5V C1 1500uF VIN VOUT. Adj. Typical application of IRU1075 in a 5V to 3.3V regulator.

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Trevor Bennett
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1 ata Sheet No. 948 FTUS ropout at Full oad Current Fast Transient esponse % oltage eference Initial ccuracy Output Current imiting Built-In Thermal Shutdown ICTIONS ow oltage rocessor pplications such as: 54C,55C, Cyrix, OW C, GT+ Termination NTIU O, KTH ow oltage emory Termination pplications Standard. Chip Set and ogic pplications 7.5 OW OOUT OSITI JUSTB GUTO SCITION The is a low dropout three-terminal adjustable regulator with minimum of 7.5 output current capability. This product is specifically designed to provide well regulated supply for low voltage IC applications such as entium 54C, 55C as well as GT+ termination for entium ro and Klamath processor applications. The is also well suited for other processors such as Cyrix, and ower C applications. The is guaranteed to have <. dropout at full load current making it ideal to provide well regulated outputs such as. with input supply voltage as low as 4.5 minimum. TYIC ICTION 5 C 500uF 00. C x 500uF Typical application of in a 5 to. regulator. Notes: entium 54C, 55C, Klamath, entium ro, are trademarks of Intel Corp. Cyrix is trademark of Cyrix Corp. ower C is trademark of IB Corp. CKG O INFOTION TJ ( C) -IN STIC -IN STIC -IN STIC TO-0 (T) TO-6 () Ultra Thin-ak T () 0 To 50 CT C C ev.. 08/0/0

2 BSOUT XIU TINGS Input oltage ()... 7 ower issipation... Internally imited Storage Temperature ange C To 50 C Operating Junction Temperature ange... 0 C To 50 C CKG INFOTION Tab is -IN STIC TO-0 (T) -IN STIC TO-6 () -IN STIC UT THIN-K T () FONT IW Tab is FONT IW Tab is OUT FONT IW IN OUT θjt=.7 C/W θj=60 C/W θj=5 C/W for " Square pad θj=5 C/W for " Square pad CTIC SCIFICTIONS Unless otherwise specified, these specifications apply over CIN=µF, COUT=0µF, and TJ=0 to 50 C. Typical values refer to TJ=5 C. T SY TST CONITION IN TY X UNITS eference oltage ine egulation oad egulation (Note ) ropout oltage (Note ) Current imit inimum oad Current (Note ) Thermal egulation ipple ejection ust in Current ust in Current Change Temperature Stability ong Term Stability S Output Noise F O IJ Io=0m, TJ=5 C, (-o)=.5 Io=0m, (-o)=.5 Io=0m,.<(-o)<7 =., J=0, 0m<Io<7.5 Io=7.5 Io=4 =., o=00m =., J=0 0ms ulse, -o=, Io=7.5 f=0hz, Co=5µF Tantalum, Io=7.5, -o= Io=0m, -o=.5, TJ=5 C, Io=0m, -o=.5 Io=0m, -o=.5, TJ=5 C =., J=0, Io=0m TJ=5 C, 000Hrs TJ=5 C, 0Hz<f<0KHz % % m %/W db µ µ % % %O Note : ow duty cycle pulse testing with Kelvin connections is required in order to maintain accurate data. Note : ropout voltage is defined as the minimum differential voltage between and required to maintain regulation at. It is measured when the output voltage drops % below its nominal value. Note : inimum load current is defined as the minimum current required at the output in order for the output voltage to maintain regulation. Typically the resistor dividers are selected such that it automatically maintains this current. ev.. 08/0/0

3 IN SCITIONS IN # IN SYBO IN SCITION resistor divider from this pin to the pin and ground sets the output voltage. The output of the regulator. minimum of 0µF capacitor must be connected from this pin to ground to insure stability. The input pin of the regulator. Typically a large storage capacitor is connected from this pin to ground to insure that the input voltage does not sag below the minimum drop out voltage during the load transient response. This pin must always be. higher than in order for the device to regulate properly. BOCK IG CUNT IIT TH SHUTOWN Figure - Simplified block diagram of the. ICTION INFOTION Introduction The adjustable ow ropout (O) regulator is a three-terminal device which can easily be programmed with the addition of two external resistors to any voltages within the range of.5 to 5.5. This regulator unlike the first generation of the three-terminal regulators such as 7 that required differential between the input and the regulated output, only needs. differential to maintain output regulation. This is a key requirement for today s microprocessors that need typically. supply and are often generated from the 5 supply. nother major requirement of these microprocessors such as the Intel 54C is the need to switch the load current from zero to several amps in tens of nanoseconds at the processor pins, which translates to an approximately 00 to 500ns current step at the regulator. In addition, the output voltage tolerances are also extremely tight and they include the transient response as part of the specification. For example Intel specification calls for a total of ±00m including initial tolerance, load regulation and 0 to 4.6 load step. The is specifically designed to meet the fast current transient needs as well as providing an accurate initial voltage, reducing the overall system cost with the need for fewer output capacitors. ev.. 08/0/0

4 Output oltage Setting The can be programmed to any voltages in the range of.5 to 5.5 with the addition of and external resistors according to the following formula: Where: ( ) = F + +IJ F =.5 Typically IJ = 50µ Typically and as shown in Figure : regulator and the load is gained up by the factor of (+/ ), or the effective resistance will be, (eff)= (+/ ). It is important to note that for high current applications, this can represent a significant percentage of the overall load regulation and one must keep the path from the regulator to the load as short as possible to minimize this effect. SITIC IN SISTNC F IJ = 50u Figure - Typical application of the for programming the output voltage. The keeps a constant.5 between the output pin and the adjust pin. By placing a resistor across these two pins a constant current flows through, adding to the IJ current and into the resistor producing a voltage equal to the (.5/) + IJ which will be added to the.5 to set the output voltage. This is summarized in the above equation. Since the minimum load current requirement of the is 0m, is typically selected to be Ω resistor so that it automatically satisfies the minimum current requirement. Notice that since IJ is typically in the range of 50µ it only adds a small error to the output voltage and should only be considered when a very precise output voltage setting is required. For example, in a typical. application where =Ω and =00Ω the error due to IJ is only 0.% of the nominal set point. oad egulation Since the is only a three-terminal device, it is not possible to provide true remote sensing of the output voltage at the load. Figure 4 shows that the best load regulation is achieved when the bottom side of is connected to the load and the top side of resistor is connected directly to the case or the pin of the regulator and not to the load. In fact, if is connected to the load side, the effective resistance between the Figure 4 - Schematic showing connection for best load regulation. Stability The requires the use of an output capacitor as part of the frequency compensation in order to make the regulator stable. Typical designs for microprocessor applications use standard electrolytic capacitors with a typical S in the range of 50 to 00 mω and an output capacitance of 500 to 000µF. Fortunately as the capacitance increases, the S decreases resulting in a fixed C time constant. The takes advantage of this phenomena in making the overall regulator loop stable. For most applications a minimum of 00µF aluminum electrolytic capacitor such as Sanyo GX series, anasonic F series as well as the Nichicon series insures both stability and good transient response. Thermal esign The incorporates an internal thermal shutdown that protects the device when the junction temperature exceeds the maximum allowable junction temperature. lthough this device can operate with junction temperatures in the range of 50 C, it is recommended that the selected heat sink be chosen such that during maximum continuous load operation the junction temperature is kept below this number. The example below shows the steps in selecting the proper regulator heat sink for the worst case current consumption using Intel 00Hz microprocessor as the load. ev /0/0

5 ssuming the following specifications: = 5 =.5 IOUT(X) = 4.6 T = 5 C The steps for selecting a proper heat sink to keep the junction temperature below 5 C is given as: ) Calculate the maximum power dissipation using: = IOUT ( - ) = 4.6 (5 -.5) = 6.9W ) Select a package from the regulator data sheet and record its junction to case (or tab) thermal resistance. Selecting TO-0 package gives us: θjc =.7 C/W ) ssuming that the heat sink is black anodized, calculate the maximum heat sink temperature allowed: ssume, θcs = 0.05 C/W (heat-sink-to-case thermal resistance for black anodized) 4) With the maximum heat sink temperature calculated in the previous step, the heat-sink-to-air thermal resistance (θs) is calculated by first calculating the temperature rise above the ambient as follows: T = TS - T = 6-5 = 8 C T = Temperature ise bove mbient T 8 θs = = =.7 C/W 6.9 5) Next, a heat sink with lower θs than the one calculated in Step 4 must be selected. One way to do this is to simply look at the graphs of the Heat Sink Temp ise bove the mbient vs. the ower issipation and select a heat sink that results in lower temperature rise than the one calculated in previous step. The following heat sinks from I and Thermalloy meet this criteria. Thermalloy I ir Flow (F) B 60B 607B 609B B 540B B TS = TJ - (θjc + θcs) TS = ( ) = 6 C I WO HQUTS: Kansas St., l Segundo, California 9045, US Tel: (0) TC Fax: (0) isit us at for sales contact information ata and specifications subject to change without notice. 0/0 ev.. 08/0/0 5

6 () TO-6 ackage -in U K S B H G N C C SYBO B C G H K N S U IN F X F 7.75 F NOT: SUNTS IN IITS. ev /0/0

7 () Ultra Thin-ak T -in U K B H G C C N SYBO B C G H K N U IN X NO NO 7.49 NO NOT: SUNTS IN IITS. ev.. 08/0/0 7

8 (T) TO-0 ackage -in e b H Q e e C b -IN C C a (5x) J F C SYBO a b b C C e e e F H J Q IN X NOT: SUNTS IN IITS. ev /0/0

9 CKG SHINT THO KG SIG T TO-6 CKG SCITION Ultra Thin-ak T TO-0 IN COUNT TS TUB TS T & Orientation Fig Fig B --- Feed irection Figure Feed irection FigureB I WO HQUTS: Kansas St., l Segundo, California 9045, US Tel: (0) TC Fax: (0) isit us at for sales contact information ata and specifications subject to change without notice. 0/0 ev.. 08/0/0 9

5V C1 1500uF VIN VOUT. Adj. Figure 1 - Typical Application of IRU1050 in a 5V to 3.38V regulator designed to meet the Intel P54C processors.

5V C1 1500uF VIN VOUT. Adj. Figure 1 - Typical Application of IRU1050 in a 5V to 3.38V regulator designed to meet the Intel P54C processors. ata Sheet No. 9426 IU050 FTUS Guaranteed