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DS21S07A SCSI Terminator
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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.
PIN CONFIGURATIONS
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)
ACTUAL FOOTPRINT SIZE
0.41" 0.26"
0.41"
0.27"
DS21S07AS
DS21S07AE
ORDERING INFORMATION
VOLTAGE (V) DS21S07AS 5 DS21S07AS+ 5 DS21S07AS/T&R 5 DS21S07AS+T&R 5 DS21S07AE 5 DS21S07AE/T&R 5 PART PINPACKAGE 16 SO 16 SO 16 SO 16 SO 20 TSSOP 20 TSSOP TOP MARK DS21T07S DS21T07S DS21T07S DS21T07S DS21T07E DS21T07E
+ Denotes lead-free package. The top mark includes a "+" on
lead-free packages. Note: All devices are specified over the 0C to +70C operating temperature range.
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REV: 022106
DS21S087A
FUNCTIONAL DESCRIPTION
The DS21S07A consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1). The bandgap reference circuit produces a precise 2.55V level that is fed to a buffer amplifier. The buffer produces a 2.85V level and can source at least 24mA 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 pulls the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals, the buffer can sink at least 200mA, and VREF will move less than 60mV. When all lines settle in the quiescent state, the regulator consumes about 2.5mA. When the DS21S07A is put into power-down mode by bringing PD low, the power-down circuitry turns off the transistors on each signal line. This isolates the DS21S07A from the signal lines and effectively removes 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 TERMPWR2 pins must be connected to the SCSI bus TERMPWR line and both the VREF1 and VREF2 pins must be tied together externally. Each DS21S07A requires a 4.7F capacitor 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 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 would be needed at each end of the SCSI cable to terminate the 27 active signal lines.
Figure 1. DS21S087A Block Diagram
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DS21S087A
Figure 2. Typical Differential SCSI Bus Configuration
NOTE 1: C1 = 4.7F TANTALUM CAPACITOR; C2 = 2.2F TANTALUM OR 4.7F ALUMINUM CAPACITOR. 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 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. NOTE 3: A HIGH-FREQUENCY BYPASS CAPACITOR (0.1F RECOMMENDED) CAN BE ADDED IN PARALLEL TO C1 FOR APPLICATIONS USING FAST RISE/FALL TIME DRIVERS.
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DS21S087A
Table 1. Pin Description
PIN TSSOP SO 1 2, 8, 12, 18 3-7, 13-16 1 -- NAME TERMPWR1 HS-GND FUNCTION Termination Power 1. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2F capacitor or 4.7F capacitor. See Figure 2. Heat Sink Ground. Internally connected to the mounting pad. Should be either grounded or electrically isolated from other circuitry. Signal Termination 1-9. 110 termination. Reference Voltage 1. Must be externally connected directly to the VREF2 pin. Must be decoupled with a 4.7F capacitor as shown in Figure 2. Ground. 0V, signal ground. Termination Power 2. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2F capacitor or 4.7F capacitor. See Figure 2. No Connection. Do not connect any signal to this pin. Reference Voltage 2. Must be externally connected directly to the VREF1 pin. Must be decoupled with a 4.7F capacitor as shown in Figure 2. 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
2-6, 10-13
R1-R9
9 10 11 17 19
7 8 9 14 15
VREF1 GND TERMPWR2 NC VREF2
20
16
PD
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DS21S087A
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to Ground.....................................................-1.0V to +7.0V Operating Temperature Range..........................................................................0C to +70C Storage Temperature Range........................................................................-55C to +125C Soldering Temperature.................................................See IPC/JEDEC J-STD-020 Specification
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 device reliability.
RECOMMENDED OPERATING CONDITIONS
(TA = 0C to +70C) PARAMETER TERMPWR Voltage PD Active PD Inactive (TA = 0C to +70C) PARAMETER TERMPWR Current Power-Down Current Termination Resistance Die Thermal Shutdown Power-Down Termination Capacitance Input Leakage High Input Leakage Low (TA = 0C to +70C) PARAMETER Output Voltage Drop-Out Voltage Line Regulation Load Regulation Current Limit Sink Current SYM VTP VPDA VPDI MIN 4.00 -0.3 2.0 TYP MAX 5.50 +0.8 VTP + 0.3 UNITS V V V NOTES
DC CHARACTERISTICS
SYMBOL ITP IPD RTERM TSD CPD IIH IIL -1.0 1.0 108 150 MIN TYP 2.5 100 110 3.0 MAX 250 5 150 112 5.0 UNITS mA mA A C pF A A NOTES 1, 3 1, 4 1, 2, 5 1, 2 1, 6 1, 2, 5, 6 1, 8 1, 7
REGULATOR CHARACTERISTICS
SYMBOL VREF VDROP LIREG LOREG ILIM ISINK MIN 2.79 TYP 2.85 0.50 1.0 1.3 350 MAX 2.93 0.75 2.0 3.0 UNITS V V % % mA mA NOTES 1, 2 3, 6 1, 4 1, 3 1 1
200
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NOTES:
1) 2) 3) 4) 5) 6) 7) 8) 4.00V < TERMPWR < 5.50V. 0.0V < signal lines < TERMPWR. All signal lines = 0V. All signal lines open. PD = 0V. Guaranteed by design; not production tested. R1 to R9 only. R1 to R9 and PD.
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PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
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DS21S087A
PACKAGE INFORMATION (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
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Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/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
(c) 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.

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