schematic diagram device description the ZHT2431 is a three terminal adjustable shunt regulator offering excellent temperature stability and output current handling capability up to 25ma. the output voltage may be set to any chosen voltage between 1.24 and 15 volts by selection of two external divider resistors. the devices can be used as a replacement for zener diodes in many applications requiring an improvement in zener performance. the ZHT2431 is particularly used in the feedback control loop of switch mode power supplies. in this application the device 1.24 volt reference enables the generation of low voltage supplies, typically 3.3 volts or 3 volts. the ZHT2431 is intended for use over the extended operating range of -55c to 125c. features surface mount sot23 package to92 package 2.5% tolerance average temperature coefficient 50 ppm/c temperature compensated for operation over the full temperature range programmable output voltage 100 m a to 25ma current sink capability low output noise -55 to 125 c operation applications shunt regulator series regulator voltage monitor over voltage/ under voltage protection switch mode power supplies high temperature adjustable precision zener shunt regulator issue 1 july 1997 ZHT2431 v z g nd v ref
electrical characteristics test conditions (unless otherwise stated):t amb =25c parameter symbol value units conditions min typ max reference voltage 2.5% v ref 1.21 1.24 1.27 v i l =10ma (fig1), v z =v ref deviation of reference input voltage over temperature v dev 5.0 15.0 mv i l =10ma, v z =v ref t a =full range (fig1) ratio of the change in reference voltage to the change in cathode voltage d v ref d v z 0.5 2.0 mv/v v z from v ref to 10v i z =10ma (fig2) reference input current i ref 0.02 0.11 0.4 m a r1=10k, r2=o/c, l l =10ma (fig2) deviation of reference input current over temperature d i ref 0.02 0.2 m a r1=10k, r2=o/c, i l =10ma t a =full range (fig2) minimum cathode current for regulation i zmin 30 100 m a ? off-state current i zoff 10 30 m a v z =15v, v ref =0v (fig3) dynamic output impedance r z 0.25 2 w v z =v ref (fig1), f=0hz, i l =10ma deviation of reference input voltage, v dev, is defined as the maximum variation of the reference input voltage over the full temperature range. the average temperature coefficient of the reference input voltage, v ref is defined as: v ref ( ppm c )= v dev x 1000000 v ref ( t 1 - t 2 ) the dynamic output impedance, rz, is defined as: r z = d v z d i z when the device is programmed with two external resistors, r1 and r2, (fig 2) , the dynamic output impedance of the overall circuit, r?, is defined as: r ? = r z ? ? 1 + r1 r2 ? ? ? with a capacitance of greater than 100pf between cathode and anode, minimum cathode current must be 0.2ma. vmax vmin t1 t2 vdev = vmax - vmin temperature ZHT2431 absolute maximum rating cathode voltage (v z ) 15v cathode current 50ma operating temperature -55 to 125c storage temperature -55 to 125c recommended operating conditions cathode voltage (min)v ref to (max) 15v cathode current (min) 100 m a to (max) 25ma power dissipation (t amb =25c, t jmax =150c) sot23 330mw to92 780mw
ZHT2431 dynamic impedance vs. frequency frequency (hz) 1k 10k 100k 0.1 w 10 1 100 1ma 10ma vref = vz change in v ref v cathode voltage cathode voltage (v) 515 10 -5 1 0 -1 -2 -3 0 2 -4 iz = 10ma power dissipation derating ambient temperature (c) 50 100 75 0 0.5 25 1.0 125 sot23 to92 reference voltage v temperature temperature (c) 025 75 50 1.232 1.234 1.244 1.242 1.240 1.238 1.236 -50 -25 100 125 cathode current v temperature temperature (c) 0 25 75 50 14 16 26 24 22 20 18 -50 -25 100 125 reference current v temperature temperature (c) 025 75 50 vref = vz 80 90 140 130 120 110 100 -50 -25 100 iz=10ma 125 vref = vz typical characteristics iz=10ma
stablity boundary conditions load capacitance(f) 1n 10n 1 0 5 30 25 20 15 10 10p 100p .1 10 pulse response time (us) 200 300 500 400 0 2.0 1.0 0 5.0 2.5 0 100 gain v frequency frequency (hz) 10k 100k 1m 0 10 60 50 40 30 20 100 1k stable stable unstable input single pulse repetitive pulse vz iz = 10ma typical characteristics i z 47 k v z test circuit for open loop voltage gain 47 k 10 m f 240 w + - i z = 10ma, t a = 25c test circuit for pulse response input monitor v z 120 w 50 w pulse generator t a = 25c test circuit for stability boundary conditions input 150 w 10k v ref < v z < 20, i z = 10ma, t a = 25c v z i z 100f ZHT2431
ZHT2431 r2 vout = 1 + r1 r2 vref series regulator v+ vout r1 30 0.01f vref vout = 1 + r1 r2 vref vout = vref + vreg min output control of a three terminal fixed regulator r2 r1 v+ vout vref zsr*** in out common r2 r1 v+ vout vout = vref 1 + r1 r2 vref higher current shunt regulator v+ output input v = 2.5v th v 2v on v = v+ off single supply comparator with temperature compensated threshold r2a r1a v+ vref r2b r1b vref 1+ r1b r2b vref over voltage / under voltage protection circuit low limit = high limit = 1+ r1a r2a vref r2 r1 vout = vref 1 + r1 r2 vref shunt regulator v+ vout outpu t application circuits
ZHT2431 input v v i z z ref i l i ref 1 m f fig 1 ? test circuit for v z =v ref input v v i z z ref i ref r1 r2 i l 1 m f fig 2 ? test circuit for v z >v ref input v i z zoff 1 m f fig 3 ? test circuit for off state current voltage regulator connection diagrams sot23 package suffix ? f top view to92 package suffix ? c bottom view part number package part mark ZHT2431f02 sot23 24f ZHT2431c02 to92 ZHT243102 dc test circuits ordering information
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