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smartswitch ? general description the AAT4285 smartswitch is a p-channel mosfet power switch designed for high-side load switching applications. the mosfet operates from a 3.0v to 13.2v input range making it ideal for applications in single or dual cell lithium-ion battery systems. the device has a typical r ds(on) of 240m ? at 12v, allow- ing a low forward voltage drop and high current han- dling capability. the device is a slew rate limited turn- on load switch and is functionally compatible with the aat4250 and aat4280 products, while offering a high operating voltage. the AAT4285 features fast load switch turn-on capability of 100s and offers a shutdown load discharge circuit to rapidly turn off a load circuit when the switch is disabled. the quies- cent supply current is very low, typically 25a. the AAT4285 is available in a pb-free, 8-pin sc70jw package and is specified over the -40c to +85c temperature range. features ?v in range: 3.0v to 13.2v ? low r ds(on) 240m typical @ 12v 310m typical at 5v ? 100s slew rate turn-on time ? fast shutdown load discharge ? low quiescent current typically 25a 1a maximum in shutdown ? ttl/cmos input logic level ? temperature range: -40c to +85c ? 8-pin sc70jw package applications ? 2 cell lithium-ion batteries ? camcorders ? handheld test equipment ? load switching AAT4285 12v slew rate controlled load switch typical application 4285.2007.04.1.0 1 AAT4285 c out 0.1f c in 1f out in gnd 4 v out gnd gnd v in on/off in on
pin descriptions pin configuration sc70jw-8 (top view) pin # symbol function 1,2 in p-channel mosfet source. bypass to ground through a 1f capacitor. 3 out p-channel mosfet drain connection. bypass to ground through a 0.1f capacitor. 4 on/off active high enable input. a logic low turns the switch off and the device consumes less than 1a of current. logic high resumes normal operation. 5, 6, 7, 8 gnd ground connection AAT4285 12v slew rate controlled load switch 2 4285.2007.04.1.0 in out on/off gnd gnd gnd gnd in 1 2 3 45 6 7 8
absolute maximum ratings 1 thermal characteristics 2 symbol description value units v in in to gnd -0.3 to 14 v v on on/off to gnd -0.3 to 14 v v out out to gnd -0.3 to v in + 0.3 v i max maximum continuous switch current 1.7 a i dm maximum pulsed current 3.4 a t j operating junction temperature range -40 to 150 c symbol description value units ja thermal resistance 140 c/w p d maximum power dissipation 714 mw AAT4285 12v slew rate controlled load switch 4285.2007.04.1.0 3 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at c ondi- tions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. 2. mounted on an fr4 board.
AAT4285 12v slew rate controlled load switch 4 4285.2007.04.1.0 electrical characteristics 1 v in = 12v, t a = -40c to +85c, unless otherwise noted. typical values are t a = 25c. symbol description conditions min typ max units v in operation voltage 3.0 13.2 v v uvlo under-voltage lockout 2.7 3.0 v v uvlo(hys) under-voltage lockout hysteresis 250 v i q quiescent current on/off = active, i out = 0 25 50 a i q(off) off supply current on/off = inactive, out = open 1.0 a i shd off switch current on/off = gnd, v out = 0 0.1 1.0 a v in = 12v 240 400 r ds(on) on resistance v in = 5v 310 500 m v in = 3.3v 380 tcr rds on resistance temperature 2800 ppm/c coefficient t d(on) output turn-on delay time 2 r load = 20 , t a = 25c 20 40 s t on turn-on rise time 2 r load = 20 , t a = 25c 100 250 s t d(off) output turn-off delay time 2 r load = 20 , t a = 25c 1 10 s r pd output pull-down resistance on/off inactive, t a = 25c 520 800 during off v on(l) on/off input logic low voltage v in = 3v to 13v 0.4 v v on(h) on/off input logic high voltage v in = 3v to 13v 1.6 v i on on/off leakage current v on/off = 13v -1.0 1.0 a 1. the AAT4285 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correlation with statistical process controls. 2. contact factory for other turn-on and delay options.
typical characteristics AAT4285 12v slew rate controlled load switch 4285.2007.04.1.0 5 on/off threshold high vs. input voltage input voltage (v) on/off threshold (v) 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 3579111 3 -40 c 25 c 85 c on/off threshold low vs. input voltage input voltage (v) on/off threshold (v) 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 357 91113 -40 c 25 c 85 c r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 220 260 300 340 380 420 3 4 5 6 7 8 9 10 11 12 2a 0.5a 0.1a 1a r ds(on) vs. temperature temperature ( c) r ds(on) (m 100 150 200 250 300 350 400 450 500 -40 -15 10 35 60 85 v in = 3.3v v in = 4.2v v in = 12v v in = 5v quiescent current vs. input voltage input voltage (v) quiescent current (a) 0 5 10 15 20 25 30 35 02468101214 quiescent current vs. temperature temperature ( c) quiescent current (a) 0 5 10 15 20 25 30 -40 -15 10 35 60 85 v in = 12v v in = 5v v in = 4.2v v in = 3.3v
AAT4285 12v slew rate controlled load switch 6 4285.2007.04.1.0 typical characteristics turn-on (v in = 12v; 600ma load) time (25s/div) on/off (5v/div) v out (5v/div) i out (500ma/div) output pull-down resistance vs. temperature temperature ( c) resistance ( 400 450 500 550 600 650 700 750 800 -40 -15 10 35 60 85 v in = 3.3v v in = 12v v in = 5v v in = 4.2v turn-off (v in = 12v; 600ma load) time (10s/div) on/off (5v/div) v out (5v/div) i out (500ma/div)
functional block diagram AAT4285 12v slew rate controlled load switch 4285.2007.04.1.0 7 functional description the AAT4285 is a slew rate controlled p-channel mosfet power switch designed for high-side load switching applications. the device operates with input voltages ranging from 3.0v to 13.2v, making it ideal for single- or multi-cell battery-powered applications. in cases where the input voltage drops below 3.0v, the AAT4285 mosfet is pro- tected from entering the saturated region of opera- tion by automatically shutting down. in addition, the ttl compatible on/off pin makes the AAT4285 an ideal level-shifted load switch. the slew rate controlling feature eliminates inrush current when the mosfet is turned on, allowing the AAT4285 to operate with a small input capacitor, or no input capacitor at all. during slewing, the current ramps linearly until it reaches the level required for the output load condition. the proprietary control method works by careful control and monitoring of the mosfet gate voltage. when the device is switched on, the gate voltage is quickly increased to the threshold level of the mosfet. once at this level, the current begins to slew as the gate voltage is slowly increased until the mosfet becomes fully enhanced. once it has reached this point, the gate is quickly increased to the full input voltage and r ds(on) is minimized. under- voltage lockout level shift in on/off ou t gnd gnd gnd gnd turn-on slew rate control
AAT4285 12v slew rate controlled load switch 8 4285.2007.04.1.0 applications information input capacitor a 1f or larger capacitor is typically recommended for c in in most applications. a c in capacitor is not required for basic operation. however, c in is useful in preventing load transients from affecting upstream circuits. c in should be located as close to the device v in pin as practically possible. ceramic, tantalum, or aluminum electrolytic capac- itors may be selected for c in . there is no specific capacitor esr requirement for c in . however, for higher current operation, ceramic capacitors are recommended for c in due to their inherent capabil- ity over tantalum capacitors to withstand input cur- rent surges from low impedance sources, such as batteries in portable devices. output capacitor for proper slew operation, a 0.1f capacitor or greater between out and gnd is recommended. the output capacitor has no specific capacitor type or esr requirement. if desired, c out may be increased without limit to accommodate any load transient condition without adversely affecting the device turn-on slew rate time. enable function the AAT4285 features an enable / disable function. this pin (on/off ) is compatible with both ttl and cmos logic. reverse output-to-input voltage conditions and protection under normal operating conditions, a parasitic diode exists between the output and input of the load switch. the input voltage should always remain greater than the output load voltage, maintaining a reverse bias on the internal parasitic diode. conditions where v out might exceed v in should be avoided since this would forward bias the internal parasitic diode and allow excessive current flow into the out pin and possibly damage the load switch. in applications where there is a possibility of v out exceeding v in for brief periods of time during nor- mal operation, the use of a larger value c in capac- itor is highly recommended. a larger value of c in with respect to c out will affect a slower c in decay rate during shutdown, thus preventing v out from exceeding v in . in applications where there is a greater danger of v out exceeding v in for extended periods of time, it is recommended to place a schottky diode from in to out (connecting the cathode to in and anode to out). the schottky diode forward voltage should be less than 0.45v. thermal considerations and high output current applications the AAT4285 is designed to deliver a continuous output load current. the limiting characteristic for maximum safe operating output load current is package power dissipation. in order to obtain high operating currents, careful device layout and circuit operating conditions need to be taken into account. the following discussions will assume the load switch is mounted on a printed circuit board utilizing the minimum recommended footprint, as stated in the layout considerations section of this datasheet. at any given ambient temperature (t a ), the maxi- mum package power dissipation can be deter- mined by the following equation: constants for the AAT4285 are maximum junction temperature, t j(max) = 125c, and package thermal resistance, ja = 140c/w. worst case conditions are calculated at the maximum operating tempera- ture where t a = 85c. typical conditions are calcu- lated under normal ambient conditions where t a = 25c. at t a = 85c, p d(max) = 286mw. at t a = 25c, p d(max) = 714mw. the maximum continuous output current for the AAT4285 is a function of the package power dissipa- tion and the r ds of the mosfet at t j(max) . the max- imum r ds of the mosfet at t j(max ) is calculated by increasing the maximum room temperature r ds by the r ds temperature coefficient. the temperature coefficient (tcr rds ) is 2800ppm/c. therefore, max r ds 125c = r ds 25c (1 + tcr rds t) max r ds 125c = 240m (1 + 0.0028 (125c - 25c)) = 307m p d(max) = t j(max) - t a ja
for maximum current, refer to the following equation: for example, if v in = 12v, r ds(max) = 307m ? and t a = 25c, i out(max) = 1.53a. if the output load cur- rent were to exceed 1.53a or if the ambient tem- perature were to increase, the internal die temper- ature would increase, and the device would be damaged. higher peak currents can be obtained with the AAT4285. to accomplish this, the device thermal resistance must be reduced by increasing the heat sink area or by operating the load switch in a duty cycled manner. high peak output current applications some applications require the load switch to operate at a continuous nominal current level with short duration, high-current peaks. the duty cycle for both output current levels must be taken into account. to do so, first calculate the power dissipation at the nominal continuous current level, and then add in the additional power dissipation due to the short duration, high-current peak scaled by the duty factor. for example, a 12v system using an AAT4285 operates at a continuous 100ma load current level and has short 2a current peaks. the current peak occurs for 500s out of a 5ms period. first, the current duty cycle is calculated: the load current is 100ma for 90% of the 5ms peri- od and 2a for 10% of the period. de-rated for temperature: the power dissipation for a 100ma load is calculat- ed as follows: the power dissipation for 100ma load at 90% duty cycle is 2.76mw. now the power dissipation for the remaining 10% of the duty cycle at 2a is calculated: the power dissipation for 2a load at 10% duty cycle is 123mw. finally, the two power figures are summed to determine the total true power dissipa- tion under the varied load. the maximum power dissipation for the AAT4285 operating at an ambient temperature of 85c is 286mw. the device in this example will have a total power dissipation of 123mw. this is well within the thermal limits for safe operation of the device; in fact, at 85c, the AAT4285 will handle a 2a pulse for up to 23% duty cycle. at lower ambient temperatures, the duty cycle can be further increased. printed circuit board layout recommendations for proper thermal management and to take advantage of the low r ds(on) of the AAT4285, a few circuit board layout rules should be followed: v in AAT4285 12v slew rate controlled load switch 4285.2007.04.1.0 9 % peak duty cycle = % peak duty cycle = x 100 ?? ?? = 10% 500s 5.0ms ?? ?? p d(max) = i out 2 r ds p d(100ma) = (100ma) 2 307m p d(100ma) = 3.07mw p d(90%d/c) = %dc p d(100ma) p d(90%d/c) = 0.90 3.07mw p d(90%d/c) = 2.76mw 240m (1 + 0.0028 (125c - 25c)) = 307m i out(max) < p d(max) r ds p d(total) = p d(100ma) + p d(2a) p d(total) = 2.76mw + 123mw p d(total) = 125.76mw p d(max) = i out 2 r ds p d(2a) = (2a) 2 307m p d(2a) = 1.23w p d(10%d/c) = %dc p d(2a) p d(10%d/c) = 0.10 1.23mw p d(10%d/c) = 123mw
AAT4285 12v slew rate controlled load switch 10 4285.2007.04.1.0 and v out should be routed using wider than normal traces, and gnd should be connected to a ground plane. to maximize package thermal dissipation and power handling capacity of the AAT4285 sc70jw-8 package, the ground plane area con- nected to the ground pins should be made as large as possible. for best performance, c in and c out should be placed close to the package pins. evaluation board layout the AAT4285 evaluation board layout follows the printed circuit board layout recommendations and can be used for good application guide. refer to figures 1 through 3. note: board layout shown is not to scale. figure 1: AAT4285 evaluation board figure 2: AAT4285 evaluation board solder component side layout and silk screen. side layout. figure 3: AAT4285 evaluation board circuit schematic diagram. vin jp1 AAT4285 en out in in gnd gnd gnd gnd c1 1f r1 100k c2 0.1f vout on/off 1 2 3 4 8 7 6 5 c1 1f x7r 16v 0805 grm21br71c105ka01 (c1 1f x5r 16v 0603 grm188r61c105ka93) c2 0.1f x5r 16v 0805 grm219r71c104ka01 (c2 0.1f x7r 16v 0603 grm188r71c104ka01)
AAT4285 12v slew rate controlled load switch 4285.2007.04.1.0 11 ordering information package information sc70jw-8 all dimensions in millimeters. package marking 1 part number (tape and reel) 2 sc70jw-8 uaxyy AAT4285ijs-3-t1 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737- 4600 fax (408) 737- 4611 ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifications or to discontinue any product or service with- out notice. except as provided in analogictechs terms and conditions of sale, analogictech assumes no liability whatsoever, an d analogictech disclaims any express or implied war- ranty relating to the sale and/or use of analogictech products including liability or warranties relating to fitness for a part icular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. in order to minimize risks associated with the customers applications, adequa te design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. testing and other quality control techniques are utilized to the extent an alogictech deems necessary to support this warranty. specific testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trad emarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holder s. 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . 0.225 all analogictech products are offered in pb-free packaging. the term pb-free means semiconductor products that are in compliance with current rohs standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. for more information, please visit our website at http://www.analogictech.com/pbfree.

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