US1175 7.5A ULTRA LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR PRELIMINARY DATASHEET DESCRIPTION FEATURES 0.5V Dropout at 7.5A (Equivalent of 67mΩ) Ω) Fast Transient Response 1% Voltage Reference Initial Accuracy Built-in Thermal Shutdown APPLICATIONS 3.3V to 2.7V Intel I740 chip set. The US1175 product 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 chip sets that requires 2.7V supply such as the Intel I740 chip set. TYPICAL APPLICATION 3.3V US1175 C1 Vin 5 Vctrl 4 Vout 3 2.7V R1 Adj Vsense 2 C3 R2 1 1175app1-1.0 5V C2 Typical application of US1175 . PACKAGE ORDER INFORMATION Tj (°C) 0 TO 125 Rev. 1.2 11/29/99 5 PIN PLASTIC 5 PIN PLASTIC TO263 (M) POWER FLEX (P) US1175CM US1175CP 8 PIN PLASTIC SOIC (S) US1175CS 2-1 US1175 ABSOLUTE MAXIMUM RATINGS Input Voltage (Vin) ........................................................... 6V Control Input Voltage (Vctrl) .................................................. 14V Power Dissipation............................................. Internally Limited Storage Temperature Range ................................... -65°C TO 150°C Operating Junction Temperature Range ..................... 0°C TO 150°C PACKAGE INFORMATION 8 PIN PLASTIC SOIC ( S ) 5 PIN PLASTIC TO263 ( M ) 5 PIN PLASTIC POWER FLEX (P) FRONT VIEW TOP VIEW Vctrl Vin Adj Vsense 1 8 2 7 3 6 4 5 FRONT VIEW 5 Vout Vout Vout Vout 4 3 2 1 θJA=55°C/W for 1" Sq pad area Vin Vctrl Vout Adj Vsense θJA=35°C/W for 0.5" square pad Vin Vctrl Vout Adj Vsense 5 4 3 2 1 θJA=35°C/W for 0.5" square pad ELECTRICAL SPECIFICATIONS Unless otherwise specified ,these specifications apply over ,Cin=1uF,Cout=10uF, and Tj=0 to 125°C.Typical values refer to Tj=25°C. Vout=Vsense. PARAMETER Reference Voltage Line Regulation Load Regulation (note 1) Dropout Voltage (note 2) (Vctrl - Vout) Dropout Voltage (note 2) (Vin - Vout) Current Limit Minimum Load Current (note 3) Thermal Regulation Ripple Rejection 2-2 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, 30 mS Pulse Vctrl=5V,Vin=5V,Io=3A,Vadj=0V 60 Tj=25,Vripple=1Vpp at 120Hz TYP 1.250 MAX 1.257 1.250 1.263 UNITS V 0.5 3 mV 2 6 mV 0.95 1.00 1.05 1.15 V 1.30 0.100 0.200 0.330 0.500 0.130 0.260 0.430 0.650 9 5 0.01 70 10 0.02 V A mA %/W dB Rev. 1.2 11/29/99 US1175 ELECTRICAL SPECIFICATIONS PARAMETER SYM TEST CONDITION Iadj 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 Vctrl=2.75V,Vin=2.05V,Vadj=0V, Control Pin Current Adjust Pin Current Note 1 : Low duty cycle pulse testing with Kelvin connections are required in order to maintain accurate data. Note 2 : Drop-out voltage is defined as the minimum differential between Vin and Vout required to maintain regulation at Vout. It is measured when the output voltage drops 1% below its nominal value. MIN TYP 15 30 50 75 50 MAX UNITS mA 120 uA 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 2 3 4 5 Rev. 1.2 11/29/99 PIN SYMBOL PIN DESCRIPTION This pin is the positive side of the reference which allows remote load sensing Vsense to achieve excellent load regulation. A resistor divider from this pin to the Vout pin and ground sets the output voltage. Adj The output of the regulator. A minimum of 10uF capacitor must be connected from this Vout pin to ground to insure stability. This pin is the supply pin for the internal control circuitry as well as the base drive for Vctrl 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 Vin 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 US1175 BLOCK DIAGRAM Vin Vout Vctrl Vsense + + 1.25V CURRENT LIMIT THERMAL SHUTDOWN Adj 1175blk1-1.0 Figure 1 - Simplified block diagram of the US1175 APPLICATION INFORMATION Introduction The US1175 adjustable regulator is a 5 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 flexebility makes the US1175 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 chip sets that require anywhere from 2.4V to 2.7V supply such as the Intel I740 chip set. The US1175 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 500 nS 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 US1175 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 US1175 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 × R2 R1 Wehre : VREF=125 . V Typically IADJ=50 uA Typically R1 & R2 as shown in figure 2 Vin Vin Vout Vout US1175 Vctrl Vctrl Vsense Adj Vref IAdj = 50uA R1 R2 1175app2-1.0 Figure 2 - Typical application of the US1175 for programming the output voltage. 2-4 Rev. 1.2 11/29/99 US1175 The US1175 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 + Iadj*R2 .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 US1175 is 10 mA , R1 is typically selected to be a 121Ω resistor so that it automatically satisfies this condition. Notice that since the Iadj is typically in the range of 50uA 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 US1175 has separate pins for the output (Vout) and the sense (Vsense), 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 US1175 with remote sensing. Vin Vin Vout US1175 Vctrl Vctrl For most applications a minimum of 100uF 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 US1175 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 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*(Vin-Vout) + (Iout/60)*(Vctrl - Vout) Pd=2*(3.3-2.7) + (2/60)*(5-2.7)=1.28 W Using table below select the proper package and the amount of copper board needed. Pkg Vsense Adj RL R1 R2 1175app3-1.0 Figure 3 - Schematic showing connection for best load regulation Stability TO263 TO263 TO263 TO263 SO8 Copper θJA(°C/W) Area 1.4"X1.4" 25 1.0"X1.0" 30 0.7"X0.7" 35 Pad Size 45 1.0"X1.0" 55 Max Pd (Ta=25°C) 4.4W 3.7W 3.1W 2.4W 2.0W Max Pd (Ta=45°C) 3.6W 3.0W 2.6W 2.0W 1.63W Note: Above table is based on the maximum junction temperature of 135°C. As shown in the above table, any of the two packages will do the job. For low cost applications the SO8 package is recommended. The US1175 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 100 mΩ and an output capacitance of 500 to 1000uF. Fortunately as the capacitance increases, the ESR decreases resulting in a fixed RC time constant. The US1175 takes advantage of this phenomena in making the overall regulator loop stable. Rev. 1.2 11/29/99 2-5