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ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 1 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated ? v in 4.75v to 24v ? load current of up to 1.2a ? internal power mosfet ? stable with low esr ceramic output capacitors ? up to 90% efficiency ? 0.1a shutdown mode ? fixed 1.4mhz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? resistor divider adjustable output: 0.81v to 15v ? sot26: available in ?green? molding compound (no br, sb) ? lead free finish/rohs compliant (note 1) the ap5100 is a current mode step-down converter with a built-in power mosfet to enable smallest solution size power conversion. with the low series resistance power switch it enables a constant output current of up to 1.2a over a wide input supply range. the load and line regulation has excellent response time over the operating input voltage and temperature range. the ap5100 is self protected, through a cycle-by-cycle current limiting algorithm and an on chip thermal protection. the ap5100 will provide the voltage conversion with a low count of widely available standard external components. the ap5100 is available in sot26 package. applications ? distributed power systems ? battery charger ? pre-regulator for linear regulators ? wled drivers typical applications bst sw fb in en c2 ap5100 r1 r2 d1 gnd v in c3 .l 1 c1 on off c6 5 4 1 6 3 v out figure 1. typical application circuit features general description
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 2 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated typical applications (continued) bst sw fb in en c2 22f 6.3v r3 100kohm ap5100 r1 49.9kohm r2 16.2kohm d1 b230a gnd v in v out 3.3v c3 22nf 3.3h c1 10f 25v on off c6 100pf 5 4 1 6 3 l1 figure 2. 1.4mhz, 3.3v output at 1a step-down converter bst sw fb in en c2 10f 16v r3 100kohm ap5100 r2 40 ohm 1% 1n5819hw-7 gnd v in c3 10nf l1 10h c1 10f 25v on off 5 4 1 6 3 6v -12v -vout -vout -vout -vout led1 led 2 led 3 r4 200kohm 1% d1 figure 3. white led driver application
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 3 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated ap5100 w g - 7 package packing green g : green w : sot26 7 : tape & reel device package code packaging (note 2) 7? tape and reel quantity part number suffix AP5100WG-7 w sot26 3000/tape & reel -7 notes: 1. eu directive 2002/95/ec (rohs). all applicable rohs exemptions applied. please visit our website at http://www.diodes.com/products/lead_free.html . 2. pad layout as shown on diodes inc. suggested pad layout document ap02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf. pin assignments 1 2 3 7 4 6 en gnd in fb sot26 5 bst ( top view ) sw ordering information
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 4 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated pin descriptions pin name pin # description bst 1 bootstrap. to form a boost circuit, a capacitor is connected between sw and bst pins to form a floating supply across the power switch driver. this capacitor is needed to drive the power switch?s gate above the supply voltage. typical values for c bst range from 0.1uf to 1uf. gnd 2 ground. this pin is the voltage reference for the regulated output voltage. all control circuits are referenced to this pin. for th is reason care must be taken in its la y out. fb 3 feedback. to set the output voltage, connect this pin to the output resistor divider or directly to v out . to prevent current limit run away du ring a current limit condition, the frequency foldback comparator lowers the oscillator frequency when the fb voltage is below 400mv. en 4 on/off control input. do not leave this pin floating. to turn the device on, pull en above 1.2v and to turn it off pull below 0.4v. if enable/disable is not used, connect a 100kohm resistor between en to v in . in 5 supply voltage. the ap5100 operates from a +4.75v to +24v unregulated input. a decoupling capacitor c1 is required to prevent large voltage spikes from appearing at the input. place this capacitor near the ic. sw 6 switch output. this is the reference for the floating top gate driver. absolute maximum ratings (note 3) symbol description rating unit esd hbm human body model esd protection 3 kv esd mm machine model esd protection 300 v v in supply voltage 26 v v sw switch voltage -0.3 to v in + 0.3 v v bst boost voltage v sw + 6 v all other pins ?0.3 to +6 v t st storage temperature -65 to +150 c t j junction temperature +150 c t l lead temperature +260 c ja junction to ambient thermal resistance (note 4) 140 c/w jc junction to case thermal resistance (note 4) 35 c/w notes: 3. exceeding these ratings may damage the device. 4. test condition for sot26: measured on approximately 1? square of 1 oz copper.
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 5 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated recommended oper ating ratings (note 5) symbol description rating unit v in supply voltage 4.75 to 24 c t a operating ambient temperature range -25 to +85 c v out output voltage 0.81 to 15 v notes: 5. the device function is not guaranteed outside of the recommended operating conditions. electrical characteristics ( v in = 12v, t a = +25 c, unless otherwise noted) notes: 6. guaranteed by design. symbol parameter test conditions min typ. max unit v fb feedback voltage 4.75v v in 24v 0.790 0.810 0.830 v i fb feedback current v fb = 0.8v 0.1 a r ds(on) switch-on resistance (note 6) 0.35 ? switch leakage v en = 0v, v sw = 0v 10 a current limit (note 6) 2.4 a f sw oscillator frequency v fb = 0.6v 1.1 1.4 1.7 mhz fold-back frequency v fb = 0v 480 khz maximum duty cycle v fb = 0.6v 87 % t on minimum on-time (note 6) 100 ns under voltage lockout threshold rising 3.8 4.0 4.2 v under voltage lockout threshold hysteresis 150 mv en input low voltage 0.4 v en input high voltage 1.2 v en input current v en = 2v 0.3 a v en = 0v 0.1 i s supply current (shutdown) v en = 0v 0.1 1.0 a i q supply current (quiescent) v en = 2v, v fb = 1v 0.4 1.0 ma thermal shutdown (note 6) 140 c
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 6 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated typical performanc e characteristics v in =12v, v out =3.3v, l=3.3uh, c1=10uf, c2=22uf, t a =+25 ? c, unless otherwise noted. steady state test (i out =0.5a) load transient test (i out =0.2a to 0.8a. step at 0.8a/us) time- 1us/div time- 100us/div start-up through enable (no load) start-up through enable (i out =1a, resistive load) time- 50us/div time- 50us/div shutdown through enable (no load) shutdown through enable (i out =1a, resistive load) time- 50us/div time- 50us/div
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 7 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated typical performanc e characteristics (continued) short circuit entry short circuit recovery time- 50us/div time- 100us/div
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 8 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated application information operation the ap5100 is a current mode control, asynchronous buck regulator. current mode control assures excellent line and load regulation and a wide loop bandwidth for fast response to load transients. figure. 4 depicts the functional block diagram of ap5100. the operation of one switching cycle can be explained as follows. at the beginning of each cycle, hs (high-side) mosfet is off. the ea output voltage is higher than the current sense amplifier output, and the current comparator?s output is low. the rising edge of the 1.4mhz oscillator clock signal sets the rs flip-flop. its output turns on hs mosfet. when the hs mosfet is on, inductor current starts to increase. the current sense amplifier senses and amplifies the inductor current. since the current mode control is subject to sub-harmonic oscillations that peak at half the switching frequency, ramp slope compensation is utilized. this will help to stabilize the power supply. this ramp compensation is summed to the current sense amplifier output and compared to the error amplifier output by the pwm comparator. when the sum of the current sense amplifier output and the slope compensation signal exceeds the ea output voltage, the rs flip-flop is reset and hs mosfet is turned off. the external schottky rectifier diode (d1) conducts the inductor current. for one whole cycle, if the sum of the current sense amplifier output and the slope compensation signal does not exceed the ea output, then the falling edge of the oscillator clock resets the flip-flop. the output of the error amplifier increases when feedback voltage (vfb) is lower than the reference voltage of 0.81v. this also increases the inductor current as it is proportional to the ea voltage. figure 4. functional block diagram
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 9 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated application information (continued) setting the output voltage the output voltage can be adjusted from 0.81v to 15v using an external resistor divider. table 1 shows a list of resistor selection for common output voltages. resistor r1 is selected based on a design tradeoff between efficiency and output voltage accuracy. for high values of r1 there is less current consumption in the feedback network. however the trade off is output voltage accuracy due to the bias current in the error amplifier. r2 can be determined by the following equation: ? ? ? ? ? ? ? ? ? = 1 0.81 out v 2 r 1 r v out (v) r 1 (k ? ) r 2 (k ? ) 1.8 80.6 (1%) 64.9 (1%) 2.5 49.9 (1%) 23.7 (1%) 3.3 49.9 (1%) 16.2 (1%) 5 49.9 (1%) 9.53 (1%) table 1. resistor selection for common output voltages inductor calculating the inductor value is a critical factor in designing a buck converter. for most designs, the following equation can be used to calculate the inductor value; sw f l ?i in v ) out v in (v out v l ? = where l ?i is the inductor ripple current. and sw f is the buck converter switching frequency. choose the inductor ripple current to be 30% of the maximum load current. the maximum inductor peak current is calculated from: 2 l ?i load i l(max) i += peak current determines the required saturation current rating, which influences the size of the inductor. saturating the inductor decreases the converter efficiency while increasing the temperatures of the inductor, the mosfet and the diode. hence choosing an inductor with appropriate saturation current rating is important. a 1h to 10h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor?s dc resistance should be less than 200m . use a larger inductance for improved efficiency under light load conditions. input capacitor the input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. the input capacitor has to sustain the ripple current produced during the on time on the upper mosfet. it must hence have a low esr to minimize the losses. due to large di/dt through the input capacitors, electrolytic or ceramics should be used. if a tantalum must be used, it must be surge protected. otherwise, capacitor failure could occur. for most applications, a 4.7f ceramic capacitor is sufficient. output capacitor the output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the output voltage. the output capacitor is a basic component for the fast response of the power supply. in fact, during load transient, for the first few microseconds it supplies the current to the load. the converter recognizes the load transient and sets the duty cycle to maximum, but the current slope is limited by the inductor value. maximum capacitance required can be calculated from the following equation:
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 10 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated 2 out v 2 ) out v v( 2 ) 2 inductor i out l(i o c ? + + = where v is the maximum output voltage overshoot. esr of the output capacitor dominates the output voltage ripple. the amount of ripple can be calculated from the equation below: esr inductor i capacitor vout = an output capacitor with ample capacitance and low esr is the best option. for most applications, a 22f ceramic capacitor will be sufficient. external diode the external diode?s forward current must not exceed the maximum output current. since power dissipation is a critical factor when choosing a diode, it can be calculated from the equation below: 0.3v out i) in v out v (1 diode p ?= note: 0.3v is the voltage drop across the schottky diode. a diode that can withstand this power dissipation must be chosen. pc board layout this is a high switching frequency converter. hence attention must be paid to the switching currents interference in the layout. switching current from one power device to another can generate voltage transients across the impedances of the interconnecting bond wires and circuit traces. these interconnecting impedances should be minimized by using wide, short printed circuit traces. the input capacitor needs to be as close as possible to the in and gnd pins. the external feedback resistors should be placed next to the fb pin. external bootstrap diode it is recommended that an external bootstrap diode be added when the input voltage is no greater than 5v or the 5v rail is available in the system. this helps improve the efficiency of the regulator. the bootstrap diode can be a low cost one such as in4148 or bat54. ap5100 bst sw 10nf boost diode 5v 1 6 figure 5. external bootstrap diode application information (continued)
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 rev. 1 11 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated marking information (1) sot26 1 2 3 6 7 4 xx : identification code y : year 0~9 x : a~z : green ( top view ) 5 w : week : a~z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week xx y w x part number package identification code ap5100w sot26 aj package information (all dimensions in mm) (1) package type: sot26
ap5100 1.2a step-down converter with 1.4mhz switching frequency ap5100 rev. 1 12 of 12 march 2010 document number: ds32130 rev. 1 - 2 www.diodes.com ? diodes incorporated important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or ot her changes without further notice to this document and any product described herein. diodes incorporated does not assume any liabi lity arising out of the application or use of this document or any product described herein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or user of this document or products desc ribed herein in such applications shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes incorporated products for any unintended or unauthorized application, customers shall indemnify and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney fee s arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized a pplication. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. life support diodes incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the chief executive officer of diodes incorporated. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporated and its representatives against any damages arising out of the use of diodes incorporated products in such safety-critical, life support devices or systems. copyright ? 2010, diodes incorporated www.diodes.com

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