august 2000 ML6518 18 line hot-insertable active scsi terminator general description nclamp = negative clamp circuit design patent pending. features n fully monolithic ic solution providing active termination for 18 lines of the scsi bus n provides onboard support for hot-insertability on the scsi bus n low dropout voltage (1v) linear regulator, trimmed for accurate termination current n low disconnect capacitance (typically < 5pf) n logic pin with active pull-up to disconnect terminator from the scsi bus n current sinking capability in excess of 8.3ma per line to handle active negation driver overshoots above 2.85v n negative clamping on all lines to handle signal assertion transients n regulator can source 400ma and sink 150ma while maintaining regulation n current limit and thermal shutdown protection the ML6518 bicmos 18 line scsi terminator provides active termination in scsi systems using single-ended drivers and receivers. active scsi termination helps to effectively control analog transmission line effects such as ringing, noise, crosstalk, and ground bounce. in addition, the ML6518 provides support for hot insertability on the scsi bus. the ML6518 provides a v-i characteristic optimized to minimize transmission line effects during both signal negation and assertion using a mosfet-based architecture. the desired v-i characteristic is achieved by trimming one resistor in the control block. internal clamping controls signal assertion transients and provides current sink capability to handle active negation driver overshoots above 2.85v. it provides a 2.85v reference through an internal low dropout (1v) linear regulator. the ML6518 also provides a disconnect function which effectively removes the terminator from the scsi bus. the disconnect mode capacitance is typically less than 5pf per line. current limiting and thermal shutdown protection are also included. block diagram termpwr linear regulator 1v dropout 2.85v discnkt control block v ref r trim mosfets with i max = 24ma nclamp 18 termination lines . . . . . . . . . nclamp nclamp . . . . . . gnd l2 l18 l1 v ref 2.85v rev. 1.0 10/25/2000
ML6518 2 rev. 1.0 10/25/2000 pin configurations ML6518 32-pin tqfp (h32-7) ML6518 28-pin soic (s28) seating plane 0.291 - 0.301 (7.39 - 7.65) pin 1 id 0.398 - 0.412 (10.11 - 10.47) 0.699 - 0.713 (17.75 - 18.11) 0.012 - 0.020 (0.30 - 0.51) 0.050 bsc (1.27 bsc) 0.022 - 0.042 (0.56 - 1.07) 0.095 - 0.107 (2.41 - 2.72) 0.005 - 0.013 (0.13 - 0.33) 0.090 - 0.094 (2.28 - 2.39) 28 0.009 - 0.013 (0.22 - 0.33) 0o - 8o 1 0.024 - 0.034 (0.61 - 0.86) (4 places) package: s28 28-pin soic clk in gain dgnd agnd vout vref vcc xxx 1 2 3 4 5 6 7 8 9 10111213141516 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 clk in gain dgnd agnd vout vref vcc xxx clk in gain dgnd agnd vout vref vcc xxx clk in gain dgnd agnd vout vref vcc xxx top view ML6518 32-pin tqfp (h32-7)
ML6518 rev. 1.0 10/25/2000 3 pin description tqfp soic pin# pin# name function 1 25 l1 signal termination for scsi bus line 1 2 26 l2 signal termination for scsi bus line 2 3 27 l3 signal termination for scsi bus line 3 4 28 l4 signal termination for scsi bus line 4 5 1 l5 signal termination for scsi bus line 5 6 2 l6 signal termination for scsi bus line 6 7 3 l7 signal termination for scsi bus line 7 8 4 l8 signal termination for scsi bus line 8 9 6 l9 signal termination for scsi bus line 9 11C14, 7, 22, gnd ground 27C30 23 15 8 discnkt terminator disconnect. logic input to disconnect the terminator from the bus when the scsi device no longer needs termination. discnkt has a 200ky internal pull-up resistor connected to termpwr for use with a mechanical switch tqfp soic pin# pin# name function 16 11 l10 signal termination for scsi bus line 10 17 12 l11 signal termination for scsi bus line 11 18 13 l12 signal termination for scsi bus line 12 19 14 l13 signal termination for scsi bus line 13 20 15 l14 signal termination for scsi bus line 14 21 16 l15 signal termination for scsi bus line 15 22 17 l16 signal termination for scsi bus line 16 23 18 l17 signal termination for scsi bus line 17 24 19 l18 signal termination for scsi bus line 18 25, 26 20, 21 termpwr po wer should be connected to the scsi termpwr line. a 22f tantalum bypass capacitor is recommended as shown in the application diagram 31, 32 24 v ref 2.85v v ref output. external decoupling with a 10f tantalum in parallel with a 0.1f ceramic capacitor is recommended as shown in the application diagram
ML6518 4 rev. 1.0 10/25/2000 absolute maximum ratings absolute maximum ratings are those values beyond which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functional device operation is not implied. signal line voltage ...... gnd C 0.3v to termpwr + 0.3v regulator output current ................................... 500ma termpwr voltage .......................................... C0.3 to 7v junction temperature ............................................. 150c storage temperature range ...................... C65c to 150c lead temperature (soldering 10 sec) .................... +260c thermal resistance ( q ja ) soic package .................................................. 75c/w tqfp package .................................................. 65c/w operating conditions temperature range ........................................ 0c to 70c termpwr voltage range ........................... 4.0v to 5.25v electrical characteristics unless otherwise specified, termpwr = 4v to 5.25v, t a = operating temperature range (note 1) parameter conditions min typ max units supply termpwr supply current l1-l18 open, discnkt open 5 7 ma l1-l18 = 0.2v, discnkt open 450 500 ma disconnect mode current discnkt = 0v 75 100 a discnkt discnkt discnkt discnkt discnkt input low voltage 1.0 v input high voltage termpwr v C1.0 output output high voltage each line measured with other 17 2.8 2.85 2.9 v lines high output current (normal mode) v out = 0.2v, each line measured 20 24 ma with other 17 lines high hot insertion peak current termpwr = 0v, v ref = 0v, 1 2 a any or all signal lines = 2.85v output clamp voltage i out = C30ma C150 150 mv sinking current (per line) v out = 3.3v 10 12 ma output capacitance discnkt = 0v, 2v p-p 100khz square 4 5 pf (micro linear method) wave biased at 1v applied to the output output capacitance discnkt = 0v, 0.4v p-p 1mhz square 6 7 pf (x3t9.2/855d method) wave biased at 0.5v applied to the output regulator output voltage sourcing 0-400ma 2.8 2.85 2.9 v sinking 0-150ma 2.8 2.85 2.9 v sinking current v line = 3.5 240 300 ma short circuit current v ref = 0v 300 ma v ref = 5v 600 ma dropout voltage l1Cl18 = 0.2v 1.0 1.2 v thermal shutdown 170 c note 1: limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
ML6518 rev. 1.0 10/25/2000 5 functional description scsi terminators are used to decrease the transmission line effects of scsi cable. termination must be provided at the beginning and end of the scsi bus to ensure that data errors due to reflections on the bus are eliminated. with the increasing use of higher data rates and cable lengths in scsi subsystems, active termination has become necessary. active termination also minimizes power dissipation and can be activated or deactivated under software control, thus eliminating the need for end user intervention. the v-i characteristics of popular scsi termination schemes are shown in figure 1. theoretically, the desired v-i characteristics are the boulay type for signal assertion (high to low) and the ideal type for signal negation (low to high). the ML6518 with its mosfet- based nonlinear termination element provides the most optimum v-i characteristics for both signal assertion and negation. the ML6518 provides active termination for 18 signal lines, thus accommodating basic scsi which requires 18 lines to be terminated. when used with the ml6599, wide scsi, which requires 27, 36 or 45 lines to be terminated, can also be accommodated. the ML6518 integrates an accurate voltage reference (1v dropout voltage) and 18 mosfet-based termination lines. a single internal resistor is trimmed to tune the v-i characteristic of the mosfets. the voltage reference circuit produces a precise 2.85v level and is capable of sourcing 24ma into each of the nine terminating lines when low (active). when the signal line is negated (driver turns off), the terminator pulls the signal line back to 2.85v. the regulator will source 400ma and sink 150ma while maintaining regulation of 2.85v. the ML6518 scsi terminator provides an active low control signal ( discnkt ) which has an internal 200ky pull-up resistor. the discnkt input isolates the ML6518 from the signal lines and effectively removes the terminator from the scsi bus with a disconnect mode current of less than 100a when pulled low. in addition, the ML6518 provides for negative clamping of signal transients and also supports current sink capability in excess of 8.3ma per signal line to handle active negation driver overshoot above 2.85v, a common occurrence with scsi transceivers. disconnect mode capacitance is a very critical parameter in scsi systems. the ML6518 provides a capacitance contribution of only 5pf. hot insertability hot insertion of a scsi device refers to the act of plugging a scsi device which is initially unpowered into a powered scsi bus. the scsi device subsequently draws power from the termpwr line during its startup routine and thereafter. hot removal refers to the act of removing a powered scsi device from a powered scsi bus. a device which performs both tasks with no physical damage to itself or other devices on the bus, nor which alters the existing state of the bus by drawing excessive currents, is termed hot-swappable. the ML6518 hot-insertable scsi terminator typically draws 1a from any given output line (l1Cl18) during a hot insertion/removal procedure, thereby protecting itself and preserving the state of the bus. the low insertion current is achieved by effectively shorting the gate to drain of the output pmos device until the 2.85v reference (v ref ) has powered up. a second pmos in series with a schottky diode is used as the shorting bypass device. after v ref reaches a sufficient level, the bypass device is turned off and the part operates normally. figure 1. v-1 characteristics of various scsi termination schemes ideal ML6518 boulay 220/330 2.85v 2.7v 2.5v 0.2v terminator (source) driver (sink) terminator (sink) driver (source) 20ma 40ma 24ma 48ma 12ma 24ma 7ma 14ma 8.5ma 17ma 3.7v 3.6v 3.3v i v
ML6518 6 rev. 1.0 10/25/2000 figure 2. application diagram showing typical scsi bus configuration with the ML6518 as outlined in annex g of the ansi scsi-3 parallel interface specification (x3t9.2/855d), the scsi bus termination shall be external to the device being inserted or removed. in other words, any terminator connected to a device being hot inserted/removed should be inactive (accomplished by grounding the discnkt pin in the case of the ML6518). if the terminator being inserted/removed were in the active state, at some point in time the bus would be terminated by either 1 or 3 terminators. in either case, data integrity on the bus will be compromised. figure 2 gives an application diagram showing a typical scsi bus configuration. to ensure proper operation, the termpwr pin must be connected to the scsi termpower line. each ML6518 requires parallel 0.1f and 10f capacitors connected between the v ref and gnd pins and the termpower line needs a 10f bypass capacitor at one node in the system. in an 8-bit wide scsi bus arrangement (a cable), a single ML6518 would be needed at each end of the scsi cable in order to terminate the 18 active signal lines. 16-bit wide scsi would use one ML6518 and one ml6599, while 32-bit wide scsi bus would require two ML6518s and one ml6599. in a typical scsi subsystem, the open collector driver in the scsi transceiver pulls low when asserted. the termination resistance serves as the pull-up when negated. figure 2 also shows a typical cable response to a pulse. the receiving end of the cable will exhibit a single time delay. when negated, the initial step will reach an intermediate level (v step ). with higher scsi data rates, sampling could occur during this step portion. in order to get the most noise margin, the step needs to be as high as possible to prevent false triggering. for this reason the regulator voltage and the resistor defining the mosfet characteristic are trimmed to ensure that the i o is as close as possible to the scsi maximum current specification. v step is defined as: v step = v ol + (i o z o ) where v ol is the driver output low voltage, i o is the current from the receiving terminator, and z o is the characteristic impedance of the cable. this is a very important characteristic that the terminator helps to overcome by increasing the noise margin and boosting the step as high as possible. termpwr line ML6518 termpwr v ref gnd l18 l2 l1 discnkt 0.1f 10f termpwr v ref gnd l18 l1 l2 ML6518 discnkt scsi xcvr scsi xcvr scsi xcvr v reg v step v reg t d t d line asserted line negated 10f 0.1f 10f . . . . . . . . . . . . v ol scsi cable
ML6518 rev. 1.0 10/25/2000 7 physical dimensions inches (millimeters) 0.048 max (1.20 max) seating plane 0.354 bsc (9.00 bsc) 0.276 bsc (7.00 bsc) 1 0.276 bsc (7.00 bsc) 0.354 bsc (9.00 bsc) 9 25 17 0.032 bsc (0.8 bsc) pin 1 id 0.012 - 0.018 (0.29 - 0.45) 0.037 - 0.041 (0.95 - 1.05) 0.018 - 0.030 (0.45 - 0.75) 0.003 - 0.008 (0.09 - 0.20) 0o - 8o package: h32-7 32-pin (7 x 7 x 1mm) tqfp seating plane 0.291 - 0.301 (7.39 - 7.65) pin 1 id 0.398 - 0.412 (10.11 - 10.47) 0.699 - 0.713 (17.75 - 18.11) 0.012 - 0.020 (0.30 - 0.51) 0.050 bsc (1.27 bsc) 0.022 - 0.042 (0.56 - 1.07) 0.095 - 0.107 (2.41 - 2.72) 0.005 - 0.013 (0.13 - 0.33) 0.090 - 0.094 (2.28 - 2.39) 28 0.009 - 0.013 (0.22 - 0.33) 0o - 8o 1 0.024 - 0.034 (0.61 - 0.86) (4 places) package: s28 28-pin soic
ML6518 8 rev. 1.0 10/25/2000 ordering information part number temperature range package ML6518ch 0c to 70c 32-pin tqfp (h32-7) ML6518cs 0c to 70c 28-pin soic (s28) life support policy fairchild? products are not authorized for use as critical components in life support devices or systems without the express written approval of the president of fairchild semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. a critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com ?2000 fairchild semiconductor corporation disclaimer fairchild semiconductor reserves the right to make changes without further notice to any products herein to improve reliability, function or design. fairchild does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights, nor the rights of others.
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