mic2587 evaluation board single channel, positive-voltage hot swap controller micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com october 2008 m9999-102108-a general description mic2587/mic2587r hot swap controller the mic2587 is a single-channel, positive-voltage hot- swap controller designed to address the need for safe insertion and removal of circuit boards into electrically live system backplanes. with few external components, the controller works in conjunction with an external n- channel mosfet to provide inrush current limiting and gate slew-rate control. additi onally, the current limit is user-programmable and works in conjunction with a user-programmable overcurrent timer to provide reliable overcurrent fault protection to the system?s circuit components. during an output overload condition, a constant-current regulation loop is engaged to ensure that the system power supply maintains regulation. as a means to reduce the power consumption in the presence of a severe overcurrent load, the mic2587 is equipped with a circuit that monitors the voltage level at the fb pin, and once engaged, allows for the current limit to ?foldback? to a lower threshold to effectively reduce the regulated current limit. once the overcurrent timer expires, the output of the mic2587 is latched off and can be reset by toggling the on pin from high-to-low-to-high. the mic2587r will automatic ally restart the turn-on cycle with a fixed duty cycle ( 5%) after the overcurrent timer has expired. a master power-good signal is provided to indicate that the output voltage of the soft- start circuit is within its valid output range. the power- good signal can be used to enable one or more downstream dc-dc converter modules. mic2587 evaluation board the mic2587 evaluation board is designed to showcase the power switching capability of the mi c2587 controller. the board is configured for switching 24v or 48v with a nominal current limit of 4.7a. several test points are included for the user to monitor the response of a number of pins (e.g. vin, gate, timer, and /pwrgd). the power-good signal is an open-drain output, with asserted status as either high impedance (-1) or active- low (-2). additionally, banana plugs are provided to allow for the use of high-current electrical cables to transfer the necessary cu rrent through the power mosfet and to the load. see the operation section for details on how to select the values for these components for desired system requirements. (please refer to the mic2587 datasheet for detailed pin descriptions and additional support information.) basic requirements the mic2587 controller requires a minimum of 10v for operation, and the evaluation board is configured to operate with 24v or 48v, depending upon the resistor divider networks that are show n in a table inserted in the circuit schematic. precautions unless the range of voltages over which the intended application for the mic2587/mic2587r controller is well controlled and carefully observed, the input and output capacitors should have a maximum voltage rating of at least 100v. thus, the rating of these capacitors is at minimum equivalent to the 100v transient maximum voltage rating of the mic2587 integrated circuits. note: the input capacitor should be an aluminum electrolytic device, as most tantalum capacitors in this voltage range are not capable of safely handling the surge currents that will flow through c in during a hot-plug event. c out , however, may be a tantalum capacitor as the mic2587 controls the di/dt and dv/dt seen by c out . ordering information part number description mic2587-1bm ev evaluation board with the mic2587-1bm device mic2587r-1bm ev evaluation board with the mic2587r-1bm device
micrel, inc. mic2587/mic2587r evaluation board october 2008 2 m9999-102108-a operation external switch the mic2587 requires an external n-channel mosfet to serve as the power swit ch device. the mic2587 pin connections for the mosfet terminals and sense resistor are shown in the attached circuit schematic. the sum110n10-09, a power mosfet in a to-263 package from vishay, is us ed as the pass device on the evaluation boards. several mosfet devices suited for use with the mic2587 are listed in table 3 at the end of the datasheet. the on control pin will switch the external mosfet on when the voltage at on is greater than the specified threshold voltage of 1.24v (typical). this pin exhibits 50mv of hysteresis. a three terminal jumper (j1) is used to either pull-up the on pin to vcc (through an external resistive divider) or tie the pin-to-ground to disable the controller. component selection for various v in table 1 below displays the resistor values selected to configure the mic2587 controller with various input voltages. the two resistor combinations are implemented as resistive divider networks to attain specific turn-on/turn-off and ?power-is-good? thresholds. these values are used for reference, but for different threshold requirements, alter native resistor combinations may be chosen that satisfy equations 8 and 9 from the mic2587 datasheet. +16v +24v +32v +48v r1 95.3k 49.9k 261k 287k r2 10.0k 3.40k 12.4k 10.0k r5 35.7k 59.0k 93.1k 143k r8 3.57k 3.57k 4.22k 4.22k v in(on) 13.8v 20.6v 29.0v 39.0v v in(off) 13.0v 19.3v 27.0v 36.6v v out(good) 14.4v 23.0v 30.3v 45.8v v out(not_good) 13.5v 21.6v 28.4v 43.0v table1. resistor combinations for various system voltage levels current limit the current-limit is determined using the following formula: i lim = v trip / r sense (1) where v trip is the circuit breaker threshold obtained from the electrical characteristics table in the mic2587 datasheet. for the mic2587 evaluation board, the nominal current limit i lim = 47mv/10m = 4.7a. using equation 1 and some basic algebra, the value for r sense can be determined given a des ired current-limit by: r sense = v trip / i lim the circuit breaker is ?tripped? upon an overcurrent condition that lasts longer than the time period t flt , which is set by capacitor c timer (c7). if c timer = 0, t flt = t ocsense , the default value of 2s. c timer may be determined for a desired t flt using the following formula 1 . c timer = (i timerup ? t flt ) / v timerh (2) where i timer , the typical current-limit timer current, is 65 a, and v th , the typical timer threshold, is 1.313v. both values are found in the electrical characteristics table of the datasheet. substituting these values into equation 2, the result is now approximated by: c timer ? 50x10 -6 (a/v) ? t flt for a 6ms overcurrent delay, the calculated value for c timer is 0.3f. the closest standard value is 0.33f. programmable output slew rate (c gate ) capacitor c gate is used to set the output slew rate and limit the inrush current. an external gate capacitor, c gate , sets the gate output rise-time (or slew rate) to turn on the external power mosfet. the source (output) of the mosfet then follows the gate once the gate voltage exceeds the v g-s threshold. the rise time is determined by the following equation: t rise ? ( v ? c total ) / i gate (3) where v = v in + 13v (13v typical enhancement for mic2587 gate output for 10v v cc 80v) and i gateon is the nominal gate pin pull-up current. the total capacitance that the gate mu st drive is the external c gate plus the parasitic capacitance, c g-s , of the external mosfet. for the sum110n10-09, c g-s is approximately 6.5nf. given the following conditions: v in = v out = 24v and c gate = 47nf t rise ? (13v ? 53.5nf)/16a ? 15ms. r7 is used for stabilization of the current limit control loop.
micrel, inc. mic2587/mic2587r evaluation board october 2008 3 m9999-102108-a circuit schematic bj2 +vout d1 smbg100a tp2 on 1 2 3 4 5 6 7 on fb pwrd gnd ctimer gate sense vcc 8 u1 mic2587/87r +vcc c6 100f c4 0.1f c8 0.01f c2 0.1f bj1 vcc r4 c7 1f vout tp7 ctimer r2 10k jp1 on r1 287k tp1 vcc c1 47f tp4 pwrgd r6 47.5k bj3 gnd tp5 gnd tp6 gnd r7 1k tp8 sense c3 0.1f c5 0.1f r3 tp9 gate q1 sub85n10-10 d2 mmbz5248 tp3 out tp10 fo r5 143k r8 4.22k +48v 287k 10k 143k 4.22k +24v 49.9k 3.4k 59k 3.57k r1 r2 r5 r8 figure 1. mic2587 evb circuit schematic
micrel, inc. mic2587/mic2587r evaluation board october 2008 4 m9999-102108-a bill of materials item part number manufacturer description qty. bj1-bj3 108-0740-001 johnson (1) banana jack, 0.256" h/s 3 c1 2222 038 59479 vishay (2) electrolytic capacitor, 47f, 100v, 20%, size 10x12 1 c2-c4 vj0805v104mxbcw1bc vishay (2) ceramic capacitor, 0.1f, 100v, 20%, y5v, size 0805 3 c5 vj0805a331fxbab vishay (2) ceramic capacitor, 330pf, 100v, 1%, cog, size 0805 1 c6 2222 0385 9101 vishay (2) electrolytic capacitor, 100f, 100v, 20%, size 10x12 1 c7 cf162e0105j avx (3) ceramic capacitor, 1f, 100v, 20%, pet-ht, size 4030 1 c8 vj0805v103mxbcw1bc vishay (2) ceramic capacitor, 0.01f, 100v, 20%, y5v, size 0805 1 d1 smbg100a/2 vishay (2) transzorb diode, 100v 1 d2 mmbz5248b-gs08 vishay (2) zener diode, 18v,5% 1 22-03-2021 molex (4) jumper, 2-pin, 0.1? center, 0.35? hole 1 j1 881545-2 tyco (5) jumper shunt 1 mh1-mh4 534-2211 keystone (6) stand-off - 5/8", 6-32,hex 4 mh1-mh4 5721-632-3/8 keystone (6) machine screws, 6-32 x 3/8 4 r1 crcw080549k9fkta vishay (2) resistor, 49.9k, 1%, size 0805 1 r2 crcw08053k40fkta vishay (2) resistor, 3.4k, 1%, size 0805 1 r3 wsr2r0100fta vishay (2) resistor, 0.01 ? , 1%, 2w, size 4527 1 r4 crcw080510r0fkta vishay (2) resistor, 10 ? , 1%, size 0805 1 r5 crcw080559k0fkta vishay (2) resistor, 59k, 1%, size 0805 1 r6 crcw080547k5fkta vishay (2) resistor, 47.5k, 1%, size 0805 1 r7 crcw08051k002fkta vishay (2) resistor, 1k, 1%, size 0805 1 r8 crcw08053k57fkta vishay (2) resistor, 3.57k, 1%, size 0805 1 q1 sum110n10-09 vishay (2) n-channel, 100v, mosfet 1 tp1-tp10 1593-2 keystone (6) turret terminal, 0.065" h/s 10 u1 mic2587-1bm or mic2587r-1bm micrel (7) single channel, positive-voltage hot swap controller 1 notes: 1. johnson: www.tdk.com 2. vishay: www.vishay.com 3. avx: www.avx.com 4. molex: www.molex.com 5. tyco: www. tycoelectronics.com 6. keystone: www.keyeleco.com 7. micrel, inc.: www.micrel.com
micrel, inc. mic2587/mic2587r evaluation board october 2008 5 m9999-102108-a pcb layout recommendation top assembly top layer
micrel, inc. mic2587/mic2587r evaluation board october 2008 6 m9999-102108-a pcb layout recommendation bottom assembly bottom layer
micrel, inc. mic2587/mic2587r evaluation board october 2008 7 m9999-102108-a 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 data sheet is belie ved to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authori zed for use as components in life support app liances, devices or systems where malfu nction of a product can reasonably be expected to result in pers onal injury. life support devices or system s are devices or systems that (a) are in tended 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 significan t injury to the user. a purchaser?s use or sale of micrel produc ts for use in life support app liances, devices or systems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2008 micrel, incorporated.
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