1 high performance schottky diode for digital applications preliminary technical data 2:24 pm , 06/05/98 features ultra-low series resistance for higher current handling picosecond switching low capacitance applications: analog and digital designs requiring circuit protection or waveform cleanup with high speed switching. package lead code identification (top view) description the hsms-2700 series of schottky diodes, commonly referred to as clipping/clamping diodes, are optimal for circuit and waveshape preservation applications with high speed switching. ultra-low series resistance, r s , makes them ideal for protecting sensitive circuit elements against higher current transients carried on data lines. with picosecond switching, the hsms-270x can respond to noise spikes with rise times as fast as 1ns. low capacitance minimizes waveshape loss that causes to signal degradation. dc electrical specifications for hsms-270x test conditions : t a =25 c, single diode. maximum forward voltage, minimum breakdown voltage, typical capacitance, typical series resistance, maximum effective carrier lifetime, hsms package marking code [1] lead code configuration package v f [mv] v br [v] c t [ pf] r s [ w ] t [ps] -2700 0 sot-23 -270b j0 b single sot-323 (3-lead sc-70) -2702 2 sot-23 -270c j2 c series pair sot-323 (3-lead sc-70) 550 [2] 15 [3] 6.7 [4] 0.65 100 [5] notes: 1. package marking code is laser marked 2. i f = 100 ma 3. i r =100 m a 4. v r =0; f=1 mhz 5. measured with karkauer method at 20 ma; guaranteed by design hsms-2700/ -2702 -270b/-270c 1 2 3 single 0, b 3 1 2 series pair 2, c
2 absolute maximum ratings test conditions : t a =25 o c, single diode. absolute maximum [1] symbol unit description hsms-2700/-2702 HSMS-270B/-270c i f ma dc forward current 350 750 i f_peak a peak surge current (1 m s pulse) 1.0 1.0 p t mw total power dissipation 250 825 p inv v peak inverse voltage 15 15 t j c junction temperature 150 150 t stg c storage temperature -65 to 150 -65 to 150 q jc c / w thermal resistance, junction to lead [2] 500 150 notes: 1. operation in excess of any one of these conditions may result in permanent damage to the device 2. t a = 25 c ; where t a is defined to be the temperature at the package pins where the conatact is made to the circuit board. linear and non-linear model spice parameters of the hsms-270x parameter unit value bv v 25 cj0 pf 6.7 eg ev 0.55 ibv a 10e-4 is a 1.4e-7 n 1.04 rs w 0.65 pb v 0.6 pt 2 m 0.5 2 nh 0.08 pf r s spice model
3 part number ordering information part number number of devices container hsms-2700 - blk hsms-2700-tr1 hsms-2700 - tr2 100 3,000 10,000 antistatic bag 7? reel 13? reel hsms-2702-blk hsms-2702-tr1 hsms-2702-tr2 100 3,000 10,000 antistatic bag 7? reel 13? reel HSMS-270B-blk HSMS-270B-tr1 HSMS-270B-tr2 100 3,000 10,000 antistatic bag 7? reel 13? reel hsms-270c-blk hsms-270c-tr1 hsms-270c-tr2 100 3,000 10,000 antistatic bag 7? reel 13? reel
page 4 figure 1. forward current vs. forward voltage at temperature for hsms-2700 and hsms-2702 figure 3. junction temperature vs. forward current as a function of heat sink temperature for the hsms-2700 and the hsms-2702 figure 5. total capacitance vs. reverse voltage figure 2. forward current vs. forward voltage at temperature for HSMS-270B and hsms-270c figure 4. junction temperature vs. forward current as a function of heat sink temperature fo the HSMS-270B and hsms-270c 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 vf - forward voltage (v) 500 .01 .1 1 10 100 if - forward current (ma) -25c 25c 75c data calculated from spice parameters. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 vf - forward voltage (v) 300 .01 .1 1 10 100 if - forward current (ma) -25c 75c 25c data calculated from spice parameters. 0 150 300 450 600 750 if - forward current (ma) 0 20 40 60 80 100 120 140 160 tj - junction temperature (c) -25c 25c 75c data calculated from spice parameters. maximum safe junction temperature 0 50 100 150 200 250 300 350 if - forward current (ma) 0 20 40 60 80 100 120 140 160 tj - junction temperature (c) -25c 25c 75c data calculated from spice parameters. maximum safe junction temperature 0 5 10 15 20 vr - reverse voltage (v) 1 2 3 4 5 6 7 ct - total capacitance (pf)
page 5 applications information schottky diode fundamentals the hsms-270x series of clipping/clamping diodes are schottky devices. a schottky device is a rectifying, metal-semiconductor contact formed between a metal and an n-doped or a p-doped semiconductor. when a metal-semiconductor junction is formed, free electrons flow across the junction from the semiconductor and fill the free- energy states in the metal. this flow of electrons creates a depletion or potential across the junction. the difference in energy levels between semiconductor and metal is called a schottky barrier. p-doped, schottky-barrier diodes excel at applications requiring ultra low turn-on voltage (such as zero-biased rf detectors). but their very low, breakdown-voltage and high series-resistance make them unsuitable for the clipping and clamping applications involving high forward currents and high reverse voltages. therefore, this discussion will focus entirely on n-doped, schottky diodes. under a forward bias (metal connected to positive in an n-doped schottky) or forward voltage, v f , there are many electrons with enough thermal energy to cross the barrier potential into the metal. once the applied bias exceeds the built-in potential of the junction, the forward current, i f , will increase rapidly as v f increases. when the schottky diode is reversed biased, the potential barrier for electrons becomes large; hence, there is a small probability that an electron will have sufficient thermal energy to cross the junction. the reverse leakage current will be in the nanoampere to microampere range, depending upon the diode type, the reverse voltage, and the temperature. in contrast to a conventional p-n junction, the current in the schottky diode is carried only by majority carriers (electrons). because no minority- carrier (hole), charge storage effects are present, schottky diodes have carrier lifetimes of less than 100 ps. this extremely fast switching time makes the schottky diode an ideal rectifier at frequencies of 50 ghz and higher. another significant difference between schottky and p-n diodes is the forward voltage drop. schottky diodes have a threshold of typically 0.3 v in comparison to that of 0.6 v in p-n junction diodes. see figure 6. figure 6. comparison, p-n junction to schottky diode through the careful manipulation of the diameter of the schottky contact and the choice of metal deposited on the n-doped silicon, the important characteristics of the diode (junction capacitance, c j ; parasitic series resistance, r s ; breakdown voltage, v br ; and forward voltage, v f ) can be optimized for specific applications. the hsms-270x series and hbat-540x series of diodes are a case in point. both diodes have similar barrier heights; and this is indicated by corresponding values of saturation current, i s . yet, different contact diameters and epitaxial-layer thickness result in very different values of c j and rs. this is seen by comparing their spice parameters in table 1. parameters hsms- 270x hsms- 540x symbol unit bv v 25 40 cj0 pf 6.7 3.0 eg ev 0.55 0.55 ibv a 10e-4 10e-4 is a 1.4e-7 1.0e-7 n 1.04 1.0 rs w 0.65 2.4 pb v 0.6 0.6 pt 2 2 m 0.5 0.5 table 1. hsms-270x and hbat-540x spice parameters u
page 6 at low values of i f (values of 1 ma or less), the forward voltages of the two diodes are nearly identical. however, as current rises above 10 ma, the lower series resistance of the hsms-270x allows for a much lower forward voltage. this gives the hsms-270x a much higher current handling capability. the tradeoff is a higher value of junction capacitance. the forward voltage and current plots illustrate the differences in these two schottky diodes, as shown in figure 7. figure 7. forward current vs. forward voltage at 25 c because the automatic, pick-and-place equipment used to assemble these products selects dice from adjacent sites on the wafer, the two diodes which go into the hsms-2702 or hsms-270c (series pair) are closely matched?without the added expense of testing and binning . current handling in clipping/clamping circuits the purpose of a clipping/clamping diode is to handle high currents, protecting delicate circuits downstream of the diode. current handling capacity is determined by two sets of characteristics, those of the chip or device itself and those of the package into which it is mounted. figure 8. two schottky diodes are used for clipping/clamping in a circuit. consider the circuit shown in figure 8, in which two schottky diodes are used to protect a circuit from noise spikes on a stream of digital data. the ability of the diodes to limit the voltage spikes is related to their ability to sink the associated current spikes. the importance of current handling capacity is shown in figure 9, where the forward voltage generated by a forward current is compared in two diodes. figure 9. comparison of two diodes the first is a conventional schottky diode of the type generally used in rf circuits, with an r s of 7.7 w . the second is a schottky diode of identical characteristics, save the r s of 1.0 w . for the conventional diode, the relatively high value of r s causes the voltage across the diode's terminals to rise as current increases. the power dissipated in the diode heats the junction, causing r s to climb, giving rise to a runaway thermal condition. in the vs 0v noisy data - spikes long cross-site cable pull-down (or pull-up) current limiting voltage limited to: vs + vd 0v - vd 0.0 0.1 0.2 0.3 0.4 0.5 0.6 vf - forward voltage (v) 300 .01 .1 1 10 100 if - forward current (ma) data calculated from spice parameters. hsms-270x hbat-540x 0.0 0.1 0.2 0.3 0.4 0.5 if - forward current (ma) 0 1 2 3 4 5 6 vf - forward voltage (v) rs = 7.7 w rs = 1.0 w v-i.atb
page 7 second diode with low r s , such heating does not take place and the voltage across the diode terminals is maintained at a low limit even at high values of current. maximum reliability is obtained in a schottky diode when the steady state junction temperature is maintained at or below 150 c, although brief excursions to higher junction temperatures can be tolerated with no significant impact upon mean- time-to-failure, mttf. in order to compute the junction temperature, equations (1) and (3) below must be simultaneously solved. where: i f = forward current i s = saturation current v f = forward voltage r s = series resistance t j = junction temperature i 0 = saturation current at 25 c n = diode ideality factor q jc = thermal resistance from junction to case (diode lead) = q package + q chip t a = ambient (diode lead) temperature equation (1) describes the forward v-i curve of a schottky diode. equation (2) provides the value for the diode's saturation current, which value is plugged into (1). equation (3) gives the value of junction temperature as a function of power dissipated in the diode and ambient (lead) temperature. the key factors in these equations are : r s , the series resistance of the diode where heat is generated under high current conditions; q chip , the chip thermal resistance of the schottky die; and q package , or the package thermal resistance. r s for the hsms-270x family of diodes is typically 0.7 w and the lowest of any schottky diode available from hewlett-packard (h-p). chip thermal resistance is typically 40 c/w; the thermal resistance of the iron-alloy-leadframe, sot-23 package is typically 460 c/w; and the thermal resistance of the copper-leadframe, sot-323 package is typically 110 c/w. the impact of package thermal resistance on the current handling capability of these diodes can be seen in figures 3 and 4. here the computed values of junction temperature vs. forward current are shown for three values of ambient temperature. the sot-323 products, with their copper leadframes, can safely handle almost twice the current of the larger sot-23 diodes. note that the term "ambient temperature" refers to the temperature of the diode's leads, not the air around the circuit board. it can be seen that the HSMS-270B and hsms-270c products in the sot-323 package will safely withstand a steady- state forward current of 550 ma when the diode's terminals are maintained at 75 c. for pulsed currents and transient current spikes of less than one microsecond in duration, the junction does not have time to reach thermal steady state. moreover, the diode junction may be taken to temperatures higher than 150 c for short time- periods without impacting device mttf. because of these factors, higher currents can be safely handled. the hsms-270x family has the highest current handling capability of any h-p diode. i f i s e 11600 v f i f r s n t 1 i s i 0 t 298 2 n e 4060 1 t 1 298 t = v i q + t j f f jc a (1) (2) (3) j j j i f i s e 11600 v f i f r s n t 1 i s i 0 t 298 2 n e 4060 1 t 1 298 t = v i q + t j f f jc a (1) (2) (3) i f i s e 11600 v f i f r s n t 1 i s i 0 t 298 2 n e 4060 1 t 1 298 t = v i q + t j f f jc a (1) (2) (3) i f i s e 11600 v f i f r s n t 1 i s i 0 t 298 2 n e 4060 1 t 1 298 t = v i q + t j f f jc a (1) (2) (3) i f i s e 11600 v f i f r s n t 1 i s i 0 t 298 2 n e 4060 1 t 1 298 t = v i q + t j f f jc a (1) (2) (3)
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