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Data Sheet No. PD94119
IRU1010
1A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR DESCRIPTION
The IRU1010 is a low dropout, three-terminal adjustable regulator with minimum of 1A output current capability. This product is specifically designed to provide well regulated supply for low voltage IC applications such as high speed bus termination and low current 3.3V logic supply. The IRU1010 is also well suited for other applications such as VGA and sound cards. The IRU1010 is guaranteed to have <1.3V dropout at full load current making it ideal to provide well regulated outputs of 2.5V to 3.6V with 4.75V to 7V input supply.
FEATURES
Guaranteed < 1.3V Dropout at Full Load Current Fast Transient Response 1% Voltage Reference Initial Accuracy Built-In Thermal Shutdown Available in SOT-223, D-Pak, Ultra Thin-Pak and 8-Pin SOIC Surface-Mount Packages
APPLICATIONS
VGA & Sound Card Applications Low Voltage High Speed Termination Applications Standard 3.3V Chip Set and Logic Applications
TYPICAL APPLICATION
D1
5V
C1 10uF Vin
3 2 1
R1 121 R2 154 C2 22uF
IRU1010
Vout
2.85V / 1A
Adj
1010app1-1.4
Figure 1 - Typical application of IRU1010 in a 5V to 2.85V SCSI termination regulator
PACKAGE ORDER INFORMATION
Tj (C) 0 To 150 2-PIN PLASTIC TO-252 (D-Pak) IRU1010CD 3-PIN PLASTIC SOT-223 (Y) IRU1010CY 2-PIN PLASTIC Ultra Thin-Pak (P) IRU1010CP 8-PIN PLASTIC SOIC (S) IRU1010CS
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IRU1010
ABSOLUTE MAXIMUM RATINGS
Input Voltage (Vin) .................................................... Power Dissipation ..................................................... Storage Temperature Range ...................................... Operating Junction Temperature Range ..................... 7V Internally Limited -65C To 150C 0C To 150C
PACKAGE INFORMATION
2-PIN PLASTIC TO-252 (D-Pak)
FRONT VIEW 3
3-PIN PLASTIC SO-223 (Y)
TOP VIEW
2-PIN ULTRA THIN-PAK (P)
FRONT VIEW
8-PIN PLASTIC SOIC (S)
TOP VIEW
Vin
3
Vin Vout Adj
Tab is Vout
3
Vin
Tab is Vout
1
Tab is Vout
Adj
2 1
1
Adj
Vin NC NC Adj
1 2 3 4
8 7 6 5
Vout Vout Vout Vout
JA=70!C/W for 0.5" Sq pad
JA=90!C/W for 0.4" Sq pad
JA=70!C/W for 0.5" Sq pad
JA=55!C/W for 1" Sq pad
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Cin=1F, Cout=10F, and Tj=0 to 150!C. Typical values refer to Tj=25!C. PARAMETER Reference Voltage Line Regulation Load Regulation (Note 1) Dropout Voltage (Note 2) Current Limit Minimum Load Current (Note 3) Thermal Regulation Ripple Rejection Adjust Pin Current Adjust Pin Current Change Temperature Stability Long Term Stability RMS Output Noise SYM Vref TEST CONDITION Io=10mA, Tj=25!C, (Vin-Vo)=1.5V Io=10mA, (Vin-Vo)=1.5V Io=10mA, 1.3V<(Vin-Vo)<7V Vin=3.3V, Vadj=0, 10mAVo
1.1 1.1 5 0.01 60 70 55 0.2 0.5 0.3 0.003
Iadj
Note 1: Low duty cycle pulse testing with Kelvin connections is required in order to maintain accurate data. Note 2: Dropout voltage is defined as the minimum differential voltage between Vin and Vout required to maintain regulation at Vout. It is measured when the output voltage drops 1% below its nominal value.
Note 3: Minimum 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.
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IRU1010
PIN DESCRIPTIONS
PIN # 1 2 3 PIN SYMBOL Adj Vout Vin PIN DESCRIPTION A resistor divider from this pin to the Vout pin and ground sets the output voltage. The output of the regulator. A minimum of 10F 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 dropout voltage during the load transient response. This pin must always be 1.3V higher than Vout in order for the device to regulate properly.
BLOCK DIAGRAM
Vin 3 2 Vout
+
1.25V CURRENT LIMIT THERMAL SHUTDOWN
+
1010blk1-1.0
1 Adj
Figure 2 - Simplified block diagram of the IRU1010
APPLICATION INFORMATION
Introduction
The IRU1010 adjustable Low Dropout (LDO) 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 1.25 to 5.5V. This regulator, unlike the first generation of the three-terminal regulators such as LM117 that required 3V differential between the input and the regulated output, only needs 1.3V differential to maintain output regulation. This is a key requirement for today's low voltage IC applications that typically need 3.3V supply and are often generated from the 5V supply. Other applications such as high speed memory termination need to switch the load current from zero to full load in tens of nanoseconds at their pins, which translates to an approximately 300 to 500ns current step at the regulator. In addition, the output voltage tolerances are sometimes tight and they include the transient response as part of the specification. The IRU1010 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.
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IRU1010
Output Voltage Setting The IRU1010 can be programmed to any voltages in the range of 1.25V to 5.5V with the addition of R1 and R2 external resistors according to the following formula: VOUT = VREF x o1 + R2 p + IADJ x R2 R1 regulator and not to the load. In fact, if R1 is connected to the load side, the effective resistance between the regulator and the load is gained up by the factor of (1+R2/ R1), or the effective resistance will be, Rp(eff)=Rp*(1+R2/ R1). 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.
PARASITIC LINE RESISTANCE
Where: VREF = 1.25V Typically IADJ = 50A Typically R1 and R2 as shown in figure 3:
Rp
Vin
Vin
Vin Vout
Vin
Vout
Vout
IRU1010
Adj Vref IAdj = 50uA R1
IRU1010
Adj R1 RL
R2
1010app2-1.0
R2
1010app3-1.0
Figure 3 - Typical application of the IRU1010 for programming the output voltage
Figure 4 - Schematic showing connection for best load regulation Stability The IRU1010 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 ESR in the range of 50 to 100m and an output capacitance of 500 to 1000F. Fortunately as the capacitance increases, the ESR decreases resulting in a fixed RC time constant. The IRU1010 takes advantage of this phenomena in making the overall regulator loop stable. For most applications a minimum of 100F aluminum electrolytic capacitor such as Sanyo MVGX series, Panasonic FA series as well as the Nichicon PL series insures both stability and good transient response. Thermal Design The IRU1010 incorporates an internal thermal shutdown that protects the device when the junction temperature exceeds the maximum allowable junction temperature. Although this device can operate with junction temperatures in the range of 150!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 for a SCSI terminator application shows the steps in sellect-
The IRU1010 keeps a constant 1.25V between the output pin and the adjust pin. By placing a resistor R1 across these two pins a constant current flows through R1, adding to the Iadj current and into the R2 resistor producing a voltage equal to the (1.25/R1)*R2 + Iadj*R2 which will be added to the 1.25V to set the output voltage. This is summarized in the above equation. Since the minimum load current requirement of the IRU1010 is 10mA, R1 is typically selected to be 121 resistor so that it automatically satisfies the minimum current requirement. Notice that since Iadj is typically in the range of 50A 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 3.3V application where R1=121 and R2=200 the error due to Iadj is only 0.3% of the nominal set point. Load Regulation Since the IRU1010 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 R2 is connected to the load and the top side of R1 resistor is connected directly to the case or the Vout pin of the
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IRU1010
ing the proper regulator in a surface-mount package. (See IRU1015 for non-surface-mount packages) Assuming the following specifications: VIN = 5V VF = 0.5V Vo = 2.85V IOUT(MAX) = 0.8A TA = 35!C Where: VF is the forward voltage drop of the D1diode as shown in Figure 5. The steps for selecting the right package with proper board area for heatsinking to keep the junction temperature below 135!C is given as: 1) Calculate the maximum power dissipation using: PD = IOUT x (VIN - VF - VOUT) PD = 0.8 x (5 - 0.5 - 2.85) = 1.32W 2) Calculate the maximum JA allowed for our example: JA(MAX) = TJ - TA 135 - 35 = = 75.6!C/W PD 1.32 To set the output DC voltage, we need to select R1 and R2: 4) Assuming R1 = 121, 1% 2.85 VOUT R2 =o -1px R1 =o - 1px 121 = 154.8 o p o p 1.25 VREF Select R2 = 154, 1%
D1
5V
C1 10uF
Vin
Vout
2.85V
C2 22uF R1 121 1% R2 154 1%
IRU1010
Adj
1010app4-1.3
Figure 5 - Final Schematic for half of the GTL+ termination regulator
Layout Consideration
The output capacitors must be located as close to the Vout terminal of the device as possible. It is recommended to use a section of a layer of the PC board as a plane to connect the Vout pin to the output capacitors to prevent any high frequency oscillation that may result due to excessive trace inductance.
3) Select a package from the datasheet with lower JA than the one calculated in the previous step. Selecting TO-252 (D-Pak) with at least 0.5" square of 0.062" FR4 board using 1 oz. copper has 70C/W which is lower than the calculated number.
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IRU1010
Notes
IR WORLD HEADQUARTERS : 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 Visit us at www.irf.com for sales contact information. Data and specifications subject to change without notice. 02/01
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Rev. 1.4 06/29/01

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