DALLAS DS2109 Data Sheet
Contents
1. 022698 7 10 DS2109 DISCONNECT MODES Table 2 a ees DS2109 ISOLATED PDI PDE Ilgus gt 32 mA FROM SCSI BUS 0 0 No Isolated 0 1 No Connected 1 0 No Connected 1 1 No Connected 0 0 Yes Isolated 0 Isolated Isolated Isolated NOTE 1 denotes pin left open circuited WIDE SCSI CONFIGURATION Figure 8 ad e TERMINATION POWER LINE 2 2 uF T L TERMPWR1I 1 7 16 PD PDI 1 4 28 GND R1 2 15 VREF J R1 2 27 R18 R2 3 14 NC R2 3 26 R17 R3 4 13 R9 R3 4 25 R16 R4 5 12 R8 R4 5 24 R15 R5 6 11 R7 R5 6 23 R14 VREF1 7 10 R6 HS GND 7 22 TCS GND 8 9 TERMPWR2 7 HS GND 8 21 HS GND DS21S07A 16 PIN SOIC 300 MIL PDO 2 20 PRE R6 10 19 R13 R7 11 18 R12 R8 12 17 R11 R9 13 16 R10 TPWR 14 15 VREF 4 7 uF 7 DS2109S 28 PIN SOIC 300 MIL i W HE 022698 8 10 DS2109 ABSOLUTE MAXIMUM RATINGS Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature 1 0V to 7 0V 0 C to 70 C 55 C to 125 C 260 C for 10 seconds This is astress rating only and functional operation o2. DS2109 DS2109S 28 PIN SOIC 300 MIL The DS2109 integrates a low drop out regulator 18 precise switched 110 ohm termination resistors and bus termination sensors into a 28 pin 300 mil SOIC package Active termination provides greater immu nity to voltage drops on the TERMPWR TERMination PoWeR line enhanced high level noise immunity intrinsic TERMPWR decoupling and very low quies cent current consumption The DS2109 contains an output port that can control the power down pin of addi tional terminators DS21S07A for Wide SCSI applica tions 022698 1 10 DS2109 REFERENCE DOCUMENTS SCSI 2 X3 131 1994 SCSI 3 Parallel Interface X3T10 855D Available from Global Engineering Documents 15 Inverness Way East Englewood CO 80112 5704 Phone 800 854 7179 303 792 2181 Fax 303 792 2192 PnP SCSI Specification PnP ISA Specification PnP BIOS Specification PnP Option ROM Specification Available from Plug and Play forum on CompuServe Go plugplay DS2109 APPLICATION ENVIRONMENT Figure 1 PERIPHERAL SUBSYSTEM Pe TERMINATOR TWO DS21S07A DS2109 AUTOMATIC EXIT POINT TERMINATOR N TS 50 POSITION HIGH DENSITY CONNECTORS HOST SCSI PROTOCOL CHIP SCSI PERIPHERAL DEVICES FUNCTIONAL DESCRIPTION The DS2109 is designed to be a single chip termination subsystem for use in PnP SCSI systems Figure 1 When embedded on a host bus adapter or mother board the DS2109 can automatically sense
3. configure the DS2109 as shown in Figure 4 The PDI Power Down Internal pin should be connected to pin 22 of the internal SCSI connector and the PDE Power Down External connected to pin 36 of the external SCSI con nector 022698 4 10 DS2109 BUS GROUND SENSING CIRCUIT Figure 3 A 3 PDI i DISABLE PDE BUS GROUND DETECT CONFIGURATION Figure 4 INTERNAL SCSI CONNECTOR 22 26 TERMPWR b 38 2 2 uF T DS2109 PDI GND 36 PDE TPWR VREF Bi 4 7 uF EXTERNAL SCSI CONNECTOR 022698 5 10 DS2109 BUS CURRENT SENSING The DS2109 has the capability to use current sensing to determine if the SCSI bus is over or under terminated Aseries 1 ohm resistor between pads R14 and TCS is inserted into the SCSI bus preferably the RST line and used to monitor the current when that line pulls low active or asserted state Based on the current mea sured the DS2109 will disconnect or connect from the SCSI bus The configuration for this automatic isolation technique is shown in Figure 6 Figure 5 shows a simplified diagram of the sensing cir cuit The voltage across the 1 ohm sense resistor is dif ferentially amplified and converted into a single ended voltage with respect to ground This is fed into a bank of comparators and measured against a reference volt age The circuit takes a measurement each time TCS is BU
4. of two automatic methods Bus Ground Sensing or Bus Current Sensing either grounded or electronically isolated from other circuitry Power Down Output Connect to DS21S07A for Wide SCSI applica tions see Figure 8 Termination Power Connect to the SCSI TERMPWR line Bypass with a 2 2 uF capacitor see Figures 4 and 6 Reference Voltage 2 85 volt reference must be decoupled with a 4 7 uF capacitor see Figures 4 and 6 Power Down External For Bus Ground Sensing Circuit connect to pin 36 of external SCSI connector see Figure 4 Termination Current Sense Used to sense current on the SCSI bus For Bus Current Sensing Circuit connect to SCSI signal line RST see Signal Termination 110 ohm termination Connect to SCSI bus signal line For Bus Current Sensing Circuit connect to SCSI controller chip see Figure 6 As with all analog circuitry the TERMPWR lines should be bypassed locally A 2 2 uF capacitor is recom mended between TPWR and ground and placed as close as possible to the DS2109 The DS2109 should be placed as close as possible to the connector to mini mize signal and power trace length thereby resulting in less input capacitance and reflections which can degrade the bus signals BUS GROUND SENSING If internal and external SCSI devices are connected to the SCSI bus the DS2109 will disconnect from the SCSI bus according to the circuit in Figure 3 To utilize this automatic disconnect method of bus sensing
5. the ter mination status of the SCSI bus and attach or isolate its resistors as needed to maintain proper bus termination External and internal active termination can be provided by the DS21S07A fee SCSI EXTERNAL CABLE INTERNAL TERMINATOR TWO DS21S07A 022698 2 10 DS2109 The DS2109 consists of 3 major functional blocks Figure 2 Voltage reference terminating resistors and isolation switches Bus current sensing circuitry Bus ground sensing circuity When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determine that the SCSI bus is prop DS2109 BLOCK DIAGRAM Figure 2 erly terminated without the DS2109 the power down buffer isolates the resistors from the SCSI bus and dis ables the power amp thereby placing the DS2109 ina low power mode the bus sensing circuitry always stays active The PDO Power Down Output pin can be con nected to the pin of a DS21S07A SCSI terminator for Wide SCSI configurations Figure 8 BUS CURRENT SENSING TCS CIRCUITRY PDI BUS GROUND 25 SENSING DISABLE DISABLE PDE PDO BUFFER BANDGAP REFERENCE 110 OHMS R14 110 OHMS R18 j j 1 j j j L I 110 OHMS R1 VREF 022698 3 10 DS2109 DETAILED PIN DESCRIPTION Table 1 PIN SYMBOL FCN DESCRIPTION 1 PDI Power Down Internal For Bus Ground Sensing Circui
6. DS2109 DALLAS SEMICONDUCTOR DS2109 Plug and Play SCSI Terminator FEATURES Fully compliant with SCSI 1 Fast SCSI and Ultra SCSI Compatible with Plug and Play SCSI Profile e Functionally compatible with DS21S07A e Provides active termination for 18 signal lines 2 tolerance on termination resistors and voltage regulator Bus termination sensing Low power down capacitance of 3 pF Onboard thermal shutdown circuitry DESCRIPTION The DS2109 is intended for one chip Plug and Play PnP SCSI termination Plug and Play SCSI requires the exit point terminator on computer motherboards or host bus adapters to automatically switch off if an exter nal device is connected to the system The DS2109 sat isfies this requirement by offering the engineer a choice of onboard current sensing circuitry or onboard ground detect circuitry If an external device is connected the DS2109 will automatically be isolated from the SCSI bus thereby maintaining proper system termination PIN ASSIGNMENT PDI 1 YY 28 J GND RI 2 27 O R18 R2 3 26 J R17 R3 4 25 R16 R4 5 24 R15 R5 6 23 1 R14 HS GND 7 22 J TCS HS GND 8 21 HS GND PDO 9 20 PDE R6 10 19 O R13 R7 11 18 R12 R8 12 17 O R1 R9 13 16 O R10 TPWR 14 15 O Vrer
7. S CURRENT SENSING CIRCUITRY Figure 5 TO SCSI CONTROLLER driven below a 0 8 volts threshold and the outputs are latched on the rising edge of TCS If Ipus is greater than 32 mA the DS2109 will be isolated from the SCSI bus It is recommended that the signal on TCS be asserted for atleast 25 msec to allow the signal and comparator out puts to settle into a known state A timing diagram of the sensing and latching operation is shown in Figure 7 It is preferred that the RST line be used for monitoring the bus termination status because RST is only asserted during power up or during a major change in bus configuration Note that R14 will have a higher input capacitance than the other lines because of the addi tional circuitry required for bus sensing The DS2109 will be isolated from the SCSI bus as shown in Table 2 FROM SCSI BUS RST R14 TCS 1 OHM ibus WNW WN 110 OHM tes T REF V DECODE AND LATCH 022698 6 10 DS2109 BUS CURRENT SENSE CONFIGURATION Figure 6 INTERNAL SCSI CONNECTOR 26 40 TERMPWR 38 DS2109 TPWR 2 2 uF Hy EXTERNAL SCSI CONTROLLER VREF TCS 2 4 7 uF R14 GND ii RST SCSI CONTROLLER BUS CURRENT SENSE TIMING DIAGRAM Figure 7 25 us min TCS COMPARATORS Fa Z x LATCH f
8. f the device at these or any other conditions above those indicated in the operation sections of this specification is not implied Exposure to absolute maximum rating conditions for extended periods of time may affect reliability RECOMMENDED OPERATING CONDITIONS 0 C to 70 C PARAMETER TERMPWR Voltage Logic 1 Logic 0 SYMBOL 0 3 0 8 V 1 DC CHARACTERISTICS PARAMETER SYMBOL TERMPWR Current Itp Itp Power Down Current Termination Resistance Die Thermal Shutdown Power Down Termination Capacitance Input Leakage High Input Leakage Low Output Current Bus Current Sense Trip Point REGULATOR CHARACTERISTICS PARAMETER Output Voltage Drop Out Voltage Line Regulation Load Regulation Sink Current SYMBOL VREF VpROP LIREG LOREG Current Limit I 700 mA 022698 9 10 DS2109 NOTES 1 PDI PDE TCS 4 00V lt TERMPWR lt 5 25V 0 0V lt signal lines lt 3 0V All signal lines 0 0V 2 3 4 5 All signal lines open 6 Power down enabled 7 Guaranteed by design not production tested 8 C44 slightly higher capacitance due to sensing circuitry 9 Excluding PDI PDE pins 10 PDO output pin 11 IBcst gt 32 mA disable termination 12 Excluding PDE PDI R14 and TCS pins 28 PIN SOIC 300 MIL ape TF Lf fo 7 I Pid i n d A2 tious U A F i a ae The chamfer on the body is optiona
9. l Ifitis not present a termi nal 1 identifier must be positioned so that 1 2 or more ofits area is contained in the hatched zone 28 PIN CIN MM LIN MM MIN 0 094 2 39 0 004 0 102 0 089 2 26 0 013 0 33 0 009 0 229 0 698 17 73 MAX 0 105 2 67 0 012 0 30 0 095 2 41 0 020 0 51 0 013 0 33 0 712 18 08 0 050 BSC 1 27 BSC 0 290 7 37 0 398 10 11 0 016 0 40 0 300 7 62 0 416 10 57 0 040 1 02 022698 10 10
10. t connect to pin 22 of internal SCSI connector see Figure 4 2 6 R1 R13 T Signal Termination 110 ohm termination Connect to SCSI bus signal 10 13 R15 18 lines For Bus Current Sensing Circuit connect to data parity and control 16 19 lines except SCSI RST line see Figure 6 24 27 7 8 21 HS GND P Heat Sink Ground Internally connected to the mounting pad Should be Figure 6 ACTIVE TERMINATION The voltage regulator circuitry bandgap reference and class AB power amplifier produces a precise laser trimmed 2 85 volt level and is capable of sourcing 24 mA into each of the terminating resistors when the signal line is low active When the external driver for a given signal line turns off the active terminator will pull that signal line to 2 85 volts quiescent state When used with an active negation driver the power amp can sink 22 mA per line while keeping the voltage reference in regulation the terminating resistors maintain their 110Q value over the entire voltage range To maintain the spe cified regulation a 4 7 uF capacitor is required between the Vrer pin and ground A high frequency cap 0 1 uF ceramic recommended can also be placed on the VREF pinin applications that use fast rise fall time drivers The power down capacitance on terminating resistors R1 R13 and R15 R18 is lt 4 pF R14 is slightly higher due to the bus current sensing circuitry The DS2109 can be removed from the SCSI bus by using either
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DALLAS DS2109 Data Sheet