iru431l 1 rev. 2.0 08/05/03 www.irf.com description the iru431l is a three-terminal adjustable shunt regu- lator that can also be used as a precision voltage refer- ence. its output voltage may be set to any value be- tween v ref (1.24v) and 15v with two external resistors as shown in the typical application circuit. other appli- cations 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 volt- age power supply applications. the iru431l only re- quires 80 m a maximum quiescent current before regu- lating, making it ideal as an efficient voltage reference for battery type applications. the iru431l has 6 1% initial accuracy. low -voltage adjustable precision shunt regulator t a ( c) 3-pin sot-23 (l3) 5-pin sot-23 (l5) 0 to 70 iru431lcl3 iru431lcl5 figure 1 - typical application of the iru431l as a shunt regulator / voltage reference. data sheet no. pd94118 features sot-23 packages voltage reference initial accuracy (1%) low operating cathode current (80 m a max) unconditionally stable with only 1 m f adjustable output from 1.24v to 15v 0.25 v typical output impedance pin to pin compatible with tlv431 precision voltage reference linear regulator controller secondary side controller for the low voltage power supply applications applications vo = v ref 3 1 + r1 r2 ( ) package order information typical application r b r1 r2 c o iru431l v in v out ref k (cathode) a (anode) v ref
iru431l 2 rev. 2.0 08/05/03 www.irf.com i k =10ma, v ka =v ref , t a =25 8 c i k =10ma, v ka =v ref v ka =v ref , i k =10ma i k =10ma, d v ka =v ref to 6v i k =10ma, r1=10k v , r2=open i k =10ma, r1=10k v , r2=open v ka =v ref v ka =6v, v ref =0v v ka =10v, v ref =0v v ka =15v, v ref =0v v ka =v ref , f<1khz, i k =0.1 to 15ma, note 1 absolute maximum ratings input voltage (v in ) .................................................... 15v continuous cathode current range .......................... -15ma to +15ma reference current range .......................................... -0.05ma to 15ma storage temperature range ...................................... -65 8 c to 150 8 c operating junction temperature range ..................... 0 8 c to 150 8 c caution: stresses above those listed in "absolute maximum ratings" may cause permanent damage to the device. cathode ref anode 1 2 3 top view anode ref nc nc cathode 3 2 1 4 5 top view v mv mv/v m a m a m a m a v 1.252 1.259 -6 1 80 0.75 5 10 0.4 1.240 1.240 6 -1 0.15 0.05 55 0.6 1.8 3.2 0.25 1.228 1.221 v ref v ref(dev) d v ref / d v ka i ref(dev) i k(min) ioff z ka0 reference voltage iru431l v ref deviation over full temperature range ratio of v ref change to cathode voltage change reference pin current i ref deviation over full temperature range minimum cathode current off state cathode current dynamic impedance parameter sym test condition min typ max units q ja =256 c/w q ja = 336 c/w package information 3 -pin sot-23 (l3) 5-pin sot-23 (l5) unless otherwise specified, these specifications apply over t a =0 to 70 8 c, co =1 m f. typical values refer to t a =25 8 c. low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient tempera- ture. electrical specifications note 1: the dynamic impedance when v ka =v ref is de- fined as: when the device is operating with two external resistors (see figure 3), the total dynamic impedance of the cir- cuit is given by: ? z ka0 ? = d v ka d i k ? z ka ? = = ? z ka0 ? 3 1 + r1 r2 d v d i ( )
iru431l 3 rev. 2.0 08/05/03 www.irf.com pin descriptions block diagram figure 2 - simplified block diagram of the iru431l. 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 1 m f 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. cathode 1.24v anode ref + 5-pin 3-pin pin symbol pin d escription 4 3 5 1, 2 1 2 3 na ref cathode anode nc the deviation parameters, v ref(dev) and i ref(dev) are de- fined 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: where: ?a v ref ? unit is ppm/ 8 c d t a is the rated operating free air temperature of the device. a v ref can be positive or negative depending on whether minimum v ref or maximum v ref respectively occurs at the lower temperature. ?a v ref ? = v ref(dev) v ref(25 8 c) 3 10 6 d t a ( )
iru431l 4 rev. 2.0 08/05/03 www.irf.com application information an example is given below on how to properly select the biasing resistor. assuming: v min = 4.5v v max = 6v v ka = 3.3v i l = 10ma the maximum value for the biasing resistor is calcu- lated using the following equations: where: v min = minimum supply voltage i l(max) = maximum load current i b(max) = maximum bias current i k(min) = maximum value for the minimum cathode current spec i r = current through r1 assuming r1 = 2k v as before, the maximum power dissipation of the resistor is calcu- lated under the maximum supply voltage as follows: 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: the iru431l keeps a constant voltage of 1.240v be- tween the ref pin and ground pin. by placing a resistor r2 across these two pins a constant current flows through r2, adding to the i ref current and into the r1 resistor producing a voltage equal to: which will be added to the 1.240v to set the output volt- age as shown in the above equation. since the input bias current of the ref pin is 0.5 m a max, it adds a very small error to the output voltage and for most applica- tions can be ignored. for example, in a typical 5v to 3.3v application where r2=1.21k v and r1=2k v the error due to the i adj is only 1mv which is about 0.03% of the nominal set point. figure 3 - typical application of the iru431l for programming the output voltage. biasing resistor (r b ) selection the biasing resistor r b is selected such that it does not limit the input current under the minimum input supply and maximum load and biasing current. p r b (max) = where: v max = maximum supply voltage p r b (max) = maximum r b power dissipation p r b (max) = = 73mw (6 - 3.3) 100 2 (v max - v ka ) r b 2 r b(max) = i b(max) = i k(min) + i r v min - v ka i b(max) + i l(max) i r = = 1.03ma i b(max) = 0.08 + 1.03 = 1.11ma r b(max) = = 108 v select r b = 100 v 3.3 - 1.24 2 4.5 - 3.3 1.11 +10 v in r2 co r1 r b iru431l i k r l i l v ka = v out vo = v ka = v ref 3 1 + + i ref 3 r1 r1 r2 ( ) 3 r1 + i ref 3 r1 1.240 r2 ( )
iru431l 5 rev. 2.0 08/05/03 www.irf.com 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 t a =25 c with the de- rating factor of -1.2mw / c. the table below summarizes the maximum power dissi- pation capability of each package versus ambient tem- perature. ambient temperature (t a ) 8 8 c pkg 25 40 50 60 70 sot-23 150mw 132mw 120mw 108mw 96mw in our previous example, the maximum power dissipa- tion of the device is calculated under no load and maxi- mum input supply condition. the maximum power is calculated using the following equation: as shown in the power dissipation table, both packages can handle this power dissipation. stability the iru431l has many different domains of stability as a function of the cathode current. as is typical of three- terminal shunt regulators, the iru431l has many do- mains of stability. the actual domain in which any prac- tical circuit operates is related to cathode current. in general the device will be unconditionally stable for any cathode current if a capacitor, 1 m f or larger, is connected between the cathode and the anode. if the cathode cur- rent is always higher than 3ma under minimum line and maximum load conditions, the capacitor value can be reduced to 0.01 m f and the system will be stable. ( ) p max = v ka 3 where: p max = maximum power dissipation of the iru431l for our example: p max = 3.3 3 = 89mw v max - v ka r b 6 - 3.3 100 ( )
iru431l 6 rev. 2.0 08/05/03 www.irf.com typical application figure 4 - low cost 3.3v to 2.7v output. u1 c1, c2 r1 r2 r3, r4 hs1 12v r3 r2 r1 u1 v out v in c1 q1 c2 r4 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 iru431l elect, 220 m f, 6.3v, ecaojfq221 6.2k v , 5%, smt 118 v , 1%, smt 100 v , 1%, smt use minimum of 1" square copper pad area for load current <4a ref desig description qty part # manuf 1 2 1 1 2 shunt regulator capacitor resistor resistor resistor heat sink ir panasonic
iru431l 7 rev. 2.0 08/05/03 www.irf.com (l3) sot-23 package 3-pin symbol a a1 b c d e e e1 h l s min 0.890 0.013 0.370 0.085 2.800 1.200 0.890 1.780 2.100 0.450 max 1.120 0.100 0.510 0.180 3.040 1.400 1.030 2.050 2.640 0.600 0.55 ref note: all measurements are in millimeters. b h e1 d e s e l c a1 a c l
iru431l 8 rev. 2.0 08/05/03 www.irf.com (l5) sot-23 package 5-pin symbol a a1 a2 b c d e e1 e e1 l a min 0.90 0.00 0.90 0.25 0.09 2.80 2.60 1.50 0.35 0 8 max 1.45 0.15 1.30 0.50 0.20 3.00 3.00 1.75 0.55 10 8 0.95 ref 1.90 ref note: all measurements are in millimeters. c l e c e1 l b e d e1 a a2 a1 a
iru431l 9 rev. 2.0 08/05/03 www.irf.com pkg desig l3 l5 package description sot-23 sot-23 parts per tube --- --- parts per reel 3000 3000 package shipment method pin count 3 5 t & r orientation fig a fig b feed direction figure a feed direction figure b 1 1 1 1 1 1 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
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