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RT8259 1 ds8259-03 march 2011 www.richtek.com 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. 1.2a, 24v, 1.4mhz step-down converter general description the RT8259 is a high voltage buck converter that can support the input voltage range from 4.5v to 24v and the output current can be up to 1.2a. current mode operation provides fast transient response and eases loop stabilization. the chip also provides protection functions such as cycle- by-cycle current limiting and thermal shutdown protection. the RT8259 is available in a sot-23-6 and tsot-23-6 packages. features z z z z z wide operating input voltage range : 4.5v to 24v z z z z z adjustable output voltage range : 0.8v to 15v z z z z z 1.2a output current z z z z z 0.3 internal power mosfet switch z z z z z high efficiency up to 92% z z z z z 1.4mhz fixed switching frequency z z z z z stable with low esr output ceramic capacitors z z z z z thermal shutdown z z z z z cycle-by-cycle over current protection z z z z z rohs compliant and halogen free applications z distributed power systems z battery charger z pre-regulator for linear regulators z wled drivers typical application circuit pin configurations (top view) sot-23-6/tsot-23-6 marking information for marking information, contact our sales representative directly or through a richtek distributor located in your area. boot gnd fb en vin phase 4 23 5 6 vin en gnd boot fb phase 4 2 3 5 6 1 l1 4.7h cb 10nf c2 22f r1 62k r2 19.6k v out 3.3v c1 10f chip enable v in 4.5v to 24v RT8259 d1 b230a open = automatic startup RT8259 package type e : sot-23-6 j6 : tsot-23-6 lead plating system g : green (halogen free and pb free)
RT8259 2 ds8259-03 march 2011 www.richtek.com function block diagram functional pin description pin no. pin name pin function 1 boot bootstrap. a capacitor is connected between phase and boot 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. 2 gnd ground. this pin is the voltage reference for the regulated output voltage. for this reason, care must be taken in its layout. this node should be placed outside of the d1 to c1 groun d path to prevent switching current spikes from inducing voltage noise into the part. 3 fb feedback. an external resistor divider from the output to gnd tapped to the fb pin sets the output voltage. the value of the divider resistors also set loop bandwidth. 4 en chip enable (active high). if the en pin is open, it will be pulled to high by internal circuit. 5 vin supply voltage. bypass vin to gnd with a suitable large capacitor to prevent large voltage spikes from appearing at the input. 6 phase switch output. v out (v) 1.2 1.8 2.5 3.3 5 8 10 15 l1 (
RT8259 3 ds8259-03 march 2011 www.richtek.com electrical characteristics parameter symbol test conditions min typ max u nit feedback reference voltage v fb 4.5v ? to be continued (v in = 12v, t a = 25 c unless otherwise specified) absolute maximum ratings (note 1) z supply voltage, v in ------------------------------------------------------------------------------------------------ 26v z phase v oltage ----------------------------------------------------------------------------------------------------- ? 0.3v to (v in + 0.3v) z boot v oltage ------------------------------------------------------------------------------------------------------- v phase + 6v z all other pins -------------------------------------------------------------------------------------------------------- 0.3v to 6 v z output voltage ------------------------------------------------------------------------------------------------------ ? 0.3v to 15v z power dissipation, p d @ t a = 25 c t/sot-23-6 ----------------------------------------------------------------------------------------------------------- 0.4w z package thermal resistance (note 2) t/sot-23-6, ja ------------------------------------------------------------------------------------------------------ 250 c/w 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 (machine mode) ----------------------------------------------------------------------------------------------- 200v recommended operating conditions (note 4) z supply voltage, v in ------------------------------------------------------------------------------------------------ 4.5v to 24v z output voltage, v out ---------------------------------------------------------------------------------------------- 0.8v to 15v z en voltage, v en ----------------------------------------------------------------------------------------------------- 0v to 5.5v z junction temperature range ------------------------------------------------------------------------------------- ? 40 c to 125 c z ambient temperature range ------------------------------------------------------------------------------------- ? 40 c to 85 c
RT8259 4 ds8259-03 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 a high effective four layers 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. parameter symbol test conditions min typ max unit shutdown current i shdn v en = 0v -- 25 --
RT8259 5 ds8259-03 march 2011 www.richtek.com typical operating characteristics frequency vs. input voltage 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55 4 6.5 9 11.514 16.519 21.524 input voltage (v) frequency (mhz) v out = 3.3v, i out = 0.3a output voltage vs. load current 3.298 3.303 3.308 3.313 3.318 3.323 3.328 3.333 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 load current (a) output voltage (v) v in = 12v v in = 24v efficiency vs. load current 0 10 20 30 40 50 60 70 80 90 100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 load current (a) efficiency (%) v in = 12v v in = 24v v out = 3.3v efficiency vs. load current 0 10 20 30 40 50 60 70 80 90 100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 load current (a) efficiency (%) v in = 12v v in = 24v v out = 5v frequency vs. temperature 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55 -50 -25 0 25 50 75 100 125 temperature (c) frequency (mhz) 1 v in = 12v, v out = 3.3v, i out = 0.3a output voltage vs. temperature 3.22 3.24 3.26 3.28 3.30 3.32 3.34 3.36 3.38 -50 -25 0 25 50 75 100 125 temperature (c) output voltage (v) v in = 12v v in = 24v i out = 0a
RT8259 6 ds8259-03 march 2011 www.richtek.com quiescent current vs. input voltage 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 4 6.5 9 11.5 14 16.5 19 21.5 24 input voltage (v) quiescent current (ma) v en = 2v, v fb = 1v quiescent current vs. temperature 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -50 -25 0 25 50 75 100 125 temperature (c) quiescent current (ma ) v in = 12v v in = 24v v en = 2v, v fb = 1v load transient response time (50 s/div) i out (500ma/div) v out (50mv/div) v in = 12v, v out = 3.3v, i out = 0.6a to 1.2a load transient response time (50 s/div) i out (500ma/div) v out (50mv/div) v in = 12v, v out = 3.3v, i out = 0a to 1.2a time (250ns/div) switching v phase (10v/div) i l (1a/div) v in = 12v, v out = 3.3v, i out = 1.2a v out (5mv/div) switching time (250ns/div) v phase (10v/div) i l (1a/div) v in = 20v, v out = 3.3v, i out = 1.2a v out (5mv/div)
RT8259 7 ds8259-03 march 2011 www.richtek.com power on from en time (250 s/div) v out (1v/div) i in (500ma/div) v in = 12v, v out = 3.3v, i out = 1.2a v en (5v/div) power off from en time (100 s/div) v out (1v/div) i in (500ma/div) v in = 12v, v out = 3.3v, i out = 1.2a v en (5v/div)
RT8259 8 ds8259-03 march 2011 www.richtek.com application information the RT8259 is a high voltage buck converter that can support the input voltage range from 4.5v to 24v and the output current can be up to 1.2a. output voltage setting the resistive voltage divider allows the fb pin to sense a fraction of the output voltage as shown in figure 1. figure 1. output voltage setting RT8259 gnd fb r1 r2 v out for adjustable voltage mode, the output voltage is set by an external resistive voltage divider according to the following equation : ?? + ?? ?? ??? ? ?? ??? ? ??? ? ??? ? ? ??? ? ??? ? ? hard ? , which means that inductance collapses abruptly when the peak design current is exceeded. the previous situation results in an abrupt increase in inductor ripple current and consequent output voltage ripple. do not allow the core to saturate! inductor selection the inductor value and operating frequency determine the ripple current according to a specific input and output voltage. the ripple current i l increases with higher v in and decreases with higher inductance. where v fb is the feedback reference voltage (0.8v typ.). external bootstrap diode connect a 10nf low esr ceramic capacitor between the boot pin and sw pin. this capacitor provides the gate driver voltage for the high side mosfet. it is recommended to add an external bootstrap diode between an external 5v and the boot pin for efficiency improvement when input voltage is lower than 5.5v or duty ratio is higher than 65%. the bootstrap diode can be a low cost one such as 1n4148 or bat54. the external 5v can be a 5v fixed input from system or a 5v output of the RT8259. phase boot 5v RT8259 10nf
RT8259 9 ds8259-03 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 current, a low esr input capacitor sized for the maximum rms current should be used. the rms current is given by : out in rms out(max) in out v v i = i 1 vv ? ?? ?? + ?? ??
RT8259 10 ds8259-03 march 2011 www.richtek.com layout consideration follow the pcb layout guidelines for optimal performance of RT8259. ` 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 sensitive components away from the lx node to prevent stray capacitive noise pick- up. ` place the feedback components to the fb pin as close as possible. ` connect gnd to a ground plane for noise reduction and thermal dissipation. figure 4. pcb layout guide thermal considerations for continuous operation, do not exceed the maximum operation junction temperature 125 c. 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 the RT8259, the maximum junction temperature of the die is 125 c. the junction to ambient thermal resistance ja is layout dependent. for t/sot-23-6 package, the thermal resistance ja is 120 c/w on 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) / (250 c/w) = 0.4w for t/sot-23-6 packages the maximum power dissipation depends on operating ambient temperature for fixed t j(max) and thermal resistance ja . for RT8259 packages, the figure 3 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. figure 3. derating curves for RT8259 packages boot gnd fb en vin phase 4 2 3 5 6 1 v out v out c b l1 c out d1 c in r2 r1 gnd 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0255075100125 ambient temperature (c) maximum power dissipation (w) t/sot-23-6 single layer pc b
RT8259 11 ds8259-03 march 2011 www.richtek.com table 3. suggested capacitors for cin and cout component supplier series inductance ( m h) dcr (m w ) current rating (a) dimensions (mm) tdk slf7045 4.7 30 2 7 x 7 x 4.5 taiyo yuden nr8040 4.7 18 4.7 8 x 8 x 4 goternd gtsd53 4.7 45 1.87 5 x 5 x 2.8 goternd gssr2 4.7 18 5.7 10 x 10 x 3.8 table 2. suggested inductors for l1 component supplier series v rrm (v) i out (a) package diodes b230a 30 2 do-214ac diodes b330a 30 3 do-214ac panjit sk23 30 2 do-214ac panjit sk33 30 3 do-214ab table 4. suggested diode for d1 component supplier part no. capacitance ( m f) case size murata grm31cr61e106k 10 1206 tdk c3225x5r1e106k 10 1206 taiyo yuden tmk316bj106ml 10 1206 murata grm31cr61c226m 22 1206 tdk c3225x5r1c226m 22 1206 taiyo yuden emk316bj226ml 22 1206
RT8259 12 ds8259-03 march 2011 www.richtek.com outline dimension a a1 e b b d c h l sot-23-6 surface mount package dimensions in millimeters dimensions in inches symbol min max min max a 0.889 1.295 0.031 0.051 a1 0.000 0.152 0.000 0.006 b 1.397 1.803 0.055 0.071 b 0.250 0.560 0.010 0.022 c 2.591 2.997 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024
RT8259 13 ds8259-03 march 2011 www.richtek.com information that is provided by richtek technology corporation is believed to be accurate and reliable. richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. no third party intellectual property infringement of the applications should be guaranteed by users when integrating richtek products into any application. no legal responsibility for any said applications is assumed by richtek. richtek technology corporation headquarter 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 fax: (8863)5526611 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 tsot-23-6 surface mount package dimensions in millimeters dimensions in inches symbol min max min max a 0.700 1.000 0.028 0.039 a1 0.000 0.100 0.000 0.004 b 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 c 2.591 3.000 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024 a a1 e b b d c h l

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