1 of 5 rev: 022106 general description fast scsi and ultra scsi require the use of active terminations at both ends of every cable segment in a scsi system with single-ended drivers and receivers. the ds21s07a scsi terminator, which is fully compliant with these standards, enables the designer to gain the benefits of active termination: greater immunity to voltage drops on the termpwr (termination power) line , enhanced high-level noise immunity, intrinsic termpwr decoupling, and very low quiescent current consumption. the ds21s07a integrates a regulator and nine precise switched 110 ? termination resistors into a monolithic ic. the ds21s07a can be electrically isolated from the scsi bus without physical removal from the scsi device. features fully compliant with scsi-1, fast scsi, and ultra scsi backward compatible to the ds2107 and ds2107a provides active termination for nine signal lines laser-trimmed 110 ? termination resistors have 2% tolerance low drop-out voltage regulator power-down mode isolates termination resistors from the bus scsi bus hot plug compatible fully supports actively negated scsi signals on-board thermal shutdown circuitry 16-pin plastic so (ds21s07as) and 20-pin plastic tssop (thin shrink small outline package) (ds21s07ae) pin configurations actual footprint size ordering information part voltage (v) pin- package top mark ds21s07as 5 16 so ds21t07s ds21s07as+ 5 16 so ds21t07s ds21s07as/t&r 5 16 so ds21t07s ds21s07as+t&r 5 16 so ds21t07s ds21s07ae 5 20 tssop ds21t07e ds21s07ae/t&r 5 20 tssop ds21t07e + denotes lead-free package. the top mark includes a ?+" on lead-free packages. note: all devices are specified ov er the 0c to +70c operating temperature range. ds21s07a scsi terminato r www.maxim-ic.com 0.41" 0.41" 0.26" 0.27" ds21s07as ds21s07ae
ds21s087a 2 of 8 functional description the ds21s07a consists of a bandgap reference, bu ffer amplifier, and nine termination resistors (figure 1). the bandgap reference circ uit produces a precise 2.55v level th at is fed to a buffer amplifier. the buffer produces a 2.85v level and can source at l east 24ma into each of the termination resistors when the signal line is low (active). when the driver fo r a given signal line turns off, the terminator pulls the signal line to 2.85v (quiescent st ate). to handle activel y negated scsi signals, the buffer can sink at least 200ma, and vref will move less than 60mv. wh en all lines settle in the quiescent state, the regulator consumes about 2.5ma. when the ds21s 07a is put into power-down mode by bringing pd low, the power-down circuitry turns off the transist ors on each signal line. this isolates the ds21s07a from the signal lines and effectively remove s it from the circuit. the power-down pin ( pd ) has an internal 50k ? pullup resistor. to place the ds21s07a into an active state, the pd pin should be left open circuited. when installed on disk drives or raid system components, the ds21s07a will not affect the scsi bus during a hot plug operation. to ensure proper operation, both the termpwr1 and ter mpwr2 pins must be connected to the scsi bus termpwr line and both the vref1 and vref2 pi ns must be tied together externally. each ds21s07a requires a 4.7 f capacitor connected between the vref pins and ground. figure 2 details a typical scsi bus configuration. in an 8-bit-wide scsi bus arrangeme nt (?a? cable), two ds21s07a?s would be needed at each end of the scsi cable to terminate the 18 active signal lines. in a 16-bit-wide scsi bus arrangement (?p? cable), three ds21s07a?s w ould be needed at each end of the scsi cable to terminate the 27 active signal lines. figure 1. ds21s087a block diagram
ds21s087a 3 of 8 figure 2. typical different ial scsi bus configuration note 1: c1 = 4.7 f tantalum capacitor; c2 = 2.2 note 2: if the ds21s07a is to be embedded into a peripheral that will act as a target on a scsi bus, it is recommended that te rmpwr be derived from the scsi cable, not generated locally. in this configurati on, if a power failure occurs in the peripheral, it will not affect the bus. note 3: a high-frequency bypass capacitor (0.1 f recommended) can be added in parallel to c1 for applications using fast rise/fall time drivers.
ds21s087a 4 of 8 table 1. pin description pin tssop so name function 1 1 termpwr1 termination power 1. should be connected to the scsi termpwr line. must be decoupled with either a 2.2 f capacitor or 4.7 f capacitor. see figure 2. 2, 8, 12, 18 ? hs-gnd heat sink ground. internally connected to the mounting pad. should be either grounded or elec trically isolated from other circuitry. 3?7, 13?16 2?6, 10?13 r1?r9 signal termination 1?9. 110 ? termination. 9 7 vref1 reference voltage 1. must be externally connected directly to the vref2 pin. must be decoupled with a 4.7 f capacitor as shown in figure 2. 10 8 gnd ground. 0v, signal ground. 11 9 termpwr2 termination power 2. should be connected to the scsi termpwr line. must be decoupled with either a 2.2 f capacitor or 4.7 f capacitor. see figure 2. 17 14 nc no connection. do not connect any signal to this pin. 19 15 vref2 reference voltage 2. must be externally connected directly to the vref1 pin. must be decoupled with a 4.7 f capacitor as shown in figure 2. 20 16 pd active-low power-down. when tied low, the ds21s07a enters a power-down mode. contains an internal 50k ? pullup resistor. strap low to deactivate the ds21s07a; leave open circuited to activate the ds21s07a
ds21s087a 5 of 8 absolute maxi mum ratings voltage range on any pin relative to ground?????????????????..-1.0v to +7.0v operating temperature range????????????????????????..0 c to +70 c storage temperature range????????????????????????-55 c to +125 c soldering temperature????????????????.see ip c/jedec j-std-020 specification this is a stress rating only and functional ope ration of the device at these or any ot her conditions above those indicated in t he operation sections of this specification is not implied. exposure to absolute maximum ra ting conditions for extended periods of time may affect device reliability. recommended operating conditions (t a = 0c to +70c) parameter sym min typ max units notes termpwr voltage v tp 4.00 5.50 v pd active v pda -0.3 +0.8 v pd inactive v pdi 2.0 v tp + 0.3 v dc characteristics (t a = 0c to +70c) parameter symbol min typ max units notes 250 ma 1, 3 termpwr current i tp 2.5 5 ma 1, 4 power-down current i pd 100 150 a 1, 2, 5 termination resistance r term 108 110 112 ? 1, 2 die thermal shutdown t sd 150 oc 1, 6 power-down termination capacitance c pd 3.0 5.0 pf 1, 2, 5, 6 input leakage high i ih -1.0 a 1, 8 input leakage low i il 1.0 a 1, 7 regulator characteristics (t a = 0c to +70c) parameter symbol min typ max units notes output voltage v ref 2.79 2.85 2.93 v 1, 2 drop-out voltage v drop 0.50 0.75 v 3, 6 line regulation li reg 1.0 2.0 % 1, 4 load regulation lo reg 1.3 3.0 % 1, 3 current limit i lim 350 ma 1 sink current i sink 200 ma 1
ds21s087a 6 of 8 notes: 1) 4.00v < termpwr < 5.50v. 2) 0.0v < signal lines < termpwr. 3) all signal lines = 0v. 4) all signal lines open. 5) pd = 0v. 6) guaranteed by design; not production tested. 7) r1 to r9 only. 8) r1 to r9 and pd .
ds21s087a 7 of 8 package information (the package drawing(s) in this data sheet may not reflect t he most current specifications . for the latest package outline information, go to www.maxim-ic.com/dallaspackinfo .)
ds21s087a 8 of 8 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 specification s 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 produ cts, inc. the dallas logo is a registered trademark of dallas semiconductor corporation. package information (continued) (the package drawing(s) in this data sheet may not reflect t he most current specifications . for the latest package outline information, go to www.maxim-ic.com/dallaspackinfo .)
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