variable frequency micropower step-up dc-dc converter the mc33468 is a micropower stepup switching voltage regulator, specifically designed for handheld and pager applications, to provide a regulated output voltage using a minimum of external parts. this device features a quiescent bias current of 3.0 m a typical. the mc33468 features a highly accurate voltage reference, an error amplifier, an oscillator, a variable frequency modulation (vfm) controller, a drive pin (ext) for an external transistor, and feedback resistors. the vout pin is fixed at 2v in the ic. the output of the converter with an inductor, a diode, a capacitor, a drive transistor, and feedback resistors can have an output of 30v. mc33468 features: ? low quiescent bias current of 3.0 m a ? high output voltage accuracy of 2.5% ? low startup voltage of 0.8 v at no load ? output voltage set with external resistors ? operating temperature range: 40 c to +85 c ? surface mount package ordering information device output voltage marking reel size tape width quantity mc33468sn20atr 2.0 0kxx* 7o 8 mm 3000 * a xxo denotes the lot number. pin description pin no. symbol description 1 gnd ground 2 v dd input 3 ext external transistor drive 4 nc no connection 5 v out voltage output pin (fixed at 2v) representative block diagram v ref gnd oscillator 5 v out 1 drive v dd 2 ext 3 on semiconductor mc33468 semiconductor technical data variable frequency micropower dctodc converter n suffix plastic package case 1212 (sot235) 15 4 2 3 (top view) ground vdd ext v out n/c pin connections 5 1 ? semiconductor components industries, llc, 2001 march, 2001 rev. 2 1 publication order number: mc33468/d
mc33468 http://onsemi.com 2 maximum ratings (t c = 25 c, unless otherwise noted.) rating symbol value unit power supply voltage (transient) v dd 12 v power supply voltage (operating) v dd 10 v external pin voltage v ext 0.3 to v dd + 0.3 v ext pin source/sink current i ext 50/50 ma power dissipation and thermal characteristics n suffix, plastic package case 1212 (sot235) maximum power dissipation @ t a = 250 c p d 150 mw thermal resistance, junctiontoair r q ja 667 c/w operating junction temperature t j 125 c operating ambient temperature t a 40 to +85 c storage temperature range t stg 55 to +125 c electrical characteristics (v dd = 1.9 v, t a = 25 c, unless otherwise noted.) characteristic symbol min typ max unit note 1 oscillator frequency f osc 180 khz b oscillator minimum supply voltage (i o = 0 ma) v dd 0.7 0.8 v b oscillator duty cycle d 65 75 % b ext output on state source current (v ext = gnd) i source 1.5 ma c off state sink current (v ext = 1.9 v) i sink 1.5 ma d total device output voltage v out 1.950 2.000 2.050 v quiescent bias current (v out = 1.9 v, i o = 0 ma) i q 15 25 m a a quiescent bias current (v out = 2.1 v, i o = 0 ma) i q 3.0 5.0 m a a internal resistor (v out to gnd) r vout 2.0 m output voltage temperature coefficient i out = 10 ma, 40 c t a 85 c v out t a 50 ppm/oc e 1. indicates test circuits shown on next page. 0 70 0 i out , output current (ma) figure 1. output voltage versus output current i out , output current (ma) figure 2. efficiency versus output current v out , output voltage (v) efficiency v in = 3.6 v 60 40 50 35 40 30 30 25 20 20 20 20 40 40 60 60 80 v in = 3.6 v
mc33468 http://onsemi.com 3 v dd v out a c e b d figure 3. test circuit schematics gnd ext v dd v out gnd ext oscilloscope v dd v out gnd ext v dd v out gnd ext a a v dd v out gnd ext a
mc33468 http://onsemi.com 4 definitions quiescent bias current current which is used to operate the switching regulator chip and is not delivered to the load. leakage current current drawn through a transistor junction, under a specified collector voltage, when the transistor is off. functional description introduction the mc33468 is a monolithic power switching regulator optimized for dctodc converter applications where power drain must be minimized. the mc33468 uses variable frequency modulation to step up the input dc voltage to a higher accurate output voltage. potential applications include low power consumer products and battery powered portable products. typical application circuits are shown in figure 4. operating description the mc33468 converter operates as a fixed ontime, variable offtime voltage mode ripple regulator. operation is intended to be in the discontinuous mode, where the inductor current ramps up to a peak value which is greater than or equal to twice the value of the dc input current during the ontime of the transistor switch. during the offtime of the transistor switch, the inductor current ramps down to zero and remains at zero until another switching cycle begins. since the v dd pin is connected to the input no external startup circuit is needed. oscillator the oscillator frequency, is internally programmed to 180 khz. the duty ratio of the oscillator is designed for a constant value of 0.75 nominal. hence the nominal ontime of the power switch is: t on d f osc 0.75 (180 khz) 4.16 m s feedback comparator the output voltage is sensed and fed to a high speed comparator noninverting input through an internal resistive divider. the comparator inverting input is connected to an internally trimmed reference. with a voltage mode ripple converter operating under normal conditions, output switch conduction is initiated and terminated by the oscillator, offtime is controlled by the high speed voltage feedback comparator. figure 4. typical 2.0 v application with bjt v in v out ext gnd v out v dd figure 5. design equations for stepup calculation equation t on d f osc l (n)(v in ) 2 (t on ) p o i l(avg) i in i l(pk) (v in v sat )(t on ) l v ripple(pp) (t on )(i o ) (c o ) the following converter design characteristics must be chosen: v in nominal operating dc input voltage v o desired dc output voltage i o desired dc output current v ripple(pp) desired peaktopeak output ripple voltage. for best performance the ripple voltage should be kept to a low value since it directly affects regulation. capacitor c o should have a low equivalent series resistance (esr). note : 1. v sat saturation voltage of the switching transistor. n estimated circuit efficiency.
mc33468 http://onsemi.com 5 figure 6. typical 2.0 v application with mosfet v in v out ext gnd v out v dd if input voltage is high enough, higher efficiency may be obtained by using a mosfet as the switch transistor, in which no gate resistor or capacitor is needed. mosfet and bjt voltage rating (v ds and v ce ) should be high enough to allow for spikes in voltage. figure 7. typical application for output voltages over 2.0 v v in v out ext gnd v out v dd d1 c out r1 r2 (2.0 v) q1 l1 inductor (l1) cd54 (15 h) diode (d1) mbrd540t1 capacitor (c out ) 47 f (tantalum type) transistor (q1) mmft3055vl resistor (r1) 150 k resistor (r2) 10 k when choosing the output capacitor, ensure that the capacitor voltage is higher than v out . select an inductor with low dc resistance and high saturation. a schottky diode is recommended for a lower voltage drop and faster switching. use external resistors that are much smaller resistance than the resistance internal to the i c (minimum of 2 m ). when r1 is much less than the internal resistance, the error is minimized.
mc33468 http://onsemi.com 6 package dimensions n suffix plastic package case 121201 (sot23) issue o dim min max millimeters a1 0.00 0.10 a2 1.00 1.30 b 0.30 0.50 c 0.10 0.25 d 2.80 3.00 e 2.50 3.10 e1 1.50 1.80 e 0.95 bsc e1 1.90 bsc l l1 0.45 0.75 notes: 1. dimensions are in millimeters. 2. interpret dimensions and tolerances per asme y14.5m, 1994. 3. datum c is a seating plane. a 1 5 23 4 d e1 b l1 e e e1 c m 0.10 c s b s a b 5x a2 a1 s 0.05 c l 0.20 --- sot235 2. 4 1. 0 0.7 max. 0.9 5 0.9 5 1.9 (unit: mm) recommended footprint for surface mount applications
mc33468 http://onsemi.com 7 notes
mc33468 http://onsemi.com 8 on semiconductor and are trademarks of semiconductor components industries, llc (scillc). scillc reserves the right to make changes without further notice to any products herein. scillc makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does scillc assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. atypicalo parameters which may be provided in scill c data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including atypicalso must be validated for each customer application by customer's technical experts. scillc does not convey any license under its patent rights nor the rights of others. scillc products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body , or other applications intended to support or sustain life, or for any other application in which the failure of the scillc product could create a sit uation where personal injury or death may occur. should buyer purchase or use scillc products for any such unintended or unauthorized application, buyer shall indemnify and hold scillc and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthori zed use, even if such claim alleges that scillc was negligent regarding the design or manufacture of the part. scillc is an equal opportunity/affirmative action employer. publication ordering information central/south america: spanish phone : 3033087143 (monfri 8:00am to 5:00pm mst) email : onlitspanish@hibbertco.com tollfree from mexico: dial 018002882872 for access then dial 8662979322 asia/pacific : ldc for on semiconductor asia support phone : 13036752121 (tuefri 9:00am to 1:00pm, hong kong time) toll free from hong kong & singapore: 00180044223781 email : onlitasia@hibbertco.com japan : on semiconductor, japan customer focus center 4321 nishigotanda, shinagawaku, tokyo, japan 1410031 phone : 81357402700 email : r14525@onsemi.com on semiconductor website : http://onsemi.com for additional information, please contact your local sales representative. mc33468/d north america literature fulfillment : literature distribution center for on semiconductor p.o. box 5163, denver, colorado 80217 usa phone : 3036752175 or 8003443860 toll free usa/canada fax : 3036752176 or 8003443867 toll free usa/canada email : onlit@hibbertco.com fax response line: 3036752167 or 8003443810 toll free usa/canada n. american technical support : 8002829855 toll free usa/canada europe: ldc for on semiconductor european support german phone : (+1) 3033087140 (monfri 2:30pm to 7:00pm cet) email : onlitgerman@hibbertco.com french phone : (+1) 3033087141 (monfri 2:00pm to 7:00pm cet) email : onlitfrench@hibbertco.com english phone : (+1) 3033087142 (monfri 12:00pm to 5:00pm gmt) email : onlit@hibbertco.com european tollfree access*: 0080044223781 *available from germany, france, italy, uk, ireland
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