1 of 9 rev: 010406 features fully compliant with scsi spi-2, spi-3, spi-4, ultra160, and ultra320 provides multimode low-voltage differential/single-ended (lvd/se) termination for nine signal line pairs autoselection of lvd or se termination 5% tolerance on se and lvd termination resistance low power-down capacitance of 3pf on-board thermal shutdown circuitry scsi bus hot plug compatible fully supports actively negated se scsi signals pin configuration ordering information part voltage (v) temp range pin-package top mark* DS2119ME 5 0 c to +70 c 28 tssop (0.173") ds2119m DS2119ME+ 5 0 c to +70 c 28 tssop (0.173") ds2119m DS2119ME/t&r 5 0 c to +70 c 28 tssop (0.173")/tape and reel ds2119m DS2119ME+t&r 5 0 c to +70 c 28 tssop (0.173")/tape and reel ds2119m + denotes a lead-free/ro hs-compliant package. * the top mark includes a "+" on lead-free packages. detailed description the ds2119m ultra3 lvd/se scsi terminator is both a low-voltage differential (lvd) and single- ended (se) terminator. the multimode operation enab les the designer to implement lvd in current products while allowing the end-user se-backward compatibility with legacy devices. if the device is connected in an lvd-only bus, the ds2119m will use lvd termination. if any se devices are connected to the bus, the ds2119m will use se termination. this is accomplished automatically inside the part by sensing the voltage on the scsi bus diffsens line. for the lvd termination, the ds2119m integrates two current sources with nine precision resistor strings. for the se termination, one regulator and nine precision 110 ? resistors are used. three ds2119m terminators are needed for a wide scsi bus. ds2119m ultra3 lvd/se scsi terminato r www.maxim-ic.com 1 23 4 56 7 8 9 1011 12 24 27 26 25 23 22 21 20 19 18 17 16 r9n r9p r8n hs gnd r7n r7p r6n r6p diff_cap diffsense mstr/slv r8p rin r2p r2n r3p r4p r4n r5p r5n iso gnd hs gnd tssop 13 14 28 15 vref rip tpwrtpwr r3n ds2119m downloaded from: http:///
ds2119m 2 of 9 reference documents small computer systems interface (scs i-3) scsi parallel interface (s pi) project: 0855-m, 1995 small computer systems interface (s csi-3) scsi parallel interfac e 2 (spi-2) project: 1142-m, 1998 small computer systems interface (s csi-3) scsi parallel interfac e 3 (spi-3) project: 1302-d, 1999 small computer systems interface (s csi-3) scsi parallel interfac e 4 (spi-4) project: 1365-d, 200x available from: american national standards institut e (ansi) phone: (212) 642-4900 global engineering documents 15 inverness way east; englewood, co 80112 phone: (800) 854-7179 functional description the ds2119 combines lvd and se termina tion with diffsens sourcing and detection. a bandgap reference is fed into two amplifiers, which creates a 1.25v reference voltage and a 2.85v reference voltage. the control logic determines wh ich of these references will be applied to the termination resistors. if the scsi bus is in lvd mode, then the 1.25v reference will be used. if the scsi bus is in se mode, then the 2.85v reference will be used. that same control logic will switch in/out parallel resistors to change the total termination re sistance accordingly. finally, in se mode, the rp pins will be switched to ground. the diffsense circuitry decodes trinary logic. ther e will be one of three voltages on the scsi control line called diffsens. two comparators and a nand gate determine if the voltage is below 0.6v, above 2.15v, or in between. that indicates the mode of the bus to be se, hvd, or lvd, respectively. the ds2119ms diff_cap pin monitors the diffsens line to determine the proper operating mode of the device. the diffsense pin can also drive the scsi diffsens line (when mstr/slv = 1) to determine the scsi bus-operating mode. the ds2119m switches to the termin ation mode that is appropriate for the bus based on the value of the diffsens voltage. these modes are: lvd mode: lvd termination is provided by a precision laser-trimmed resistor string with two current sources. this c onfiguration yields a 105 ? differential and 150 ? common-mode impedance. a fail-safe bias of 112mv is maintain ed when no drivers are connected to the scsi bus. se mode: when the external driver for a given signal lin e turns off, the active terminator will pull that signal line to 2.85v (quies cent state). when used with an active negation driver, the power amp can sink 22ma per line and the referen ce voltage will move less than 100mv. the terminating resistors maintain their 110 ? value. hvd isolation mode: the ds2119m identifies that there is an hvd (high-voltage differential) device on the scsi bus and isolates the termination pins from the bus. when iso = 1, the termination pins are isolated from the scsi bus, v ref remains active. during thermal shutdown, the termination pins are is olated from the scsi bus and v ref becomes high impedance. the diffsense driver is shut down duri ng either of these two events. to ensure proper operation, the tpwr pin should be connected to the scsi bus termpwr line. as with all analog circuitry, the termpwr and v dd lines should be bypassed locally. a 2.2 f capacitor and a 0.01 f high-frequency capacitor are recommended betw een tpwr and ground and placed as close downloaded from: http:///
ds2119m 3 of 9 as possible to the ds2119m. the ds2119m should be pl aced as close as possible to the scsi connector to minimize signal and power-trace length, thereby resulting in less input capacitance and reflections, which can degrade the bus signals. to maintain the specified regulation, a 4.7 f capacitor is required between the v ref pin (vref) and ground of each ds2119m. a high frequency cap (0.1 f ceramic recommended) can also be placed on the v ref pin in applications that use fast rise/fall time dr ivers. a typical scsi bus configuration is shown in figure 2. diffsens noise filtering: the ds2119m incorporates a digital filter to remove high-frequency transients on the diffsens c ontrol line, thereby eliminatin g erroneous switching between modes. this filter eliminates the need for the external capacitor and resistor, which heretofore performed this function. notes: 1) diffsens. refers to the scsi bus signal. 2) diffsense. refers to the dallas semiconductor pin name and internal circuitry relating the diffsens driver. downloaded from: http:///
ds2119m 4 of 9 figure 1. ds2119m block diagram downloaded from: http:///
ds2119m 5 of 9 figure 2. scsi bus configuration downloaded from: http:///
ds2119m 6 of 9 pin description pin name function 1 vref reference voltage. 2.85v reference in se mo de and 1.25v reference in lvd mode; must be decoupled with a 4.7f cap. 2C5, 7C12, 18C21, 23C26 rxp, rxn signal termination. connect to scsi bus signal lines. 6, 22 hs gnd heat sink ground. internally connected to the mounting pad. should be grounded. 13 iso isolation. when pulled high, the ds2119m is olates its bus pins (rxp, rxn) from the scsi bus. 14 gnd ground. signal ground; 0v. 15 mstr/slv master/slave. mode-select for the noncontrolling terminator. when pulled high, mstr enables the diffsense driver. 16 diffsense diffsense. output to drive the scsi bus diffsens line. 17 diff_cap diffsense capacitor. connect a 0.1f capacitor for diffsense filter. input to detect the type of device (differential or single-ended) on the scsi bus. 27, 28 tpwr termination power. connect to the scsi termpwr line and decouple with a 2.2f capacitor. recommended operating conditions parameter symbol min typ max units notes se mode v tpwr(se) 4.0 5.5 v termpower voltage lvd mode v tpwr(lvd) 2.7 5.5 v logic 0 v il -0.3 +0.8 v logic 1 v ih 2.0 v tpwr + 0.3 v operating temperature v amb 0 70 c downloaded from: http:///
ds2119m 7 of 9 single-ended characteristics parameter symbol min typ max units notes se termination resistance r se 104.5 110 115.5 ? 1 se voltage reference v ref 2.7 2.85 3.0 v se output current l ose 25.4 ma 2 output capacitance c out 3 pf 3 low-voltage differenti al characteristics parameter symbol min typ max units notes differential mode termination resistance r dm 100 110 ? common mode termination resistance r cm 110 190 ? differential mode bias v dm 100 125 mv 4 common mode bias v cm 1.125 1.375 v dc characteristics parameter symbol min typ max units notes termpower current i tpmr 12 ma 4 input leakage high i ih -1.0 a input leakage low i il 1.0 a output current high i oh -1.0 ma 5, 7 output current low i ol 4.0 ma 6, 7 diffsens se operating range v seor -0.3 0.5 v diffsens lvd operating range v lvdor 0.7 1.9 v diffsens hvd operating range v hvdor 2.4 v tpwr + 0.3 v diffsense driver output voltage v dso 1.2 1.4 v 8, 9 diffsense driver source current i dsh 5 15 ma 8, 10, 12 diffsense driver sink current i dsl 20 200 a 8, 11 thermal shutdown 150 oc 3 downloaded from: http:///
ds2119m 8 of 9 regulator characteristics (t a = 0c to +70c) parameter symbol min typ max units notes line regulation li reg 1.0 2.5 % load regulation lo reg 1.3 3.5 % current limit i lim 550 ma sink current i sink 200 ma notes: 1) v line = 0v to 3v. 2) v line = 0.2v. 3) guaranteed by design. 4) all lines open. 5) v out = 2.4v. 6) v out = 0.4v. 7) se/lvd/hvd pins only. 8) mstr/slv = 1. 9) i ds = 0ma to 5ma. 10) v dso = 0v. 11) v dso = 2.75v. 12) tpwr = 5.5v. downloaded from: http:///
ds2119m 9 of 9 maxim/dallas semiconductor cannot assume res ponsibility for use of any circuitry other than circuitry entirely embodied in a ma xim/dallas semiconductor product. no circuit patent licenses are implied. maxi m/dallas semiconductor reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2006 maxim integrated products ? printed usa the maxim logo is a registered trademark of maxim integrated products, inc. the dallas logo is a registered trademark of dallas semiconductor corporation. package information (the package drawing(s) in this data s heet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/dallaspackinfo .) downloaded from: http:///
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