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mic2545a/2549a programmable current-limit high-side switch general description the mic2545a and mic2549a ar e integrated high-side power switches optimized for low-loss dc power switching and other power-management applications, including advanced configuration and power interface (acpi). the mic2545a/49a is a cost-effective, highly-integrated solution that requires few external components to satisfy usb and acpi requirements. load current management features include a precision, resistor-programmable output current-limit and a soft-start circuit, which minimizes inrush current when the switch is enabled. thermal shutdown, along with adjustable current- limit, protects the switch and the attached device. the mic2545a/49a?s open-drain flag output is used to indicate current-limiting or thermal shutdown to a local controller. the mic2549a has an additional internal latch which turns the output off upon thermal shutdown, providing robust fault control. the enable signal is compatible with both 3v and 5v logic, and is also used as the thermal shutdown latch reset for the mic2549a. the mic2545a and mic2549a are available in active-high and active-low enable versions in 8-pin dip, soic, and tssop packages. data sheets and support documentation can be found on micrel?s web site at: www.micrel.com . features ? 2.7v to 5.5v input ? adjustable current-limit up to 3a ? reverse current flow blocking ? 90a typical on-stat e supply current ? 1a typical off-state supply current ? 50m ? maximum on-resistance ? open-drain fault flag ? thermal shutdown ? thermal-shutdown output latch (mic2549a) ? 2ms (slow) soft-start tu rn-on, fast turnoff ? available with active-high or active-low enable applications ? usb power distribution ? pci bus power switching ? notebook pc ? acpi power distribution ? pc card hot swap applications ? inrush current-limiting _________________________________________________________________________________________________________________________ typical application micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 (408) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com june 2011 m9999-062711-a
micrel, inc. mic2545a/2549a june 2011 2 m9999-062711-a ordering information part number enable temperature range latch pb-free package MIC2545A-1BM active high ?40c to +85 c no no 8-pin sop mic2545a-1bn active high ?40c to +85 c no no 8-pin dip mic2545a-1bts active high ?40c to +85 c no no 14-pin tssop mic2545a-2bm active low ?40c to +85 c no no 8-pin sop mic2545a-2bn active low ?40c to +85 c no no 8-pin dip mic2545a-2bts active low ?40c to +85 c no no 14-pin tssop mic2545a-1ym active high ?40c to +85 c no yes 8-pin sop mic2545a-1yn active high ?40c to +85 c no yes 8-pin dip mic2545a-1yts active high ?40c to +85 c no yes 14-pin tssop mic2545a-2ym active low ?40c to +85 c no yes 8-pin sop mic2545a-2yn active low ?40c to +85 c no yes 8-pin dip mic2545a-2yts active low ?40c to +85 c no yes 14-pin tssop mic2549a-1bm active high ?40c to +85 c yes no 8-pin sop mic2549a-1bn active high ?40c to +85 c yes no 8-pin dip mic2549a-1bts active high ?40c to +85 c yes no 14-pin tssop mic2549a-2bm active low ?40c to +85 c yes no 8-pin sop mic2549a-2bn active low ?40c to +85 c yes no 8-pin dip mic2549a-2bts active low ?40c to +85 c yes no 14-pin tssop mic2549a-1ym active high ?40c to +85 c yes yes 8-pin sop mic2549a-1yn active high ?40c to +85 c yes yes 8-pin dip mic2549a-1yts active high ?40c to +85 c yes yes 14-pin tssop mic2549a-2ym active low ?40c to +85 c yes yes 8-pin sop mic2549a-2yn active low ?40c to +85 c yes yes 8-pin dip mic2549a-2yts active low ?40c to +85 c yes yes 14-pin tssop
micrel, inc. mic2545a/2549a june 2011 3 m9999-062711-a pin configuration 8-pin sop (m) 8-pin dip (n) 14-pin tssop (ts) pin description pin number sop, dip pin number tssop pin name pin function 1 1 en enable (input): logic-compatible enable input ( ? 1 version is active high, ? 2 version is active low). high input > 1.8v typical; low input < 1.4v typical. do not float. mic2549a only: also resets thermal-shutdown latch. 2 3 flg fault flag (output): active-low, open-dr ain output. indicates overcurrent or thermal shutdown. mic2549a only: latched low on thermal shutdown. 3 5 gnd ground: supply return. 4 7 ilim current limit: sets current-limit thre shold using an external resistor (r set ) connected to ground. 76.8 ? < r set < 459 ? . 5, 7 8, 12 in supply input: output mosfet drain. also powers internal circuitry. both in pins must be externally connected together. 6, 8 10, 14 out switch output: output mosfet source . both out pins must be externally connected together. 2, 4, 6, 9, 11, 13 nc not internally connected.
micrel, inc. mic2545a/2549a june 2011 4 m9999-062711-a absolute maximum ratings (1) supply voltage (v in ) .................................................... + 7.0v output voltage (v out ). ................................................ + 7.0v output current (i out ) .................................internally limited enable input (v en ) ........................................... ? 0.3v to + 7v fault flag voltage (v flg )............................................. + 7.0v fault flag current (i flg ) ..............................................50ma storage temperature (t s).........................?65c to +150c junction temperature (t j ) ........................internally limited lead temperature (solde ring, 5sec .) ......................... 260c esd rating (3) ..............................................................1500v operating ratings (2) supply voltage (v in )..................................... +2.7v to +5.5v ambient temperature (t a ) .......................... ?40c to +85c package thermal resistance pdip ( ja ) ........................................................130c/w soic ( ja ) ........................................................160c/w tssop ( ja ) (4) ..................................................100c/w current-limit set range (5) .................................. 0.5a to 3a electrical characteristics (4) v in = + 5v; t a = 25c, bold values indicate ?40c to +85c, unless noted. symbol parameter condition min. typ. max. units switch off, out = open (6) 0.75 5 a 90 125 supply current switch on, out = open (6) 150 a v en enable high transition (6) 2.4 1.6 enable input voltage enable low transition (6) 1.5 0.8 v v en = v oh(min) = 2.4v 0.01 1 enable input current v en = v ol(max) = 0.8v 0.01 1 a enable input capacitance note 7 1 pf r ds(on) switch resistance i out = 500ma 35 50 m ? i limit = 0.5a to 3a, v out = 1v to 4v (5) 184 230 276 current-limit factor i limit = 1a to 2.5a, v out = 1v to 4v (5) 195 230 264 v output leakage current switch off, v out = 0v 1 10 a t on output turn-on delay r l = 10 ? , c l = 1f, figures 1a, 1b 1 2 5 ms t r output turn-on rise time r l = 10 ? , c l = 1f, figures 1a, 1b 0.75 1.8 4.9 ms t off output turn-off delay r l = 10 ? , c l = 1f, figures 1a, 1b 25 s notes: 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. hand ling precautions recommended. human body model, 1.5k in series with 100pf. 4. assumes 4-layer pcb is used. 5. current limit is determined by i limit = set r 230 , where r set is in ? s, and 230 is typical current-limit factor in volts. 6. off is 0.8v and on is 2.4v for the mic2545a-1 and mic2549a-1. off is 2.4v and on is 9.8v for the mic2545a-2 and mic2549a-2. the enable input has about 100mv of hysteresis. 7. guaranteed by design but not production tested.
micrel, inc. mic2545a/2549a june 2011 5 m9999-062711-a electrical characteristics (4) (continued) v in = + 5v; t a = 25c, bold values indicate ?40c to +85c, unless noted. symbol parameter condition min. typ. max. units t f output turn-off fall time r l = 10 ? , c l = 1f, figures 1a, 1b 23 s t j increasing 135 overtemperature threshold shutdown t j decreasing 120 c error flag off current v flg = 5v 0.01 1 a en pulse reset width mic2549a thermal-shutdown latch (7) 1 s t su v in to en set-up mic2549 (7) , figure 1c 0 s current-limit response time v out = 0v to i out = 2a, i set = 1a (7) 40 s v ol error flag output resistance i flg = 10ma 4 15 ? test circuit functional characteristics test circuit
micrel, inc. mic2545a/2549a june 2011 6 m9999-062711-a timing diagrams figure 1a. mic2545a/49a-2 figure 1b. mic2545a/49a-1 figure 1c. input-to-enable setup timing
micrel, inc. mic2545a/2549a june 2011 7 m9999-062711-a timing diagrams (continued) figure 2a. mic2545a-2 timing: output is reset by toggling en figure 2b. mic2545a-2 timing
micrel, inc. mic2545a/2549a june 2011 8 m9999-062711-a typical characteristics
micrel, inc. mic2545a/2549a june 2011 9 m9999-062711-a typical characteristics (continued)
micrel, inc. mic2545a/2549a june 2011 10 m9999-062711-a functional characteristics
micrel, inc. mic2545a/2549a june 2011 11 m9999-062711-a functional characteristics (continued)
micrel, inc. mic2545a/2549a june 2011 12 m9999-062711-a block diagram
micrel, inc. mic2545a/2549a june 2011 13 m9999-062711-a functional description the mic2545a and mic2549a are high-side n-channel switches available with active-high or active-low enable inputs. fault conditions turn off or inhibit turn-on of the output transistor and activate the open-drain error flag transistor making it sink current to ground. input and output in is the power supply conne ction to the logic circuitry and the drain of the output mosfet. out is the source of the output mosfet. in a typical circuit, current flows from in to out toward the load. if v out is greater than v in , current will flow from out to in since the switch is bidirectional when enabled. 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 out > v in ) when the switch is disabled. in this situation, the mic2545a/49a avoids undesirable current flow from out to in. both in pins must be connected together, and both out pins must be connected together. thermal shutdown thermal shutdown shuts off the output mosfet and signals the fault flag if the die temperature exceeds 135c. 10c of hysteresis prevents the switch from turning on until the die temperature drops to 125c. overtemperature detection functions only when the switch is enabled. the mic2549a features an internal latch which causes the part to remain off after thermal shutdown until a reset pulse is provided via the enable pin (pin1).while in current-limit, the thermal shutdown latch prevents on/off cycling of the output. refer to figure 2 for timing diagram. the flag remains low until reset. enable input en must be driven logic high or logic low, or be pulled high or 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. current-limit operation the current limit is user adjustable with an external set resistor. current limiting in the range of 500ma to 3a is available with a set point ac curacy of better than 30% (20% for i set 1 to 2.5a). the current-limit circuit prevents damage to the output mosfet and external load. the current-limit response of the mic2545a/49a is based on the type of load that is applied to the output and is defined in three parts: 1. the first mode of operation is where the device enters a constant-current mode preventing further increases in output current. the value of this current, i limit , is defined by the value of r set as explained further in this section. 2. when a short circuit is applied to the output of an enabled device the output current immediately folds back to a value less than i limit called i short . this further protects the load and reduces device power dissipation. refer to the ?typical characteristics: output current vs. output voltage? graph for details. 3. when a load is increased, the output current will proportionally increase up to the current-limit threshold, i th , as shown in the ?functional characteristics: current-limit response? graph. the device in this case will suppl y current slightly higher than the current-limit se t point defined by r set . as the load is increased further the current folds back to i limit . the nominal current-limit value, i limit , is set with an external resistor between i lim (pin 4) and gnd (pin 3). for a desired current-limit, the value of the external set resistor is given by: ? ? ? ? ? ? ? ? = limit set i 230 r where: 76.8 ? < r set < 459 ? refer to the ?typical charac teristics: current-limit vs r set ? graph for more details. current through r set increases with output current. the voltage across r set could be monitored with a high- impedance comparator to provide an indication of output current. r set should be between 76.8 ? and 459 ? (1% resister value). fault flag flg is an n-channel, open-drain mosfet output. the fault-flag is active (low) fo r current-limit or thermal shutdown conditions. the flag output mosfet is capable of sinking a 10ma load to typically 100mv above ground. for applications with v in = 3.6v, it is recommended that flag current be limited to 5ma or less.
micrel, inc. mic2545a/2549a june 2011 14 m9999-062711-a application information supply filtering a 0.1f to 1f bypass capacitor from in to gnd, located near the mic2545a and mic2549a, is strongly recommended to control supply transients. without a bypass capacitor, an output short may cause sufficient ringing on the input (from supply lead inductance) to damage internal control circuitry. input transients must not exceed the absolute maximum supply voltage (v in (max) = 6v) even for a short duration. figure 3. supply bypassing power dissipation the device's junction temperature depends on several factors such as the load, pcb layout, ambient temperature, and package ty pe. equations that can be used to calculate power dissipation and junction temperature are found below. calculation of power dissipation can be accomplished by the following equation: p d = r ds(on) (i out ) 2 to relate this to junction temperature, the following equation can be used: t j = p d ja + t a where: t j = junction temperature t a = ambient temperature ja = the thermal resistance of the package transient overcurrent filter the inrush current from the connection of a heavy capacitive load may cause the fault flag to fall for 10s to 200s while the switch is in a constant-current mode, charging the capacitance. adding an optional series resistor-capacitor (r set2 ) in parallel with rset, as shown in figure 4, allows the transient current-limit to be set to a different value than steady state. a typical usb hot-plug inrush is 2a to 3a for 10s to 20s. if r set is 435 ? (530ma), an r set2 of 88? (2.5a) and c set of 1f (rc 90s) allows transient surge of 3a to pass for 90s without tripping the overcurrent flag (flg). usb power dissipations the mic2545a is ideal for meeting usb power distribution requirements. figure 7 depicts a usb host application. r set should be set to a value providing a current-limit >500ma. the accu rate current-limit of the mic2545a will reduce power supply current requirements. also, fast reaction to short-circuit faults prevent voltage droop in mobile pc applications. printed circuit board hot-plug the mic2545a/49a is an ideal inrush current-limiter suitable for hot-plug applicati ons. due to the integrated charge pump, the mic2545a/49a presents a high impedance when off and slowly becomes a low impedance as it turns on. this ?soft start? feature effectively isolates power supplies from highly-capacitive loads by reducing inrush current during hot-plug events. figure 5 shows how the mic2545a may be used in a hot-plug application.
micrel, inc. mic2545a/2549a june 2011 15 m9999-062711-a figure 4. usb host application figure 5. hot-plug application
micrel, inc. mic2545a/2549a june 2011 16 m9999-062711-a package information 8-pin dip (n)
micrel, inc. mic2545a/2549a june 2011 17 m9999-062711-a package information (continued) 8-pin soic (m)
micrel, inc. mic2545a/2549a june 2011 18 m9999-062711-a package information (continued) 14-pin tssop (ts) 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 micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. this information is not intended as a warranty and micrel does not assume responsibility for it s use. micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. no license, whether express, implied, arising by estoppel or other wise, to any intellectual property rights is granted by this document. except as provided in micrel?s terms and conditions of sale for such products, mi crel assumes no liability whatsoever, and micrel disclaims any express or implied warranty relating to the sale and/or use of micrel products including l iability or warranties relating to fitness for a particular purpose, merchantability, or infringement of an y patent, copyright or other intellectual p roperty right. micrel products are not designed or authorized for use as components in life suppor t appliances, devices or systems where malfu nction of a product reasonably be expected to result in pers onal injury. life support devices or system s are devices or systems that (a) are intended for surgical impla into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. a purchaser?s use or sale of micrel products for use in life support appliances, 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. can nt ? 2004 micrel, incorporated.

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