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IRU1175
7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
PRELIMINARY DATASHEET
FEATURES
0.5V Dropout at 7.5A (Equivalent of 67m) Fast Transient Response 1% Voltage Reference Initial Accuracy Built-in Thermal Shutdown
DESCRIPTION
The IRU1175 is a 7.5A regulator with extremely low dropout voltage using a proprietary bipolar process that achieves comparable equivalent on resistance to that of discrete MOSFETs. This product is specifically designed to provide well regulated supply for applications requiring very low dropout such as 2.8V from 3.3V ATX power supplies where the same efficiency as the switcher can be achieved without the cost and complexity associated with switching regulators. One such application is the new graphic chipsets that requires 2.7V supply such as the Intel I740 chipset.
APPLICATIONS
3.3V to 2.7V Intel I740 chipset
TYPICAL APPLICATION
3.3V
C1 100uF
Vin Vctrl
5 4 3 2 1
R1 100 1% R2 124 1% C2 10uF C3 100uF
IRU1175
Vout Adj Vsense
2.7V
1175app1-1.0
5V
Typical application of IRU1175
PACKAGE ORDER INFORMATION
Tj (C) 0 TO 125 5-PIN PLASTIC 5-PIN PLASTIC 8-PIN PLASTIC TO-263 (M) ULTRA THIN-PAK (P) SOIC (S) IRU1175CM IRU1175CP IRU1175CS
Rev. 1.2 11/29/99
2-79
IRU1175
ABSOLUTE MAXIMUM RATINGS
Input Voltage (V in) ................................................. 6V Control Input Voltage (V ctrl) ....................................... 14V Power Dissipation..................................................... Internally Limited Storage Temperature Range ...................................... -65C TO 150C Operating Junction Temperature Range ...................... 0C TO 150C
PACKAGE INFORMATION
8-PIN PLASTIC SOIC ( S )
TOP VIEW
5-PIN PLASTIC TO-263 ( M )
FRONT VIEW 5 4 3 2 1
5-PIN PLASTIC ULTRA THIN-PAK (P)
FRONT VIEW 5 4 3 2 1
Vctrl Vin Adj Vsense
1 2 3 4
8 7 6 5
Vout Vout Vout Vout
Vin Vctrl Vout Adj Vsense
Vin Vctrl Vout Adj Vsense
JA=55C/W for 1" Sq pad area
JA=35C/W for 0.5" square pad
JA=35C/W for 0.5" square pad
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over, Cin=1F, Cout =10F, and Tj=0 to 125C. Typical values refer to Tj=25C. V out =Vsense. PARAMETER Reference Voltage SYM Vref TEST CONDITION MIN Vctrl=2.75V, Vin=2V, Io=10mA 1.243 Tj=25, Vadj=0V Vctrl=2.7to12V, Vin=2.05V to 5.5V, 1.237 Io=10mA to 7.5A, Vadj=0V Vctrl=2.5Vto7V, Vin=1.75Vto5.5V Io=10mA , Vadj=0V Vctrl=2.75V, Vin=2.1V, Io=10mA to 7.5A, Vadj=0V Vadj=0V for all conditions below. Vin=2.05V, Io=1.5A Vin=2.05V, Io=3A Vin=2.05V, Io=5A Vin=2.05V, Io=7.5A Vadj=0V for all conditions below. Vctrl=2.75V, Io=1.5A Vctrl=2.75V, Io=3A Vctrl=2.75V, Io=5A Vctrl=2.75V, Io=7.5A Vctrl=2.75V, Vin=2.05V, dVo=100mV Vadj=0V 7.7 Vctrl=5V, Vin=3.3V, Vadj=0V 30mS Pulse Vctrl=5V, Vin=5V, Io=3A,Vadj=0V 60 Tj=25, Vripple=1Vpp at 120Hz TYP 1.250 1.250 MAX 1.257 1.263 UNITS V
Line Regulation Load Regulation (note 1) Dropout Voltage (note 2) (V ctrl - Vout )
0.5 2 0.95 1.00 1.05 1.15 0.100 0.200 0.330 0.500 9 5 0.01 70
3 6
mV mV V
1.30 0.130 0.260 0.430 0.650 V
Dropout Voltage (note 2) (V in - Vout )
Current Limit Minimum Load Current (note 3) Thermal Regulation Ripple Rejection
10 0.02
A mA %/W dB
2-80
Rev. 1.2 11/29/99
IRU1175
ELECTRICAL SPECIFICATIONS
PARAMETER
Control Pin Current
SYM
TEST CONDITION
Vadj=0V for all below conditions. Vctrl=2.75V, Vin=2.05V, Io=1.5A Vctrl=2.75V, Vin=2.05V, Io=3A Vctrl=2.75V, Vin=2.05V, Io=5A Vctrl=2.75V, Vin=2.05V, Io=7.5A
MIN
TYP
15 30 50 75 50
MAX
UNITS
mA
Adjust Pin Current
Iadj
Vctrl=2.75V, Vin=2.05V, Vadj=0V
120
A
Note 1: Low duty cycle pulse testing with Kelvin connections are required in order to maintain accurate data. Note 2: Dropout voltage is defined as the minimum differential between V in and V out 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.
PIN DESCRIPTIONS
PIN # 1 PIN SYMBOL PIN DESCRIPTION Vsense This pin is the positive side of the reference which allows remote load sensing to achieve excellent load regulation. 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. This pin is the supply pin for the internal control circuitry as well as the base drive for the pass transistor. This pin must always be higher than the Vout pin in order for the device to regulate. (see specifications) 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 Vout in order for the device to regulate. (see specifications)
2 3
Adj Vout
4
Vctrl
5
Vin
Rev. 1.2 11/29/99
2-81
IRU1175
BLOCK DIAGRAM
Vin Vout
Vctrl
+
1504
Vsense
+
1.25V CURRENT LIMIT
THERMAL SHUTDOWN
1175blk1-1.0
Adj
Figure 1 - Simplified block diagram of the IRU1175
APPLICATION INFORMATION
Introduction The IRU1175 adjustable regulator is a five-terminal device designed specificaly to provide extremely low dropout voltages comparable to the PNP type without the disadvantage of the extra power dissipation due to the base current associated with PNP regulators.This is done by bringinging out the control pin of the regulator that provides the base current to the power NPN and connecting it to a voltage that is grater than the voltage present at the Vin pin.This flexibility makes the IRU1175 ideal for applications where dual inputs are available such as a computer motherboard with an ATX style power supply that provides 5V and 3.3V to the board. One such application is the new graphic chipsets that require anywhere from 2.4V to 2.7V supply such as the Intel I740 chipset. The IRU1175 can easily be programmed with the addition of two external resistors to any voltages within the range of 1.25 to 5.5 V. Another major requirement of these graphic chips 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 300 to 500nS of 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.
The IRU1175 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 number of output capacitors. Another feature of the device is its true remote sensing capability which allows accurate voltage setting at the load rather than at the device. Output Voltage Setting The IRU1175 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: R2 VOUT = VREF 1+ + IADJ x R 2 R1 Where: V =125 V Wehre : VREF=1.25V Typically . IADJ=50A Typically R1 & R2 as shown in Figure 2
Vin
Vin Vout
Vout
IRU1175 Vctrl
Vctrl Adj Vsense Vref R1
IAdj = 50uA
R2
1175app2-1.0
Figure 2 - Typical application of the IRU1175 for programming the output voltage
2-82
Rev. 1.2 11/29/99
IRU1175
The IRU1175 keeps a constant 1.25V between the Vsense pin and the Vadj pin. By placing a resistor R1 across these two pins and connecting the Vsense and Vout pin together, 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 + I *R2. adj This voltage is then 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 IRU1175 is 10mA, R1 is typically selected to be a 121 resistor so that it automatically satisfies this condition. Notice that since the Iadj is typically in the range of 50A it only adds a small error to the output voltage and should be considered when very precise output voltage setting is required. Load Regulation Since the IRU1175 has separate pins for the output (V out ) and the sense (V sense), it is ideal for providing true remote sensing of the output voltage at the load. This means that the voltage drops due to parasitic resistance such as PCB traces between the regulator and the load are compensated for using remote sensing. Figure 3 shows a typical application of the IRU1175 with remote sensing.
Vin
Vin Vout
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 IRU1175 incorporates an internal thermal shutdown that protects the device when the junction temperature exceeds the allowable maximum junction temperature. Although this device can operate with junction temperatures in the range of 150C, it is recommended that the selected heat sink be chosen such that during maximum continuos load operation the junction temperature is kept below this number. The example below shows the steps in selecting the proper surface mount package. Assuming, the following conditions: Vout =2.7V Vin=3.3V Vctrl=5V Iout =2A DC Avg Calculate the maximum power dissipation using the following equation: Pd=Iout *(V in-V out ) + (Iout /60)*(V ctrl - Vout ) Pd=2*(3.3-2.7) + (2/60)*(5-2.7)=1.28 W
IRU1175 Vctrl
Vctrl Adj Vsense R1 RL
Using table below select the proper package and the amount of copper board needed. Pkg TO-263 TO-263 TO-263 TO-263 SO-8 Copper 1.4"X1.4" 1.0"X1.0" 0.7"X0.7" Pad Size 1.0"X1.0" JA(C/W) Area 25 30 35 45 55 Max Pd (Ta=25C) 4.4W 3.7W 3.1W 2.4W 2.0W Max Pd (Ta=45C) 3.6W 3.0W 2.6W 2.0W 1.63W
R2
1175app3-1.0
Figure 3 - Schematic showing connection for best load regulation Stability The IRU1175 requires the use of an output capacitor as part of the frequency compensation in order to make the regulator stable. Typical designs for the microprocessor applications use standard electrolytic capacitors with 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 IRU1175 takes advantage of this phenomena in making the overall regulator loop stable.
Note: Above table is based on the maximum junction temperature of 135C. As shown in the above table, any of the two packages will do the job. For low cost applications the SO-8 package is recommended.
Rev. 1.2 11/29/99
2-83
IRU1175
Notes
2-84
Rev. 1.2 11/29/99

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