DS2109 MAXIM | Alldatasheet

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Technical content

Plug and Play SCSI Terminator DS2109 022698 1/10

FEATURES

  • Fully compliant with SCSI–1, Fast SCSI and Ultra SCSI
  • Compatible with Plug and Play SCSI Profile
  • Functionally compatible with DS21S07A
  • 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 PIN ASSIGNMENT GND R18 R17 R16 R15 R14 TCS HS–GND PDE R13 R12 R11 R10 V REF PDI HS–GND HS–GND PDO TPWR DS2109, DS2109S 28–PIN SOIC (300 MIL)

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. 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.

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). 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 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. DS2109 APPLICATION ENVIRONMENT Figure 1 PERIPHERAL SUBSYSTEM EXTERNAL TERMINATOR (TWO DS21S07A)DS2109 AUTOMATIC EXIT–POINT TERMINATOR HOST SCSI PROTOCOL CHIP SCSI PERIPHERAL DEVICES INTERNAL TERMINATOR (TWO DS21S07A) SCSI INTERNAL CABLES SCSI EXTERNAL CABLE 50–POSITION HIGH DENSITY CONNECTORS

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- 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 in a 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. DS2109 BLOCK DIAGRAM Figure 2 VREF TCS R14 R18

110 OHMS

110 OHMSBANDGAP

BUS GROUND SENSING CIRCUIT Figure 3 PDE PDI DISABLE BUS GROUND DETECT CONFIGURATION Figure 4 VREF INTERNAL SCSI CONNECTOR EXTERNAL SCSI CONNECTOR 22 26 TERMPWR 2.2 µF 4.7 µF DS2109 PDI TPWR GND PDE

The DS2109 has the capability to use current sensing to determine if the SCSI bus is over– or under–terminated. A series 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 driven below a 0.8 volts threshold and the outputs are latched on the rising edge of TCS. If IBUS 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 at least 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. BUS CURRENT SENSING CIRCUITRY Figure 5 REF DECODE AND LATCH TCSR14

1 OHM

110 OHM

TO SCSI CONTROLLER FROM SCSI BUS (–RST)

BUS CURRENT SENSE CONFIGURATION Figure 6 VREF INTERNAL SCSI CONNECTOR 26 40 –RST –RST SCSI CONTROLLER EXTERNAL SCSI CONTROLLER TERMPWR DS2109 TPWR GND R13 R15 R18 TCS R14 2.2 µF 4.7 µF BUS CURRENT SENSE TIMING DIAGRAM Figure 7 25 µs min TCS COMPARATORS LATCH

PDI PDE IBUS > 32 mA? DS2109 ISOLATED FROM SCSI BUS? 0 0 No Isolated 0 1 No Connected 1 0 No Connected 1 1 No Connected 0 0 Yes Isolated 0 1 Yes Isolated 1 0 Yes Isolated 1 1 Yes Isolated NOTE: “1” denotes pin left open circuited. WIDE SCSI CONFIGURATION Figure 8 PD VREF2 NC TERMPWR2 4.7 µF GND R18 R17 R16 R15 R14 TCS HS–GND PDE R13 R12 R11 R10 V REF PDI HS–GND HS–GND PDO TPWR TERMPWR1 V REF1 GND DS21S07A 16–PIN SOIC (300 MIL) 2.2 µF TERMINATION POWER LINE DS2109S 28–PIN SOIC (300 MIL) 4.7 µF

ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground –1.0V to +7.0V Operating Temperature 0 °C to 70°C Storage Temperature –55 °C to +125°C Soldering Temperature 260 °C for 10 seconds * This is a stress rating only and functional operation of 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 SYMBOL MIN TYP MAX UNITS NOTES TERMPWR Voltage VTP 4.00 5.25 V Logic 1 VIH 2.0 VTP +0.3 V 1 Logic 0 VIL –0.3 +0.8 V 1 DC CHARACTERISTICS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES TERMPWR Current ITP ITP 10 500 mA mA 2, 4 2, 5 Power Down Current IPD 1 2 mA 2, 3, 6 Termination Resistance R TERM 108 110 112 ohms 2, 3 Die Thermal Shutdown TS D 150 °C 2 Power Down Termination Capacitance C PD C 14 4.5 pF pF 2, 3, 6, 7 2,3,6,7,8 Input Leakage High IIH –1.0 µA 2, 12 Input Leakage Low IIL 1.0 µA 2, 9, 12 Output Current IO 4 mA 10 Bus Current Sense Trip Point IBCST 32 mA 11 REGULATOR CHARACTERISTICS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Output Voltage VREF 2.79 2.85 2.91 V 2, 3 Drop Out Voltage VDROP 0.75 1.0 V 4, 7 Line Regulation LIREG 1.0 2.0 % 2, 5 Load Regulation LO REG 1.3 3.0 % 2, 3 Current Limit IL 700 mA 2 Sink Current ISINK 400 mA 2

The chamfer on the body is optional. If it is not present, a termi- nal 1 identifier must be positioned so that 1/2 or more of its area is contained in the hatched zone. DS2109 022698 10/10 NOTES: 1. PDI, PDE, TCS 2. 4.00V < TERMPWR < 5.25V. 3. 0.0V < signal lines < 3.0V. 4. All signal lines = 0.0V. 5. All signal lines open. 6. Power down enabled. 7. Guaranteed by design; not production tested. 8. C 14 slightly higher capacitance due to sensing circuitry. 9. Excluding PDI, PDE pins. 10. PDO output pin. 11. IBCST > 32 mA – disable termination. 12. Excluding PDE, PDI, R14, and TCS pins. 28–PIN SOIC (300 MIL) PKG 28–PIN DIM MIN MAX A IN. MM 0.094 2.39 0.105 2.67 A1 IN. MM 0.004 0.102 0.012 0.30 A2 IN. MM 0.089 2.26 0.095 2.41 b IN. MM 0.013 0.33 0.020 0.51 C IN MM 0.009 0.229 0.013 0.33 D IN. MM 0.698 17.73 0.712 18.08 e IN. MM

0.050 BSC

1.27 BSC

E1 IN. MM 0.290 7.37 0.300 7.62 H IN MM 0.398 10.11 0.416 10.57 L IN MM 0.016 0.40 0.040 1.02 Θ 0° 8°