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Data Sheet No. PD94118
IRU431L / IRU431AL
LOW -VOLTAGE ADJUSTABLE PRECISION SHUNT REGULATOR DESCRIPTION
The IRU431L family are three-terminal adjustable shunt regulators that can also be used as precision voltage references. 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 80mA maximum quiescent current before regulating, making it ideal as a voltage reference for battery type applications. The IRU431L has 61% initial accuracy while IRU431AL provides 60.5% initial accuracy.
FEATURES
SOT-23 Packages Voltage Reference Initial Accuracy (1% for IRU431L and 0.5% for IRU431AL) Low Operating Cathode Current (80mA max) Unconditionally Stable with only 1mF Adjustable Output from 1.24V to 15V 0.25V Typical Output Impedance Pin to Pin Compatible with TLV431
APPLICATIONS
Precision Voltage Reference Linear Regulator Controller Secondary Side Controller for the low voltage power supply applications
TYPICAL APPLICATION
VIN RB R1 VOUT
IRU431L
Vo = VREF 3o1 + o R1 p R2
Co 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 5-PIN SOT-23 (L5) IRU431LCL5 IRU431ALCL5 3-PIN SOT-23 (L3) IRU431LCL3 IRU431ALCL3
Rev. 1.8 02/20/02
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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 -658C To 1508C 08C To 1508C
PACKAGE INFORMATION
5-PIN SOT-23 (L5)
TOP VIEW
3-PIN SOT-23 (L3)
TOP VIEW 2 Cathode
NC 1 NC 2 Cathode 3
5
Anode Anode 3
4
Ref
1 Ref
JA=256C/W
JA=336C/W
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over TA=0 to 708C, Co =1mF. Typical values refer to TA=258C. Low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient temperature. PARAMETER SYM TEST CONDITION MIN 1.228 1.221 1.234 1.228 TYP 1.240 1.240 1.240 1.240 6 -1 0.15 0.05 55 0.6 1.8 3.2 0.25 MAX UNITS 1.252 1.259 1.246 1.252 V V mV -6 1 mV/V mA mA mA mA
Reference Voltage VREF IK=10mA, VKA=VREF, TA=258C IRU431L IK=10mA, VKA=VREF Reference Voltage VREF IK=10mA, VKA=VREF, TA=258C IRU431AL IK=10mA, VKA=VREF VREF Deviation over full VREF(DEV) VKA=VREF, IK=10mA temperature range Note 1 Ratio of VREF change to DVREF/DVKA IK=10mA, DVKA=VREF to 6V cathode voltage change Reference Pin Current IK=10mA, R1=10KV, R2=open IREF Deviation over full IREF(DEV) IK=10mA, R1=10KV, R2=open temperature range Note 1 Minimum Cathode Current IK(MIN) VKA=VREF Off State Cathode Current Ioff VKA=6V, VREF=0V VKA=10V, VREF=0V VKA=15V, VREF=0V Dynamic Impedance ZKA0 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: o VREF(DEV) 6 p 3 10 VREF(258C) DTA
80 0.75 5 10 0.4
V
Where: ?aVREF? unit is ppm/8C DTA is the rated operating free air temperature of the device. aVREF can be positive or negative depending on whether minimum VREF or maximum VREF respectively occurs at the lower temperature.
?aVREF? =
2
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Rev. 1.8 02/20/02
IRU431L / IRU431AL
Note 2: The dynamic impedance when VKA=VREF is defined as: ?ZKA0? = DVKA DIK When the device is operating with two external resistors (See figure 3), the total dynamic impedance of the circuit is given by: ?ZKA? = DV R1 = ?ZKA0? 3o1 + o p DI R2
PIN DESCRIPTIONS
SOT-23 5-PIN PIN# 4 SOT-23 3-PIN PIN# 1 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. The output of the shunt regulator. A capacitor of 1mF minimum value must be connected from this pin to Anode pin to insure unconditional stability. 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. These pins are not connected internally.
3
2
Cathode
5
3
Anode
1, 2
NA
NC
BLOCK DIAGRAM
Cathode
Ref
+
1.24V
Anode
Figure 2 - Simplified block diagram of the IRU431L.
Rev. 1.8 02/20/02
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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 3o1 + o R1 p + IREF 3 R1 R2 An example is given below on how to properly select the biasing resistor. Assuming: VMIN = 4.5V VMAX = 6V VKA = 3.3V IL = 10mA The maximum value for the biasing resistor is calculated using the following equations: RB(MAX) = VMIN - VKA IB(MAX) + IL(MAX)
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 o p3 R1 + IREF 3 R1 p R2 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 0.5mA 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=1.21KV and R1=2KV the error due to the IADJ is only 1mV which is about 0.03% of the nominal set point. VIN
R B IK R1 IL Co R2 R L
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 = 2KV as before, IR = 3.3 - 1.24 = 1.03mA 2
VKA = VOUT
IRU431L
IB(MAX) = 0.08 + 1.03 = 1.11mA RB(MAX) = 4.5 - 3.3 = 108V 1.11 +10
Select RB = 100V Figure 3 - Typical application of the IRU431L for programming the output voltage. 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. The maximum power dissipation of the resistor is calculated under the maximum supply voltage as follows: 2 (VMAX - VKA) PRB(MAX) = RB Where: VMAX = Maximum supply voltage PRB(MAX) = Maximum RB power dissipation PRB(MAX) = (6 - 3.3) = 73mW 100
2
4
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Rev. 1.8 02/20/02
IRU431L / IRU431AL
Thermal Design The IRU431L is offered in the surface mount SOT-23 (L) packages. The SOT-23 package has the maximum power dissipation capability of 150mW at TA=25C with the derating factor of -1.2mW / C. The table below summarizes the maximum power dissipation capability of each package versus ambient temperature. Ambient Temperature (TA) -8C 8 40 50 60 70
132mW 120mW 108mW 96mW
Pkg
SOT-23
25
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, 1mF 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 0.01mF and the system will be stable.
150mW
In our previous example, the maximum power dissipation of the device is calculated under no load and maximum input supply condition. The maximum power is calculated using the following equation: PMAX = VKA 3 o VMAX - VKA p RB
Where: PMAX = Maximum power dissipation of the 431L For our example: 6 - 3.3 PMAX = 3.3 3 o p = 89mW 100 As shown in the power dissipation table, both packages can handle this power dissipation.
Rev. 1.8 02/20/02
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5
IRU431L / IRU431AL
TYPICAL APPLICATION
VIN
C1
Q1
VOUT
C2
R4 R1 R2
12V
U1
R3
Figure 4 - Low cost 3.3V to 2.7V output.
Ref Desig U1 C1, C2 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,220mF, 6.3V, ECAOJFQ221 Panasonic 6.2KV, 5%, SMT 118V, 1%, SMT 100V, 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
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Rev. 1.8 02/20/02

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