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US431L/431AL
LOW -VOLTAGE ADJUSTABLE PRECISION SHUNT REGULATOR
PRELIMINARY DATASHEET
FEATURES
SOT23-5 package 0.5% Voltage Reference Initial Accuracy (US431AL) Low Operational Cathode Current (80 uA max) Unconditionally Stable with only 1uF Adjustable Output from 1.24V to 6V 0.25 Typical Output Impedance Pin to Pin Compatible with TLV431
DESCRIPTION
The US431L product is a 3 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 6V with two external resistors as shown in the typical application circuit. Other applications of this device include the use as a merged amplifier and reference in applications such as Linear regulator or as the secondary side controller in low voltage power supply applications. The US431L only requires 80uA 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
RB
V IN
R1
VO US431
R2 Co
R1 Vo = Vref x 1 + R2
431app1-1.0
Typical application of the US431L as a shunt regulator / voltage reference.
PACKAGE ORDER INFORMATION
Ta (C) 0 TO 70 0 TO 70 5 LEAD SOT23-5 US431LCL US431ALCL 3 PIN PLASTIC TO-92 US431LCZ US431ALCZ 8 PIN PLASTIC SOIC US431LCS US431ALCS
Rev. 1.2 5/11/98
2-1
US431L/431AL
ABSOLUTE MAXIMUM RATINGS
Input Voltage (Vin) ............................................................. 7V Continuous Cathode Current Range ......................................... -20 mA to +20 mA Reference Current Range ...................................................... -0.05 mA to 3 mA Storage Temperature Range ................................ -65C TO 150C Operating Junction Temperature Range ...................... 0C TO 150C
PACKAGE INFORMATION
5 PIN SOT 23 (L)
TOP VIEW
3 PIN PLASTIC TO-92 (Z)
BOTTOM VIEW 1 2
8 PIN PLASTIC SOIC (S)
TOP VIEW
NC 1 NC 2 Cathode
3
5 Anode
Ref Anode Cathode
Cathode Anode
1
8 Ref 7 NC 6 Anode 5 NC
NC 2
3 4 Ref
3
NC 4
JA = 450C/W
JA = 162C/W
JA=160C/W
ELECTRICAL SPECIFICATIONS
Unless otherwise specified ,these specifications apply over Ta=0 to 70 C, CO =1uF. Typical values refer to Ta=25 C.Low duty cycle pulse testing are used which keeps junction and case temperatures equal to the ambient temperature. PARAMETER SYM TEST CONDITION MIN TYP MAX UNITS Reference Voltage Vref IK=10mA,VKA=Vref,Ta=25C 1.228 1.240 1.252 V US431L IK=10mA,VKA=Vref 1.221 1.240 1.259 Reference Voltage Vref IK=10mA,VKA=Vref,Ta=25C 1.234 1.240 1.246 V US431AL IK=10mA,VKA=Vref 1.228 1.240 1.252 Vref deviation over full Vref(dev) VKA=Vref, IK=10mA 4 12 mV temperature range Note 1 Ratio of Vref change to dVref/dVKA IK=10mA , dVKA=Vref to 6 V -1.5 -2.7 mV/V Cathode voltage change Reference pin current IK=10mA , R1=10k , R2=open 0.15 0.5 uA Iref deviation over full Iref(dev) IK=10mA , R1=10k , R2=open 0.05 0.3 uA temperature range Note 1 Minimum cathode current IK(min) VKA=Vref 55 80 uA Off state cathode current Ioff VKA=6V , Vref=0V 0.001 0.1 uA Dynamic impedance Zka0 VKA=Vref, f<1 kHz, 0.25 0.4 IK=0.1 to 15 mA , 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 coeficient of the reference input voltage is defined as : Vref ( dev) 6 x 10 Vref ( 25 C) Vref = TA Where: Vref unit is ppm/ C TA is the rated operating free air temperature of the device. Vref can be positive or negative depending on whether minimum Vref or maximum Vref, respectively occurs at the lower temperature. Note 2 : Thedynamic impedance when VKA = Vref is defined as : VKA IK When the device is operating with two external Zka0 = resistors (see Figure 2), the total dynamic impedance of the circuit is given by: Zka = V R1 = Zka0 x 1 + I R2
2-2
Rev. 1.2 5/11/98
US431L/431AL
Pin Descriptions
SOT 23 PIN# 4 3 TO 92 PIN# 1 3 8 PIN SOIC PIN# 8 1 PIN SYMBOL Ref Cathode Pin Description A resistor divider from this pin to the Cathode pin and ground sets the output voltage. The output of the shunt regulator .A minimum of 1uF capacitor 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 & all other pins must be at higher potential with respect to this pin. These pins are not connected internally.
5
2
3,6
Anode
1,2
NA
2,4,5,7
NC
BLOCK DIAGRAM
Cathode
Ref
+
1.24V
431blk1-1.0
Anode
Figure 1 - Simplified block diagram of the US431L
Rev. 1.2 5/11/98
2-3
US431L/431AL
APPLICATION INFORMATION
Output Voltage Setting The US431L can be programmed to any voltages in the range of 1.24 to 6V with the addition of R1 and R2 external resistors according to the following formula: R1 Vo = VKA = Vref x 1 + + Iref x R1 R2 The US431L 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 the (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 0.5 uA 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=1.21k and R1=2k the error due to the Iadj is only 1mV which is about 0.03% of the nominal set point. The maximum value for the biasing resistor is calculated using the following equations : VMIN - VKA IB MAX + ILMAX IBMAX = IKMIN + IR Where : VMIN = Minimum supply voltage ILMAX = Maximum load current IBMAX = Maximum bias current IKMIN = Maximum value for the minimum cathode current spec IR = Current through R1 RBMAX = Assuming R1=2k as before, 3.3 - 1.24 = 103 mA . 2 IBMAX = 0.08 + 1.03 = 1.11 mA 4.5 - 3.3 RB MAX = = 108 1.11+ 10 Selecting RB = 100 IR = The maximum power dissipation of the resistor is calculated under the maximum supply voltage as follows : ( VMAX - VKA ) 2 PRB(MAX ) = RB Where : VMAX = Maximum supply voltage PRB(MAX ) = Maximum RB power dissipation PRB(MAX ) =
RB
V IN
IK R1 IL Co R2
431app2-1.0
VKA = VO US431
RL
(6 - 3.3) 2
100
= 73 mW
Thermal Design Figure 2 - Typical application of the US431L 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. An example is given below on how to properly select the biasing resistor. Assuming : VMIN = 4.5 V VMAX = 6 V VKA = 3.3 V IL = 10 mA The US431L is offered in the plastic TO-92 (Z) or the surface mount SOT23-5 (L) packages. The TO-92 package has the maximum power dissipation capability of 775mW at Ta=25C with the derating factor of -6.2mW/ C.The SOT23-5 package has the maximum power dissipation capability of 150mW at Ta =25C with the derating factor of -1.2mW/C. Table below summarizes the maximum power dissipation capability of each package versus ambient temperature. Ambient Temperature (Ta) -C Pkg 25 40 50 60 70 TO 92 775mW 682mW 620mW 558mW 496mW SOT23-5 150mW 132mW 120mW 108mW 96mW
2-4
Rev. 1.2 5/11/98
US431L/431AL
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 : VMAX - VKA PMAX = VKA x RB Where : PMAX = Maximum power dissipation of the 431L For our example : 6 - 3.3 PMAX = 3.3 x = 89 mW 100 As shown in the power dissipation table, both packages can handle this power dissipation. Stability The US431L has many different regions of stability domain as a function of the cathode current which are typical characteristics of the 3 terminal shunt regulators. However in general the device will be unconditionaly stable for any cathode current if the capacitor, CO = 1 uF or bigger is connected from Cathode to Anode pins. If the cathode current is always kept higher than 500uA under minimum line and maximum load conditions , the CO can be cut to 0.01uF and the system will be stable.
Rev. 1.2 5/11/98
2-5
US431L/431AL
TYPICAL APPLICATION
I740 Application
VIN
C1 R1
Q1
VOUT
C2
12V U1
R2
R3
431app3-1.1
Figure 3- Low cost 3.3V to 2.7V 0utput for Intel I740 application.
Ref Desig U1 C1,2 R1 R2 R3 HS1
Description Shunt Regulator Capacitor Resistor Resistor Resistor Heat Sink
Qty 1 2 1 1 1
Part # Manuf US431L Unisem Elect,220uF,6.3V,ECAOJFQ221 Panasonic 6.2k, 5%, SMT 118, 1%, SMT 100, 1% SMT Use minimum of 1" Square Copper Pad area for load current <4A
2-6
Rev. 1.2 5/11/98

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