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rev. 1.00 1 september 02, 2011 rev. 1.00 pb september 02, 2011 HT7466 3a step-down dc to dc converter feature ? input voltage range: 4.75v to 24v ? variable output voltage range: 1.222v to 20v ? 3a output current ? effciency up to 91% ? fixed 380khz operating frequency ? 20 m a shutdown current ? internal power mosfet switch ? stable operation using low esr ceramic capacitors ? over temperature protection ? cycle-by-cycle over current protection ? soft-start function ? under voltage lockout protection ? 8-pin sop package applications ? battery chargers ? distributed power systems ? led power supplies ? dsl modems ? linear regulator pre power processing ? set-top-boxes, dvd players, lcd displays general description the ht 7466 i s a dc -dc b uck re gulator. t he b uilt- in high driver nmos provides a monolithic solution for high effciency step-down dc-dc converter . w ith 3a o utput c urrent, t he wi de i nput v oltage r ange a nd stable output voltage regulation can widely use in all kinds of application, like communication, power for high power led, battery char ger, etc. the protection function include over current and over temperature protection. the soft start function prevent inrush supply current and output overshoot when initial startup. the under voltage lockout is set to 4.1v . it prevents abnormal situation occurring. the HT7466 requires a minimum number of standard external components and is available in a 8-pin sop package for small area pcb application. application circuit b 330a vin en ss gnd comp ht 7466 bs sw fb 22uf 10 uf l 10nf 10nf r 2 r 1 v in v out ? ? ? ? ? ? ? ? + = 2 21 r rr vv fb out 4. 75~ 24v c 4 c 1 c 2 c 3 r 3 c 6 c 5 effciency vs output current
rev. 1.00 2 september 02, 2011 HT7466 block diagram pin assignment
pin description pin no. pin name description 1 ss soft-start input. if the soft start function is to be used then an external capacitor should be connected between this pin and ground. if the soft start function is not required the pin should be left open. 2 bs internal power nmos gate drive boost input. a 10nf or greater value capacitor should be connected from sw to bs for additional power nmos gate driving purposes. 3 vin power supply input. the input supply pin for the device, vin, is connected to a supply voltage between 4.75v to 24v. 4 sw power switching output. the internal power mos drain is connected to the inductor, diode and vin. 5 gnd ground. device ground voltage reference. 6 fb feedback pin. the feedback pin is connected to an external resistor divider to measure the output voltage. 7 comp error amplifer output. used for compensation of the regulation control loop. connect a series rc network from comp to gnd to compensate the regulation control loop. the comp pin value is 1.222v. 8 en enable input. this pin is set high to turn on the regulator and low to turn it off. the pin should be left unconnected if not used.
rev. 1.00 3 september 02, 2011 HT7466 absolute maximum ratings maximum input supply v oltage ............................ 26v switch node v oltage .............................................. 26v feedback v oltage ..................................................... 6v en v oltage ............................................................... 6v comp v oltage ........................................................... 6v ss v oltage ................................................................ 6v maximum junction t emperature ....................... 150 c note: these are stress ratings only . stresses exceeding the range specifed under absolute maximum ratings may cause substantial damage to the device. functional operation of this device at other conditions beyond those l isted i n t he sp ecifcation i s n ot i mplied a nd p rolonged e xposure t o e xtreme c onditions m ay a ffect device reliability. recommended operating conditions input supply v oltage ................................ 4.75v ~ 24v ambient t emperature range ............... -40 c ~ +85 c electrical characteristics v in =12v, t a=25 c, unless otherwise specifed refer to circuit of figure 1. ( note 1) symbol parameter test condition min. typ. max. unit v fb feedback voltage 4.75v v in 24v 1.194 1.222 1.250 v v uvlo under voltage lockout threshold 4.1 v under voltage lockout threshold hysteresis 200 mv i q quiescent current v fb =1.5v, v en =high 1.0 1.2 ma i ss shutdown supply current v en =0v 20 30 p a f osc oscillator frequency 380 khz short circuit frequency v fb =0v 20 35 50 khz d max maximum duty cycle v fb =1.0v 90 % i sw upper switch leakage v en =0v, v sw =0v 0 10 p a r ds switch on resistance (note 2) i out =3a 95 m : i limit current limit 4.3 a error amplifer voltage gain (note 2) 70 db error amplifer trans-conductance (note 2) 800 p a/v v en enable threshold 4.75v v in 24v 0.9 1.0 1.5 v t j thermal shutdown 150 c note: 1. specifications are production tested at t a=room temperature. specifications over the -40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical quality controls (sqc). 2. designer test specifcations.
rev. 1.00 4 september 02, 2011 HT7466 functional description setting the output voltage the HT7466 is a step down switching dc/dc converter device. the device switching output, sw , is connected to a standard converter lc flter circuit for buck c onversion. t he out put c urrent i s sense d usi ng an external voltage divider network connected to the load output voltage and ground, and the sense voltage feedback to the device on the fb pin. by comparing this sense voltage with an internally generated 1.222 voltage reference, suitable regulation can be implemented to achieve the required output voltage. by selecting suitable val ues of ext ernal voltage divider resistors, the desired output voltage can be adjusted to the required level. the output voltage can be calculated using the following formula: where r2 is the resistor divider lower resistor and r1 is the upper resistor, and the r1, r2 must be k w level. compensation components care m ust be t aken whe n se lecting e xternal components. the comp pin is the output of the error amplifer and must be properly connected to an external rc network to ensure regulator loop stability. the va lues of t he c ompensation c omponents gi ven in t able 1 yield a s table control loop for the output voltage and capacitor given. table 1 compensation v alues for t ypical output voltage/capacitor combinations. v out l r3 c4 r1 r2 c6 c5 2.5v 15 m h 3.9k w 5.6nf 10.5k w 10k w 22 m f ceramic 3.3v 15 m h 4.7k w 4.7nf 17.0k w 10k w 22 m f ceramic 5.0v 15 m h 7.5k w 2.7nf 30.9k w 10k w 22 m f ceramic bootstrap circuit in this device bootstrap capacitor is connected from sw to bs pin, the step-down converter is use n-channel mosfet , and mos source pin is foating to gr ound, t his dr ive c ircuit of t he a pplication i s called high-side circuit, and the drive circuit used in t his ki nd of si tuation i s c alled boot strap c ircuit. large capacitor values can keep internal high-side n-channel mosfe t ga te vol tage gre ater t han z ero when power mos is turn on; usually a 10nf capacitor is suffcient for most applications. current limit protection the device has a cycle-by-cycle current limit to protect the internal power mosfet . if the inductor current r eaches t he c urrent l imit t hreshold o f 4 .3a, the mosfet oscillator frequency will be transformed from 380khz to a short circuit frequency of 35khz and the output current will remain at its current limit value. over temperature protection a thermal shutdown is implemented to prevent damage due t o e xcessive he at a nd powe r di ssipation. typically the thermal shutdown threshold is 150c. the thermal shutdown is triggered the device stops switching and when the device thermal falls until the temperature hysteresis windows the device will be starts switching again. application information inductor the inductor is required to supply a constant current to the output load while being driven by the switched input voltage. the choice of inductor af fects steady state operation as well as transient behavior and loop st ability. t here a re t hree i mportant e lectrical parameters which need to be considered when choosing an inductor: ? the inductor value ? dcr - copper wire resistance ? the saturation current inductor choice is especially important as it is important to ensure the inductor does not saturate under its peak current conditions, the general rule of ke eping t he i nductor c urrent pe ak-to-peak ripple approximately 30% of the nominal output current. using this value of ripple current is a good compromise between exces sive output voltage ripple and e xcessive c omponent si ze a nd c ost. al so e nsure that the inductor has a low dcr to minimize power losses. input/output capacitor input capacitor because the v in pin is connected to the internal power mosfet, when the power mosfet is switching and the input current is discontinuous, therefore an input capacitor c1 (in p cb layout c1 and c8 is parallels input capacitor) is required to supply the ac current to the step-down converter while maintaining the dc input voltage. a low esr ceramic capacitor is required to keep noise to a minimum.
rev. 1.00 5 september 02, 2011 HT7466 output capacitor the output capacitor is required to maintain the dc output volta ge. ceramic or low esr elect rolytic capacitors is the rule to choice of external load capacitor is also critical and low esr value capacitors must be used to ensure stability . this capacitor must be connected very close to the inductor , with short traces for good noise performance. schottky diode the out put di ode c onducts whe n t he i nternal powe r mosfet is switched of f. there are three important electrical parameters to consider when choosing the diode: ? the diode maximum reverse voltage value must be greater than the maximum input voltage. ? short recovery time and low forward voltage -- use a schottky diode type. ? diode current rating should be greater than the maximum load current. layout considerations circuit board layout is a very important consideration for switching regulators if they are to function properly. poor c ircuit l ayout m ay re sult i n re lated noise problems. in order to minimise emi and switching noise, follow the guidelines below: ? all tracks should be as wide as possible. ? the input and output capacitors, c1 (c8) and c6 (c7), should be placed close to the vin, vout and gnd pins (c1 and c8 is parallel; c6 and c7 is parallel). ? the schottky diode d and inductor l must be placed close to the sw pin. ? feedback resistor, r1 (r1-1) and r2, must be placed close to the fb and gnd pins (r1 and r1-1 is series). ? a full ground plane is always helpful for better emi performance. a recommended pcb layout with component locations is shown below. top layer bottom layer
rev. 1.00 6 september 02, 2011 HT7466 package information note that the package information provided here is for consultation purposes only . as this information may be updated at regular intervals users are reminded to consult the holtek website (http://www.holtek.com.tw/english/ literature/package.pdf) for the latest version of the package information. 8-pin sop (150mil) outline dimensions for thermally enhanced variations only (exposed pad) ms-012 symbol dimensions in inch min. nom. max. a D 0.236 b D 0.154 c 0.012 D 0.020 c' D 0.193 d D D 0.067 d1 0.059 D D e D 0.050 D e2 0.039 D D f D D 0.006 g 0.016 D 0.050 h 0.004 D 0.010 0 D 8 symbol dimensions in mm min. nom. max. a D 6.00 D b D 3.90 D c 0.31 D 0.51 c' D 4.90 D d D D 1.70 d1 1.50 D D e D 1.27 D e2 1.00 D D f D D 0.15 g 0.40 D 1.27 h 0.10 D 0.25 0 D 8
rev. 1.00 7 september 02, 2011 HT7466 reel dimensions sop 8n (150mil) symbol description dimensions in mm a reel outer diameter 330.01.0 b reel inner diameter 100.01.5 c spindle hole diameter 13.0 +0.5/-0.2 d key slit width 2.00.5 t1 space between flange 12.8 +0.3/-0.2 t2 reel thickness 18.20.2
rev. 1.00 8 september 02, 2011 HT7466 carrier tape dimensions

sop 8n (150mil) symbol description dimensions in mm w carrier tape width 12.0 +0.3/-0.1 p cavity pitch 8.00.1 e perforation position 1.750.10 f cavity to perforation (width direction) 5.50.1 d perforation diameter 1.550.1 d1 cavity hole diameter 1.50 +0.25/-0.00 p0 perforation pitch 4.00.1 p1 cavity to perforation (length direction) 2.00.1 a0 cavity length 6.40.1 b0 cavity width 5.20.1 k0 cavity depth 2.10.1 t carrier tape thickness 0.300.05 c cover tape width 9.30.1
rev. 1.00 9 september 02, 2011 HT7466 holtek semiconductor inc. (headquarters) no.3, creation rd. ii, science park, hsinchu, taiwan tel: 886-3-5631999 fax: 886-3-563-1189 http://www.holtek.com.tw holtek semiconductor inc. (taipei sales offce) 4f-2, no. 3-2, yuanqu st., nankang software park, taipei 115, taiwan tel: 886-2-2655-7070 fax: 886-2-2655-7373 fax: 886-2-2655-7383 (international sales hotline) holtek semiconductor inc. (shenzhen sales offce) 5f, unit a, productivity building, no.5 gaoxin m 2nd road, nanshan district, shenzhen, china 518057 tel: 86-755-8616-9908, 86-755-8616-9308 fax: 86-755-8616-9722 holtek semiconductor (usa), inc. (north america sales offce) 46729 fremont blvd., fremont, ca 94538, usa tel: 1-510-252-9880 fax: 1-510-252-9885 http://www.holtek.com copyright ? 2011 by holtek semiconductor inc. the information appearing in this data sheet is believed to be accurate at the time of publication. however, holtek assumes no responsibility arising from the use of the specifications described. the applications mentioned herein are used solely for the purpose of illustration and holtek makes no warranty or representation that such applications will be suitable without further modifcation, nor recommends the use of its products for application that may present a risk to human life due to malfunction or otherwise. holtek's products are not authorized for use as critical components in life support devices or systems. holtek reserves the right to alter its products without prior notifcation. for the most up-to-date information, please visit our web site at http://www.holtek.com.tw .

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