Data Sheet No. PD94118 IRU431L / IRU431AL LOW -VOLTAGE ADJUSTABLE PRECISION SHUNT REGULATOR DESCRIPTION FEATURES SOT-23 and SOIC Packages 0.5% Voltage Reference Initial Accuracy (IRU431AL) Low Operating Cathode Current (80µA max) Unconditionally Stable with only 1µF Adjustable Output from 1.24V to 15V 0.25Ω Typical Output Impedance Pin to Pin Compatible with TLV431 The IRU431L is a three-terminal adjustable shunt regulator that can also be used as a precision voltage reference. Its output voltage may be set to any value between Vref(1.24V) and 15V with two external resistors as shown in the typical application circuit. Other applications of this device include being used as a merged amplifier and reference in applications such as a linear regulator or as the secondary side controller in low voltage power supply applications. The IRU431L only requires 80µA maximum quiescent current before regulating, making it ideal as a voltage reference for battery type applications. APPLICATIONS Precision Voltage Reference Linear Regulator Controller Secondary Side Controller for the Low Voltage Power Supply Applications TYPICAL APPLICATION VIN RB VOUT R1 IRU431L Co R2 Vo = Vref × o1 + R1 p R2 Figure 1 - Typical application of the IRU431L as a shunt regulator / voltage reference. PACKAGE ORDER INFORMATION Ta (°C) 0 To 70 0 To 70 Rev. 1.5 07/13/01 5-PIN SOT-23 (L5) IRU431LCL5 IRU431ALCL5 PKG MARK 431L 431A 3-PIN SOT-23 (L3) IRU431LCL3 IRU431ALCL3 PKG MARK 431L 431A 8-PIN PLASTIC SOIC (S) IRU431LCS IRU431ALCS 1 IRU431L / IRU431AL ABSOLUTE MAXIMUM RATINGS Input Voltage (Vin) .................................................... Continuous Cathode Current Range .......................... Reference Current Range .......................................... Storage Temperature Range ...................................... Operating Junction Temperature Range ..................... 15V -15mA To +15mA -0.05mA To 1mA -65$C To 150$C 0$C To 150$C PACKAGE INFORMATION 5-PIN SOT-23 (L5) 3-PIN SOT-23 (L3) TOP VIEW TOP VIEW NC 1 Cathode 1 8 Ref NC 2 7 NC Anode 3 NC 2 Cathode 3 TOP VIEW 2 Cathode 5 Anode 8-PIN PLASTIC SOIC (S) Anode 3 1 Ref 4 Ref NC 4 θJA = 450°C/W θJA = 450°C/W 6 Anode 5 NC θJA=160°C/W ELECTRICAL SPECIFICATIONS Unless otherwise specified, these specifications apply over Ta=0 to 70$C, Co =1µF. Typical values refer to Ta=25$C. Low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient temperature. PARAMETER SYM Reference Voltage Vref IRU431L Reference Voltage Vref IRU431AL Vref deviation over full Vref(dev) temperature range Ratio of Vref change to ∆Vref/∆VKA cathode voltage change Reference pin current Iref deviation over full Iref(dev) temperature range Minimum cathode current IK(min) Off state cathode current Ioff Dynamic Impedance ZKA0 TEST CONDITION IK=10mA, VKA=Vref, Ta=25$C IK=10mA, VKA=Vref IK=10mA, VKA=Vref, Ta=25$C IK=10mA, VKA=Vref VKA=Vref, IK=10mA Note 1 IK=10mA, dVKA=Vref to 6V IK=10mA, R1=10KΩ, R2=open IK=10mA, R1=10KΩ, R2=open Note 1 VKA=Vref VKA=6V, Vref=0V VKA=10V, Vref=0V VKA=15V, Vref=0V VKA=Vref, f<1KHz, IK=0.1 to 15mA, Note 2 Note 1: The deviation parameters, Vref(dev) and Iref(dev) are defined as the differences between the maximum and the minimum values obtained over the rated temperature range. The average full range temperature coefficient of the reference input voltage is defined as: 'αVref' = 2 Vref(dev) 6 o p × 10 Vref(25$C) MIN 1.228 1.221 1.234 1.228 TYP 1.240 1.240 1.240 1.240 6 MAX 1.252 1.259 1.246 1.252 UNITS V -1 -6 mV/V 0.15 0.05 1 µA µA 55 0.6 1.8 3.2 0.25 80 0.75 5 10 0.4 µA µA V mV Ω Where: 'αVref' unit is ppm/$C ∆TA is the rated operating free air temperature of the device. αVref can be positive or negative depending on whether minimum Vref or maximum Vref respectively occurs at the lower temperature. ∆TA Rev. 1.5 07/13/01 IRU431L / IRU431AL Note 2: The dynamic impedance when VKA=Vref is defined as: 'ZKA0' = ∆VKA ∆IK When the device is operating with two external resistors (See figure 3), the total dynamic impedance of the circuit is given by: 'ZKA' = ∆V R1 = 'ZKA0' × o1 + p ∆I R2 PIN DESCRIPTIONS SOT-23 5-PIN PIN# 4 SOT-23 3-PIN PIN# 1 8-PIN SOIC PIN# 8 PIN SYMBOL Ref PIN DESCRIPTION Resistors from the Ref pin to the cathode pin and to ground form a divider that sets the output voltage. 3 2 1 Cathode The output of the shunt regulator. A capacitor of 1µF minimum value must be connected from this pin to Anode pin to insure unconditional stability. 5 3 3, 6 Anode Ground pin. This pin must be connected to the lowest potential in the system and all other pins must be at higher potential with respect to this pin. 1, 2 NA 2, 4, 5, 7 NC BLOCK DIAGRAM These pins are not connected internally. Cathode Ref 1.24V + Anode Figure 2 - Simplified block diagram of the IRU431L Rev. 1.5 07/13/01 3 IRU431L / IRU431AL APPLICATION INFORMATION Output Voltage Setting The IRU431L can be programmed to any voltages in the range of 1.24 to 15V with the addition of R1 and R2 external resistors according to the following formula: Vo = VKA = Vref × o1 + R1 p + Iref × R1 R2 The IRU431L keeps a constant voltage of 1.240V between the Ref pin and ground pin. By placing a resistor R2 across these two pins a constant current flows through R2, adding to the Iref current and into the R1 resistor producing a voltage equal to: (1.240 / R2) × R1 + Iref × R1 which will be added to the 1.240V to set the output voltage as shown in the above equation. Since the input bias current of the Ref pin is 0.5µA max, it adds a very small error to the output voltage and for most applications can be ignored. For example, in a typical 5V to 3.3V application where R2=1.21KΩ and R1=2KΩ the error due to the Iadj is only 1mV which is about 0.03% of the nominal set point. RB V IN V KA = VO IK R1 IRU431L IL Co RL R2 431app2-1.0 Figure 3 - Typical application of the IRU431L for programming the output voltage. The maximum value for the biasing resistor is calculated using the following equations: RB(MAX) = VMIN - VKA IB(MAX) + IL(MAX) IB(MAX) = IK(MIN) + IR Where: VMIN = Minimum supply voltage IL(MAX) = Maximum load current IB(MAX) = Maximum bias current IK(MIN) = Maximum value for the minimum cathode current spec IR = Current through R1 Assuming R1 = 2KΩ as before, IR = 3.3 - 1.24 = 1.03mA 2 IB(MAX) = 0.08 + 1.03 = 1.11mA RB(MAX) = 4.5 - 3.3 = 108Ω 1.11 +10 Selecting RB = 100Ω The maximum power dissipation of the resistor is calculated under the maximum supply voltage as follows: 2 PR (MAX) = B (VMAX - VKA) RB Where: VMAX = Maximum supply voltage PR (MAX) = Maximum RB power dissipation B 2 Biasing Resistor (RB) Selection The biasing resistor RB is selected such that it does not limit the input current under the minimum input supply and maximum load and biasing current. An example is given below on how to properly select the biasing resistor. Assuming: VMIN = 4.5V VMAX = 6V VKA = 3.3V IL = 10mA 4 PR (MAX) = B (6 - 3.3) = 73mW 100 Thermal Design The IRU431L is offered in the plastic 8-pin SOIC or the surface mount SOT-23 (L) packages. The 8-pin SOIC package has the maximum power dissipation capability of 775mW at Ta=25°C with the derating factor of -6.2mW/ °C. The SOT-23 package has the maximum power dissipation capability of 150mW at Ta =25°C with the derating factor of -1.2mW / °C. Rev. 1.5 07/13/01 IRU431L / IRU431AL The table below summarizes the maximum power dissipation capability of each package versus ambient temperature. Pkg 25 Ambient Temperature (Ta) -°C 40 50 60 8-Pin SOIC 775mW SOT-23 150mW 682mW 132mW 620mW 120mW 558mW 108mW 70 496mW 96mW In our previous example, the maximum power dissipation of the device is calculated under no load and maximum input supply condition. Stability The IRU431L has many different domains of stability as a function of the cathode current. As is typical of threeterminal shunt regulators, the IRU431L has many domains of stability. The actual domain in which any practical circuit operates is related to cathode current. In general the device will be unconditionally stable for any cathode current if a capacitor, 1µF or larger, is connected between the cathode and the anode. If the cathode current is always higher than 3mA under minimum line and maximum load conditions, the capacitor value can be reduced to 0.01µF and the system will be stable. The maximum power is calculated using the following equation: VMAX - VKA p PMAX = VKA × o RB Where: PMAX = Maximum power dissipation of the 431L For our example: 6 - 3.3 p = 89mW PMAX = 3.3 × o 100 As shown in the power dissipation table, both packages can handle this power dissipation. Rev. 1.5 07/13/01 5 IRU431L / IRU431AL TYPICAL APPLICATION I740 Application Q1 V IN V OUT C1 C2 R4 R1 12V R2 U1 R3 431app3-1.2 Figure 4 - Low cost 3.3V to 2.7V output for Intel I740 application. Ref Desig U1 C1,2 R1 R2 R3,R4 HS1 Description Shunt Regulator Capacitor Resistor Resistor Resistor Heat Sink Qty 1 2 1 1 2 Part # Manuf IRU431L IR Elect,220µF,6.3V,ECAOJFQ221 Panasonic 6.2KΩ, 5%, SMT 118Ω, 1%, SMT 100Ω, 1% SMT Use minimum of 1" square copper pad area for load current <4A 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 Rev. 1.5 07/13/01