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general description the max5943 is a fully integrated power-management ic for firewire applications. this device controls two external power n-channel mosfets to regulate current from the input power supply to the load and performs low-voltage-drop, power-supply oring. the max5943 operates over a 7.5v to 37v input range and provides inrush and output current limit in addition to a diode oring function suitable for firewire applications. the max5943 firewire/ieee 1394 protective circuit (figure 12) is ul recognized. the max5943 allows the safe insertion and removal of firewire peripherals into a live firewire port by providing inrush current control and an output current-limiting func- tion. the oring feature provides a very efficient way to protect the firewire port when connected to another firewire peripheral that sources a higher voltage. by turn- ing off both external mosfets, the max5943 provides a true bidirectional load disconnect. a low-current shut- down mode disables the max5943, resulting in less than 10? supply current. a pin-selectable input allows latched or autoretry fault management after a fault. the max5943a features a current-limit function that actively limits the current drawn by the load with a pro- grammable timeout. the max5943b?ax5943e do not actively limit the load current but provide a circuit-breaker function. see the selector guide for the default and pro- grammable circuit-breaker timeouts. the max5943 operates over the -40? to +85? extended temperature range and is available in a 16-pin qsop package. applications firewire desktop/notebook port firewire peripheral device current limit firewire hub hot swap features provides safe hot swap for 7.5v to 37v power supplies ul-recognized firewire/ieee 1394 protective circuit low-drop power oring with ultra-fast turn-off programmable active current limit (max5943a) programmable circuit breaker (max5943b?ax5943e) 5% current-limit sensing accuracy programmable current-limit/circuit-breaker timeout fast current-limit response to output short- circuit conditions (max5943a) drives external n-channel power mosfets overcurrent fault status output latched or autoretry overcurrent fault management 10? shutdown current on/off control allows undervoltage lockout programming fast load disconnect control through on input max5943 firewire current limiter and low-drop oring switch controller ________________________________________________________________ maxim integrated products 1 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 on in sense gate1 n.c. gate2 out n.c. gnd top view max5943 qsop fault tim or_adj ilim latch n.c. onq1 pin configuration ordering information 19-3378; rev 2; 10/07 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. typical operating circuit and selector guide appear at end of data sheet. firewire is a registered trademark of apple computers, inc. ieee 1394 is a trademark of the institute of electrical and electronics engineers trademark. ul is a registered trademark of underwriters laboratories, inc. part temp range pin-package max5943aeee -40 c to +85 c 16 qsop MAX5943BEEE -40 c to +85 c 16 qsop max5943ceee -40 c to +85 c 16 qsop max5943deee -40 c to +85 c 16 qsop max5943eeee -40 c to +85 c 16 qsop
max5943 firewire current limiter and low-drop oring switch controller 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = 7.5v to 37v, gnd = 0v, and t a = -40? to +85?, unless otherwise noted. typical values are at v in = 12v, t a = +25?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. (voltages referenced to gnd, unless otherwise noted.) in ............................................................................-0.3v to +80v out ........................................................................-0.3v to +80v sense to in..............................................................-1v to +0.3v gate1 to sense......................................................-0.3v to +8v gate2 to out (internally clamped).........................-0.3v to +8v fault .....................................................................-0.3v to +85v on, tim, ilim, latch, or_adj, onq1 ..........-0.3v to (in + 0.3v) continuous power dissipation (t a = +70?) 16-pin qsop (derate 8.3mw/? above +70?)...........667mw operating temperature range ...........................-40? to +85? maximum junction temperature .....................................+150? storage temperature range .............................-60? to +150? esd rating (human body model)......................................2000v lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units supplies supply voltage range v in 7.5 37 v supply current i in v on = 3v, no load 1.3 2.3 ma shutdown current i sd v on = 0.4v 5 10 a in default undervoltage lockout v uvlo v in rising, on = in 6.2 6.5 6.8 v in default undervoltage lockout hysteresis 0.35 v on undervoltage lockout threshold v on_ref v on rising 1.20 1.24 1.275 v on undervoltage lockout threshold hysteresis 70 mv on input bias current i on 1a gate2 (current-limit/circuit-breaker control) gate2 pullup current i g2u (note 2) 36 45 54 ? 7.5v v in 8v 4.25 5.5 6.5 gate2 high voltage v g2 v gate2 - v out 8v v in 37v 4.5 5.5 6.5 v ilim = gnd 47.5 50 52.5 ilim = floating 37 39 41 current-limit/circuit-breaker threshold voltage v th v in - v sense ilim = in 55 58.5 61 mv ilim = gnd 70 75 80 ilim = floating 54 59 64 fast pulldown current-limit threshold voltage (max5943a) v thf v in - v sense (note 3) ilim = in 83 88 93 mv gate2 pulldown current (max5943a) i g2d v th < (v in - v sense) < v thf , t < t ilim 335 435 535 ? gate2 fast pulldown current (max5943a) i g2df (v in - v sense) > v thf , v gate2 = v out + 4.5v 80 125 200 ma gate2 peak pulldown current (max5943a) i g2dp (v in - v sense ) = 1v 1.0 a
max5943 firewire current limiter and low-drop oring switch controller _______________________________________________________________________________________ 3 electrical characteristics (continued) (v in = 7.5v to 37v, gnd = 0v, and t a = -40? to +85?, unless otherwise noted. typical values are at v in = 12v, t a = +25?.) (note 1) parameter symbol conditions min typ max units gate2 pulldown current during any gate2 turn-off condition i g2off v gate2 = v out + 4.5v (note 4) 80 125 200 ma gate1 (oring control) or_adj = gnd 3 5 7 or_adj = floating 5.5 7.5 9.5 oring switch turn-on current threshold voltage v or (v in - v sense ) rising or_adj = in 8.5 10.5 12.8 mv oring switch turn-on current threshold voltage hysteresis (v in - v sense ) falling 0.5 mv gate1 pullup current i g1u (note 5) 36 45 54 ? 7.5v v in 8v 4.25 5.5 6.5 gate1 high voltage v g1 v gate1 - v sense 8v v in 37v 4.5 5.5 6.5 v gate1 turn-off switch on- resistance r g1 measured between gate1 and sense when (v in - v sense ) < v or 23 logic inputs i ix current into or out of input for tri-state logic condition -3 +3 i ixl current out of input for logic low 20 ilim, or_adj input-logic tristate current tolerance (note 6) i ih current into input for logic high 20 ? v il v on > v on_ref 0.7 v latch, onq1 input-logic low voltage i il latch, onq1 = gnd, v on > v on_ref 1a latch, onq1 input-logic high voltage v ih v on > v on_ref 1.8 v latch, onq1 input current i ih all voltages = v in , v on > v on_ref 1a tim, ilim, latch, or_adj, out, onq1 shutdown mode input current i ih_sd all voltages = v in , v on 0.4v 1 a fault output low voltage v ol low-impedance state, i fault = 5ma 0.12 0.25 v fault output high leakage current i oh high-impedance state, v fault = 37v 1 a timing tim = in 1.78 2.02 2.26 ms r tim = 4k 0.87 1.04 1.21 ms r tim = 50k 9.2 11.05 12.9 ms current-limit timeout (max5943a) t ilim current-limit mode (note 7) tim = floating 120 175 225 ms
max5943 firewire current limiter and low-drop oring switch controller 4 _______________________________________________________________________________________ electrical characteristics (continued) (v in = 7.5v to 37v, gnd = 0v, and t a = -40? to +85?, unless otherwise noted. typical values are at v in = 12v, t a = +25?.) (note 1) parameter symbol conditions min typ max units tim = in or tim 3.4v 0.45 0.51 0.57 ms r tim = 4k 27 32.5 38 ? r tim = 50k 228 345 403 ? circuit-breaker mode, max5943b tim = floating 3.75 5.5 7 ms tim = in or tim 3.4v 0.89 1.00 1.13 ms r tim = 4k 54 65 76 ? r tim = 50k 575 690 806 ? circuit-breaker mode, max5943c tim = floating 7.5 10.9 14 ms tim = in 1.78 2.02 2.26 ms r tim = 4k 109 130 151 ? r tim = 50k 1.15 1.38 1.61 ms circuit-breaker mode, max5943d tim = floating 15 21.9 28 ms tim = in or tim 3.4v 3.56 4.05 4.52 ms r tim = 4k 217 260 303 ? r tim = 50k 2.3 2.76 3.23 ms circuit-breaker timeout (max5943b?ax5943e) (note 7) t cb circuit-breaker mode, max5943e tim = floating 30 44 56 ms automatic restart delay after current-limit/circuit-breaker timeout t off latch = gnd (note 8) 128 x (t ilim or t cb ) ms gate1 turn-off time (oring response time) t or from v or trigger until (v gate1 - v in ) < 1v, c gate1 = 10nf 100 ns turn-off response time t on_off time from v on < (v on_off - hysteresis) until (v gate2 - v out ) < 1v, gate2 = open (note 9) 0.34 0.6 ? minimum delay from on low to low-current shutdown mode t sd on step from 1.3v to 0.4v 50 ? note 1: all min/max parameters are tested at +25? and +85?. limits at -40? are guaranteed by design. note 2: measured at both v gate2 = v out = 0v and v gate2 = v out = v in . note 3: the typical value of parameter v thf is 1.5 x v th . note 4: current-limit/circuit-breaker timeout; in or on low. note 5: see the typical operating circuit . measured at v gate1 = v sense . note 6: the tristate (?loating? logic condition will be entered if the pin current is within these limits. note 7: r tim is connected from tim to gnd. the maximum timeout period is enforced to prevent arbitrarily long operation in cur- rent-limit mode. therefore, the relationship between resistor value and timeout changes for large values of r tim . see current-limit timeout vs. r tim in the typical operating characteristics for nominal values. note 8: parameter t off is a direct multiple of t ilim (or t cb ), so the limits for t off track the limits for t ilim (or t cb ). note 9: if the on voltage goes below v on_ref - hysteresis, then gate2 goes low immediately to disconnect power from the load quickly (within t on_off ).
max5943 firewire current limiter and low-drop oring switch controller _______________________________________________________________________________________ 5 supply current vs. supply voltage max5943 toc01 supply voltage (v) supply current (ma) 35 30 20 25 15 10 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 1.0 540 t a = +85 c t a = +25 c t a = -40 c shutdown supply current vs. supply voltage max5943 toc02 supply voltage (v) shutdown supply current ( a) 35 30 20 25 15 10 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0 540 current-limit/circuit-breaker threshold voltage vs. temperature max5943 toc03 temperature ( c) threshold voltage (mv) 60 35 10 -15 46.5 47.0 47.5 48.0 48.5 49.0 49.5 50.0 50.5 51.0 51.5 52.0 46.0 -40 85 ilim = gnd v in = 32v v in = 12v v in = 7.5v current-limit/circuit-breaker threshold voltage vs. temperature max5943 toc04 temperature ( c) threshold voltage (mv) 60 35 10 -15 56.5 57.0 57.5 58.0 58.5 59.0 59.5 60.0 60.5 61.0 61.5 62.0 56.0 -40 85 ilim = in v in = 32v v in = 12v v in = 7.5v current-limit/circuit-breaker threshold voltage vs. temperature max5943 toc05 temperature ( c) threshold voltage (mv) 60 35 10 -15 36.5 37.0 37.5 38.0 38.5 39.0 39.5 40.0 40.5 41.0 41.5 42.0 36.0 -40 85 ilim = floating timeout period vs. r tim max5943 toc06 r tim (k ) timeout period ( s) 100 10 0.1 1 10 100 0.01 1 1000 max5943a max5943e oring threshold voltage vs. temperature max5943 toc07 temperature ( c) oring threshold voltage (mv) 60 35 -15 10 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 4.0 -40 85 5.5 6.5 7.5 8.5 9.5 10.5 11.5 4.5 or_adj = in or_adj = open or_adj = gnd gate currents vs. temperature max5943 toc08 temperature ( c) gate currents ( a) 60 35 10 -15 -40 85 gate2 44.5 45.0 45.5 46.0 46.5 47.0 44.0 gate1 gate1 drive voltage vs. temperature max5943 toc09 temperature ( c) gate1 drive voltage (v) 60 35 10 -15 5.233 5.236 5.239 5.242 5.245 5.248 5.251 5.254 5.257 5.260 5.230 -40 85 typical operating characteristics (v in = +12v, t a = +25?, unless otherwise noted.)
max5943 firewire current limiter and low-drop oring switch controller 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v in = +12v, t a = +25?, unless otherwise noted.) gate2 drive voltage vs. temperature max5943 toc10 temperature ( c) gate2 drive voltage (v) 60 35 10 -15 5.203 5.206 5.209 5.212 5.215 5.218 5.221 5.224 5.227 5.230 5.200 -40 85 on high voltage vs. temperature max5943 toc11 temperature ( c) on high voltage (v) 60 35 10 -15 1.252 1.254 1.256 1.258 1.260 1.250 -40 85 on low voltage vs. temperature max5943 toc12 temperature ( c) on low voltage (v) 60 35 10 -15 -40 85 1.182 1.184 1.186 1.188 1.190 1.192 1.194 1.196 1.198 1.200 1.180 fault low voltage vs. temperature max5943 toc13 temperature ( c) fault low voltage (mv) 60 35 10 -15 -40 85 20 40 60 80 100 120 140 160 180 200 0 i fault = 5ma oring threshold response time max5943 toc14 i in 500ma/div v out 5v/div (v gate - v sense ) 5v/div v in 10v/div 100 s/div or_adj = in turn-off response time max5943 toc15 i in 1a/div v out 10v/div v gate2 10v/div v on 2v/div 200ns/div max5943a short-circuit event (v in = 37v) max5943 toc16 i in 1a/div v out 50v/div v gate2 50v/div v in 50v/div 400 s/div tim = in ilim = gnd v fault 50v/div
max5943 firewire current limiter and low-drop oring switch controller _______________________________________________________________________________________ 7 max5943a short-circuit event (v in = 37v) max5943 toc17 i in 10a/div v out 50v/div v gate2 50v/div v in 50v/div 100ns/div ilim = gnd v fault 50v/div max5943a short-circuit response (v in = 8v) max5943 toc18 i in 1a/div v out 10v/div v gate2 10v/div v in 10v/div 400 s/div tim = in v fault 10v/div max5943a short-circuit response (v in = 8v) max5943 toc19 i in 10a/div v out 10v/div v gate2 10v/div v in 10v/div 100ns/div v fault 10v/div max5943e short-circuit response (v in = 24v) max5943 toc20 i in 166a/div v out 50v/div v gate2 50v/div v in 50v/div 200 s/div v fault 50v/div max5943e short-circuit response (v in = 8v) max5943 toc21 i in 60a/div v out 10v/div v gate2 10v/div v in 10v/div 100 s/div v fault 10v/div tim = in oring switchover waveform max5943 toc22 i in1 500ma/div v out 1v/div 200 s/div i in2 500ma/div v in1 = 12v v on2 rising = 12v v in2 = 128v c out = 0 typical operating characteristics (continued) (v in = +12v, t a = +25?, unless otherwise noted.)
max5943 firewire current limiter and low-drop oring switch controller 8 _______________________________________________________________________________________ oring switchover waveform (v in2 rising above v in1 ) max5943 toc23 i in1 500ma/div v out 1v/div 10 s/div i in2 500ma/div v in1 = 12v v on2 rising = 12v v in2 = 13v c out = 0 oring switchover waveform (v in2 falling below v in1 ) max5943 toc24 i in1 500ma/div v out 1v/div 20 s/div i in2 500ma/div v in1 = 12v v on2 falling = 12v v in2 = 13v c out = 0 max5943a hot plug-in load capacitance into active port (no fault) max5943 toc25 i in 2a/div v fault 10v/div 400 s/div v out 10v/div c load = 220 f tim = in v gate2 10v/div max5943a hot plug-in load capacitance into active port (current-limit timeout) max5943 toc26 i in 1a/div v fault 10v/div 400 s/div v out 10v/div c load = 470 f tim = in v gate2 10v/div typical operating characteristics (continued) (v in = +12v, t a = +25?, unless otherwise noted.)
max5943 firewire current limiter and low-drop oring switch controller _______________________________________________________________________________________ 9 pin description pin name function 1on on/off-control input. on sets the undervoltage lockout threshold and resets the part after a fault latch. drive on high to enable the device. drive on low to disable the device. connect on to in for the default undervoltage lockout threshold. connect a resistor-divider from in to on and gnd to program the desired undervoltage lockout threshold. 2 fault current-fault, active-low, open-drain output. fault asserts and latches low after a current-limit/circuit- breaker fault has exceeded the current-limit/circuit-breaker timeout period (see the fault section ). 3 tim current-limit/circuit-breaker timeout adjustment input. connect tim to in for the default timeout period or connect a resistor from tim to gnd to program the current-limit/circuit-breaker timeout period. 4 ilim current-limit/circuit-breaker threshold input. leave ilim open for a 40mv circuit-breaker threshold, connect to gnd for a 50mv circuit-breaker threshold, or connect to in for a 60mv circuit-breaker threshold (see the current limiting section). 5 latch latch or autoretry fault management selection input. connect latch to in to select latch-off mode after a current-limit/circuit-breaker timeout. connect latch to gnd for autorestart mode after a current- limit/circuit-breaker timeout. 6 or_adj oring switch turn-on current threshold adjustment input. select one of three oring switch turn-on threshold settings: connect or_adj to gnd, connect or_adj to in, or leave or_adj floating (see the power-supply oring section). 7, 10, 13 n.c. no connection. not internally connected. 8 onq1 oring switch manual turn-on input. drive onq1 low to enable power-supply oring. drive onq1 high to set gate1 high to allow reverse current flow. onq1 is disabled when v in is below the uvlo threshold, v on is below the v on_ref threshold, and after a current/circuit-breaker fault. 9 gnd ground 11 out output voltage sense. connect to the output. 12 gate2 current-limiter switch gate drive output. connect gate2 to the gate of the 2nd n-channel mosfet. gate2 is a charge pump with a 45? pullup current to 5.5v (typ) above out when active (see the typical operating circuit ). 14 gate1 oring switch gate-drive output. connect gate1 to the gate of the 1st n-channel mosfet. gate1 is a charge pump with a 45? pullup current to 5.5v (typ) above sense when active (see the typical operating circuit ). 15 sense current-sense negative input. connect a current-sense resistor, r sense, from in to sense (see the typical operating circuit ). 16 in input power and current-sense positive input. connect in to the positive terminal of the current-sense resistor and to the power source (see the typical operating circuit ).
max5943 firewire current limiter and low-drop oring switch controller 10 ______________________________________________________________________________________ detailed description the max5943 performs hot-swapping, power-supply oring, and current limiting for firewire power-supply applications. the max5943 incorporates two mosfet drivers (gate1 and gate2) to control two external n-channel power mosfets to perform low-voltage-drop power-supply oring (gate1) and hot swapping and current limiting (gate2) from the input power supply to the load. a sense resistor provides accurate current- limiting/circuit-breaker function. gate1 and gate2 provide true load disconnect to prevent current flowing from either direction between in and out. the max5943 remains in low-current shutdown mode when v on is below the 0.4v threshold. low-current shutdown mode disables the max5943, resulting in less than 10? supply current. shutdown places all logic inputs in a high-impedance state allowing the inputs to be connected to in without drawing additional current from the supply. when the input supply voltage (v in ) is above 7.5v and v on is above the v on_ref threshold, the max5943 turns on, sourcing 45? current from gate2 (current regulation) to enhance q2 slowly. for the max5943a, if the voltage across the current-sense resistor, v is , is greater than the programmed current-limit threshold, the max5943a regulates the gate2 voltage to limit the load current at the current-limit level so that v is is equal to v th . in normal operation, v is drops below v th and gate2 rises to approximately 5.5v above out. since the max5943b?ax5943e do not regulate the load current, a capacitor can be added from gate2 to gnd to limit inrush current during startup (see the applications information section). sense sense gate1 6.5v 1.24v gate1 gate2 out max5943a?max5943e power source (fast current- limit threshold) circuit-breaker (current-limit) threshold or comparator threshold gnd latch tim x128 fault + - + - + - + - + - 0.4v shutdown mode on comparator ( ) max5943a only. uvlo comparator + - fault management latch or autoretry autoretry timeout period fault timeout gate1 drive cp1 cp2 gate charge pumps out gate2 gate2 drive onq1 or_adj ilim on r sense q1 q2 figure 1. max5943 functional diagram
max5943 firewire current limiter and low-drop oring switch controller ______________________________________________________________________________________ 11 the max5943 current-limit/circuit-breaker timeout is programmable by connecting an external resistor from tim to gnd. the max5943a has a default 2ms current- limit timeout. the max5943b, max5943c, max5943d, and max5943e have 0.5ms, 1ms, 2ms, and 4ms default circuit-breaker timeouts, respectively. gate1 controls the max5943 oring function. initially, gate1 is off (onq1 = low) and the load current con- ducts through the body diode of q1. gate1 rises to 5.5v above sense when v is exceeds v or , thereby enhancing q1 and reducing the voltage drop, power dissipation, and heat generation in the power-supply path. when a voltage greater than v in is connected at out, the higher voltage source commences, providing current to the load. the max5943 rapidly turns off gate1 upon v is falling below v or - hysteresis, thus blocking the higher voltage from back-driving v in . gate1 also turns off when the load current drops, causing v is to fall below the v or hysteresis. current limiting/circuit breaker current limiting (max5943a only) the max5943a limits the load current by monitoring the voltage across r sense at all times and by regulating the current to the load as necessary to keep v is to its pro- grammable current-limit threshold voltage (v th ). set the maximum current limit (i limit ) by placing the appropriate sense resistor between in and sense, where i limit = v th /r sense . when the load current is less than i limit , gate2 rises to v g2 (5.5v) to fully enhance mosfet q2 (see the typical operating circuit) . when the load current attempts to draw more than i limit , the max5943a? gate2 pulldown current (i g2d ) regulates the current through q2 causing out to act as a constant-current source. the output current is limited to the programmed i limit . if the current-limit condition persists after the current-limit timeout (t ilim ) period has expired, gate2? strong pulldown current (i g2 off ) quickly turns off gate2 to disconnect the load from the power supply. fault then asserts low (figure 2a). if the current-limit duration is less than t ilim , gate2 pulls to v g2 (figure 2b). during an output short circuit or a gross overload, the load current overshoots and causes v is to exceed the fast pulldown current-limit threshold voltage (v thf ). the max5943a responds with much stronger gate2 pulldown currents (i g2dp and/or i g2df ) to quickly bring the load current back down to the pro- grammed current limit. i out v in v out v gate1 v gate2 v fault i out v out v gate1 v gate2 v fault t ilim < t ilim i limit i limit i limit x r load i limit x r load (a) (b) figure 2. max5943a current-limit timing diagram
max5943 firewire current limiter and low-drop oring switch controller 12 ______________________________________________________________________________________ max5943b?ax5943e circuit breaker the max5943b?ax5943e provide a circuit-breaker function that protects against excessive load currents and short-circuit conditions. the load current is monitored by sensing the voltage across an external sense resistor (r sense ) and disconnects the load from the power source when the voltage across r sense ,v is , exceeds the programmed circuit-breaker thresholds (v th ) for longer than the circuit-breaker timeout period, t cb . unlike the max5943a, when an output short circuit or overcurrent occurs, the max5943b?ax5943e keep gate2 fully enhanced. the short-circuit current is limit- ed only by the input source impedance, r sense , q1? r ds(on), q2? r ds(on) , and any parasitic impedance in the power path. if the excessive current condition per- sists (as indicated by v is > v th ) for longer than t cb , gate2 turns off with a strong pulldown (i g2 off ) to quickly disconnect the power source from the load and fault asserts low (figure 3). exercise caution when using the max5943b?ax5943e. unlike the max5943a, the max5943b?ax5943e do not limit the load current during t cb . high current during t cb may cause damage to external devices connected in the power path. current-limit/circuit-breaker thresholds the max5943 allows three selectable current-limit/cir- cuit-breaker thresholds (v th ). choose the voltage threshold by connecting ilim to the appropriate level; see table 1. current-limit/circuit-breaker timeout period (t ilim /t cb ) the max5943? current-limit/circuit-breaker timeout function disconnects power from the load if the current- limit or circuit-breaker threshold voltage exceeds its maximum limit for a programmable amount of time. connect tim to in for the max5943 default timeout periods (see table 2). adjust the fault timeout period (t ilim/ t cb ) by connect- ing a resistor (r tim ) from tim to gnd (see the typical operating characteristics ). calculate the fault-limit timeout period using the following equation: where r tim is in k , t ilim /t cb is in ms, and k = 1 for max5943a, k = 32 for max5943b, k = 16 for max5943c, k = 8 for max5943d, and k = 4 for the max5943e. tmstms rk k ilim cb tim () () . () == 025 i out i limit t cb v in v g2 v g2 v out v gate1 v gate2 v fault figure 3. max5943b?ax5943e circuit-breaker timing diagram table 1. current-limit/circuit-breaker trip threshold level ilim connection v th (mv) open 40 gnd 50 in 60 part default timeout, tim = in (ms) programmable timeout range (4k < r tim < 50k ) maximum timeout, tim = floating (ms) max5943a 2 1.04ms to 11.05ms 175 max5943b 0.5 32.5? to 345? 4.8 max5943c 1 65? to 690? 9.6 max5943d 2 130? to 1.38ms 19.2 max5943e 4 260? to 2.76ms 38.4 table 2. max5943_ timeout periods
max5943 firewire current limiter and low-drop oring switch controller ______________________________________________________________________________________ 13 timing accuracy is guaranteed for r tim ranging from 4k to 50k . large r tim values can be used, which reduces timing accuracy. a maximum timeout period is enforced to prevent arbitrarily long operation in current- limit/circuit-breaker conditions. long durations in current-limit/circuit-breaker mode may produce excessive heating and electrical stresses in r sense , q1, q2, and any other components in the power path. use component values rated to handle electrical stresses during the timeout period. power-supply oring (onq1 = low) gate1 controls the max5943 oring function. the max5943 accomplishes a very-low-voltage-drop diode oring function using an n-channel power mosfet, q1. initially, gate1 is off (onq1 = low) and the load current conducts through the body diode of q1 (figure 4). gate1 rises to 5.5v above sense when v is exceeds v or , enhancing q1. q1? low r ds(on) provides a very- low-voltage drop across its source to drain, reducing volt- age drop, power dissipation, and heat generation in the power-supply path created by a traditional diode. the max5943 continuously monitors the load current by the voltage drop, v is , across the current-sensing resistor. q1 turns off rapidly when v is decreases below v or minus its hysteresis. set the max5943 oring threshold (v or ) by connecting or_adj to gnd for a 5mv threshold, or to in for a 10mv threshold, or leave it open for a 7.5mv threshold. connect onq1 to gnd for normal oring function. drive onq1 high to force q1 on, regardless of the load current condition, as long as the voltages at in and on exceed v uvlo and v on_ref , respectively, and the device is not in a current fault shutdown. when a higher voltage supply is connected at out (figure 5), the sense voltage drops below the program- mable oring threshold. the max5943 immediately turns off q1, blocking reverse current flow from out to in. the power is then routed from the higher supply input to the load (figure 6). sense gate1 or_adj onq1 gnd gate2 out q1 q2 in to firewire port max5943 on v in r sense + v is - figure 4. q1 current path during inital startup i load r sense sense gate1 or_adj onq1 gnd gate2 out in v ina v inb > v ina from battery source to firewire port i ina = 0 max5943 on r sense sense gate1 or_adj onq1 gnd gate2 out in v inb from power source i inb max5943 on figure 5. max5943 oring controller rerouting load current v ina i ina i inb v inb v inb > v ina v out figure 6. max5943 power switch over oring timing diagram
max5943 firewire current limiter and low-drop oring switch controller 14 ______________________________________________________________________________________ reverse current override (onq1 = high) drive onq1 high to disable the power-supply oring function. disabling the max5943 oring function allows reverse current flow through the power-supply system. when onq1 is high, gate1 remains fully enhanced as long as v in is greater than v uvlo , v on is above the v on_ref threshold, and the max5943 is not in a cur- rent-limit or circuit-breaker fault condition. the max5943 reverse-current flow feature permits a higher voltage source connected to one port to route power to another port, as long as the voltage at in remains above the minimum 7.5v operating range (see figure 7). undervoltage lockout the max5943 operates from 7.5v to 37v and has a default 6.5v undervoltage lockout threshold. the external mosfets remain off as long as v in > 6.5v and v on < v on_ref . the turn-on threshold is programmable by connecting a resistor-divider at on. when v on > 1.24v and v in > 7.5v, gate2 is enhanced to 5.5v, with respect to out and the max5943 goes into normal operation. program the max5943? turn-on voltage using the fol- lowing formula: where v turn_on is the desired turn-on voltage of the max5943. choose an r2 value in the 1k range to minimize error due to the on bias current. when operating the max5943, on must remain above its 1.24v threshold. if v on falls below its 1.24v thresh- old, the power-supply mosfets (q1 and q2) turn off immediately (less than 1?). this allows the power sup- ply to disconnect in the event of a fault condition detected by the system, such as shorting of the output to a different power-supply voltage or a firewire signal pin. if possible transient conditions exist at the main power-supply line (in), place an rc filter at on to reject transient voltage dips and to prevent unneces- sary power-supply interruptions. the max5943 remains in low-current shutdown mode when v on is below the 0.4v threshold. low-current shutdown mode disables the max5943 resulting in less than 10? supply current. shutdown places all logic inputs in a high-impedance state allowing the inputs to be connected to in without drawing additional current from the supply. an internal delay, t sd , allows q1 and q2 to be turned off before the max5943 enters low- current shutdown mode. fault status output (fault) fault is a high-voltage open-drain output that pulls low when a current-limit/circuit-breaker fault shutdown has occurred. fault remains low until the next startup cycle. r v r turn on 1 124 12 =? ? ? ? ? ? ? _ . sense gate1 or_adj gnd latch ilim gate2 port1 out in max5943 tim on onq1 fault sense gate1 or_adj gnd latch ilim gate2 port2 out in max5943 tim on onq1 fault figure 7. max5943 operating in reverse-current mode (routing power from port 1 to port 2) max5943 r2 r1 v in in gnd on figure 8. setting the max5943 turn-on voltage max5943 r2 r1 v in in latch gnd on figure 9. resetting max5943 after a latched fault condition
max5943 firewire current limiter and low-drop oring switch controller ______________________________________________________________________________________ 15 fault management the max5943 offers either latch or autoretry fault man- agement configurable by the latch input. connect latch to in for latch fault management or connect latch to gnd for autoretry fault management. in latch fault management, fault latches low, gate1 and gate2 latch off indefinitely. cycle on low and then high to unlatch and restart the max5943. however, the max5943 will not enter a startup cycle until t off has expired. figure 9 illustrates a way to reset the max5943 after a fault using a pushbutton switch. in autoretry fault management, the max5943_ attempt to restart after a t off of 128 x t ilim (or 128 x t cb ) limit- ing the duty cycle of the mosfets to 1/129 under con- tinuous fault conditions. fault deasserts every time a restart attempt is made. applications information startup consideration max5943a during startup, a large capacitor at out may result in a charging current equivalent to the current limit. choose a current-limit timeout that will allow a successful startup. the timeout can be approximated using the following equation: \where i limit is the programmed current limit, c out is the capacitor at out, v in is the supply voltage, and i load is the load current during startup. with in = 12v, c out = 330?, i limit = 1.5a, and i load = 0, the max5943 commences by charging the output capacitor with 1.5a for approximately 2.7ms. therefore, the max5943a current-limit timeout period (t ilim ) should be greater than 2.7ms for a successful startup. otherwise, the max5943a powers up in fault management mode by exceeding the current-limit timeout period. max5943b?ax5943e the max5943b?ax5943e do not control the inrush current during startup. inrush current control can be implemented by placing a resistor and capacitor at gate2 (figure 10) to slowly ramp up the gate voltage, thus limiting the inrush current. the inrush current can be approximated using the following formula: where i g2u is gate2? 45? sourcing current and i load is the load current at startup. to prevent the max5943b?ax5943e from starting up in a fault condition set: optimizing for short-circuit conditions choosing r sense select a sense resistor that causes the circuit-breaker voltage drop at a current-limit/circuit-breaker level above the maximum normal operating current. typically, set the overload current at 1.2 to 1.5 times the full load current. choose the sense-resistor power rating to accommodate an overcurrent condition: p rsense = i 2 limit x r sense where p rsense is the power dissipated across r sense during a current-limit/circuit-breaker fault. under short-circuit conditions, it is imperative that the appropriate sense resistor is utilized. operating the max5943b?ax5943e at high input voltages can cause very large currents during the circuit-breaker timeout period. the peak current will be limited by the saturation current of q2 or the series resistance in the power path (r total ). using a 30m on-resistance mosfet at gate1 and gate2 and a 30m sense resistor results in a short-cir- cuit current approximately equal to: i sc = v in /r total where: r total = r sense + 2 x (r on ) = 30m + 2 x (30m ) = 90m for example, an input voltage of 20v produces a current at approximately 222a (or i sat of q2, whichever is less) in the power path for the circuit-breaker timeout period. choose an r sense capable of handling the high power dissipation during a short-circuit event. i v r inrush th sense < i c c ii inrush out gate g u load =+ 2 2 t cv ii ilim out in limit load > ? q1 q2 c gate c out r sense sense gate1 gate2 gnd out load 45 a in + - v in i c i load max5943b?ax5943e 1k figure 10. controlling the max5943b?ax5943e inrush c urrent
max5943 firewire current limiter and low-drop oring switch controller 16 ______________________________________________________________________________________ mosfet selection select external mosfets according to the application current level. the mosfets?on-resistance (r ds(on) ) should be chosen low enough to have minimum voltage drop at full load to limit the mosfet power dissipation. high r ds(on) also causes large output ripple if there is a pulsating load. determine the device power rating to accommodate startup, a short-circuit condition, and when the device is in autoretry mode. during normal operation, the external mosfets dissipate little power. the power dissipated in normal operation is: p = i load 2 x r ds(on) the most power dissipation occurs during a short-circuit event, resulting in high power dissipated in q2 (figure 11) during the timeout period for the max5943a, where the power dissipated across q2 is: p q2 = (v in - v is ?v q1 ) x i limit for the max5943b?ax5943e, a short-circuit event results in high power dissipated in both q1 and q2 dur- ing the timeout period (figure 13) where the total power dissipated in either mosfet is: p = i sc 2 x r ds(on) where: i sc = v in /r eq and r eq = r sense +r ds(on1) + r ds(on2) v q1 v q2 v is sense gate1 gate2 out in +- +- +- v in max5943a figure 11. power dissipated across mosfets during a short- circuit fault for max5943a r2 0.020 1% 0.25w c3 1 f c4 0.1 f l1 ferrite 250 r3 1k r4 1k r5 100k r6 100k dmmt3906 q1b q1a gnd nc out gate2 n.c. gate1 sense in r1 200k c2 0.01 f c1 1 f j1 v in j2 gnd r7 100k tp1 v in tp2 gnd tp3 port 0 tp4 fault r8 100k tp5 on tp6 v pullup 135 j3 n1 si2318ds n2a si7222dn n2b 246 port 0 on fault tim ilim latch or_adj n.c. onq1 1 2 3 4 5 6 7 89 10 11 12 13 14 15 16 max5943aeee u1 figure 12. ul-recognized single-port firewire protective circuit
max5943 firewire current limiter and low-drop oring switch controller ______________________________________________________________________________________ 17 the programmable timeout of the max5943 allows the use of mosfets with low power ratings. a mosfet typically withstands single-shot pulses with higher dis- sipation than the specified package rating. a single-port firewire protective circuit employing the max5943a has been ul recognized as a result of extensive safety testing by underwriters laboratories. it is the circuits themselves, not any individual component thereof, that are ul recognized. the circuit is further described in application note 3984 ul recognized, ieee 1394 single- and dual-port firewire protective circuits available at www.maxim-ic.com/appnotes.cfm/ appnote_number/3984. the circuit provides: 2.5a (adjustable) current limiting to the load at initial connection or in overload fault condition 2ms (adjustable) current-limit timeout before load disconnect for excessive load current automatic-restart attempts after a fault shutdown condition <0.8% current-limited duty cycle in continuous fault condition 6.5v undervoltage shutdown protection low-drop oring in multiple power-source applica- tions, and fault reporting r ds(on)1 r ds(on)1 r sense sense gate1 gate2 out isc in v in max5943b?max5943e figure 13. power dissipated across mosfets during a short- circuit fault for max5943b?ax5943e figure 14. two-port firewire power provider using max5943a and max5944 sense gate1 or_adj onq1 gnd latch gate2 out in max5943a tim on ilim fault 15m si7958dp si7958dp sense gate1 or_adj onq1 gnd latch gate2 out in max5943a tim on ilim fault 15m si7958dp si7958dp sensea gate1a gate2a outa ina max5944 ona onq1 gnd onb faulta faultb 30m si7958dp si7958dp 30m irf7478 irf7478 max5033 sgnd v in on fb gnd vd in4148 in4148 in4148 bst lx phy power out cable on not sleep current-limit sense port 1 sense port 0 sense cable power source battery- power source in4148 cpa sense port 0 port 1 senseb gate1b gate2b outb inb
max5943 firewire current limiter and low-drop oring switch controller 18 ______________________________________________________________________________________ chip information transistor count: 2324 process: bicmos sense gate1 or_adj onq1 gnd max5943 equivalent circuit latch ilim fault on gate2 out q1 q2 load disconnect switch very-low-drop oring diode current-limit/circuit-breaker and inrush control in to firewire port firewire port supply max5943a tim r3 + v is - r sense r1 r2 typical operating circuit part current limiter/ circuit breaker default timeout (ms) programmable timeout range max5943a current limit 2 1.04ms to 11.05ms max5943b circuit breaker 0.5 32.5? to 345? max5943c circuit breaker 1 65? to 690? max5943d circuit breaker 2 130? to 1.38ms max5943e circuit breaker 4 260? to 2.76ms selector guide 30m si7958dp si7958dp sense gate1 or_adj onq1 gnd latch ilim fault on gate2 out q1 q2 in + - v in = 12v to firewire port firewire port supply max5943a tim 4k 10k 1k 7.15k typical application circuit firewire power management the max5943 serves to regulate and protect firewire power over a system interface. the max5943 program- mable features make it suitable for both power provider and power receiver applications. figure 14 shows a high-end two-port firewire power management system using two max5943as and a dual-channel max5944 firewire current-limiting ic. transient protection if in or out experiences a fast voltage transient, the drain-to-gate parasitic capacitance of q1 and/or q2 may be sufficient to briefly enhance one of the transis- tors, allowing current glitch. if the circuit is subjected to large transients, connect capacitors from the gate to source across the appropriate mosfet, preventing the parasitic capacitance from turning on the device. caution: the additional gate-to-source capacitance causes the turn-off time of the mosfets to increase due to the additional charge of the capacitor. use the minimum capacitor value to prevent currents from flow- ing in hot-plug situations.
max5943 package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) qsop.eps firewire current limiter and low-drop oring switch controller ______________________________________________________________________________________ 19
max5943 firewire current limiter and low-drop oring switch controller maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 20 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2007 maxim integrated products is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 8/04 initial release 1 1/05 corrected table 2 and figures 10, 11, and 12 12, 15, 16, 17 2 10/07 added firewire/ieee and ul information, inserted new figure 12, and updated package outline 1, 16, 17, 18, 20

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