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december 1999 1 MIC2537 MIC2537 micrel MIC2537 quad power distribution switch final information general description the MIC2537 is a cost-effective high-side power switch with four independently controlled channels, optimized for bus- powered universal serial bus (usb) applications. few exter- nal components are necessary to satisfy usb requirements. the MIC2537 satisfies the following usb requirements: each switch channel supplies up to 100ma as required by usb bus-powered downstream devices; fault current is limited to typically 250ma, well below the ul 25va safety require- ments; and a flag output is available to indicate fault condi- tions to the local usb controller. soft start eliminates the momentary voltage drop on the upstream port that may occur when the switch is enabled in bus-powered applications. additional features include thermal shutdown to prevent catastrophic switch failure from high-current loads and 3.3v and 5v logic compatible enable inputs. the MIC2537 is available in active-high and active-low ver- sions in a 16-lead sop package. typical application en oc MIC2537 3.3v usb controller v bus d+ dC gnd v bus d+ d C gnd mic5207-3.3 ldo regulator in out gnd 33f* ferrite bead d+ d C v+ ena in flga nc enb outa flgb outb bold lines indicate 0.1" wide, 1-oz. copper high-current traces. downstream usb port 1 100ma max. downstream usb port 2 100ma max. 33f* 0.1 f v bus d+ d C gnd v bus d+ d C gnd 33f* enc outd flgc end nc flgd gnd downstream usb port 3 100ma max. downstream usb port 4 100ma max. 33f* 0.01f 0.01f 0.01f 0.01f 4.7 f 1f gnd upstream v bus 4.75v to 5.25v 500ma max. * 33f, 16v tantalum or 100f, 10v electrolytic per port outc 10k en oc en oc en oc 10k 10k 10k typical bus-powered hub features ? compliant to usb specifications ? 3v to 5.5v input ? 100ma minimum continuous load current per port ? 425m ? typical on-resistance ? < 400ma current limit ? individual open-drain fault flag leads ? 3v/5v-compatible enable inputs ? active-high (-1) and active-low (-2) versions ? 100 a max. on-state supply current ? <1 a typical off-state supply current ? 16-lead sop package ?C 40 c to 85 c operation applications ? usb keyboards ? usb bus-powered docking stations ? notebook docking stations ? notebook pcs ? pda ? general power distribution micrel, inc. ?1849 fortune drive ?san jose, ca 95131 ?usa ?tel + 1 (408) 944-0800 ?fax + 1 (408) 944-0970 ?http://www.mic rel.com
MIC2537 micrel december 1999 2 MIC2537 pin description pin number pin name pin function 1 flga flag a: (output): channel a open-drain fault flag output. 2 ena enable a (input): channel a control input. 3 outa output a: channel a switch output. 4 gnd ground: supply return. connect both leads to ground. 5, 12 nc not internally connected 6 outb output b: channel b switch output. 7 enb enable b (input): channel b control input. 8 flgb flag b (output): channel b open-drain fault flag output. 9 flgc flag c (output): channel c open-drain fault flag output. 10 enc enable c (input): channel c control input. 11 outc output c: channel c switch output. 13 in positive supply input 14 outd output d: channel d switch output. 15 end enable d (input): channel d control input. 16 flgd flag d (output): channel d open-drain fault flag output. pin configuration 1 2 3 4 16 15 14 13 flgd end outd in flga ena outa gnd MIC2537-x 5 6 7 8 12 11 10 9 nc outc enc flgc nc outb enb flgb 16-lead sop (m) ordering information part number enable temperature range package MIC2537-1bm active high C 40 c to +85 c 16-lead sop MIC2537-2bm active low C 40 c to +85 c 16-lead sop
december 1999 3 MIC2537 MIC2537 micrel electrical characteristics v in = +5v; t a = 25 c; unless noted. parameter condition min typ max units supply current note 4 , switch off, outa C d = open 0.75 5 a note 4 , all switches on, outa C d = open 70 100 a enable input threshold low-to-high transition 1.8 2.4 v high-to-low transition, note 4 0.8 1.6 v enable input current v en = v oh(min) = 2.4v 0.01 1 a v en = v ol(max) = 0.8v 0.01 1 a enable input capacitance 1pf switch resistance single switch, 100ma load 425 700 m ? output turn-on delay r l = 50 ? , c l = 1 f, note 5 0.51 ms output turn-on rise time r l = 50 ? , c l = 1 f, note 5 0.2 0.5 ms output turnoff delay r l = 50 ? , c l = 1 f, note 5 150 300 s output turnoff fall time r l = 50 ? , c l = 1 f, note 5 148 300 s output leakage current each output (switch off) 1 10 a current limit threshold ramped load applied to enable output, note 6 300 500 ma continuous load current each output, flg not active 100 ma short circuit current limit each output (enabled into load), v out = 4.0v 150 250 400 ma overtemperature shutdown t j increasing 135 c threshold t j decreasing 125 c error flag output resistance v in = 5v, i l = 10ma 10 ? v in = 3.3v, i l = 10ma 12 ? error flag off current v flag = 5v 0.01 1 a note 1. exceeding the absolute maximum rating may damage the device. note 2. the device is not guaranteed to function outside its operating rating. note 3. devices are esd sensitive. handling precautions recommended. human body model, 1.5k ? in series with 100pf. note 4. off is 0.8v and on is 2.4v for the MIC2537-1. off is 2.4v and on is 0.8v for the MIC2537-2. the enable input has approximately 200mv of hysteresis. see control threshold charts. note 5. see timing diagrams. note 6. see functional characteristics: current-limit response graph. absolute maximum ratings (note 1) supply voltage (v in ) .....................................................+6v fault flag voltage (v flg ) .............................................. +6v fault flag current (i flg ) ............................................ 25ma output voltage (v out ) .................................................. +6v output current (i out ) ............................... internally limited control input (v en ) ......................................... C 0.3v to 12v storage temperature (t s ) ....................... C 65 c to +150 c lead temperature (soldering 5 sec.) ....................... 260 c esd rating, note 3 ....................................................... 2kv operating ratings (note 2) supply voltage (v in ) ...................................... +3v to +5.5v ambient operating temperature (t a ) ........ C 40 c to +85 c thermal resistance sop ( ja ) .......................................................... 120 c/w
MIC2537 micrel december 1999 4 MIC2537 typical characteristics 0 20 40 60 80 100 23456 supply current ( a) supply voltage (v) supply current vs. supply voltage t a = 25 c r l = 0 20 40 60 80 100 -40 -20 0 20 40 60 80 100 supply current ( a) temperature ( c) supply current vs. temperature v in = 5v v in = 3.3v r l = 0 100 200 300 400 500 23456 on-resistance (m ? ) supply voltage (v) ouput on-resistance variation vs. supply voltage t a = 25 c i l = 100ma 0 100 200 300 400 500 -40 -20 0 20 40 60 80 100 on resistance (m ? ) temperature ( c) output on-resistance variation vs. temperature v in = 5v i l = 100ma 0 50 100 150 200 250 300 23456 current (ma) supply voltage (v) overcurrent threshold and current limit vs. supply voltage i thr i lim t a = 25 c 0 50 100 150 200 250 300 -40 -20 0 20 40 60 80 100 current (ma) temperature ( c) overcurrent threshold and current limit vs. temperature i thr i lim v in = 5v 0 0.5 1.0 1.5 2.0 23456 enable voltage (v) supply voltage (v) control threshold vs. supply voltage v ih v il t a = 25 c 0 0.5 1.0 1.5 2.0 -40 -20 0 20 40 60 80 100 threshold voltage (v) temperature ( c) control threshold vs. temperature v ih v il v in = 5v 0 100 200 300 400 500 -40 -20 0 20 40 60 80 100 time ( s) temperature ( c) output rise time vs. temperature v in = 5v c l = 0.01 f r l = 44 ? 0 0.5 1.0 1.5 -40 -20 0 20 40 60 80 100 time ( s) temperature ( c) output fall time vs. temperature v in = 5v c l = 0.01 f r l = 44 ?
december 1999 5 MIC2537 MIC2537 micrel functional characteristics input voltage response (input voltage rising: MIC2537-2) time (25ms/div.) i out (100ma/div.) v i n (2v/div.) v out (2v/div.) v flg (2v/div.) en = 0v r l = 24 ? current limit transient response (heavy load applied to output: MIC2537-2) time (25 s/div.) i out (500ma/div.) v e n (5v/div.) v out (5v/div.) v flg (10v/div.) v in = 5v 1v current limit response (ramped load: MIC2537-2) time (5ms/div.) i out (100ma/div.) v e n (5v/div.) v out (5v/div.) v flg (10v/div.) v in = 5v 1v 250ma current limit threshold 180ma short circuit current limit input voltage response (input voltage decreasing: MIC2537-2) time (25ms/div.) i out (100ma/div.) v i n (2v/div.) v out (2v/div.) v flg (2v/div.) e n = 0v r l = 24 ?
MIC2537 micrel december 1999 6 MIC2537 test circuit device under test c l out r l v out timing diagrams 90% v out 10% 90% 10% t r t f output rise and fall times v en 50% 90% v out 10% t off t on active-low switch delay times (MIC2537-2) v en 50% 90% v out 10% t off t on active-low switch delay times (MIC2537-1)
december 1999 7 MIC2537 MIC2537 micrel functional diagram 1.2v reference thermal shutdown charge pump outd gate control in ena gate control outa flgd charge pump end osc. flga current limit current limit gnd MIC2537 flg b current limit outb gate control charge pump enb current limit outc flgc gate control charge pump enc
MIC2537 micrel december 1999 8 MIC2537 functional description the MIC2537-1 and MIC2537-2 are quad high-side switches with active-high and active-low enable inputs, respectively. fault conditions turn off or inhibit turn-on of one or more of the output transistors, depending upon the type of fault, and activate the open-drain error flag transistors making them sink current to ground. input and output in (input) is the power supply connection to the logic circuitry and the drain of each output mosfet. outx (output) is the source of each respective mosfet. in a typical circuit, current flows through the switch from in to outx toward the load. if v out is greater than v in , current will flow from out to in since the mosfet is bidirectional when on. the output mosfet and driver circuitry are also designed to allow the mosfet source to be externally forced to a higher voltage than the drain (v outx > v in ) when the output is off. in this situation, the MIC2537 prevents reverse current flow. thermal shutdown thermal shutdown shuts off the affected output mosfet and signals the corresponding fault flags if the die tempera- ture exceeds 135 c. 10 c of hysteresis prevents the switch from turning on until the die temperature drops to 125 c. overtemperature detection functions only when at least one switch is enabled. current-limit induced thermal shutdown internal circuitry increases the output mosfet on-resis- tance until the series combination of the mosfet on-resis- tance and the load impedance limits output current to ap- proximately 200ma. the resulting increase in power dissipa- tion may cause the shorted channel to go into thermal shutdown. in addition, even though individual channels are thermally isolated, it is possible they may shut down when an adjacent channel is shorted. when this is undesirable, shut- down of the channels not shorted can be avoided by exter- nally responding to the fault and disabling the current limited channel before the shutdown temperature is reached. the delay between the flag indication of a current limit fault and thermal shutdown will vary with ambient temperature, board layout, and load impedance, but is typically several seconds. the usb controller must therefore recognize a fault and disable the appropriate channel within this time. current sensing and limiting the current-limit threshold is preset internally. the preset level prevents damage to the output mosfet and external load but allows a minimum current of 0.15a through the output mosfet of each channel. the current-limit circuit senses a portion of the output fet switch current. the current sense resistor shown in the block diagram is virtual and has no voltage drop. the reaction to an overcurrent condition varies with the following three sce- narios: switch enabled into short circuit if a switch is powered on or enabled into an excessive load or short circuit, the switch immediately goes into a constant- current mode, slowly increasing the output voltage. the fault flag goes low until the load is reduced. short circuit applied to output when a heavy load or short circuit is applied to an enabled switch, a large transient current may flow until the current- limit circuitry responds. once this occurs, the device limits current to less than the short circuit current-limit specification. see the functional characteristics: current-limit transient response graph for details. current-limit response the MIC2537 current-limit profile exhibits a small foldback effect of approximately 100ma. once this current-limit thresh- old is exceeded the device enters constant-current mode. this constant current is specified as the short-circuit current limit in the electrical characteristics table. it is important to note that the MIC2537 will deliver load current up to the current-limit threshold. see the functional characteristics: current-limit response graph for details. fault flag flgx is an open-drain n-channel mosfet output. fault flags are active (low) for current limit or thermal shutdown. each flag output mosfet is capable of sinking a 10ma load to approximately 200mv above ground. several flgx pins may be wired-nor connected to a common pull-up resistor.
december 1999 9 MIC2537 MIC2537 micrel applications information supply filtering a 0.1 f to 1 f bypass capacitor from in to gnd, located at the device, is strongly recommended to control supply tran- sients. without a bypass capacitor, an output short may cause sufficient ringing on the input (from supply lead induc- tance) to damage internal control circuitry. input or output transients must not exceed the absolute maximum supply voltage (v in(max) = 6v) even for a short duration. MIC2537 flga flgb ena outa outb gnd in enb v in 3v to 5.5v nc nc outc enc end flgc flgd outd 0.1f to 1f figure 1. supply bypassing enable input en must be driven logic high or logic low for a clearly defined input. floating the input may cause unpredictable operation. en should not be allowed to go negative with respect to gnd. soft start the MIC2537 presents a high impedance when off and slowly becomes a low impedance as it turns on. this reduces inrush current and related voltage drop that results from charging a capacitive load, satisfying the usb voltage droop require- ments. transient overcurrent fault-flag filter when the MIC2537 is enabled, large values of capacitance at the output of the device will cause inrush currents to flow that exceed the short circuit current-limit threshold of the device and cause the flag to activate. the duration of this time depends on the size of the output capacitance. see func- tional characteristics: switch turn-on and turnoff charcteristics for details. during the charging time, the device enters into constant-current mode and the flag is activated. as the capacitance is charged the current de- creases below the short circuit current-limit threshold and the flag will be deasserted. flga flgb flgc flgd 10k 50k 0.3f overcurrent usb controller figure 2. transient filter in usb applications it is required that output bulk capacitance shown in typical application is utilized to meet transient regulation requirements during hot-plug events. when the MIC2537 is enabled, the flag will go active for about 5ms depending on output capacitance. additionally, during hot- plug events, inrush currents may cause the flag to go active for approximately 30 s. if these false overcurrent indica- tions are a system problem, they can be masked by an rc filter on the flag output (see figure 2). alternatively, a 15ms debounce routine may be programmed into the usb logic controller to eliminate the need for an rc filter. bus-powered hub port switching the usb specification requires that bus-powered hubs imple- ment port switching on either a ganged or individual basis. the specific implementation must be reported via the hub descriptor status register. individual port switching has advantages in that a fault on one port will not prevent the other ports from operating correctly. in addition, a soft-start circuit must be included in order to reduce inrush currents when the switch is enabled. to meet this requirement, the MIC2537 has been designed to slowly ramp its output. suspend current for hubs, universal serial bus specification revision 1.1 section 7.2.3, stipulates that the maximum suspend current for a configured hub is 2.5ma. this number is derived by allocating 500 a for up to four downstream ports plus 500 a for the hub s internal functions. a nonconfigured hub is considered a low-power device and cannot consume more than 500 a. in a nonconfigured state all downstream devices will be switched off. in most cases, a nonconfigured hub is not a practical state for the system. therefore, the 2.5ma speci- fication is the applicable target specification for the suspend state. in a bus-powered hub with less than 4 ports, the hub may use the additional current for internal functions. the 500 a worst case suspend current must be further divided among the data port termination resistors and internal functions. the termination resistors will consume 3.6v (16.5k ? C 5%) = 230 a. this leaves only 270 a for internal functions. assuming 100 a as the maximum usb controller suspend current, 170 a remains for the rest of the system. the MIC2537 will consume 100 a maximum, leav- ing a margin of 70 a.
MIC2537 micrel december 1999 10 MIC2537 usb voltage regulation usb specifications require a minimum downstream voltage supply of 4.40v from a bus-powered hub port (see applica- tion note 17 for details). the usb specification allows for a 100mv drop across the hub, leaving 250mv for pcb, up- stream cable, and connector resistance. therefore, the on- resistance of the switch for each port, not including pcb resistance, must be about 100mv 100ma = 1 ? . the MIC2537 has a maximum on-resistance of 700m ? , which easily satisfies this requirement. overcurrent indication the usb specification does not require bus-powered hubs to report overcurrent conditions to the host since the hub is already current-limited at the upstream port. however, if it is desired to report overcurrent, the hub descriptor status register must be programmed to indicate this. the MIC2537 provides a flag output for this application.
december 1999 11 MIC2537 MIC2537 micrel package information 45 0 C 8 0.244 (6.20) 0.228 (5.79) 0.394 (10.00) 0.386 (9.80) seating plane 0.020 (0.51) ref 0.020 (0.51) 0.013 (0.33) 0.157 (3.99) 0.150 (3.81) 0.050 (1.27) 0.016 (0.40) 0.0648 (1.646) 0.0434 (1.102) 0.050 (1.27) bsc pin 1 dimensions: inches (mm) 0.0098 (0.249) 0.0040 (0.102) 16-lead sop (m)
MIC2537 micrel december 1999 12 MIC2537 micrel inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 web http://www.micrel.com this information is believed to be accurate and reliable, however no responsibility is assumed by micrel for its use nor for an y infringement of patents or other rights of third parties resulting from its use. no license is granted by implication or otherwise under any patent or pat ent right of micrel inc. ? 1999 micrel incorporated

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