DROPOUT POSITIVE ADJUSTABLE REGULATOR Guaranteed 1.3V Dropout Ful
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IRU1010
DROPOUT POSITIVE ADJUSTABLE REGULATOR
Guaranteed 1.3V Dropout Full Load Current Fast Transient Response Voltage Reference Initial Accuracy Built-in Thermal Shutdown Available SOT-223, D-Pak, Ultra Thin-Pak 8-pin SOIC Surface-mount Packages
DESCRIPTION
IRU1010 dropout, three-terminal adjustable regulator with minimum output current capability. This product specifically designed provide well regulated supply voltage applications such high speed termination current 3.3V logic supply. IRU1010 also well suited other applications such sound cards. IRU1010 guaranteed have <1.3V dropout full load current making ideal provide well regulated outputs 2.5V 3.6V with 4.75V input supply.
APPLICATIONS
Sound Card Applications Voltage High Speed Termination Applications Standard 3.3V Chipset Logic Applications
TYPICAL APPLICATION
10uF
US1010 IRU1010
Vout
2.85V
1010app1-1.4
22uF
Typical application IRU1010 2.85V SCSI termination regulator
PACKAGE ORDER INFORMATION
(°C) 2-PIN PLASTIC TO-252 IRU1010CD 3-PIN PLASTIC SOT-223 IRU1010CY 2-PIN PLASTIC Ultra Thin-Pak IRU1010CP 8-PIN PLASTIC SOIC IRU1010CS
Rev. 10/30/00
2-11
IRU1010
ABSOLUTE MAXIMUM RATINGS
Input Voltage Power Dissipation Internally Limited Storage Temperature Range -65° 150° Operating Junction Temperature Range 150°
PACKAGE INFORMATION
2-PIN PLASTIC TO-252
FRONT VIEW
3-PIN PLASTIC SO-223
VIEW
2-PIN ULTRA THIN-PAK
FRONT VIEW
8-PIN PLASTIC SOIC
VIEW
Vout
Vout
Vout
Vout Vout Vout Vout
Vout
JA=70°C/W 0.5"
JA=90°C/W 0.4"
JA=70°C/W 0.5"
JA=55°C/W
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 1.250 Io=10mA, (Vin-Vo)=1.5V 1.237 1.250 Io=10mA, 1.3V<(Vin-Vo)<7V Vin=3.3V, Vadj=0, 10mA<Io<1A Note Io=1A Vin=3.3V, dVo=100mV Vin=3.3V, Vadj=0V 30mS Pulse, Vin-Vo=3V, Io=1A f=120HZ, Co=25µF Io=0.5A, 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 0.01 0.003 0.02 1.257 1.263 UNITS
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.
2-12
Rev. 10/30/00
IRU1010
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 dropout 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
1010blk1-1.0
Figure Simplified block diagram IRU1010
APPLICATION INFORMATION
Introduction
IRU1010 adjustable Dropout (LDO) regulator three-terminal device which easily programmed with addition external resistors voltages within range 1.25 5.5V. 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 voltage applications that typically need 3.3V supply often generated from supply. Other applications such high speed memory termination 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. IRU1010 specifically designed meet fast current transient needs well providing accurate initial voltage, reducing overall system cost with need fewer output capacitors.
Rev. 10/30/00
2-13
IRU1010
Output Voltage Setting
IRU1010 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
IRU1010 US1010
Vref
Vout
IAdj 50uA
1010app2-1.0
US1010 IRU1010
Figure Typical application IRU1010 programming output voltage IRU1010 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 IRU1010 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.
1010app3-1.0
Figure Schematic showing connection best load regulation
Stability
IRU1010 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. IRU1010 takes advantage this phenomena making overall regulator loop stable.For 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 IRU1010 only three-terminal device, possible provide true remote sensing output voltage load. Figure shows that best load
2-14
Rev. 10/30/00
IRU1010
Thermal Design
IRU1010 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 SCSI terminator application shows steps selecting proper regulator surface-mount package. (See IRU1015 non-surface-mount packages) Assuming following specifications: 2.85 IOUT
output voltage, need select Assum R1=121 VOUT 2.85 154.8 VREF SelectR2=154
10uF
Vout
2.85V
22uF
IRU1010 US1010
Where; forward voltage drop D1diode shown Figure steps selecting right package with proper board area heatsinking keep junction temperature below 135° given Calculate maximum power dissipation using: IOUT VOUT) 2.85 Calculate maxi allowed ample:
1010app4-1.3
Figure Final Schematic half GTL+ termination regulator
Layout Consideration
output capacitors must located close Vout terminal device possible. recommended section layer board plane connect output capacitors prevent high frequency oscillation that result excessive trace inductance.
Select package from datasheet with lower than calculated previous step.
Selecting TO-252 (D-Pak) with least 0.5" square 0.062" board using copper which lower than calculated number.
Rev. 10/30/00
2-15
IRU1010
Notes
2-16
Rev. 10/30/00
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