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rt8032 1 ds8032-02 march 2011 www.richtek.com pin configurations (top view) wdfn-12l 4x3 ordering information note : richtek products are : ` rohs compliant and compatible with the current require- ments of ipc/jedec j-std-020. ` suitable for use in snpb or pb-free soldering processes. marking information for marking information, contact our sales representative directly or through a richtek distributor located in your area. 1.2mhz/1.2a buck converter with programmable average input current limit features z z z z z programmable average input current limit z z z z z 3v to 5.5v input range z z z z z 1.2a output current z z z z z up to 95% efficiency z z z z z 1.2mhz switching frequency z z z z z no schottky diode required z z z z z force continues mode operation z z z z z low r ds(on) internal switches : 230m z z z z z small 12-lead wdfn package z z z z z external compensation for optimal transient response z z z z z external soft-start z z z z z input over voltage protection z z z z z rohs compliant and halogen free general description the rt8032 is a synchronous, step-down dc/dc converter with input current limit function. the average input current limit can be programmed by an external resistor. its input voltage range is from 3v to 5.5v and provides an adjustable regulated output voltage from 0.8v to 5v while delivering up to 1.2a of output current. the internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external schottky diode. current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. the rt8032 is operated in forced continuous pwm mode which minimizes ripple voltage and reduces the noise and rf interference. the 100% duty cycle in low dropout operation can maximize the battery life. applications z distributed power systems z battery charger z dsl modems z pre-regulator for linear regulators z 3g/3.5g data card shdn/ss nc pgnd sw fb comp iset vout vin gnd vout nc 11 10 9 1 2 3 4 5 12 67 8 pgnd 13 rt8032 package type qw : wdfn-12l 4x3 (w-type) lead plating system g : green (halogen free and pb free)
rt8032 2 ds8032-02 march 2011 www.richtek.com functional pin description pin no. pin name pin function 1 shdn/ss shutdown and soft-start control input. conn ect this pin to a supply voltage that is >1.4v to enable the ic and to a supply voltage that is <0.4v to shutdown the ic . an rc network from the shutdown command signal to the pin will provide a soft-start function by the rising time of the fb pin 2, 7 nc no internal connection. 3 gnd ground. return the feedback resistive dividers to this ground, which in turn connects to pgnd at one point. 4 sw internal power mosfet switches output. connect this pin to the output inductor. 5, 13 (exposed pad) pgnd power ground. the exposed pad must be soldered to a large pcb and connected to pgnd for maximum power dissipation. 6, 8 vout output of the converter. a filter capacitor is placed from v out to gnd. 9 vin power input. internal vcc for the ic. a 10 f ceramic capacitor is recommended as close as to vin and gnd as possible 10 iset average input current limit setting. place a resistor and capacitor in parallel from the pin to gnd 11 comp error amplifier output. the current comparator threshold increases with the control voltage. connect external compensation elements to the pin to stabilize the control loop. 12 fb feedback input. receives the feedback voltage from a resistive divider connected across the output. typical application circuit vin 9 rt8032 v in 3 pgnd sw 4 comp fb 12 11 gnd 5, exposed pad (13) c in 10f l 4.7h r1 112k r2 32k r c 120k c c 60nf v out 1 shdn/ss 10 iset r lim 24k c c1 680nf r c1 1k c out 2200nf vout 6, 8 c c2 1.1nf r ss 1meg c ss 57nf 3.6v
rt8032 3 ds8032-02 march 2011 www.richtek.com function block diagram driver pwm control 0.4v oc limit current sense slope com osc otp comp gnd fb vin pgnd sw + - + - + - + - error amplifier v ref soft-start shdn/ss input current limit setting iset + - 0.95v vin vout
rt8032 4 ds8032-02 march 2011 www.richtek.com absolute maximum ratings (note 1) z supply input voltage, v in ---------------------------------------------------------------------------------------- ? 0.3v to 6v z switching voltage, sw ------------------------------------------------------------------------------------------ ? 0.3v to (v in + 0.3v) z other i/o pin v oltages ------------------------------------------------------------------------------------------- ? 0.3v to 6v z power dissipation, p d @ t a = 25 c wdfn-12l 4x3 ----------------------------------------------------------------------------------------------------- 1.667w z package thermal resistance (note 2) wdfn-12l 4x3, ja ----------------------------------------------------------------------------------------------- 60 c/w wdfn-12l 4x3, jc ----------------------------------------------------------------------------------------------- 7.5w z junction temperature --------------------------------------------------------------------------------------------- 150 c z lead temperature (soldering, 10 sec.) ------------------ ----------------------------------------------------- 260 c z storage temperature range ------------------------------------------------------------------------------------ ? 65 c to 150 c z esd susceptibility (note 3) hbm (human body mode) -------------------------------------------------------------------------------------- 2kv mm (ma chine mode) ---------------------------------------------------------------------------------------------- 200v electrical characteristics (v in = 5v, t a = 25 c, unless otherwise specified) parameter symbol test conditions min typ max unit feedback reference voltage v ref 0.784 0.8 0.816 v active, not switching, v fb = 0.75v -- 550 -- a dc bias current (pvdd, vdd total) en =0 -- -- 1 a v in rising 2.3 2.43 2.55 v under voltage lockout threshold v in falling 2.13 2.29 2.43 v switching frequency 1 1.2 1.4 mhz logic-high voltage v ih v en rising 1.4 -- -- v en threshold logic-low voltage v il v en falling -- -- 0.4 v switch on resistance, high r pmos i sw = 0.2a -- 230 -- m switch on resistance, low r nmos i sw = 0.2a -- 230 -- m input average current limit i av g r lim = 25.5k 0.4 0.45 0.5 a peak current limit i lim 1.6 1.9 -- a output voltage line regulation v in = 3v to 5.5v -- 0.1 1 %/v output voltage load regulation 0ma < i load < 1.2a -- -- 1 % recommended operating conditions (note 4) z junction temperature range ------------------------------------------------------------------------------------ ? 40 c to 125 c z ambient temperature range ------------------------------------------------------------------------------------ ? 40 c to 85 c
rt8032 5 ds8032-02 march 2011 www.richtek.com note 1. stresses listed as the above ? absolute maximum ratings ? may cause permanent damage to the device. these are for stress ratings. functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. note 2. ja is measured in the natural convection at t a = 25 c on 4-layers high effective thermal conductivity test board of jedec 51-7 thermal measurement standard. note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions.
rt8032 6 ds8032-02 march 2011 www.richtek.com typical operating characteristics efficiency vs. output current 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 1.2 output current (a) efficiency (%) v in = 5v, v out = 3.6v reference voltage vs. input voltage 0.800 0.802 0.804 0.806 0.808 0.810 0.812 0.814 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) reference voltage (v) v out = 3.6v, i out = 0a output voltage vs. output current 3.55 3.56 3.57 3.58 3.59 3.60 3.61 3.62 3.63 3.64 3.65 0 0.2 0.4 0.6 0.8 1 1.2 output current (a) output voltage (v) v in = 5v frequency vs. input voltage 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) frequency (mhz) v out = 3.6v, i out = 0a frequency vs. temperature 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 -50 -25 0 25 50 75 100 125 temperature frequency (mhz) v in = 5v, v out = 3.6v, i out = 0a ( c) output voltage vs. temperature 3.55 3.56 3.57 3.58 3.59 3.60 3.61 3.62 3.63 3.64 3.65 -50-25 0 25 50 75100125 temperature output voltage (v) v in = 5v, i out = 0a ( c)
rt8032 7 ds8032-02 march 2011 www.richtek.com power off from v in time (10ms/div) i in (500ma/div) v out (5v/div) i out (500ma/div) i out = 0.33a v in (5v/div) switching time (500ns/div) i l (500ma/div) v out (5mv/div) v in = 5v, v out = 3.6v, i out = 0.5a v sw (5v/div) power on from v in time (10ms/div) i in (500ma/div) v out (5v/div) i out (500ma/div) i out = 0.33a v in (5v/div) input current limit time (2.5ms/div) i in (500ma/div) v out (2v/div) i out (1a/div) v in = 5v, v out = 3.6v, i out = 0a to 1.5a input current limit vs input voltage 0.30 0.35 0.40 0.45 0.50 0.55 0.60 4 4.25 4.5 4.75 5 5.25 5.5 input voltage (v) input current limit (a) i out = 1a, r lim = 24k input current limit v s temperature 0.30 0.35 0.40 0.45 0.50 0.55 0.60 -50 -25 0 25 50 75 100 125 temperature input current limit (a) ( c) v in = 5v, i out = 1a, r lim = 24k
rt8032 8 ds8032-02 march 2011 www.richtek.com application information output voltage programming the output voltage is set by an external resistive divider according to the following equation : where v ref equals to 0.8v typical. the resistive divider allows the fb pin to sense a fraction of the output voltage as shown in figure 1. figure 1. setting the output voltage ? ? ? ? ? ? + = r2 r1 1 v v ref out rt8032 fb gnd v out r1 r2 input average current limit setting the input current limit circuit is programmed by an external resistor on iset. this allows the user to program a maximum average input current. for applications such as usb that the current from the bus must be limited, the value of r lim and c c1 can be calculated as following equation. r lim = 0.8 / (70 x 10 -6 x i in (a)) c c1 = 16 x 10 -6 / r lim , , r c1 = 1k soft-start the soft-start function is combined with shutdown. when the shdn/ss pin is brought above 1v (typ.), the ic will be enabled. the components of r ss and c ss provide a slow ramping voltage on the shdn/ss pin to provide a soft-start function. input over voltage protection the rt8032 equips input over voltage protection function. when the input voltage exceeds 6v, the next switching cycle of the ic will be terminated. once the input voltage is lower than 6v, the ic will enter normal operation again. 100% duty cycle operation when the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. further reduction of the supply voltage forces the main switch to remain on for more than one cycle and eventually reaching 100% duty cycle. the output voltage will then be determined by the input voltage minus the voltage drop across the internal p-mosfet and the inductor. inductor selection for a given input and output voltage, the inductor value and operating frequency determine the ripple current. the ripple current i l increases with higher v in and decreases with higher inductance. ? ? ? ? ? ? ? ? ? ? ? ? ? = in out out l v v 1 l f v i inductor core selection once the value for l is known, the type of inductor must be selected. high efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. as the inductance increases, core losses decrease. unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. ferrite core material saturates ? hard ? , which means that inductance collapses abruptly when the peak design current is exceeded. this result in an abrupt increase in inductor ripple current and consequent output voltage ripple. do not allow the core to saturate! different core materials and shapes will change the size/ current and price/current relationship of an inductor. toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar characteristics. the choice of which style inductor to use mainly depends on the price vs. size requirements and any radiated field/emi requirements.
rt8032 9 ds8032-02 march 2011 www.richtek.com c in and c out selection the input capacitance, c in , is needed to filter the trapezoidal current at the source of the top mosfet. to prevent large ripple voltage, a low esr input capacitor sized for the maximum rms current should be used. rms current is given by : this formula has a maximum at v in = 2v out , where i rms = i out /2. this simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. choose a capacitor rated at a higher temperature than required. several capacitors may also be paralleled to meet size or height requirements in the design. the selection of c out is determined by the effective series resistance (esr) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. loop stability can be checked by viewing the load transient response as described in a later section. the output ripple, v out , is determined by : the output ripple is highest at maximum input voltage since i l increases with input voltage. multiple capacitors placed in parallel may be needed to meet the esr and rms current handling requirements. dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. special polymer capacitors offer very low esr but have lower capacitance density than other types. tantalum capacitors have the highest capacitance density but it is important to only use types that have been surge tested for use in switching power supplies. aluminum electrolytic capacitors have significantly higher esr but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. ceramic capacitors have excellent low esr characteristics but can have a high voltage coefficient and audible piezoelectric effects. the high q of ceramic capacitors with trace inductance can also lead to significant ringing. 1 v v v v i i out in in out out(max) rms ? = ? ? ? ? ? ? + out l out 8fc 1 esr i v thermal considerations for continuous operation, do not exceed absolute maximum operation junction temperature. the maximum power dissipation depends on the thermal resistance of ic package, pcb layout, the rate of surroundings airflow and temperature difference between junction to ambient. the maximum power dissipation can be calculated by following formula : p d(max) = (t j(max) ? t a ) / ja where t j(max) is the maximum operation junction temperature, t a is the ambient temperature and the ja is the junction to ambient thermal resistance. for recommended operating conditions specification of rt8032, the maximum junction temperature is 125 c. the junction to ambient thermal resistance ja is layout dependent. for wdfn-12l 4x3 packages, the thermal resistance ja is 60 c/w on the standard jedec 51-7 four layers thermal test board. the maximum power dissipation at t a = 25 c can be calculated by following formula : p d(max) = (125 c ? 25 c) / (60 c/w) = 1.667w for wdfn-12l 4x3 the maximum power dissipation depends on operating ambient temperature for fixed t j(max) and thermal resistance ja . for rt8032 package, the figure 2 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. figure 2. derating curves for rt8032 package 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0255075100125 ambient temperature (c) maximum power dissipation (w) wdfn-12l 4x3 four layers pcb
rt8032 10 ds8032-02 march 2011 www.richtek.com layout consideration follow the pcb layout guidelines for optimal performance of rt8032. ` keep the traces of the main current paths as short and wide as possible. ` put the input capacitor as close as possible to the device pins (vin and gnd). ` lx node is with high frequency voltage swing and should be kept at small area. keep analog components away from the lx node to prevent stray capacitive noise pickup. ` connect feedback network behind the output capacitors. keep the loop area small. place the feedback components near the rt8032. ` connect all analog grounds to a command node and then connect the command node to the power ground behind the output capacitors. ` an example of pcb layout guide is shown in figure 3 for reference. shdn/ss nc pgnd sw fb comp iset vout vin gnd vout nc 11 10 9 1 2 3 4 5 12 67 8 pgnd 13 c in l r1 r2 r c c c r lim c c1 c out c c2 r ss c ss v out r c1 v in figure 3. pcb layout guide component supplier series inductance ( h) dcr (m ) current rating (ma) dimensions (mm) taiyo yuden nr3015 4.7 120 1020 3x3x1.5 table 1. inductors component supplier part no. capacitance ( f) case size tdk c2012x5r0j106m 10 0805 taiyo yuden JMK212BJ106ML 10 0805 vishay 592d228x06r3x2t269 2200 1415x7.37x2.2 (mm) table 2. capacitors for c in and c out recommended component selection for typical application
rt8032 11 ds8032-02 march 2011 www.richtek.com richtek technology corporation headquarter 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 fax: (8863)5526611 information that is provided by richtek technology corporation is believed to be accurate and reliable. richtek reserves the ri ght to make any change in circuit design, specification or other related things if necessary without notice at any time. no third party intellectual property inf ringement of the applications should be guaranteed by users when integrating richtek products into any application. no legal responsibility for any said applications i s assumed by richtek. richtek technology corporation taipei office (marketing) 5f, no. 95, minchiuan road, hsintien city taipei county, taiwan, r.o.c. tel: (8862)86672399 fax: (8862)86672377 email: marketing@richtek.com outline dimension dimensions in millimeters dimensions in inches symbol min max min max a 0.700 0.800 0.028 0.031 a1 0.000 0.050 0.000 0.002 a3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 d 3.950 4.050 0.156 0.159 d2 3.250 3.350 0.128 0.132 e 2.950 3.050 0.116 0.120 e2 1.650 1.750 0.065 0.069 e 0.500 0.020 l 0.350 0.450 0.014 0.018 w-type 12l dfn 4x3 package 1 1 2 2 note : the configuration of the pin #1 identifier is optional, but must be located within the zone indicated. det ail a pin #1 id and tie bar mark options

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