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rt8035 ? ds8035-05 october 2012 www.richtek.com 1 copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? features z z z z z 2.5v to 5.5v input range z z z z z 800ma output current z z z z z 1.25mhz fixed frequency pwm operation z z z z z 95% efficiency z z z z z no schottky diode required z z z z z 0.6v reference allows low output voltage z z z z z low dropout operation : 100% duty cycle z z z z z small 10-lead wdfn package z z z z z rohs compliant and halogen free applications z portable instruments z microprocessors and dsp core supplies z cellular phones z wireless and dsl modems z pc cards dual 800ma, 1.25mhz synchronous ste p-down converter general description the rt8035 is a high-efficiency pulse-width-modulated (pwm) dual step-down dc/dc converter. capable of delivering up to 800ma output current over a wide input voltage range from 2.5v to 5.5v, the rt8035 is ideally suited for portable electronic devices that are powered from 1-cell li-ion battery or from other power sources such as cellular phones, pdas, pc wlan card and hand-held devices. three operating modes are available including : pwm mode, low-dropout mode and shut-down mode. the internal synchronous rectifier with low r ds(on) dramatically reduces conduction loss at pwm mode. no external schottky diode is required in practical application. the rt8035 enters low-dropout mode when normal pwm cannot provide regulated output voltage by continuously turning on the upper p-mosfet. the rt8035 enters shut- down mode and consumes less than 0.1 a when the en pin is pulled low. the switching ripple is easily smoothed-out by small package filtering elements due to the fixed operating frequency of 1.25mhz. the rt8035 is available in the wdfn-10l 3x3 package. ordering information marking information pin configurations (top view) wdfn-10l 3x3 en1 fb1 lx2 gnd lx1 gnd vin1 en2 fb2 vin2 9 8 7 9 1 2 3 4 5 10 gnd 11 gd=ym dnn gd= : product code ymdnn : date code rt8035gqw gd : product code ymdnn : date code rt8035zqw gd ym dnn rt8035 package type qw : wdfn-10l 3x3 (w-type) lead plating system g : green (halogen free and pb free) z : eco (ecological element with halogen free and pb free) 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.
rt8035 2 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? function block diagram functional pin description pin no. pin name pin function 1 en1 chip enable of channel 1 (active high). 2 fb1 feedback input of channel 1. 3 vin2 power supply input of channel 2. 5 lx2 switching node of channel 2. 6 en2 chip enable of channel 2 (active high). 7 fb2 feedback input of channel 2. 8 vin1 power supply input of channel 1. 10 lx1 switching node of channel 1. 4, 9, 11 gnd (exposed pad) ground. the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. typical application circuit comp rc rs1 rs2 en1/en2 vin1/vin2 lx1/lx2 fb1/fb2 uvlo & power good detector v ref slope compensation current sense osc & shutdown control current limit detector driver control logic gnd pwm comparator error amplifier vin1 8 rt8035 v in1 lx1 10 fb1 2 gnd 4, 9 11 (exposed pad) v out1 1 en1 chip enable lx2 5 fb2 7 v out2 vin2 3 v in2 6 en2 4.7f c in1 c in2 4.7f l1 2.2h l2 2.2h c ff1 c ff2 r1 110k r2 110k c out1 10f r3 110k r4 110k c out2 10f
rt8035 3 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? absolute maximum ratings (note 1) z supply input voltage vin1, vin 2 ---------------------------------------------------------------------------------- ? 0.3v to 6.5v z lx1, lx2 pin voltage ------------------------------------------------------------------------------------------------- ? 0.3v to (v in +0.3v) z other pins voltage ---------------------------------------------------------------------------------------------------- ? 0.3v to 6.5v z power dissipation, p d @ t a = 25 c wdfn-10l 3x3 --------------------------------------------------------------------------------------------------------- 1.471w z package thermal resistance (note 2) wdfn-10l 3x3, ja --------------------------------------------------------------------------------------------------- 68 c/w wdfn-10l 3x3, jc --------------------------------------------------------------------------------------------------- 7.8 c/w z lead temperature (soldering, 10 se c.) --------------------------------------------------------------------------- 260 c z junction temperature ------------------------------------------------------------------------------------------------- 150 c z storage temperature range ---------------------------------------------------------------------------------------- ? 65 c to 150 c z esd susceptibility (note 3) hbm (human body model) ------------------------------------------------------------------------------------------ 2kv electrical characteristics (v in = 3.6v, t a = 25 c unless otherwise specified) parameter symbol test conditions min typ max unit input voltage range v in 2.5 -- 5.5 v reference voltage v ref 0.588 0.6 0.612 v quiescent current i q i out = 0ma, v fb = v ref + 5% -- 70 -- a shutdown current i shdn -- 0.1 1 a v in rising -- 2.1 -- under voltage lock out threshold uvlo hysteresis -- 0.18 -- v oscillator frequency f osc v in = 3.6v, i out = 300ma 1 1.25 1.5 mhz enable high-level input voltage v en_h v in = 2.5v to 5.5v 1.25 -- v in enable low-level input voltage v en_l v in = 2.5v to 5.5v -- -- 0.9 v thermal shutdown temperature t sd -- 160 -- c peak current limit i lim v in = 2.5v to 5.5 v 1.1 1.5 -- a switch on resistance, high r ds(on)_p i out = 200ma, v in = 3.6v -- 0.25 -- switch on resistance, low r ds(on)_n i out = 200ma, v in = 3.6v -- 0.26 -- output line regulation v in = 2.5v to 5.5v (note 5) -- 0.04 0.4 %/v output load regulation 50ma < i load < 0.8a (note 5) -- 0.5 -- % recommended operating conditions (note 4) z supply input voltage -------------------------------------------------------------------------------------------------- 2.5v to 5 .5v z junction temperature range ---------------------------------------------------------------------------------------- ? 40 c to 125 c z ambient temperature range ---------------------------------------------------------------------------------------- ? 40 c to 85 c
rt8035 4 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? note 1. stresses beyond those listed ? absolute maximum ratings ? may cause permanent damage to the device. these are stress ratings only, and 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 may affect device reliability. note 2. ja is measured at t a = 25 c on a high effective thermal conductivity four-layer test board per jedec 51-7. jc is measured at the exposed pad of the package. note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions. note 5. guarantee by design.
rt8035 5 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? typical operating characteristics frequency vs. temperature 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 -50 -25 0 25 50 75 100 125 temperature (c) frequency (mhz) 1 v in = 3.3v, v out = 1.2v reference voltage vs. temperature 0.580 0.585 0.590 0.595 0.600 0.605 0.610 0.615 0.620 -50 -25 0 25 50 75 100 125 temperature (c) reference voltage (v) v in = 2.5v, v out = 1.2v, i out = 0.1a reference voltage v s. input voltage 0.580 0.585 0.590 0.595 0.600 0.605 0.610 0.615 0.620 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) reference voltage (v) v out = 1.2v, i out = 0.1a current limit vs temperature 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 -50 -25 0 25 50 75 100 125 temperature (c) current limit (a) v in = 3.3v, v out = 1.2v output voltage vs. output current 1.180 1.185 1.190 1.195 1.200 1.205 1.210 1.215 1.220 1.225 1.230 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 output current (a) output voltage (v) v in = 3.3v efficiency vs. output current 0 10 20 30 40 50 60 70 80 90 100 0.001 0.01 0.1 1 output current (a) efficiency (%) v in = 2.5v v in = 3.3v v in = 5.5v v out = 1.2v
rt8035 6 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? load transient response time (100 s/div) v out (50mv/div) i out (1a/div) v in = 2.5v, v out = 1.2v, i out = 0.1a to 0.8a load transient response time (100 s/div) v out (50mv/div) i out (1a/div) v in = 2.5v, v out = 1.2v, i out = 0.4a to 0.8a power off from en time (50 s/div) v out (1v/div) v en (1v/div) i out (1a/div) v in = 2.5v, v out = 1.2v, i out = 0.8a switching time (250ns/div) v out (5mv/div) v lx (2v/div) i out (1a/div) v in = 2.5v, v out = 1.2v, i out = 0.8a power on from v in time (5ms/div) v out (1v/div) v in (1v/div) i out (1a/div) v in = 2.5v, v out = 1.2v i out = 0.8a power on from en time (250 s/div) v out (1v/div) v en (1v/div) i out (1a/div) v in = 2.5v, v out = 1.2v, i out = 0.8a
rt8035 7 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? ? ? ? ? ? ? + out l out 8fc 1 esr i v applications information the basic rt8035 application circuit is shown in typical application circuit. external component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by c in and c out . 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. having a lower ripple current reduces the esr losses in the output capacitors and the output voltage ripple. highest efficiency operation is achieved at low frequency with small ripple current. this, however, requires a large inductor. a reasonable starting point for selecting the ripple current is i l = 0.4(i max ). the largest ripple current occurs at the highest v in . to guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation : 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 ? ? ? ? ? ? ? ? ? ? ? ? ? = in out out l v v 1 l f v i ? ? ? ? ? ? ? ? ? ? ? ? ? = in(max) out l(max) out v v 1 i f v l inductance collapses abruptly when the peak design current is exceeded. this results 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. 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 : 1 v v v v i i out in in out out(max) rms ? = 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. note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to further derate the capacitor, or 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 :
rt8035 8 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? 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. using ceramic input and output capacitors higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. their high ripple current, high voltage rating and low esr make them ideal for switching regulator applications. however, care must be taken when these capacitors are used at the input and output. when a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, v in . at best, this ringing can couple to the output and be mistaken as loop instability. at worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at v in large enough to damage the part. output voltage setting the resistive divider allows the fb pin to sense a fraction of the output voltage as shown in figure 1. ) r2 r1 (1 v v ref out + = figure 1. setting output voltage where v ref is the internal reference voltage (0.6v typ.) checking transient response the regulator loop response can be checked by looking at the load transient response. switching regulators take several cycles to respond to a step in load current. when a load step occurs, v out immediately shifts by an amount equal to i load (esr), where esr is the effective series resistance of c out . i load also begins to charge or discharge c out generating a feedback error signal used by the regulator to return v out to its steady-state value. during this recovery time, v out can be monitored for overshoot or ringing that would indicate a stability problem. 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, the maximum junction temperature is 125 c. the junction to ambient thermal resistance ja is layout dependent. for wdfn-10l 3x3 package, the thermal resistance ja is 68 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) / (68 c/w) = 1.471w for wdfn-10l 3x3 for adjustable voltage mode, the output voltage is set by an external resistive divider according to the following equation : rt8035 gnd fb r1 r2 v out
rt8035 9 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? layout considerations follow the pcb layout guidelines for optimal performance of rt8035. ` keep the trace of the main current paths as short and wide as possible. ` put the input capacitor as close as possible to the device pins (vin1 / vin2 and gnd). ` lx 1 / lx 2 node is with high frequency voltage swing and should be kept at small area. keep analog components away from the lx 1 / lx 2 node to prevent stray capacitive noise pick-up. ` place the feedback components as close as possible to the fb1 / fb2 pins. ` the gnd and exposed pad must be connected to a strong ground plane for heat sinking and noise protection. figure 2. derating curve of maximum power dissipation the maximum power dissipation depends on operating ambient temperature for fixed t j(max) and thermal resistance ja . the figure 2 of derating curve allows the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. en1 fb1 lx2 gnd lx1 gnd vin1 en2 fb2 vin2 9 8 7 9 1 2 3 4 5 10 gnd 11 l1 c in1 c out1 r3 v out2 v out1 r4 r2 v out1 r1 l2 c in2 c out2 v out2 c ff1 c ff2 gnd figure 3. pcb layout guide 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 25 50 75 100 125 ambient temperature (c) maximum power dissipation (w) 1 four layers pcb wdfn-10l 3x3
rt8035 10 ds8035-05 october 2012 www.richtek.com copyright 2012 richtek technology corporation. all rights reserved. is a registered trademark of ri chtek technology corporation. ? table 1. recommended inductors table 2. recommended capacitors for c in and c out supplier inductance ( h) dimensions (mm) series taiyo yuden 2.2 3.00 x 3.00 x 1.50 nr 3015 gotrend 2.2 3.85 x 3.85 x 1.80 gtsd32 sumida 2.2 4.50 x 3.20 x 1.55 cdrh2d14 sumida 4.7 4.50 x 3.20 x 1.55 cdrh2d14 taiyo yuden 4.7 3.00 x 3.00 x 1.50 nr 3015 gotrend 4.7 3.85 x 3.85 x 1.80 gtsd32 supplier capacitance ( f) package part number tdk 4.7 0603 c1608jb0j475m murata 4.7 0603 grm188r60j475ke19 taiyo yuden 4.7 0603 JMK107BJ475RA taiyo yuden 10 0603 jmk107bj106ma tdk 10 0805 c2012jb0j106m murata 10 0805 grm219r60j106me19 murata 10 0805 grm219r60j106ke19 taiyo yuden 10 0805 jmk212bj106rd
rt8035 11 ds8035-05 october 2012 www.richtek.com richtek technology corporation 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 richtek products are sold by description only. richtek reserves the right to change the circuitry and/or specifications without notice at any time. customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a richtek product. information furnish ed by richtek is believed to be accurate and reliable. however, no responsibility is assumed by richtek or its subsidiaries for its use; nor for any infringeme nts of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of r ichtek or its subsidiaries. outline dimension 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 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 2.950 3.050 0.116 0.120 d2 2.300 2.650 0.091 0.104 e 2.950 3.050 0.116 0.120 e2 1.500 1.750 0.059 0.069 e 0.500 0.020 l 0.350 0.450 0.014 0.018 w-type 10l dfn 3x3 package d 1 e a3 a a1 d2 e2 l b e see detail a

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