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Analog Devices Inc./Maxim Integrated DS21T05S/T&R
- Part No.:
- DS21T05S/T&R
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Category:
- Signal Terminators
- Package:
- 16-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
DS21T05S/T&R.pdf
- Description:
- IC TERMINATOR SCSI 300MIL 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,893
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Product details
Overview
DS21T05S/T&R from Dallas Semiconductor (now Maxim Integrated) is a monolithic SCSI active terminator IC for Fast and Ultra SCSI single-ended buses. It integrates nine laser-trimmed 110-Ω termination resistors, a precision 2.85V reference regulator with ≤1.0V dropout, and power-down control. It delivers 24 mA per line sourcing capability and supports hot-plug operation in disk drive and RAID controller terminations.
For engineers reviewing the DS21T05S/T&R datasheet, DS21T05S/T&R pinout, DS21T05S/T&R application, or DS21T05S/T&R equivalent, key selection criteria include TERMPWR voltage range (4.0–5.5 V), termination resistance tolerance (±5%), thermal shutdown threshold (150°C), quiescent current (5 mA), and SOIC-16 (300-mil) package compatibility with SCSI bus layout constraints.
Technical Context
The DS21T05S implements a bandgap-based 2.55V reference buffered to 2.85V output, enabling precise active termination across nine SCSI signal lines. Its regulator sustains ≥24 mA sourcing per line when signals are low and sinks up to 200 mA total during actively negated transitions, with <60 mV VREF shift.
Power-down mode is controlled via an open-drain PD pin with internal 50 kΩ pull-up; pulling PD low disables all termination paths, isolating the device from the bus. Both TERMPWR1/TERMPWR2 must connect to the same SCSI TERMPWR line, and VREF1/VREF2 require external 4.7 µF decoupling.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Termination Resistance | 110 Ω ±5% - laser-trimmed for compliance with SCSI-1/Fast/Ultra active termination standards |
| Reference Voltage | 2.85 V (typ) - stable bias for termination logic; maintains integrity under load and temperature variation |
| Dropout Voltage | ≤1.0 V - enables reliable operation down to 4.0 V TERMPWR, critical for marginal bus power conditions |
| Quiescent Current | 5 mA (typ) - low static power draw essential for system-level thermal and efficiency budgets |
| Thermal Shutdown | 150 °C - protects against latch-up or damage during sustained high-current or ambient overtemperature events |
| Signal Line Sinking | 200 mA total - handles actively negated SCSI signals without reference collapse or bus contention |
| Operating Temperature | 0°C to +70°C - validated for commercial-grade storage subsystem environments |
Pinout & Package
DS21T05S is housed in a 16-pin plastic narrow SOIC (300-mil body width), RoHS-compliant, surface-mount package with standard 1.27 mm pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 9 | TERMPWR1 / TERMPWR2 | Dual inputs tied to SCSI TERMPWR line; provide redundant power routing and reduce trace inductance |
| 2–6, 11–14 | R1–R5, R6–R9 | Nine 110-Ω switched termination resistors - each connects one SCSI signal line to VREF for active pull-up |
| 7, 15 | VREF1 / VREF2 | Reference voltage outputs requiring external 4.7 µF decoupling; must be shorted externally for stability |
| 8 | GND | Signal ground return path - shared reference for all termination and regulator circuitry |
| 10 | NC | No-connect pin - left unconnected per design; no internal connection or function |
| 16 | PD | Power-down enable input with internal 50 kΩ pull-up - open-circuit = active, grounded = isolation mode |
Key Features
| Feature | Design Value |
|---|---|
| SCSI Standard Compliance | Fully compliant with SCSI-1, Fast SCSI, and Ultra SCSI active termination requirements - eliminates need for discrete resistor networks |
| Laser-Trimmed Resistors | 110 Ω ±5% tolerance - ensures consistent signal integrity and noise immunity across all nine terminated lines |
| Hot-Plug Compatibility | Safe insertion/removal while bus is powered - prevents glitches or bus lockup during RAID module replacement |
| Thermal Protection | On-die thermal shutdown at 150°C - prevents catastrophic failure during sustained overload or poor airflow |
| Low Quiescent Power | 5 mA typical supply current - reduces heat generation and simplifies thermal management in dense storage enclosures |
Applications
| RAID Controller Termination | Disk Drive Backplane Termination |
|---|---|
Use Scenario: Termination at both ends of an 8-bit or 16-bit SCSI bus in enterprise RAID arrays with hot-swap bays. IC Role / Device Role / Timing Role: Active SCSI terminator providing regulated 2.85V pull-up on all signal lines to maintain signal integrity at >20 MB/s transfer rates. Use Value: Eliminates timing skew and reflections caused by passive termination, enabling stable Ultra SCSI operation under variable cable lengths and loads. | Use Scenario: Embedded termination on SAS/SATA-to-SCSI bridge boards or legacy SCSI disk drive PCBs. IC Role / Device Role / Timing Role: Monolithic replacement for discrete 110-Ω resistor + regulator solutions, reducing BOM count and board area. Use Value: Laser-trimmed resistors ensure ±5% matching across all nine lines, improving common-mode noise rejection and EMI performance. |
| SCSI Host Adapter Termination | Industrial SCSI Data Acquisition System |
Use Scenario: Termination on SCSI host adapters used in medical imaging or broadcast video capture systems. IC Role / Device Role / Timing Role: Provides active termination with thermal shutdown and power-down control for robust field operation. Use Value: Power-down mode (via PD pin) allows software-controlled bus isolation during firmware updates or diagnostics without hardware intervention. | Use Scenario: Termination in ruggedized SCSI data loggers deployed in factory automation or test equipment. IC Role / Device Role / Timing Role: Regulator-based active terminator maintaining stable VREF despite TERMPWR droop during motor startup or surge events. Use Value: Dropout voltage ≤1.0 V ensures reliable termination even when TERMPWR sags to 4.0 V - common in industrial power supplies with long cables. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar SCSI active termination applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| DS21T05Z | Same die, 150-mil SOIC package - smaller footprint but higher thermal resistance | Preferred for space-constrained PCBs where thermal margin permits | Select DS21T05Z only if board layout cannot accommodate 300-mil SOIC width and thermal derating is verified |
| MAX3221E | RS-232 transceiver - not a functional alternative; included erroneously in some distributor cross-references | Not suitable for SCSI termination; lacks termination resistors, reference regulator, and PD control | DS21T05S/T&R has no drop-in RS-232-compatible substitute; MAX3221E must be excluded from SCSI termination BOMs |
Compared with DS21T05Z, DS21T05S/T&R offers lower thermal resistance due to larger SOIC body, enabling higher sustained current delivery in dense backplanes; neither part is interchangeable with non-terminator ICs like MAX3221E, which serve entirely different interface protocols and lack SCSI-specific regulation and switching architecture.
Availability
DS21T05S/T&R is available at Aetrix Electronics and suitable for RAID controller designs, disk drive backplanes, SCSI host adapters, and industrial data acquisition systems requiring stable component supply and long-term obsolescence management.
Supply support for DS21T05S/T&R includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Dallas Semiconductor, acquired by Maxim Integrated in 2001, specialized in precision analog, timing, and interface ICs for industrial and storage applications.
The DS21T05S/T&R belongs to Dallas' SCSI interface product line, engineered specifically to replace bulky discrete active termination networks with a single monolithic solution meeting Fast and Ultra SCSI electrical specifications.
FAQ
What is the primary function of the DS21T05S/T&R in a SCSI system?
The DS21T05S/T&R serves as a monolithic active SCSI terminator, providing nine precisely matched 110-Ω termination resistors with a regulated 2.85V reference voltage. It replaces discrete resistor networks and voltage regulators in Fast and Ultra SCSI implementations, ensuring signal integrity, noise immunity, and compliance with SCSI-1 through Ultra SCSI standards. The DS21T05S/T&R integrates thermal shutdown and power-down control to enhance system reliability.
How does the DS21T05S/T&R handle hot-plug operations on a live SCSI bus?
The DS21T05S/T&R is designed for SCSI bus hot-plug compatibility: its internal architecture isolates termination paths during insertion/removal, preventing bus glitches or contention. When powered, it sources 24 mA per line and sinks up to 200 mA total without destabilizing VREF. The DS21T05S/T&R remains electrically benign during hot-swap events because its PD pin defaults to active (open-circuit), and its regulator tolerates transient TERMPWR fluctuations inherent in live-backplane environments.
What external components are required for proper operation of the DS21T05S/T&R?
The DS21T05S/T&R requires two external components: a 4.7 µF tantalum capacitor between VREF1 and VREF2 (tied together externally) to stabilize the reference voltage, and decoupling capacitors (2.2 µF or 4.7 µF) on TERMPWR1 and TERMPWR2 pins. A 0.1 µF high-frequency bypass capacitor may be added in parallel to the 4.7 µF VREF capacitor for fast-edge driver applications. No additional resistors or regulators are needed - the DS21T05S/T&R integrates all active termination functions.
Can the DS21T05S/T&R be used in both 8-bit and 16-bit SCSI configurations?
Yes - the DS21T05S/T&R terminates nine signal lines per device. In an 8-bit (narrow) SCSI bus, two DS21T05S/T&R units are required per end (18 lines). In a 16-bit (wide) SCSI bus, three DS21T05S/T&R units are required per end (27 lines). Each DS21T05S/T&R operates independently, and multiple units can be paralleled on the same TERMPWR and VREF rails, provided total current demand remains within specification limits.
What is the role of the PD pin on the DS21T05S/T&R, and how should it be configured?
The PD (Power Down) pin on the DS21T05S/T&R controls termination enable/disable state. It features an internal 50 kΩ pull-up resistor, so leaving PD open-circuited activates the device. To enter power-down mode - isolating all nine termination resistors from the SCSI bus - PD must be driven low (<0.8 V). This feature allows software or system logic to dynamically disable termination during diagnostics or firmware updates. The DS21T05S/T&R remains fully functional with PD left unconnected in standard operation.
DS21T05S/T&R Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Series:
- -
- Package/Case:
- 16-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- SCSI, LVD, SE
- Number of Terminations:
- 9
- Voltage - Supply:
- 4V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
DS21T05S/T&R FAQ
1.How can I place an order for DS21T05S/T&R through Aetrix?
Please submit a Request for Quotation (RFQ) for DS21T05S/T&R on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for DS21T05S/T&R reliable?
The price and inventory of DS21T05S/T&R are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for DS21T05S/T&R is usually 5 days.
3.What payment methods are accepted for DS21T05S/T&R?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for DS21T05S/T&R transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for DS21T05S/T&R?
DS21T05S/T&R orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your DS21T05S/T&R order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for DS21T05S/T&R?
For technical support, including DS21T05S/T&R datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your DS21T05S/T&R requirements.
6.How does Aetrix verify that DS21T05S/T&R is sourced from the original manufacturer or authorized distributors?
All DS21T05S/T&R products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that DS21T05S/T&R meets industry standards.
7.What is the process for return or replacement of DS21T05S/T&R?
All DS21T05S/T&R units undergo pre-shipment inspection (PSI). If there is an issue with DS21T05S/T&R, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The DS21T05S/T&R part is unused and in its original packaging.
Return procedure for DS21T05S/T&R:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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