Data Sheet No. PD94132 IRU1176 FEATURES 7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR WITH SHUTDOWN INPUT DESCRIPTION Guaranteed <0.65V Dropout at 7.5A Fast Transient Response 1% Voltage Reference Initial Accuracy Built-In Thermal Shutdown The IRU1176 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. The IRU1176 also provides a convenient shutdown pin that allows the regulator to be shutdown and reduce the input current consumption. Unlike the PNP type regulators this device does not have high quiescent current during the start up mode making it ideal for applications where there is limited current capability such operation from the 5V standby supply of the computer power supply. One application is the new generation of RDRAM memory that needs to provide 2.5V from 3.3V input and be able to operate from 5VSB as well. APPLICATIONS 3.3V to 2.7V Intel I740 Chip Set TYPICAL APPLICATION 3.3V C1 IRU1176 VIN 7 VIN 6 VCTRL 5 VOUT 4 Adj 3 SD 2 VSENSE 1 2.7V R1 C3 R2 5V C2 SD Q1 Enable Figure 1 - Typical application of IRU1176. PACKAGE ORDER INFORMATION TJ (°C) 0 To 125 Rev. 1.4 03/18/02 7-PIN PLASTIC TO-263 (M) IRU1176CM www.irf.com 7-PIN PLASTIC Ultra Thin-PakTM (P) IRU1176CP 1 IRU1176 ABSOLUTE MAXIMUM RATINGS Input Voltage (V IN) .................................................... Control Input Voltage (V CTRL) ..................................... Power Dissipation ..................................................... Storage Temperature Range ...................................... Operating Junction Temperature Range ..................... 7V 14V Internally Limited -65°C To 150°C 0°C To 150°C PACKAGE INFORMATION 7-PIN PLASTIC ULTRA THIN-PAKTM (P) 7-PIN PLASTIC TO-263 (M) FRONT VIEW FRONT VIEW 7 Tab is V OUT 6 5 4 3 2 1 V IN V IN V CTRL V OUT Adj SD V SENSE 7 6 5 4 3 2 Tab is V OUT 1 θJA=35°C/W for 0.5" square pad V IN V IN V CTRL V OUT Adj SD V SENSE θJA=35°C/W for 0.5" square pad ELECTRICAL SPECIFICATIONS Unless otherwise specified, these specifications apply over CIN=1mF, COUT=10mF and TJ=0 to 1258C. Typical values refer to TJ=258C. VOUT=VSENSE. PARAMETER Reference Voltage SYM VREF TEST CONDITION VCTRL=2.75V, VIN=2V, Io=10mA, TJ=258C, V ADJ=0V MIN 1.225 TYP 1.250 MAX 1.275 VCTRL=2.7 to 12V, VIN=2.05V to 5.5V, 1.225 1.250 1.275 UNITS V Io=10mA to 7.5A, VADJ=0V Line Regulation Load Regulation (Note 1) Dropout Voltage (Note 2) (V CTRL - VOUT) Dropout Voltage (Note 2) (V IN - VOUT) Current Limit Minimum Load Current (Note 3) Thermal Regulation Ripple Rejection SD Threshold Voltage SD Input Current 2 VCTRL=2.5V to 7V, VIN=1.75V to 5.5V, 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=4A 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=4A VCTRL=2.75V, Io=7.5A VCTRL=2.75V, VIN=2.05V, DVo=100mV VADJ=0V VCTRL=5V, VIN=3.3V, V ADJ=0V 30ms Pulse VCTRL=5V, VIN=5V, Io=4A, VADJ=0V, TJ=258C, VRIPPLE=1V PP at 120Hz 7.7 60 0.5 mV 5 mV 0.95 1.00 1.05 1.15 V 0.075 0.150 0.200 0.375 V 9 5 0.01 70 VCTRL-1.4 VCTRL=5V, SD=0V www.irf.com 10 0.02 94 VCTRL-2.2 130 A mA %/W dB V mA Rev. 1.4 03/18/02 IRU1176 PARAMETER SYM Control Pin Current Adjust Pin Current IADJ 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=4A VCTRL=2.75V, VIN=2.05V, Io=7.5A VCTRL=2.75V, VIN=2.05V, V ADJ=0V, 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 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. MIN TYP MAX UNITS mA 50 120 mA 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 VSENSE PIN DESCRIPTIONS This pin is the positive side of the reference which allows remote load sensing to achieve excellent load regulation. 2 SD When this pin is pulled lower than 1.4V with respect to the VCTRL pin the device is shutdown. To enable the operation leave this pin open. Internal to device, there is a pull-up resistor. 3 Adj A resistor divider from this pin to the VOUT pin and ground sets the output voltage. 4 VOUT The output of the regulator. A minimum of 10mF capacitor must be connected from this pin to ground to insure stability. 5 VCTRL 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 V OUT pin in order for the device to regulate. (See specifications) 6, 7 VIN 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) Rev. 1.4 03/18/02 www.irf.com 3 IRU1176 BLOCK DIAGRAM VIN 6,7 4 VOUT VCTRL 5 1 VSENSE + 1.25V + CURRENT LIMIT THERMAL SHUTDOWN SD 2 3 Adj OUTPUT SHUTDOWN Figure 2 - Simplified block diagram of the IRU1176. APPLICATION INFORMATION Introduction The IRU1176 adjustable regulator is a five-terminal device designed specifically 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 bringing 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 IRU1176 ideal for applications where dual inputs are available such as a computer mother board with an ATX style power supply that provides 5V and 3.3V to the board. One such application is the new graphic chip sets that require anywhere from 2.4V to 2.7V supply such as the Intel I740 chip set. The IRU1176 can easily be programmed with the addition of two external resistors to any voltages within the range of 1.25 to 5.5V. 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 IRU1176 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 4 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 IRU1176 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 3 o 1 + R2 p + IADJ 3 R2 R1 Where: VREF = 1.25V Typically IADJ = 50mA Typically R1 & R2 as shown in Figure 3: VIN V IN VOUT VOUT IRU1176 VCTRL V CTRL SD V SENSE Adj V REF R1 Open IADJ = 50uA R2 Figure 3 - Typical application of the IRU1176 for programming the output voltage. www.irf.com Rev. 1.4 03/18/02 IRU1176 The IRU1176 keeps a constant 1.25V between the V SENSE 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)3R2 + IADJ3R2. 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 IRU1176 is 10mA, R1 is typically selected to be a 121V resistor so that it automatically satisfies this condition. Notice that since the Iadj is typically in the range of 50mA it adds a small error to the output voltage and should be considered when very precise output voltage setting is required. Load Regulation Since the IRU1176 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 4 shows a typical application of the IRU1176 with remote sensing. VI N V IN Panasonic FA series as well as the Nichicon PL series insures both stability and good transient response. Shutdown Operation The IRU1176 can be disabled by pulling the SD pin low using an open collector device such as a low cost 2N3904 general purpose transistor as shown in the application circuit. The current sink of the pin is equal to: ISINK = Assuming, the following conditions: VOUT = 2.7V VIN = 3.3V VCTRL = 5V IOUT = 2A (DC Avg) V OUT V CTRL V SENSE RL Adj R1 Calculate the maximum power dissipation using the following equation: PD = IOUT 3 (V IN - VOUT) +o o R2 IOUT p3 p (V CTRL - VOUT) 60 2 PD = 2 3 (3.3 - 2.7) +o o p 3 (5 - 2.7) = 1.28W 60 Figure 4 - Schematic showing connection for best load regulation. Using table below select the proper package and the amount of copper board needed. Stability The IRU1176 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 100mV and an output capacitance of 500 to 1000mF. Fortunately as the capacitance increases, the ESR decreases resulting in a fixed RC time constant. The IRU1176 takes advantage of this phenomena in making the overall regulator loop stable. For most applications a minimum of 100mF aluminum electrolytic capacitor such as Sanyo, MVGX series, Rev. 1.4 03/18/02 Where: R = 50KV Typically Thermal Design The IRU1176 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 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 shows the steps in selecting the proper surface mount package. IRU1176 VC T R L (V CTRL - 1.4) R Pkg M or P M or P M or P M or P Copper θJA(°C/W) Area 1.4"X1.4" 25 1.0"X1.0" 30 0.7"X0.7" 35 Pad Size 45 Max Pd (TA=25°C) 4.4W 3.7W 3.1W 2.4W Max Pd (TA=45°C) 3.6W 3.0W 2.6W 2.0W Note: Above table is based on the maximum junction temperature of 1358C. As shown in the above table, any of the two packages will do the job. For lower cost applications the Ultra ThinPak package is recommended. www.irf.com 5 IRU1176 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 6 www.irf.com Rev. 1.4 03/18/02