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january 2011 ? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a adjustable over-current protection load switches features ? 2.8v to 36v input voltage range ? typical r ds(on) =88m ? ? 0.4a to 2a adjustable current limit (min.) ? slew rate controlled ? esd protected, above 2000v hbm ? thermal shutdown ? active low enable ? uvlo protection ? power-good output applications ? motor drives ? digital cameras ? consumer electronics ? industrial ? computing ? hard disk drives ? telecom equipment figure 1. mlp (top view) figure 2. mlp (bottom view) figure 3. so8 (top view) description the accupower? fpf270x series is a family of current-limit load switches t hat provide full protection to systems and loads from excess current conditions. minimum current limit is adjus table from 0.4a to 2.0a. the fpf270x contains a slew-rate-controlled n-channel mosfet and slew-rated turn-on to prevent power bus disturbances from being caus ed by ?hot plugging? loads or momentary excess load demands. the input voltage range is 2.8v to 36v. loads can be activated or deactivated with a low-voltage logic-compatible on pin. fault conditions can be monitored using the error flag pin and/or the power-good pin. each member of the fpf270x family serves a category of load-fault response. a ll devices clamp the load current so that it c annot exceed an externally programmed current level. an over temperature feature provides further device protec tion in case of excessive levels of power dissipation. fpf2700 responds to an over load condition that lasts longer than a fixed blanking period by turning off the load, followed by a retry after the auto-restart time. fpf2701 responds to an over load condition that lasts longer than a fixed blanking period by latching off the load. the load remains off unless either the on pin is toggled or the input voltage cycles through uvlo. fpf2702 is intended to be used with external fault management. like the fpf2700 and fpf2701, it sets the fault signal pin low when it activates current clamping. this device is in tended for applications where external fault management coordinates the overload response with the fpf2702. the fpf270x is available in a space-saving pb and halogen free, 8-lead mlp 3x3mm and so8 packages. ordering information part number current limit [a] current limit blanking time [ms] auto-restart time [ms] on pin activity package fpf2700mpx 0.4 ? 2.0 0.5 127.5 active low mlp3x3 fpf2701mpx 0.4 ? 2.0 0.5 na active low mlp3x3 fpf2702mpx 0.4 ? 2.0 na na active low mlp3x3 FPF2700MX 0.4 ? 2.0 0.5 127.5 active low so8 fpf2701mx 0.4 ? 2.0 0.5 na active low so8 fpf2702mx 0.4 ? 2.0 na na active low so8
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 2 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches application diagram figure 4. typical application block diagram figure 5. block diagram off on vin on iset vout flagb pgood gnd v in 2.8v ? 36v to load r set c in 36v max. c out
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 3 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches pin configurations figure 6. mlp (bottom view) figure 7. so8 (top view) pin definitions pin # name description 1 vin supply input. input to the power switch and the supply voltage for the ic. 2 pgood power-good output. open-drain output to indica te that output volt age has reached 90% of input voltage. 3 iset current limit set input. a resistor from i set to ground sets the current limit for the switch. 4 on on control input. active low. 5 gnd ground 6 nc no connection. leave open or connect to ground. 7 flagb fault output. active low, open-drain output t hat indicates current limit, under-voltage, or over -temperature state. 8 vout switch output. out put of the power switch. 1 2 3 4 8 7 6 5 8 7 6 5 1 2 3 4 vin pgood iset on vout flagb nc gnd vout flagb nc gnd gnd vin pgood iset on
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 4 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches absolute maximum ratings stresses exceeding the absolute maximum ratings may damage the device. the devic e may not function or be operable above the recommended operating c onditions and stressing the parts to these levels is not recommended. in addition, extended exposure to stresses above the recommended operati ng conditions may affect device reliability. the absolute maximum ratings are stress ratings only. symbol parameter min. max. unit pgood, flagb, vin to gnd -0.3 40 v vout to gnd -0.3 v in + 0.3 v on to gnd -0.3 6 v p d power dissipation (t a =25c) mlp 3x3 (1) , see figure 8 1.25 w so8 (1) , see figure 10 1.00 i sw maximum continuous switch current 3.5 a t j operating junction te mperature -40 +125 c t stg storage temperature -65 +150 c esd electrostatic discharge protection level human body model, jesd22-a114 2000 v charged device model, jesd22-c101 2000 ? ja thermal resistance, junction to ambient mlp 3x3 (1) , see figure 8 80 c/w so8 (1) , see figure 10 102 note: 1. thermal resistance, ja , is determined with the device mounted on a one inch square pad, 2oz copper pad, and a 1.5 x 1.5in. board of fr-4 material. figure 8. 80c/w mounted on a 1in 2 pad of 2oz. copper figure 9. 226c/w mounted on a minimum pad of 2oz. copper figure 10. 102c/w mounted on a 1in 2 pad of 2oz. copper figure 11. 181c/w mounted on a minimum pad of 2oz. copper recommended operating conditions the recommended operating conditions table defines the conditions for actual device oper ation. recommended operating conditions are specified to ens ure optimal performance to the datasheet specificat ions. fairchild does not recommend exceeding them or designing to absolute maximum ratings. symbol parameter min. max. unit v in input supply voltage 2.8 36.0 v t a ambient operating te mperature -40 85 c
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 5 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches electrical characteristics v in =2.8 to 36v and t a =-40 to +85c unless otherwise noted. typical values are at v in =12v and t a =25c. symbol parameter conditions min. typ. max. unit basic operation v in operating volt age 2.8 36.0 v i q quiescent current v in =12v, v on =0v, i out =0a 92 140 a i shdn shutdown current v in =36v, v on =3.3v, i out =0a 5 14 a r on on-resistance t a =25c, v in =12v 88 114 m ? t a =-40 to +85c, v in =12v 140 t a =25c, v in =5v 88 114 t a =-40 to +85c, v in =5v 140 v ih on input logic high voltage v in =2.8 to 36v 2.0 v v il on input logic low voltage v in =2.8 to 36v 0.8 v i lk on input leakage v on =5.5v or gnd -1 1 a i swoff off switch leakage v in =36v, v on =3.3v, v out =0v 0.01 a v flagb(lo) flagb output logic low voltage v in =5v, i sink =1ma 0.1 0.2 v i flagb(hi) flagb output logic high leakage current v in =36v, switch on, v flagb =36v 1 a v pgood pgood trip voltage v in =5v, v out as percent of v in , v out rising 90 % v pgood(hys) pgood hysteresis v in =5v, v out as percent of v in , v out falling 3 % v pgood(lo) pgood output logic low voltage v in =5v, i sink =1ma 0.1 0.2 v i pgood(hi) pgood output high leakage current v in =36v, switch on, v pgood =36v 1 a protections i lim current limit t a =25c 0.8 x i nom 1.0 x i nom 1.2 x i nom a i sc short circuit current limit v out < 2v, switch in over- current condition 0.75 x i nom a tsd thermal shutdown shutdown threshold 140 c return from shutdown 110 hysteresis 30 uvlo under-voltage shutdown v in increasing 2.3 2.5 2.7 v uvlo_ hyst under-voltage shutdown hy steresis 100 mv dynamic t don turn on delay r l =500 ? , c l =2uf 2.7 ms t doff turn off delay 0.1 t r v out rise time 7.5 t f v out fall time 1.5 t blank over-current blanking time fpf2700/1, t a =25c 0.25 0.50 0.75 ms t restart auto-restart time fpf2700, t a =25c 63.8 127.5 191.2 ms t clr current-limit response time v in =12v, v on =0v 50 s
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 6 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches timing diagram figure 12. timing diagram typical performance characteristics v in = 12v and t a = 25c. 1.20 1.23 1.25 1.28 1.30 1.33 1.35 1.38 1.40 0 5 10 15 20 25 30 35 40 on ? threshold ? voltage ? (v) supply ? voltage ? (v) v ih v il t a = ? 25c 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 \ 50 \ 25 0 25 50 75 100 125 150 on ? threshold ? voltage ? (v) t j , ? junction ? temperature ? ( o c) v ih v il v in = ? 12v figure 13. on threshold vs. supply figur e 14. on threshold vs. temperature 60 70 80 90 100 110 120 130 0 5 10 15 20 25 30 35 40 quiescent ? current ? (a) supply ? voltage ? (v) v on = ? 0v t a = ? 25c t a = ?\ 40c t a = ? 85c t a = ? 125c 0 2 4 6 8 10 12 0 5 10 15 20 25 30 35 40 quiescent ? current ? (a) supply ? voltage ? (v) v on = ? 5v t a = ? 25c t a = ?\ 40c t a = ? 85c t a = ? 125c figure 15. quiescent current vs. s upply voltage (on) figure 16. quiescent current vs. supply voltage (off) v out v on v out 10 90 t r 10 90 t f 50 3.3 10 90 50 t don t doff t on = t r + t don t off = t f + t doff
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 7 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches typical performance characteristics v in = 12v and t a = 25c. figure 17. on resistance vs. supply voltage figur e 18. on resistance vs. junction temperature 1.0 1.5 2.0 2.5 3.0 3.5 4.0 \ 50 \ 25 0 25 50 75 100 125 150 turn \ on ? delay ? (ms) t j , ? junction ? temperature ? ( o c) v in = ? 12v r l = ? 500 ? c l = ? 2f figure 19. turn-on delay vs. junction temperature fi gure 20. output rise time vs. junction temperature figure 21. turn-off delay vs. junction temperature fi gure 22. output fall time vs. junction temperature
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 8 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches typical operation character istics of fpf2700 and fpf2701 when v out <2v, the current limit is set to 75% of i lim . figure 23. normal startup to 0.5x i lim figure 24. out shorted to gnd, short condition persists (soa protection fo llowed by current-limited operation) figure 25. out overloaded with 1.5x i lim (long-duration overload) figure 26. out shorted to gnd, short condition removed (soa protection followed by normal operation) figure 27. out overloaded with 1.5x i lim (transient overload)
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 9 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches typical operation characteristics of fpf2702 figure 28. out shorted to gnd, short condition persists (soa protection current limit followed by current limit) figure 29. out overloaded with 1.5x i lim (long-duration overload)
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 10 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches typical performance characteristics fpf270x v in = 12v and t a = 25c. figure 30. 12v turn-on delay (r l =500 ? , c out =2f) figure 31. 12v turn-off delay (r l =500 ? , c out =2f) figure 32. 12v blanking time (output overloaded and t blank expired, fpf2700/01, i lim =1a, i load =3.3a, c out =f, r load =500 ? ) v oc (2) figure 33. 12v restart time (switch turned on into persistent over-current condition,t restart ~127.5ms) figure 34. soft overload and constant current (i load > i lim , fpf2702 enters constant current mode, running at i lim ) figure 35. out shorted to gnd, short condition removed (soa protection followed by a normal operation, fpf2700 / fpf2701) note: 2. v oc signal forces the device into an over-current condition by loading a 500m ? resistor to the output through an nmos. v oc is the gate drive of the nmos.
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 11 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches application information description of operation the fpf270x family of curr ent limit load switches is designed to meet the power r equirements of a variety of applications with wide input voltage range of 2.8v to 36v and adjustable current-limit va lue. the fpf270x family offers control and protecti on while providing optimum operation current for safe desi gn practices. the core of each switch is a typical 88m ? (v in = 12v) n-channel mosfet and a controller capabl e of functioning over an input voltage range of 2.8v to 36v. fpf270x offers adjustabl e current limiting, under- voltage lockout (uvlo), power-good indicator (pgood), fault flag output (flagb), and thermal shutdown protection. in the event of an over-current condition, the load switch lim its the load to the current limit value. the current limit value for each switch can be adjusted from 400ma to 2a through the iset pin. on/off control the on pin is active low fo r and controls the state of the switch. pulling the on pin continuously to low holds the switch in on stat e. the switch moves into off state when the on pin is pulled high. the on pin can be pulled high to a maximum voltage of 5.5v. an under-voltage condition on the input voltage or a junction temperature in ex cess of 140c overrides the on control and turns off the switch. in addition, an over- current condition causes the switch to turn off in the fpf2700 and fpf2701 after the expiration of the blanking time. the fpf2700 has an auto-restart feature that automatically turns t he switch on again after the auto-restart time. for the fpf2701, the on pin must be toggled to turn the switch on again. the fpf2702 does not turn off in response to an over-current condition; it remains operating in constant -current mode as long as on is enabled and the therma l shutdown or uvlo have not activated. the on pin does not have internal pull- down or pull-up resistors and should not be left floating. fault reporting upon detection of an over-cu rrent condition, an input uvlo, or an over-temperat ure condition, the flagb signals the fault mode by activating low. in the event of an over-current condition for the fpf2700 or fpf2701, the flagb goes low at the end of the blanking time (figure 24 and figure 25). flagb goes low immediately for the fpf2702 (figure 29). if the over-current condition lasts longer than blanking time, flagb remains low through the auto-restart time for the fpf2700. for the fpf 2701, flagb is latched low and on must be toggled to release it. for fpf2702, flagb is low during a fault and immediately returns high at the end of the fault condition. flagb is an open-drain mosfet that requires a pull-up resistor. the maximum pull-up voltage is 36v (figure 29). during shutdown, the pull-dow n on flagb is disabled to reduce current draw from the supply. a 100k ? pull-up resistor is recommended in the application. current limiting the current limit ensures t hat the current through the switch doesn't exceed a maximum value while not limiting at less than a minimu m value. the current-limit level is adjustable through an external resistor connected between the i set pin and gnd. the typical current limit le vel is adjustable from 500ma to 2.5a. the minimum current limit (i lim(min) ) range is from 0.4a to 2.0a, including 20% current-limit tolerance. the fpf2700 and fpf2701 have a blanking time during which the switch acts as a constant-current source (figure 27). if the over-current condition persists beyond the blanking time, the fpf2700 latches off and shuts the switch off (figure 32). if the on pin is kept active, an auto-restart feature releases the switch and turns the switch on again after the auto-restart time (figure 33). if the over-current condition persists beyond the blanking time, the fpf2701 latch-off f eature shuts the switch off. the switch is kept off until t he on pin is toggled or input power is cycled. the fp f2702 has no current-limit blanking period, so it remains in a constant-c urrent state until the on pin is deactivat ed or the thermal shutdown turns off the switch. besides the current-limiting f unctionality, the switch is protected by the therma l shutdown protection and an independent soa protection circuit is available. soa protection current limit (i out > 12a) fpf270x has an soa protecti on feature to protect the load switch in response to current surges exceeding 12a in normal operation. if a short-circuit event occurs (i out >12a), the switch is turned off in about 1s by an independent safe operating area (soa) protection circuit (figure 26, figure 28). this feature protects the switch in case of sudden, high-current events at the output, such as a short to gnd. the switch turns on automatically after a turn- on delay of about 2.7ms. short-circuit current limit (v out < v scth = 2v) when the output voltage drops below the short-circuit threshold voltage, v scth , the current-limit value re- conditions itself to the short- circuit current limit value, which is 75% of the nominal current limit (0.75 x i lim, ) (figure 24). this prevents early thermal shutdown by reducing the power dissipati on of the device. the v scth value is set at 2v. at about v out = 2.1v, the switch is removed from short-circuit current-limiting mode and the current limit is set to the nominal current limit value. setting the current limit value the fpf270x has an adjustable 0.4a to 2.0a minimum current limit set through an external resistor, r set , connected between iset and gnd. a precision r set value must be used, such as 1% tolerance or lower, to minimize the total current limit tolerance of the system. use the following equation to ca lculate the value of the resistor for intended typical current limit value:
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 12 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches ) a ( i 5 . 277 ) k ( r ) typ ( lim set ? ? (1) i lim(typ) is the typical current limit value based on a given r set . table 1. r set selection guide r set (k ? ) current limit [a] tol. (%) min. typ. max. 111 2.00 2.50 3.00 20 124 1.79 2.24 2.69 20 147 1.51 1.89 2.27 20 182 1.22 1.52 1.83 20 220 1.01 1.26 1.51 20 274 0.81 1.01 1.22 20 374 0.59 0.74 0.89 20 549 0.40 0.51 0.61 20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 100 200 300 400 500 600 r set (k ? ) i limit (a) figure 36. i lim vs. r set under-voltage lockout (uvlo) the under-voltage lockout featur e turns off the switch if the input voltage drops below the under-voltage lockout threshold. with the on pin active (on pin pulled low), the input voltage rising abov e the under-voltage lockout threshold causes a controll ed turn-on of the switch (figure 37). the uvlo threshold voltage is set internally at 2.5v for v in rising. the under-voltage lockout threshold has a 0.1v hysteresis. figure 37. under-voltage lockout performance power good fpf270x has a power good feat ure. the pgood pin is an open-drain mosfet that asserts high when the output voltage reaches 90% of the input voltage (figure 26). a typical 3% pgood hysteresis is added to pgood to prevent pgood from chattering as v out falls near the pgood threshold voltage. the pgood pin requires an external pull-up resistor connected to an external volt age source compatible with input levels of other chips connected to this pin. pgood is kept low when the device is inactive. to save current in the off state, the pull-up resistor of the pgood pin can be connect ed to the output voltage when there is no battery, prov ided that compatibility with the input levels of other dev ices connected to pgood is observed. a typical value of 100k ? is recommended for the pull up resistor. when t he power-good feature is not used in the application, the pgood pin can be connected to gnd. thermal shutdown thermal shutdown protects t he die from internally or externally generated excessive temperatures. during an over-temperature condition; as the temperature increases above 140c, flag b is activated and the switch is turned off. when the die cools down sufficiently (die temperature drops below the threshold level), the switch automatically turns on again. to avoid unwanted thermal oscillations, a 30c (typical) thermal hysteresis is implemented between thermal shutdown entry and exit temperatures. proper board lay out is required to prevent premature thermal shutdown (see figure 38 for thermal shutdown behavior on fpf2702) . figure 38. fpf2702 thermal shutdown behavior
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 13 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches soa (fpf2702) during extended output-short conditions, excessive power dissipation occurs in the load switch. fpf2700 and pfp2701 are protected by turning off the load switch after blanking time. fpf2702 has no blanking time feature; please refer to note 3. it is possible to estimate the soa for the two fpf2702 packages, mpx and mx, through their respective soa curves shown in figure 39 and figure 40. these curves provide a reference on how long the load switch survives under the worst-case scenario with minimum pad size of one square inch. (1) figure 39. fpf2702 mpx soa figure 40. fpf2702 mx soa note: 3. to protect fpf2702 from an extended short condition, additional protection must be implemented in the system to protect the device. for example, the flagb and pgood signal can be used to monitor the short-circuit fault condition. in applications where fpf2702 can be exposed to persistent short-circuit conditions, it should be used only with external fault management control to protect the switch.
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 14 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches input capacitor to limit the voltage drop on the input supply caused by transient inrush currents w hen the switch is turned on into a discharged load capacitor or short-circuit; an input capacitor, c in , is recommended between the in and gnd pins. the fpf270x featur es a fast current limit response time (50 s). during this period, the device relies on the input capacitor to supply the load current. a 10 f to 100 f ceramic capacitor is adequate for c in in most cases. larger c in values may be required in high- voltage or high-current applic ations. an electrolytic capacitor can be used in para llel to further reduce the voltage drop. output capacitor a 0.1 f to 1 f capacitor, c out , should be placed between the out and gnd pins . this capacitor helps prevent parasitic board induc tances from forcing the output voltage below ground when the switch turns off. this capacitor should have a low dissipation factor. an x7r multilayer ceramic chip (mlcc) capacitor is recommended. during startup, the total output current consists of both the load current and the char ge current of the output capacitor. for the fpf2700 and fpf2701; if the total output current exceeds the se t current limit threshold (determined via r set ) for longer than the blanking time, the device may not be able to start properly. this imposes an upper limit to the value of the output capacitor, given the load current and the selected current limit value. c out should not exceed the c outmax calculated in equation 2 or the switch does not start properly due to the set current limit: v min _ lim max out / s 500 i c ? ? ? (2) high-voltage operation (output capacitor) during a hard short condition on the output while operating at great er than 24v v in , a large instantaneous inrush current is deliver ed to the shorted output. a capacitor must be placed at the output pin, acting as a current source to suppor t the instantaneous current draw (table 2). a low-esr capacitor is recommended. once the value of the out put capacitor is determined from table 2, equation 2 must be reevaluated. table 2. c out selection guide v in (v) capacitance ( f) 24< v in 27 22 27< v in 32 47 32< v in 36 68 power dissipation during normal operation as a switch, the power dissipation of the device is small and has little effect on the operating temperature of the part. the maximum power dissipation for the switch in normal operation occurs just before the switch enters into current limit. this may be calculat ed using the equation: ) max ( on 2 ) max ( lim ) ation normaloper ( max _ d r ) i ( p ? ? (3) t he maximum junction temperature should be limited to 125c under normal operation. junction temperature can be calculated us ing the equation: a ja d j t p t ? ? ? ? (4) where: ? t j is junction temperature; ? p d is power dissipation on the switch; ? ja is the thermal resistance, junction-to-ambient of the package; and ? t a is ambient temperature. design example for a 12v application and i lim (max) = 1a, maximum power dissipation in a normal operation is calculated as: mw 140 140 . 0 ) 1 ( p 2 ) v 12 vin )( ation normaloper ( max _ d ? ? ? ? (5) fpf2702 p d(max) during oc: if device is in over-current condition and v out >2v, power dissipation can be calculated as: p d = (v in - v out ) x i lim (max) (6) if device is in short-circuit current limit and v out < 2v, power dissipation can be calculated as: p d = (v in - v out ) x (0.75 x i lim (max) ) (7) design example: using fpf2702 in a v in = 5v application where i lim (max) = 2a, assuming v out = 2.5v; power dissipation across the switch is calculated as: p d = (5 - 2.5) x 2 = 5w (8) whereas in a short-circuit current-limit condition (v out 0v), power dissipation is calculated as: p d = ((v in - v out ) x (0.75 x i lim (max) ) = (5 - 0) x (0.75 x 2) = 7.5w (9)
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 15 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches pcb layout recommendations for the best performance, all traces should be as short as possible. to be most e ffective, the input and output capacitors should be placed close to the device to minimize the effects that parasitic trace inductances may have on normal and short-circuit operation (figure 42). using wide traces for in, out, and gnd pins helps minimize parasitic electrical effects as well as the case- to-ambient thermal impedance. to minimize the interference between analog ground (chip ground, pin 5) and power ground during load current excursion, the gr ound terminal of the input and output capacitors and the r set resistor should be routed directly to chip ground and away from power ground. improving thermal performance improper layout could result in higher junction temperature and trigger the rmal shutdown protection. this is particularly significant for the fpf2702, where the device operates in c onstant current mode under overload conditions. during fault conditions, the power dissipation of the switch could exceed the maximum absolute power dissipation. the following techniques improve the thermal performance of this family of devices. these techniques are listed in order of the significance of their impact. 1. thermal performance of the load switch can be improved by connecting the die attach pad (dap) of the mlp 3x3 package to the gnd plane of the pcb. 2. embedding two exposed through-hole vias into the dap provides a path for heat to transfer to the back gnd plane of the pcb. a dr ill size of round, 15 mils (0.4mm) with 1-ounce copper plating is recommended for appropriate solder reflow. a smaller-size hole prevents the solder from penetrating into the via, re sulting in device lift-up. similarly, a larger hole consumes excessive solder and may result in voiding the dap. figure 41. two through-hole open vias embedded in the dap 3. the in, out, and gnd pi ns dissipate most of the heat generated during high-l oad current condition. the layout suggested in figure 42 and figure 43 is strongly recommended illustrating a proper layout for devices in mlp 3x3 packages. in, out, and gnd pins are connect ed to adequate copper so that heat may be transferr ed as efficiently as possible out of the devic e. the low-power flagb and on pins traces may be laid-out diagonally from the device to maximize the area available to the ground pad. place the input and output capacitors as close as possible to the device. figure 42. proper layout of output and ground copper area (top, sst, and ast layers) figure 43. proper layout (bottom and asb layers)
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 16 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches fpf270x demonstration board the fpf270x demonstrat ion board has components and circuitry to demonstrate t he load switch?s functions and features. thermal perfo rmance of the board is improved using the tec hniques recommended in the layout recommendations section. additional information about demonstration board can be found in the fpf270x board users guide. figure 44. top, sst, and ast layers figure 45. bottom and asb layers
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 17 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches physical dimensions 8 0 see detail a notes: unless otherwise specified a) this package conforms to jedec ms-012, variation aa, issue c, b) all dimensions are in millimeters. c) dimensions do not include mold flash or burrs. d) landpattern standard: soic127p600x175-8m. e) drawing filename: m08arev13 land pattern recommendation seating plane 0.10 c c gage plane x 45 detail a scale: 2:1 pin one indicator 4 8 1 c m ba 0.25 b 5 a 5.60 0.65 1.75 1.27 6.20 5.80 3.81 4.00 3.80 5.00 4.80 (0.33) 1.27 0.51 0.33 0.25 0.10 1.75 max 0.25 0.19 0.36 0.50 0.25 r0.10 r0.10 0.90 0.406 (1.04) option a - bevel edge option b - no bevel edge figure 46. 8-lead, small outline package (sop) package drawings are provided as a servic e to customers considering fairchild co mponents. drawings may change in any manner without notice. please note the revision and/or date on the drawi ng and contact a fairchild semiconductor representative to ver ify or obtain the most recent revision. package specifications do not expand the terms of fairchild?s worldwide terms and conditions, specifically the warranty therein, which covers fairchild products. always visit fairchild semiconductor?s online pack aging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/ .
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 18 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches physical dimensions bottom view top view side view notes: a. package conforms to jedec mo-229 except where noted. b. dimensions are in millimeters. c. dimensions and tolerances per asme y14.5m, 1994. d. land pattern recommendation is based on fsc design only. e. drawing filename: mkt-mlp08vrev1. 0.05 0.00 a b c recommended land pattern 0.15 c 0.08 c 3.00 3.00 0.15 c 2x 2x seating plane 0.10 c (0.20) 1.94 3.30 0.56 8x 5 8 4 1 0.65 2.52 1.70 0.47 8x 1 4 5 8 pin 1 ident 2.45 2.35 (0.35) 4x 0.10 cab 0.05 c 0.40 0.30 8x 0.65 1.75 1.65 0.40 0.30 8x 0.80 max pin1 ident figure 1. 8-lead, 3x3mm molded leadless package (mlp) package drawings are provided as a servic e to customers considering fairchild co mponents. drawings may change in any manner without notice. please note the revision and/or date on the drawi ng and contact a fairchild semiconductor representative to ver ify or obtain the most recent revision. package specifications do not expand the terms of fairchild?s worldwide terms and conditions, specifically the warranty therein, which covers fairchild products. always visit fairchild semiconductor?s online pack aging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/ .
? 2010 fairchild semiconductor corporation www.fairchildsemi.com fpf2700 / fpf2701 / fpf2702 ? rev. 1.0.2 19 fpf2700 / fpf2701 / fpf2702 ? accupower? 0.4~2a ad justable over-current protection load switches

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