1.5A DROPOUT POSITIVE ADJUSTABLE REGULATOR FEATURES Guaranteed 1.

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1.5A DROPOUT POSITIVE ADJUSTABLE REGULATOR FEATURES Guaranteed 1.

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IRU1015
1.5A DROPOUT POSITIVE ADJUSTABLE REGULATOR FEATURES
Guaranteed 1.3V Dropout Full Load Current Fast Transient Response Voltage Reference Initial Accuracy Output Current Limiting Built-in Thermal Shutdown
IRU1015 dropout three-terminal adjustable regulator with minimum 1.5A output current capability. This product specifically designed provide well regulated supply voltage applications such 486DX4 processor, P55CI/O supply well high speed termination current 3.3V logic supply. IRU1015 also well suited other applications such sound card. IRU1015 guaranteed have <1.3V dropout full load current making ideal provide well regulated outputs 2.5V 3.6V with 4.75V input supply.
APPLICATIONS
486DX4 Supply Voltage Supply Voltage Sound Card Applications Voltage High Speed Termination Applications Standard 3.3V Chipset Logic Applications
TYPICAL APPLICATION
1500uF
US1015
Vout
3.3V 1.5A
1500uF
1015app1-1.1
Typical application IRU1015 3.3V regulator
Notes: P55C trademark Intel Corp.
PACKAGE ORDER INFORMATION
(°C) 3-PIN PLASTIC TO-220 IRU1015CT 3-PIN PLASTIC TO-263 IRU1015CM 3-PIN PLASTIC TO-252 IRU1015CD
Rev. 3/26/98
2-25
IRU1015
ABSOLUTE MAXIMUM RATINGS
Input Voltage Power Dissipation Internally Limited Storage Temperature Range -65° 150° Operating Junction Temperature Range 150°
PACKAGE INFORMATION
3-PIN PLASTIC TO-220
FRONT VIEW
3-PIN PLASTIC TO-263
FRONT VIEW
3-PIN PLASTIC TO-252
FRONT VIEW
Vout Vout
Vout Vout
Vout
JT=2.7°C/W JA=60°C/W
JA=35°C/W Square
JA=70°C/W 0.5" Square
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over, Cin=1µF, Cout =10µF, Tj=0 150° Typical values refer Tj=25° PARAMETER Reference Voltage Line Regulation Load Regulation (note Dropout Voltage (note Current Limit Minimum Load Current (note Thermal Regulation Ripple Rejection Adjust Current Adjust Current Change Temperature Stability Long Term Stability Output Noise VREF TEST CONDITION Io=10mA, Tj=25° (Vin-Vo)=1.5V 1.243 Io=10mA, (Vin-Vo)=1.5V 1.237 Io=10mA, 1.3V<(Vin-Vo)<7V Vin=3.3V, Vadj=0, 10mA<Io<1.5A Note Io=1.5A Vin=3.3V, dVo=100mV Vin=3.3V, Vadj=0V 30mS Pulse, Vin-Vo=3V, Io=1.5A f=120HZ, Co=25µF Io=0.75A, Vin-Vo=3V Io=10mA, Vin-Vo=1.5V, Tj=25 Io=10mA, Vin-Vo=1.5V Io=10mA, Vin-Vo=1.5V, Tj=25 Vin=3.3V, Vadj=0V, Io=10mA Tj=125° 1000 Tj=25° 10hz<f<10khz 1.250 1.250 1.257 1.263 0.02 UNITS
0.01 0.003
IADJ
Note duty cycle pulse testing with Kelvin connections required order maintain accurate data. Note Dropout voltage defined minimum differential voltage between required maintain regulation Vout measured when output voltage drops below nominal value.
Note Minimum load current defined minimum current required output order output voltage maintain regulation. Typically resistor dividers selected such that automatically maintains this current.
2-26
Rev. 3/26/98
IRU1015
DESCRIPTIONS
SYMBOL Vout DESCRIPTION resistor divider from this Vout ground sets output voltage. output regulator. minimum 10µF capacitor must connected from this ground insure stability. input regulator. Typically large storage capacitor connected from this ground insure that input voltage does below minimum drop voltage during load transient response. This must always 1.3V higher than Vout order device regulate properly.
BLOCK DIAGRAM
Vout
1.25V CURRENT LIMIT
THERMAL SHUTDOWN
1015blk1-1.0
Figure Simplified block diagram IRU1015
APPLICATION INFORMATION
Introduction
IRU1015 adjustable Dropout (LDO) regulator three-terminal device which easily programmed with addition external resistors voltages within range 1.25 V.This regulator unlike first generation regulators such LM117 that required differential between input regulated output, only needs 1.3V differential maintain output regulation. This requirement today's microprocessors that need typically 3.3V supply often generated from supply. Another major requirement these microprocessors need switch load current from zero full load tens nanoseconds their pins, which translates approximately 500nS current step regulator. addition, output voltage tolerances sometimes tight they include transient response part specification. IRU1015 specifically designed meet fast current transient needs well provide accurate initial voltage, reducing overall system cost with need fewer output capacitors.
Rev. 3/26/98
2-27
IRU1015
Output Voltage Setting
IRU1015 programmed voltages range 1.25V 5.5V with addition external resistors according following formula: VOUT VREF IADJ Where VREF Typically IADJ Typically shown figure regulation achieved when bottom side connected load side resistor connected directly case Vout regulator load. fact, connected load side, effective resistance between regulator load gained factor (1+R2/ R1), effective resistance will Rp(eff)=Rp*(1+R2/ R1). important note that high current applications, this represent significant percentage overall load regulation must keep path from regulator load short possible minimize this effect.
Vout
Vout
PARASITIC LINE RESISTANCE
US1015 IRU1015
Vref
Vout
US1015 IRU1015
IAdj 50uA
1015app2-1.0
Figure Typical application IRU1015 programming output voltage.
1015app3-1.0
IRU1015 keeps constant 1.25V between output adjust pin. placing resistor across these pins constant current flows through adding Iadj current into resistor producing voltage equal (1.25/R1)*R2 Iadj*R2 which will added 1.25V output voltage. This summarized above equation. Since minimum load current requirement IRU1015 10mA, typically selected resistor that automatically satisfies minimum current requirement. Notice that since Iadj typically range 50µA only adds small error output voltage should only considered when very precise output voltage setting required. example, typical 3.3V application where R1=121 R2=200 error Iadj only 0.3% nominal point.
Figure Schematic showing connection best load regulation
Stability
IRU1015 requires output capacitor part frequency compensation order make regulator stable. Typical designs microprocessor applications standard electrolytic capacitors with typical range 100m output capacitance 1000µF. Fortunately capacitance increases, decreases resulting fixed time constant. IRU1015 takes advantage this phenomena making overall regulator loop stable. most applications minimum 100µF aluminum electrolytic capacitor such Sanyo MVGX series, Panasonic series well Nichicon series insures both stability good transient response.
Load Regulation
Since IRU1015 only three-terminal device, possible provide true remote sensing output voltage load. Figure shows that best load
2-28
Rev. 3/26/98
IRU1015
Thermal Design
IRU1015 incorporates internal thermal shutdown that protects device when junction temperature exceeds maximum allowable junction temperature. Although this device operate with junction temperatures range 150° recommended that selected heat sink chosen such that during maximum continuous load operation junction temperature kept below this number. example below shows steps selecting proper regulator heat sink 486DX4-120 processor. Assuming following specifications: 3.45 IOUT
T=Temperature Rise Above Ambient
Next, heatsink with lower than calculated step must selected. this simply look graphs "Heat Sink Temp Rise Above Ambient" "Power Dissipation" select heat sink that results lower temperature rise than calculated previous step. following heat sinks from AAVID Thermaloy meet this criteria.
Thermalloy AAVID 6041PB 574602 Flow (LFM) Required Required
steps selecting proper heat sink keep junction temperature below 135° given Calculate maximum power dissipation using: VIN- 3.45 =186 Select package from regulator data sheet record junction case Tab) thermal resistance. Selecting TO-220 package gives =2.7° Assuming that heat sink black anodized, calculate maximum Heat sink temperature allowed: Assume, cs=0.05° (heat-sink-to-case thermal resistance black anodized) TJ-PD =135 -186 (2.7+ 0.05 =129 With maximum heat sink temperature calculated previous step, heat-sink-to-air thermal resistance (sa) calculated first calculating temperature rise above ambient follows: =129
Rev. 3/26/98
Note: further information regarding above companies their latest product offerings application support contact your local representative numbers listed below: AAVID Thermalloy (603) 3400 (214) 243-4321
Designing Microprocessor Applications
mentioned before IRU1015 designed specifically provide power generation voltage processors requiring voltages range 2.5V 3.6V generated stepping down supply. These processors demand fast regulator that supports their large load current changes. worst case current step seen regulator anywhere range with slew rate 500nS which could happen when processor transitions from "Stop Clock" mode "Full Active" mode. load current step processor actually much faster, order 20nS, however, decoupling capacitors placed cavity processor socket handle this transition until regulator responds load current levels. Because this requirement selection high frequency output capacitor imperative design these regulator circuits. Figure shows effects fast transient output voltage regulator. shown this figure, output capacitor produces instanta-
2-29
IRU1015
neous drop equal (VESR =ESR*I) effect will equal rate change output current times inductance capacitor =L*I/t). output capacitance effect droop output voltage proportional time takes regulator respond change current, where response time regulator. Sanyo MVGX series good choice achieve both price performance goals.The 6MV1500GX, 1500µF, 6.3V less than typical. Selecting single capacitor achieves design goal. next step calculate drop capacitance discharge make sure that this drop voltage less than selected drop previous step. With output capacitance being 1500µF;
1500 Where regulator response time output voltage, need select Assuming 121,
LOAD CURRENT
1015plt1-1.0
LOAD CURRENT RISE TIME
Figure Typical regulator response fast load current step example regulator design meet specification 486DX4-120Mhz given below. Assume specification processor shown Table
Type Processor 486DX4 Vout Nominal 3.45 Imax Allowed Output Tolerance ±150
VOUT 3.45 VREF Select R2=215 Selecting both resistors tolerance results least amount error introduced resistor dividers leaving ±2.5% error budget IRU1015 reference which well within initial accuracy device. Finally, input capacitor selected follows: Assuming that input voltage drop 150mV before main power supply responds, that main power supply response time 50mSec, then minimum input capacitance 1.2A load step given
Table GTL+ specification Pentium first step select voltage step allowed output output capacitor's ESR: Assuming regulator's initial accuracy plus resistor divider tolerance (±2.5% 3.45V nominal), then total step allowed ESL, Assuming that drop -10mV, remaining step will Therefore output capacitor must
0.15
2-30
Rev. 3/26/98
IRU1015
should less than; (VIN VOUT VDROP) Where VDROP Input voltage drop allowed step Maximum regulator ropout volt Load curr step 3.45 -0.15
Layout Consideration
output capacitors must located close Vout terminal device possible. recommended section layor board plane connect putput capacitors prevent high frequency oscillation that result excessive trace inductance.
=0.167
Select single 1500µF same type output capacitors exceeds requirements. Figure shows completed schematic example.
1500uF
Vout
3.45V
1500uF
US1015 IRU1015
1015app4-1.1
Figure Final schematic regulator design
Rev. 3/26/98
2-31
IRU1015
Notes
2-32
Rev. 3/26/98

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