted pwrgd asserted - high impedance t pgl1 v pgth v pgth t pgl2 t pgh2 v drain /pwrgd figure 5. drain to power-good response
mic2588/mic2594 micrel m9999-083005 7 september 2005 typical characteristics [section under construction] 0 1 2 3 4 5 6 -40 -20 0 20 40 60 80 100 supply current (ma) temperature (c) supply current vs. temperature 0 1 2 3 4 5 6 15 25 35 45 55 65 75 85 supply current (ma) supply voltage (v) supply current vs. supply voltage t a = 25c 0 2 4 6 8 10 12 -40 -20 0 20 40 60 80 100 v gate (v) temperature (c) gate drive (v gate - v ee ) vs. temperature 0 2 4 6 8 10 12 10 20 30 40 50 60 70 80 v gate (v) supply voltage (v) gate drive (v gate - v ee ) vs. supply voltage t a = 25c 0 10 20 30 40 50 60 -40 -20 0 20 40 60 80 100 i gateon (a) temperature (c) gate pull-up current vs. temperature 0 50 100 150 200 250 300 350 -40 -20 0 20 40 60 80 100 i gateoff (ma) temperature (c) gate sink current vs. temperature 1.2 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 -40 -20 0 20 40 60 80 100 uv pin threshold (v) temperature (c) uv pin threshold vs. temperature v uvh v uvl 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 -40 -20 0 20 40 60 80 100 ov pin threshold (v) temperature (c) ov pin threshold vs. temperature v ovh v ovl 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 -40 -20 0 20 40 60 80 100 power good threshold (v) temperature (c) power good threshold vs. temperature v pgth+ v pgthC 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 -40 -20 0 20 40 60 80 100 volpg (v) temperature (c) power-good low voltage vs. temperature 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 -40 -20 0 20 40 60 80 100 vonh (v) temperature (c) on pin threshold vs. temperature 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 -40 -20 0 20 40 60 80 100 voffl (v) temperature (c) off pin threshold vs. temperature
mic2588/mic2594 micrel m9999-083005 8 september 2005 40 42 44 46 48 50 52 54 56 58 60 -40 -20 0 20 40 60 80 100 v trip (mv) temperature (c) circuit breaker trip voltage vs. temperature test circuit /pwrg d drain uv ov vd d se ns e gate vee 1 8 7 6 5 4 3 2 r1 698k? 1% r3 12.4k? 1% r2 11.8 k? 1% c1 1u f r (see photos) se ns e *d1 smat70 a m irf540 1 r fdb k 10 k? c3 0.1uf c fdb k r4 10? -48v ou t -48v rt n c5 100uf c4 0.1uf -48 v in (long pin) -48v rtn (long pin) c2 0.22uf mic2588-2bm r5 47 k? i load mic2588/mic2594 test circuit
mic2588/mic2594 micrel m9999-083005 9 september 2005 functional characteristics time (100s/div.) i load (2a/div) v sense (50mv/div) v gate (5v/div) turn-on (circuit breaker trip) into large c load r sense = 0.01? c 5 = 1500f c fdbk = 6.8nf c 3 = 0.22f circuit breaker trips time (25ms/div.) i load (1a/div) drain (50v/div) /pwrgd (50v/div) v gate (5v/div) hot-plug turn-on response r sense = 0.05? c fdbk = 22nf c 3 = 0.47f r fdbk = 1.2k? time (100s/div.) i load (2a/div) drain (50v/div) v gate (5v/div) overcurrent response (short circuit) r sense = 0.01? c fdbk = 22nf c 2 = c 3 = 0.22f short circuit applied time (5ms/div.) i load (500ma/div) drain (20v/div) /pwrgd (20v/div) v gate (10v/div) turn-on response r sense = 0.05? c fdbk = 22nf
september 2005 10 m9999-083005 mic2588/mic2594 micrel functional diagram logic + circuit breaker internal pg vee sense vdd + C 45 ? a 50mv v pgth gate + C v th(uv/ov) uv + C ov + C v dd1 v ee internal vdd and reference generator nuisance trip filter (400 ? s) current limit state v ee en v ee denotes -2 option v ee 100 ? a /pwrgd drain pwrgd 6v clamp for power good circuitry only v ref1 v dd1 v dd1 mic2588 block diagram
mic2588/mic2594 micrel m9999-083005 11 september 2005 functional description hot swap insertion when circuit boards are inserted into systems carrying live supply voltages (hot swapped), high inrush currents often result due to the charging of bulk capacitance that resides across the circuit boards supply pins. these current spikes can cause the systems supply voltages to temporarily go out of regulation, causing data loss or system lock-up. in more extreme cases, the transients occurring during a hot swap event may cause permanent damage to connectors or on-board components. the mic2588 and the mic2594 are designed to address these issues by limiting the magnitude of the transient or inrush cur - rent during hot swap events. this is achieved by controlling the rate at which power is applied to the circuit board (di/dt and dv/dt management). additionally, the mic2588 and the mic2594 incorporate input voltage supervisory functions and current limiting, thereby providing robust protection for both the system and the circuit board. start-up cycle when the input voltage to the controller is between the over - voltage and undervoltage thresholds (mic2588) or is greater than v on (mic2594), a start cycle is initiated to deliver power to the load. at this time, the gate pin of the controller ap - plies a constant charging current (i gateon ) to the gate of the external mosfet (m1). c fdbk creates a miller integrator out of the mosfet circuit, which limits the slew-rate of the voltage at the drain of m1. the drain voltage rate-of-change (dv/dt) of m1 is: dv m1 dt i c C i c drain gate(C) fdbk gateon fdbk ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? where i gate(+) = gate charging current = i gateon ; i gate(C) ? Ci gate(+) , due to the extremely high transconduc - tance values of power mosfets; and i c dv m1 dt gate(C) fdbk drain ? ? ? ? relating the above to the maximum transient (or inrush) current charging the load capacitance upon hot swap or power-up involves an extension of the same formula: i c d v m 1 dt i c C i c | i | c c inrush load drain inrush load gateon fdbk inrush load gateon fdbk ? ? ? ? ? ? ? ? ? ? ? ? ? ? i (1) the presence of c3 and r fdbk prevent turn-on of the external pass device by limiting the hot swap current surges induced by ac coupled transients from the drain to the gate of m1 (i.e., c fdbk + c gd (m1)). an appropriate value for c3 may be determined using the formula for a capacitive voltage divider. the maximum voltage on c3 at turn-on must be less than v threshold of m1. 1. for a standard 10v enhancement n-channel mosfet, v threshold is about 4.25v. 2. choose 2v as the maximum voltage to avoid turn- on transients. c3 = ? c fdbk + c gd (m1) ? v in (max) C v gs (m1) v gs (m1) v gs (m1) [c3 + ? c fdbk + c gd (m1) ? ] = v in (max) ? c fdbk + c gd (m1) ? v gs (m1) c3 = ? v in (max) C v gs (m1) ?? c fdbk + c gd (m1) ? ( 2) where v in (max) = v dd C v ee (min). for example, we can determine appropriate capacitor values given a hot swap controller that is required to maintain the inrush current into a 220f load capacitance at 2a maximum and an input supply voltage as high as v in (max) = 75v. one of the suggested mosfets to be used with the mic2588/ mic2594 is an sum110n10-09,a 100v d 2 pak device which has a typical c gd of 750pf. calculating a value for c fbdk using equation 1 yields: c 220 f 4 5 a 2a 4.95nf fdbk ? ? ? ? ? good engineering practice suggests the use of the worst- case parameter values for i gateon from the dc electrical characteristics section: c 220 f 6 0 a 2a 6.6nf fdbk ? ? ? ? ? where the nearest standard 5% value is 6.8nf. substituting 6.8nf into equation 2 from above yields: c 6 .8nf 750pf 75v C 2 v 2v 0.275 f 3 ? ? ? ? ? ? ? ? ? for c3, the nearest standard 5% value is 0.22f. while the value for r fdbk is not critical, it should be chosen to allow a maximum of a few milliamperes to ?ow in the gate-drain circuit of m1 during turn-on. while the ?nal value for r fdbk is determined empirically, initial values between r fdbk = 15k to 27k for systems with a maximum value of v in (max) = 75v are appropriate. resistor r4, in series with the mosfet's gate, minimizes the potential for parasitic high frequency oscillations from occurring in m1. while the exact value of r4 is not critical, commonly used values for r4 range from 10 to 33. power-good (pwrgd or /pwrgd) output for the mic2588-1 and the mic2594-1, the power-good output signal (pwrgd) will be high impedance when v drain drops below v pgth , and will pull down to v drain when v drain is above v pgth . for the mic2588-2 and the mic2594-2, /pwrgd will pull down to the potential of the v drain pin when v drain drops below v pgth , and will be high impedance when v drain is above v pgth . hence, the -1 parts have an active-high pwrgd signal and the -2 parts have an active-low /pwrgd output. either pwrgd or /pwrgd may be used as an enable signal for one or more
september 2005 12 m9999-083005 mic2588/mic2594 micrel subsequent dc/dc converter modules or for other system uses as desired. when used as an enable signal, the time necessary for the pwrgd (or /pwrgd) signal to pull-up (when in high impedance state) will depend upon the load (rc) that is present on this output. circuit breaker function the mic2588 and the mic2594 employ an electronic circuit breaker that protects the mosfet and other system compo - nents against faults such as short circuits. the current limit threshold is set via an external resistor, r sense , connected between the v ee and sense pins and is determined by: v trip r sense i lim ? (3) where v trip is the circuit breaker trip threshold speci?ed in the electrical characteristics table. an internal 400s timer limits the length of time (t flt ) for which the circuit can draw current in excess of its programmed threshold before the circuit breaker is tripped. this short delay prevents nuisance tripping of the circuit breaker due to system transients while providing rapid protection against large-scale transient faults. whenever the voltage across r sense exceeds 50mv, two things happen: 1. a constant-current regulation loop is engaged and is designed to hold the voltage across r sense equal to 50mv. this protects both the load and the mic2588 circuit from excessively high currents. this loop will engage in less than 1s from the time at which the overvoltage condition on r sense occurs. 2. the internal 400s timer is started. if the 400s timeout period expires, the circuit breaker trips and the gate pin is immediately pulled low by an internal current pull-down. this operation turns off the mosfet quickly and disconnects the input from the load. undervoltage/overvoltage detectionmic2588 the mic2588 has uv and ov input pins. these pins can be used to detect input supply rail undervoltage and overvoltage conditions. undervoltage lockout prevents energizing the load until the supply input is stable and within tolerance. in a similar fashion, overvoltage turn-off prevents damage to sensitive circuit components should the input voltage exceed normal operational limits. each of these pins is internally connected to an analog comparator with 20mv of hysteresis. when the uv pin falls below its v uvl threshold or the ov pin is above its v ovh threshold, the gate pin is immediately pulled low. the gate pin will be held low until uv exceeds its v uvh threshold or ov drops below its v ovl threshold. the uv and ov circuits threshold trip points are programmed using the resistor divider r1, r2, and r3 as shown in the typical application. the equations to set the trip points are shown below. for the following example, the circuits nominal uv threshold is set to v uv = 37v and the nominal ov threshold is placed at v ov = 72v, values commonly used in central of?ce power distribution applications. v v (typ) r1 +r 2 + r3 r2 +r 3 v v (typ) r1 +r 2 + r3 r3 uv uvl ov ovh ? ? ? ? ? ? ? ? ? ? (4) (5) given v uv , v ov , and any one resistor value, the remaining two resistor values can be found. a suggested value for r3 is that which will provide a minimum of 100a of current through the voltage divider chain at v dd = v uv . this yields the following as a starting point: r3 v (typ) 100 a 12.23k ovh ? ? ? ? the closest standard 1% value for r3 = 12.4k. using equa - tions 3 and 4 above, solving for r2 and r1 yields: r2 r3 v v C 1 r2 12.4k 72v 37v C 1 r2 11.729k ov uv ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? the closest standard 1% value for r2 = 11.8k. next, the value for r1 is calculated: r1 r3 v C 1.223v 1.223v C r 2 r1 12.4k 72v C 1 .223v 1.223v C 11.8k? r1 705.808k ov ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? the closest standard 1% value for r1 = 698k. using standard 1% resistor values, the circuits nominal uv and ov thresholds are: v uv = 36.5v v ov = 71.2v good general engineering design practices must consider the tolerances associated with these parameters, including but not limited to, power supply tolerance, undervoltgae and overvoltage tolerances, and the tolerances of the external passive components. programmable uvlo hysteresismic2594 the mic2594 has user-programmable hysteresis by means of the on and off pins. this allows setting the part to turn on at a voltage v1, and not turn off until a second voltage v2, where v2 < v1. this can signi?cantly simplify dealing with source impedances in the supply bus while at the same time increasing the amount of available operating time from a loosely regulated power supply (for example, a battery supply). similarly to the mic2588, each of these pins is internally connected to an analog comparator with 20mv of hysteresis. the mic2594 holds the output off until the voltage at the on pin exceeds its v onh threshold value given in the electrical characteristics table. once the output has been enabled by the on pin, it will remain on until the voltage at
mic2588/mic2594 micrel m9999-083005 13 september 2005 the off pin falls below its v offl threshold value, or the part turns off due to a fault. should either event occur, the gate pin is immediately pulled low and will remain low until the on pin once again exceeds its v onh threshold. the circuits turn-on and turn-off points are set using the resistor divider r1, r2, and r3 as shown in the typical application. the equations to establish the trip points are shown below. in the following example, the circuits nominal on threshold is set to v on = 40v and the circuits nominal off threshold is v off = 35v. v = v (typ) r1 r2 r3 r3 v = v (typ) r1 r2 r3 r2 r3 on onh off offl ? ? ? ? ? ? ? ? ? ? ? ? ? given v off , v on , and any one resistor value, the remaining two resistor values can be readily found. a suggested value for r3 is that which will provide a minimum of 100a of cur - rent through the voltage divider chain at v dd = v off . this yields the following as a starting point: r3 = v (typ) 100 a 12.23k offl ? ? ? the closest standard 1% value for r3 = 12.4k. solving for r2 and r1 yields: r2 = r 3 v v C 1 r2 = 12.4k 40v 35v C 1 r2 = 1 .771k on off ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? the closest standard 1% value for r2 = 1.78k. r1 = r 3 v C 1.223v 1.223v C r 2 r1 = 12.4k 40v C 1 .223v 1.223v C 1.78k? r1 = 391.380k on ? ? ? ? ? ? ? ? the closest standard 1% value for r1 = 392k. using standard 1% resistor values, the circuits nominal on and off thresholds are: v on = 40.1v v off = 35v good general engineering design practices must consider the tolerances associated with these parameters, including but not limited to, power supply tolerance, undervoltgae and overvoltage tolerances, and the tolerances of the external passive components.
september 2005 14 m9999-083005 mic2588/mic2594 micrel applications information optional external circuits for added protection/perfor - mance in many telecom applications, it is very common for circuit boards to encounter large-scale supply-voltage transients in backplane environments. because backplanes present a complex impedance environment, these transients can be as high as 2.5 times steady-state levels, or 120v in worst- case situations. in addition, a sudden load dump anywhere on the circuit card can generate a very high voltage spike at the drain of the output mosfet which, in turn, will ap - pear at the drain pin of the mic2588/mic2594. in both cases, it is good engineering practice to include protective measures to avoid damaging sensitive ics or the hot swap controller from these large-scale transients. two typical scenarios in which large-scale transients occur are de - scribed below: 1. an output current load dump with no bypass (charge bucket or bulk) capacitance to v ee . for example, if l load = 5h, v in = 56v and t off = 0.7s, the resulting peak short-circuit current prior to the mosfet turning off would reach: 56v 0. 7 s 5 h 7.8a ? ? ? ? ? ? if there is no other path for this current to take when the mosfet turns off, it will avalanche the drain-source junction of the mosfet. since the total energy represented is small relative to the sturdiness of modern power mosfets, its unlikely that this will damage the transistor. however, the actual avalanche voltage is unknown; all that can be guaranteed is that it will be greater than the v bd(d-s) of the mosfet. the drain of the transistor is connected to the drain pin of the mic2588/ mic2594, and the resulting transient does have enough voltage and energy to damage this, or any, high-voltage hot swap controller. 2. if the loads bypass capacitance (for example, the input ?lter capacitors for dc-dc converter module(s)) are on a board from which the board with the mic2588/mic2594 and the mosfet can be unplugged, the same type of inductive transient damage can occur to the mic2588/mic2594. for many applications, the use of additional circuit compo - nents can be implemented for optimum system performance and/or protection. the circuit, shown in figure 6, includes several components to address some the following system (dynamic) responses and/or functions: 1) suppression of transient voltage spikes, 2) elimination of false tripping of the circuit breaker due to undervoltage and overcurrent glitches, and 3) the implementation of an external reset circuit. it is not mandatory that these techniques be utilized, how - ever, the application environment will dictate suitability. for protection against sudden on-card load dumps at the drain pin of the mic2588/mic2594 controller, a 68v, 1w, 5% zener diode clamp (d2) connected from the drain to the vee of the controller can be implemented, as shown. to protect the controller from large-scale transients at the card input, a 100v clamp diode (d1, smat70a or equivalent) can be used. in either case, very short lead lengths and compact layout design is strongly recommended to prevent unwanted transients in the protection circuitry. power buss inductance often produces localized (plug-in card) high-voltage transients during a turn-off event. managing these repeated voltage stresses with suf?cient input bulk capacitance and/or tran - sient suppressing diode clamps is highly recommended for maximizing the life of the hot swap controller(s). /pwrg d drain uv ov vd d se ns e gate vee 1 8 7 6 5 4 3 2 r1 698k? 1% r3 12.4k? 1% r2 11.8k? 1% c1 0. 47 f *c6 0.47uf *r5 47 k? *d1 100v m1 sum110n10-09 c3 0.33uf r4 10? -48v ou t -48v rt n c5 47uf c4 0. 1uf -48 v in -48v rt n c2 0.22uf mic2588-2bm *r6 2.7 k? system re se t r se ns e 0.0 1? 5% * m2 r fdb k 10k? c fdb k 10nf 100v *r7 10 k? * optional components (see applications information for more details ) an sot-363 is recommended for m2. d2 is a 68v, 1w zener diode. d2 is *d2 68 v figure 6 optional components for added performance/protection
september 2005 15 m9999-083005 mic2588/mic2594 micrel for systems that experience known load current surges exceeding the 400s internal overcurrent ?lter (t flt ), the rc circuit consisting of r6 and c6 provides a means for additional overcurrent ?ltering to eliminate false tripping of the circuit breaker due to these transient load current surges. it is highly recommended to limit the increase of the overcurrent ?lter to approximately 2x the internal ?lter to allow the mosfet to operate within its thermal speci?ca - tions and soa. r6 and c6 act as a low-pass ?lter to reduce the slew rate of the sense pin voltage. the sense pin current is nominally 200na, resulting in a slight voltage drop across r6 that will combine in series with the voltage across r sense to produce an effective circuit breaker trip voltage of v trip C (r6 i sense ). the following equation can be used to select component values for a given overcurrent ?lter delay. C (r c) ln 1 C v trip C v(t o ) v(t) C v(t o ) t ocdly ? (8) where v trip is the typical circuit breaker trip voltage speci?ed in the electrical speci?cations, v(t0) is the voltage drop across the sense resister before the short or overcurrent condition occurs, and v(t) is the voltage drop across the sense resis - tor when the short or overcurrent is applied. the following example sets an overcurrent delay of 1ms for a 7.5a load current surge with a 2a steady-state load current and 5a current limit (r sense = 10m?). v trip = 50mv v(t 0 ) = 2a 10m? = 20mv v(t) = 7.5a 10m? = 75mv using equation 8, for r6 = 2.7k?, c6 is 0.47f. the capacitor (c2) connected from uv to reference (v ee ) is used as a glitch ?lter for the input undervoltage monitor. c2 combines with the resistive network at the uv pin to form an rc time constant to slow the uv pin voltage fall time whenever the input voltage experiences a negative (magnitude) transient. during start-up, the uv rise time will also be affected by a longer rc time constant due to r1, therefore, the output start cycle will be delayed until the uv pin crosses its threshold. the circuit in figure 6 consisting of m2, r7, r8, and a digital control signal, can be used to reset the controller after the gate (and output) turns off. once the output has been latched off, applying a low-high-low pulse on the gate of m2 via the system enable control can toggle the uv pin. system enable is a user de?ned signal referenced to v ee . sense resistor selection the sense resistor is nominally valued at: v trip(typ) i hot_swap(nom) r sense(nom) ? (9) where v trip(typ) is the typical (or nominal) circuit breaker threshold voltage (50mv) and i hot_swap(nom) is the nomi - nal load current level necessary to trip the internal circuit breaker. to accommodate worse-case tolerances in the sense re - sistor (for a 1% initial tolerance, allow 3% tolerance for variations over time and temperature) and circuit breaker threshold voltages, a slightly more detailed calculation must be used to determine the minimum and maximum hot swap load currents. as the mic2588s minimum current limit threshold voltage is 40mv, the minimum hot swap load current is determined where the sense resistor is 3% high: 40mv 1.03 r sense(nom) 38.8mv r sense(nom) i hot_swap(min) ? ? ? ? keep in mind that the minimum hot swap load current should be greater than the application circuits upper steady-state load current boundary. once the lower value of r sense has been calculated, it is good practice to check the maximum hot swap load current (i hot_swap(max) ) that the circuit may let pass in the case of tolerance build-up in the opposite direction. here, the worse case maximum is found using a v trip(max) threshold of 60mv and a sense resistor 3% low in value: 60mv 0.97 r sense(nom) 61.9mv r sense(nom) i hot_swap(max) ? ? ? ? in this case, the application circuit must be sturdy enough to operate up to approximately 1.5x the steady-state hot swap load current. for example, if an mic2588 circuit must pass a minimum hot swap load current of 4a without nuisance trips, r sense should be set to: 40mv 4a 10m? r sense(nom) ? ? where the nearest 1% standard value is 10.0m?. at the other tolerance extremes, i hot_swap(max) for the circuit in question is then simply: 61.9mv 10m? 6.19a i hot_swap(max) ? ? with a knowledge of the application circuits maximum hot swap load current, the power dissipation rating of the sense resistor can be determined using p = i 2 r. here, the current is i hot_swap(max) = 6.19a and the resistance r sense(max) = (1.03)(r sense(nom) ) = 10.3m?. thus, the sense resistors maximum power dissipation is: p max = (6.19a) 2 (10.3m?) = 0.395w a 0.5w sense resistor is a good choice in this application. power mosfet selection selecting the proper external mosfet for use with the - mic2588/mic2594 involves three straightforward tasks: ?choice of a mosfet which meets minimum voltage requirements. ?selection of a device to handle the maximum continuous current (steady-state thermal issues). ?verify the selected parts ability to withstand any peak currents (transient thermal issues). power mosfet operating voltage requirements the ?rst voltage requirement for the mosfet is easily stated:
september 2005 16 m9999-083005 mic2588/mic2594 micrel the drain-source breakdown voltage of the mosfet must be greater than v in(max) , or v dd C v ee (min). the second breakdown voltage criterion that must be met is the gate-source voltage. for the mic2588/mic2594, the gate of the external mosfet is driven up to a maximum of 11v above vee. this means that the external mosfet must be chosen to have a gate-source breakdown voltage of 12v or more; 20v is recommended. most power mosfets with a 20v gate-source voltage rating have a 30v drain-source breakdown rating or higher. for many 48v telecom applica - tions, transient voltage spikes can approach, and sometimes exceed, 100v. the absolute maximum input voltage rating of the mic2588/mic2594 is 100v; therefore, a drain-source breakdown voltage of 100v is suggested for the external mosfet. additionally, an external input voltage clamp is strongly recommended for applications that do not utilize conditioned power supplies. power mosfet steady-state thermal issues the selection of a mosfet to meet the maximum continuous current is a fairly straightforward exercise. first, arm yourself with the following data: ?the value of i load(cont, max.) for the output in question (see sense resistor selection). ?the manufacturers datasheet for the candidate mos - fet. ?the maximum ambient temperature in which the device will be required to operate. ?any knowledge you can get about the heat sinking avail - able to the device (e.g., can heat be dissipated into the ground plane or power plane, if using a surface-mount part? is any air?ow available?). the datasheet will almost always give a value of on resistance for a given mosfet at a gate-source voltage of 4.5v and 10v. for mic2588/mic2594 applications, choose the gate- source on resistance at 10v and call this value r on . since a heavily enhanced mosfet acts as an ohmic (resistive) device, almost all thats required to determine steady-state power dissipation is to calculate i 2 r. the one addendum to this is that mosfets have a slight increase in r on with in - creasing die temperature. a good approximation for this value is 0.5% increase in r on per c rise in junction temperature above the point at which r on was initially speci?ed by the manufacturer. for instance, if the selected mosfet has a calculated r on of 10m? at at j = 25c, and the actual junc - tion temperature ends up at 110c, a good ?rst cut at the operating value for r on would be: r on 10m?[1 + (110 C 25)(0.005)] 14.3m? the ?nal step is to make sure that the heat sinking available to the mosfet is capable of dissipating at least as much power (rated in c/w) as that with which the mosfets performance was speci?ed by the manufacturer. here are a few practical tips: 1. the heat from a to-263 power mosfet ?ows almost entirely out of the drain tab. if the drain tab can be soldered down to one square inch or more, the copper will act as the heat sink for the part. this copper must be on the same layer of the board as the mosfet drain. 2. air?ow works. even a few lfm (linear feet per - minute) of air will cool a mosfet down substan - tially. if you can, position the mosfet(s) near the inlet of a power supplys fan, or the outlet of a processors cooling fan. 3. the best test of a candidate mosfet for an ap - plication (assuming the above tips show it to be a likely ?t) is an empirical one. check the mosfets temperature in the actual layout of the expected ?nal circuit, at full operating current. the use of a thermocouple on the drain leads, or infrared pyrom - eter on the package, will then give a reasonable idea of the devices junction temperature. power mosfet transient thermal issues if the prospecitve mosfet has been shown to withstand the environmental voltage stresses and the worse-case steady- state power dissipation is addressed, the remaining task is to verify if the mosfet is capable of handling extreme overcur - rent load faults, such as a short circuit, without overheating. a power mosfet can handle a much higher pulsed power without damage than its continuos power dissipation ratings imply due to an inherent trait, thermal inertia. with respect to the speci?cation and use of power mosfets, the parameter of interest is the transient thermal impedence, or z , which is a real number (variable factor) used as a multiplier of the thermal resistance (r ). the multiplier is determined using the given transient thermal imepedence graph, normalized to r , that displays curves for the thermal impedence versus power pulse duration and duty cycle. the single-pulse curve is appropriate for most hot swap applications. z is speci?ed from junction-to-case for power mosfets typically used in telecom applications. the following example provides a method for estimating the peak junction temperature of a power mosfet in determin - ing if the mosfet is suitable for a particular application. v in (vdd C vee) = 48v, i lim = 4.2a, and the power mosfet is sum110n10-09 (to-263 package) from vishay-siliconix. this mosfet has an r on of 9.5m? (t j = 25c), the junc - tion-to-case thermal resistance (r (j-c) ) is 0.4c/w, junc - tion-to-ambient thermal resistance (r (j-a) ) is 40c/w, and the transient thermal impedence curve is shown in figure 7. consider, say, the mosfet is switched on at time t1 and the steady-state load current passing through the mosfet is 3a. at some point in time after t1, at time t2, there is an unexpected short-circuit applied to the load, causing the mic2588/mic2594 controller to adjust the gate output voltage and regulate the load current for 400s at the pro - grammed current limit value, 4.2a in this example. during this short-circuit load condition, the dissipation in the mosfet is calculated by: p d (short) = v ds i lim v ds = 0v C (-48v) = 48v p d (short) = 48v 4.2a = 201.6w for 400s. at ?rst glance, it would appear that a very hefty mosfet is required to withstand this extreme overload condition. upon further examination, the calculation to approximate the peak junction temperature is not a dif?cult task. the ?rst step is to determine the maximum steady-state junction temperature,
september 2005 17 m9999-083005 mic2588/mic2594 micrel then add the rise in temperature due to the maximum power dissipated during a transient overload caused by a short circuit condtion. the equation to estimate the maximum steady-state junction temperature is given by: t j (steady-state) ? t c (max) + t j (10) t c (max) is the highest anticipated case temperaure, prior to an overcurrent condition, at which the mosfet will operate and is estimated from the following equation based on the highest ambient temperature of the system environment. t c (max) = t a (max) + p d (r (j-a) C r (j-c) ) (11) lets assume a maximum ambient of 60c. the power dis - sipation of the mosfet is determined by the current through the mosfet and the on-resistance (i 2 r), which we will esti - mate at 17m? (speci?cation given at t j = 125c). using our example information and substituting into equation 11, t c (max) = 60c + [((3a) 2 17m?) (40 C 0.4)c/w] = 66.06c substituting the variables into equation 10, t j is determined by: t j (steady-state) ? t c (max)+[r on +(t c (max)Ct c )(0.005) (r on )][i 2 (r (j-a) Cr (j-c) )] ? 66.06c+[17m?+(66.06cC25c)(0.005/c) (17m?)][(3a) 2 (40C0.4)c/w] ? 66.06c + 7.30c ? 73.36c since this is not a closed-form equation, getting a close ap - poroximation may take one or two iterations. on the second iteration, start with t j equal to the value calculated above. doing so in this example yields; t j (steady-state) ? 66.06c+[17m?+(73.36cC25c)(0.005/c) (17m?)][(3a) 2 (40C0.4)]c/w ? 73.62c another iteration shows that the result (73.63c) is converg - ing quickly, so well estimate the maximum t j(steady-state) at 74c. the use of the transient thermal impedence curves is necessary to determine the increase in junction temperature associated with a worst-case transient condition. from our previous calculation of the maximum power dissipated during a short circuit event for the mic2588/mic2594, we calculate the transient junction temperature increase as: t j (transient) = p d (short) r (j-c) multiplier (12) assume the mosfet has been on for a long time C several minutes or more C and delivering the steady-state load current of 3a to the load when the load is short circuited. the control - ler will regulate the gate output voltage to limit the current to the programmed value of 4.2a for approximately 400s before immediately shutting off the output. for this situation and almost all hot swap applications, this can be considered a single pulse event as there is no signi?cant duty cycle. from figure 7, ?nd the point on the x-axis (square-wave pulse duration) for 1ms, allowing for a healthy margin of the 400s t flt , and read up the y-axis scale to ?nd the intersection of the single pulse curve. this point is the normalized transient thermal impedence (z (j-c) ), and the effective transient thermal impedence is the product of r (j-c) and the multiplier, 0.45 in this example. solving equation 12, t j (transient) = (201.6w) (0.4c/w) 0.45 = 36.3c finally, add this result to the maximum steady state junction temperature calculated previously to determine the estimated maximum transient junction temperature of the mosfet: t j (max.transient) = 74c + 36.3c = 110.3c, which is safely under the speci?ed maximum junction temperature of 200c for the sum110n10-09. figure 7. transient thermal impedance - sum110n10-09
september 2005 18 m9999-083005 mic2588/mic2594 micrel pcb layout considerations 4-wire kelvin sensing because of the low value typically required for the sense resistor, special care must be used to measure accurately the voltage drop across it. speci?cally, the measurement technique across each r sense must employ 4-wire kelvin sensing. this is simply a means of making sure that any voltage drops in the power traces connecting to the resistors are not picked up by the signal conductors measuring the voltages across the sense resistors. figure 8 illustrates how to implement 4-wire kelvin sensing. as the ?gure shows, all the high current in the circuit (from v ee through r sense , and then to the source of the output mosfet) ?ows directly through the power pcb traces and r sense . the voltage drop resulting across r sense is sampled in such a way that the high currents through the power traces will not introduce any parasitic voltage drops in the sense leads. it is recommended to connect the hot swap controllers sense leads directly to the sense resistors metalized contact pads. other layout considerations figure 9 is a suggested pcb layout diagram for the mic2588/ mic2594. many hot swap applications will require load currents of several amperes. therefore, the power (v ee and return) trace widths (w) need to be wide enough to allow the current to ?ow while the rise in temperature for a given copper plate (e.g., 1oz. or 2oz.) is kept to a maximum of 10c to 25c. the return (or power ground) trace should be the same width as the positive voltage power traces (input/load) and isolated from any ground and signal planes so that the controllers power is common mode. also, these traces should be as short as possible in order to minimize the ir drops between the input and the load. finally, the use of plated-through vias will be necessary to make circuit connections to the power, ground and signal planes of multi-layer pcbs. r sense power trace from v ee pcb track width: 0.03" per ampere using 1oz cu power trace to mosfet source signal trace to mic2588/mic2594 v ee pin signal trace to mic2588/mic2594 sense pin note: each sense lead trace shall be balanced for best performance with equal length/equal aspect ratio. r sense metalized contact pads figure 8. 4-wire kelvin sense connections for r sense c fdb k r4 *power mosfet (to-263) w w w via to the power (vee output) pl ane current flow from the load current flow to the load - drawing is not to scale - *see table 1 fo r part numbers and vendor s ^r1 placed on bottom sid e power plane - --- --- - (red ) gr ound plane ------- (black) trace width (w) guidelines and additional inf ormation given in "pcb layout recommendations" section of the datasheet via to the bottom side via to the ground plane *sense resistor (wsr-2 or wsl2512 ) d1 mic2588-2bm vd d drain gate ov ve e /pwrg d uv se ns e r fdb k r3 r2 ^r1 c3 via to the return (vdd) plane via to the power (vee output) pl ane ground pad c1 via to the return (vdd) plane figure 9. recommended pcb layout for sense resistor, power mosfet, overvoltage/undervoltage resistive divider network, and timer capacitors
september 2005 19 m9999-083005 mic2588/mic2594 micrel mosfet and sense resistor vendors device types, part numbers, and manufacturer contacts for power mosftets and sense resistors are provided in table 1. mosfet vendors key mosfet type(s) breakdown voltage (v dss ) contact information vishay - siliconix sum75n06-09l (to-263) sum70n06-11 (to-263) sum50n06-16l (to-263) 60v 60v 60v www.siliconix.com (203) 452-5664 sup85n10-10 (to-220ab) sub85n10-10 (to-263) sum110n10-09 (to-263) sum60n10-17 (to-263) 100v 100v 100v 100v www.siliconix.com (203) 452-5664 international recti?er irf530 (to-220ab) irf540n (to-220ab) 100v 100v www.irf.com (310) 322-3331 renesas 2sk1298 (to-3pfm) 2sk1302 (to-220ab) 2sk1304 (to-3p) 60v 100v 100v www.renesas.com (408) 433-1990 resistor vendors sense resistors contact information vishay - dale wsl and wsr series www.vishay.com/docswsl_30100.pdf (203) 452-5664 irc oars series lr series second source to wsl www.irctt.com/pdf_?les/oars.pdf www.irctt.com/pdf_?les/lrc.pdf (828) 264-8861 table 1. mosfet and sense resistor vendors
september 2005 20 m9999-083005 mic2588/mic2594 micrel /pwrgd signal drive capability the /pwrgd signal can be used to drive an optoisolator or an led. the use of an optoisolator is sometimes needed to protect i/o signals (e.g., /pwrgd, reset, enable) of both the controller and downstream dc-dc converter(s) from damage caused by common mode transients. such /pwrg d drain uv ov vd d se ns e gate vee 1 8 7 6 5 4 3 2 r1 698k? 1% r3 12.4k? 1% r2 11.8 k? 1% c1 1u f r se ns e 0.01? 5% *d1 smat70 a 100v m1 sum1 10n 10-0 9 r fdb k 15 k? c3 0.22uf c fdb k 6.8n f 100v r4 10? -48v ou t -48v rt n c5 100u f c4 0. 1uf -48v in (long pin ) -48v rtn (long pin) *c6 0.33uf mic2588-2bm -48v rt n (short pin) dc-dc converte r in- in+ on/off # out+ ou t- +2.5v r tn +2.5v ou t nominal undervoltage and overvoltage thresholds: v uv = 36. 5v v ov = 71.2 v * optional components (see applications information for more details ) # an external pull-up resistor for the power-good signal is necessary fo r dc-dc supplies (and all other load modules) not equipped with internal pull-up impedence vd d *c2 22nf 1 6 5 2 moc207-m r5 43k? figure 10. optoisolator driven by /pwrgd signal is the case when an emi ?lter is utilized to prevent dc-dc converter switching noise from being injected back onto the power supply. the circuit of figure 10 shows how to con - ?gure an optoisolator driven by the /pwrgd signal of the mic2588 controller.
mic2588/mic2594 micrel m9999-083005 21 september 2005 package information 45 0C8 0.244 (6.20) 0.228 (5.79) 0.197 (5.0) 0.189 (4.8) seating plane 0.026 (0.65) max ) 0.010 (0.25) 0.007 (0.18) 0.064 (1.63) 0.045 (1.14) 0.0098 (0.249 ) 0.0040 (0.102) 0.020 (0.51) 0.013 (0.33) 0.157 (3.99) 0.150 (3.81) 0.050 (1.27) typ pin 1 dimensions: inches (mm) 0.050 (1.27) 0.016 (0.40) 8-pin soic (m) 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 the information furnished by micrel in this datasheet 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 the customer. micrel products are noth 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 purchasers use or sale of micrel products for use in life support appliances, devices or systems is at purchaser s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2005 micrel, incorporated.

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