DS2107A DALLAS | Alldatasheet

Document overview

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Technical content

FEATURES

  • Fully compliant with SCSI and SCSI-2 standards
  • Backward compatible to the DS2107S
  • Provides active termination for 9 signal lines
  • Laser-trimmed 110 ohm termination resistors have 1% tolerance
  • Low dropout voltage
  • Power-down mode isolates termination resistors from the bus
  • Handles actively negated SCSI signals
  • Onboard thermal shutdown circuitry
  • 16-pin plastic SOIC (DS2107AS) and 20-pin plastic thin SSOP (DS2107AE) PIN ASSIGNMENT 8 9 DS2107AS 16-Pin SOIC (300 mil) TERMPWR1 VREF1 GND PD VREF2 NC TERMPWR2 DS2107AE 20-Pin TSSOP (173 mil) TERMPWR1 VREF1 GND PD VREF2 NC TERMPWR2 HS–GND HS–GND HS–GND HS–GND 10 11 ACTUAL FOOTPRINT SIZE .41” .41” .27” .26” DS2107AS DS2107AE

DESCRIPTION

The SCSI-2 standard recommends the use of active ter- minations at both ends of every cable segment in a SCSI system with single-ended drivers and receivers. The DS2107A SCSI Terminator, which is fully compliant with the standard, enables the designer to gain the benefits of active termination: greater immunity to volt- age drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS2107A integrates a regulator and nine precise switched 110 ohm termination resistors into a monolithic IC.

The DS2107A consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1). The bandgap reference circuit produces a precise 2.55V level which is fed to a buffer amplifier. The buffer pro- duces a 2.85V level and is capable of sourcing at least 24 mA into each of the termination resistors when the signal line is low (active). When the driver for a given signal line turns off, the terminator will pull the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals, the buffer can sink 200 mA. When all lines settle in the quiescent state, the regulator will consume about 5 mA. When the DS2107A is put into power- down mode by bringing PD low, the power-down circuit- ry will turn off the transistors on each signal line. This will isolate the DS2107A from the signal lines and effective- ly remove it from the circuit. The power-down pin (PD) has an internal 50K ohm pull-up resistor. To place the DS2107A into an active state, the PD pin should be left open circuited. To ensure proper operation, both the TERMPWR1 and TERMPWR2 pins must be connected to the SCSI bus TERMPWR line and both the VREF1 and VREF2 pins must be tied together externally. Each DS2107A re- quires parallel 0.1 µF and 4. 7 µF capacitors connected between the VREF pins and ground. Figure 2 details a typical SCSI bus configuration. In an 8-bit wide SCSI bus arrangement (“A” Cable), two DS2107A’s would be needed at each end of the SCSI cable in order to termi- nate the 18 active signal lines. In a 16-bit wide SCSI bus arrangement (“P” Cable), three DS2107A’s would be needed at each end of the SCSI cable in order to termi- nate the 27 active signal lines. DS2107A BLOCK DIAGRAM Figure 1 GND TERMPWR1 TERMPWR2 PD Power Down Circuitry 50K Ohm Bandgap Reference

110 Ohms

TYPICAL SCSI BUS CONFIGURATION Figure 2 Termination Power Line SCSI Bus Transceiver SCSI Bus Transceiver SCSI Bus Transceiver SCSI Bus Transceiver DS2107A TERMPWR1 TERMPWR2 VREF1 VREF2 GND R1 R2 R9 DS2107A TERMPWR1 TERMPWR2 VREF1 VREF2 GND R1 R9 SCSI Cable NOTES: 1. C1 = 0.1µF ceramic C2 = 4.7µF tantalum C3 = 2.2 µF tantalum or 4.7 µF aluminum 2. If the DS2107A is to be embedded into a peripheral that will act as a target on a SCSI bus, it is recommended that TERMPWR be derived from the SCSI cable, not generated locally. In this configuration, if a power failure occurs in the peripheral, it will not affect the bus.

1 1 TERMPWR1 Termination Power 1. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2µF or 4.7µF. See Figure 2. 3 2 R1 Signal Termination 1. 110 ohm termination. 4 3 R2 Signal Termination 2. 110 ohm termination. 5 4 R3 Signal Termination 3. 110 ohm termination. 6 5 R4 Signal Termination 4. 110 ohm termination. 7 6 R5 Signal Termination 5. 110 ohm termination. 9 7 VREF1 Reference Voltage 1. Must be externally connected directly to the VREF2 pin. Must be decoupled with a 4.7µF and a 0.1µF as shown in Figure 2. 10 8 GND Ground. Signal ground; 0.0V. 11 9 TERMPWR2 Termination Power 2. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2µF or 4.7µF. See Figure 2. 13 10 R6 Signal Termination 6. 110 ohm termination. 14 11 R7 Signal Termination 7. 110 ohm termination. 15 12 R8 Signal Termination 8. 110 ohm termination. 16 13 R9 Signal Termination 9. 110 ohm termination. 17 14 NC No Connect. 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 4.7µF and a 0.1µF as shown in Figure 2. 20 16 PD Power Down. When tied low, the DS2107A enters a power-down mode. Contains an internal 50K pull-up. Strap low to deactivate the DS2107A, leave open circuited to activate the DS2107A. 2,8,12,18 N/A HS–GND Heat Sink Ground. Internally connected to the mounting pad. Should be either grounded or electrically isolated from other cir- cuitry.

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 maxi- mum 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 PD Active VPDA -0.3 0.8 V PD Inactive VPDI 2.0 VTP +0.3 V DC CHARACTERISTICS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES TERMPWR Current ITP ITP 5 250 mA mA 1,3 1,4 Power Down Current IPD 100 µA 1,2,5 Termination Resistance R TERM 108 110 112 ohms 1,2 Die Thermal Shutdown TSD 150 °C 1 Power Down Termination Capacitance C PD 8.5 10 pF 1,2,5,6 PD Hysteresis H PD 280 mV 1 REGULATOR CHARACTERISTICS (0°C to 70°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Output Voltage VREF 2.79 2.85 2.91 V 1,2 Drop Out Voltage VDROP 0.75 1.0 V 3,6 Line Regulation LIREG 1.0 2.0 % 1,4,6 Load Regulation LO REG 1.3 3.0 % 1,2,6 Current Limit ILIM 300 350 400 mA 1 Sink Current ISINK 200 mA 1 NOTES: 1. 4.00V < TERMPWR < 5.25V. 2. 0.0V < signal lines < 3.0V. 3. All signal lines = 0.0V. 4. All signal lines open. 5. PD = 0.0V. 6. Guaranteed by design; not production tested.

DS2107AS SCSI TERMINATOR 16-PIN SOIC (300 MIL) A FC E phi J GK L HB DIM MIN MAX 16-PINPKG A IN. MM B IN. MM C IN. MM E IN. MM F IN. MM G IN. MM H IN. MM J IN. MM K IN. MM 0.402 10.21 0.412 10.46 0.290 7.37 0.300 7.65 0.089 2.26 0.095 2.41 0.004 0.102 0.012 0.30 0.094 2.38 0.105 2.68 0.398 10.11 0.416 10.57 0.009 0.229 0.013 0.33 0.013 0.33 0.019 0.48 L IN. MM 0.016 0.40 0.040 1.02

0.050 BSC

1.27 BSC

0° 8°phi

DS2107AE SCSI TERMINATOR 20-PIN TSSOP (PRELIMINARY) D HE SEE DETAIL A DETAIL A A B L G c phi n DIM MIN MAX A MM – 1.10 A1 MM 0.05 – A2 MM 0.75 1.05 C MM 0.09 0.18 L MM 0.50 0.70 e1 MM 0.65 BSC B MM 0.18 0.30 D MM 6.40 6.90 E MM 4.40 NOM G MM 0.25 REF H MM 6.25 6.55 phi 0° 8°