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Home > Products > Integrated Circuits (ICs) > Interface > Drivers, Receivers, Transceivers

Texas Instruments DS8921N

Name: DS8921N
Brand: Texas Instruments
SKU: DS8921N
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: DS8921N

Manufacturer:: Texas Instruments

Category:: Drivers, Receivers, Transceivers

Package:: 8-DIP (0.300", 7.62mm)

Datasheet:: DS8921N.pdf

Description:: IC TRANSCEIVER FULL 1/1 8PDIP

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Product details

Overview

DS8921N from Texas Instruments is a dual-function differential line driver and receiver IC in a single 8-pin PDIP package, designed for ST506/ST412/ESDI disk drive interfaces and RS-422 applications. It delivers 12 ns typical driver propagation delay, ±200 mV receiver input sensitivity over ±7 V common-mode range, and 0.5 ns typical output skew - enabling robust noise-immune data transmission in legacy storage subsystems.

For engineers reviewing the DS8921N datasheet, DS8921N pinout, DS8921N application, or DS8921N equivalent, key selection criteria include TTL/CMOS compatibility, industrial-grade timing precision (12 ns driver t_pd, 14 ns receiver t_pd), ±7 V common-mode tolerance, 0.5 ns output skew, and PDIP-8 packaging for through-hole prototyping and legacy board repair.

Technical Context

The DS8921N integrates a unipolar differential driver with complementary DO+/DO− outputs and a hysteresis-equipped receiver with RI+/RI− inputs and single-ended RO output. Its driver operates with 10 ns typical single-ended t_pd and 5 ns typical transition time under 5 V supply, while the receiver provides 70 mV typical hysteresis and ±200 mV threshold to reject slow-edge noise in long-cable disk drive links.

This device implements TTL/CMOS-compatible logic levels on DI and RO pins, supports ±7 V differential input voltage range, and maintains functional operation across 0°C to +70°C ambient - matching ST506/ST412 timing budgets and ESDI signal integrity requirements without external level-shifting circuitry.

Key Specifications

Parameter	Value and Actual Design Meaning
Supply Voltage	4.5 V to 5.5 V - ensures stable operation with standard 5 V TTL power rails and tolerates ±10% rail variation.
Driver Propagation Delay	10 ns typical - enables reliable 2 Mbps data transmission in ST506/ESDI disk drive control paths.
Receiver Propagation Delay	14 ns typical - meets ST412 timing window constraints for head positioning and sector read/write synchronization.
Input Sensitivity	±200 mV - detects valid differential signals even with cable attenuation or ground offset up to ±7 V common-mode voltage.
Output Skew	0.5 ns typical - minimizes differential pair timing mismatch critical for jitter-sensitive disk drive data recovery.
Receiver Hysteresis	70 mV typical - suppresses false triggering from EMI-induced slow transitions on twisted-pair cables.
Operating Temperature	0°C to +70°C - certified for commercial-grade disk controller and host adapter environments.

Pinout & Package

DS8921N uses an 8-pin Plastic Dual In-line Package (PDIP) with 9.81 mm × 6.35 mm body size and 0.3 inch lead pitch - optimized for through-hole mounting on legacy disk drive controller PCBs and test fixtures.

Pin/Terminal	Circuit Role	Design Meaning
VCC	Power Supply Input	5 V supply connection; requires local 0.1 µF bypass capacitor to GND for high-frequency noise suppression.
GND	Ground Reference	Common return path for driver/receiver I/O and internal biasing; must be low-impedance for signal integrity.
DI	Driver Input	TTL/CMOS-compatible digital input controlling driver state; accepts 0.8 V / 2.0 V logic thresholds.
DO+	Driver Non-inverting Output	Positive differential output driving twisted-pair or parallel wire; paired with DO− for balanced signaling.
DO−	Driver Inverting Output	Negative differential output; complements DO+ to generate 100 Ω–120 Ω differential impedance drive.
RI+	Receiver Non-inverting Input	Differential input terminal accepting +200 mV threshold detection; used with RI− for noise-rejecting reception.
RI−	Receiver Inverting Input	Differential input terminal completing receiver pair; supports ±7 V common-mode range and hysteresis.
RO	Receiver Output	TTL-compatible single-ended output; sinks 8 mA at 0.5 V VOL and sources −400 µA at 2.5 V VOH.

Key Features

Feature	Design Value
Integrated Driver + Receiver	Single-package solution eliminates inter-device skew and reduces PCB footprint vs discrete transceivers.
RS-422 Compliance	Meets EIA RS-422 electrical specifications including ±7 V common-mode range and 200 mV sensitivity.
Low Output Skew	0.5 ns typical skew between DO+ and DO− ensures precise differential edge alignment for timing-critical disk protocols.
Input Hysteresis	70 mV typical hysteresis prevents chatter on slow-rising/falling signals induced by long cable reflections.
TTL/CMOS Compatibility	Direct interface with microcontroller GPIO, FPGA I/O, and legacy ASICs without level-shifting components.

Applications

ST506 Disk Drive Interface	ST412 Disk Drive Interface
Use Scenario: Bidirectional command/data transfer between host controller and MFM hard disk drive using ST506 protocol. IC Role / Device Role / Timing Role: DS8921N acts as line transceiver converting TTL-level host signals to differential drive for head positioning and sector read/write commands. Use Value: 12 ns driver t_pd and 14 ns receiver t_pd meet ST506 timing budget for 5 MHz clocked transfers with 200 ns setup/hold margins.	Use Scenario: Control signal conditioning in ST412-compatible floppy and hard disk controllers with extended cable runs. IC Role / Device Role / Timing Role: DS8921N provides noise-immune differential signaling for step/direction pulses and status feedback over 1–2 meter ribbon cables. Use Value: ±7 V common-mode tolerance accommodates ground potential differences between drive and controller chassis in multi-drive systems.
ESDI Disk Drive Interface	RS-422 Industrial Data Link
Use Scenario: High-speed data streaming between ESDI host adapter and 10–20 MB/s hard drives in workstations and servers. IC Role / Device Role / Timing Role: DS8921N serves as physical layer transceiver translating CMOS data bursts into differential pairs for ESDI's 20 MHz clock domain. Use Value: 0.5 ns output skew preserves signal integrity at 20 Mbps, preventing bit errors caused by differential edge misalignment.	Use Scenario: Reliable serial communication between PLC and remote I/O modules in factory automation cabinets. IC Role / Device Role / Timing Role: DS8921N functions as RS-422 line driver/receiver for Modbus RTU or custom protocols over 100+ meter twisted-pair wiring. Use Value: 70 mV receiver hysteresis rejects 50/60 Hz magnetic interference and switching noise common in industrial enclosures.

ST506 Disk Drive Interface

ST412 Disk Drive Interface

Use Scenario: Bidirectional command/data transfer between host controller and MFM hard disk drive using ST506 protocol.

IC Role / Device Role / Timing Role: DS8921N acts as line transceiver converting TTL-level host signals to differential drive for head positioning and sector read/write commands.

Use Value: 12 ns driver t_pd and 14 ns receiver t_pd meet ST506 timing budget for 5 MHz clocked transfers with 200 ns setup/hold margins.

Use Scenario: Control signal conditioning in ST412-compatible floppy and hard disk controllers with extended cable runs.

IC Role / Device Role / Timing Role: DS8921N provides noise-immune differential signaling for step/direction pulses and status feedback over 1–2 meter ribbon cables.

Use Value: ±7 V common-mode tolerance accommodates ground potential differences between drive and controller chassis in multi-drive systems.

ESDI Disk Drive Interface

RS-422 Industrial Data Link

Use Scenario: High-speed data streaming between ESDI host adapter and 10–20 MB/s hard drives in workstations and servers.

IC Role / Device Role / Timing Role: DS8921N serves as physical layer transceiver translating CMOS data bursts into differential pairs for ESDI's 20 MHz clock domain.

Use Value: 0.5 ns output skew preserves signal integrity at 20 Mbps, preventing bit errors caused by differential edge misalignment.

Use Scenario: Reliable serial communication between PLC and remote I/O modules in factory automation cabinets.

IC Role / Device Role / Timing Role: DS8921N functions as RS-422 line driver/receiver for Modbus RTU or custom protocols over 100+ meter twisted-pair wiring.

Use Value: 70 mV receiver hysteresis rejects 50/60 Hz magnetic interference and switching noise common in industrial enclosures.

Equivalent & Alternatives

The following parts are listed as comparable options for similar differential line driver and receiver applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
DS8921AM/NOPB	SOIC-8 package (4.90 mm × 3.91 mm); identical electrical specs and temperature range (0°C to +70°C).	Suitable for surface-mount production boards; not compatible with through-hole sockets or legacy PDIP footprints.	Select DS8921AM/NOPB when space-constrained PCB layout or automated SMT assembly is required.
SN75172N	Separate driver and receiver ICs; no integrated dual-function design; higher 25 ns typical propagation delay.	Requires two ICs and additional board area; lacks built-in skew control and hysteresis optimization of DS8921N.	Choose SN75172N only if redesign allows component count increase and timing margin relaxation.

Compared with DS8921AM/NOPB, DS8921N offers direct through-hole replacement for legacy repairs; compared with SN75172N, DS8921N reduces BOM count, improves timing precision, and simplifies layout - making it optimal for ST506/ST412 retrofit and RS-422 link consolidation.

Availability

DS8921N is available at Aetrix Electronics and suitable for ST506 disk drive controller refurbishment, ST412-based industrial motion control systems, and RS-422 point-to-point data links requiring stable component supply and long-term obsolescence management.

Supply support for DS8921N 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

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets since 1930.

The DS8921N belongs to TI's legacy interface IC product line, engineered specifically for backward-compatible integration into ST506/ST412/ESDI storage subsystems and robust RS-422 data links where reliability and timing predictability are critical.

FAQ

What is the operating temperature range for DS8921N?

The DS8921N is rated for commercial temperature operation from 0°C to +70°C. This range aligns with ST506 and ST412 disk drive controller specifications and ensures stable performance in standard office and industrial enclosure environments. The DS8921N does not support extended industrial temperatures; for −40°C to +85°C operation, the DS8921AT variant must be selected. DS8921N maintains full electrical compliance-including 14 ns receiver t_pd and ±200 mV sensitivity-across its entire specified temperature range.

Does DS8921N require external termination resistors?

Yes, DS8921N requires an external differential termination resistor placed at the far end of the transmission line - typically 100 Ω to 120 Ω - to match the characteristic impedance of twisted-pair or parallel-wire cabling. This termination prevents signal reflections that degrade timing margins in ST506/ESDI applications. The DS8921N itself does not integrate termination; its driver output impedance is designed to drive such external loads directly. Proper termination is essential to achieve the specified 0.5 ns output skew and 12 ns driver propagation delay.

Can DS8921N interface directly with 3.3 V logic systems?

No, DS8921N is not 3.3 V logic compatible. It requires a 5 V supply (4.5 V to 5.5 V) and features TTL/CMOS input thresholds (V_IL = 0.8 V, V_IH = 2.0 V) and output levels (V_OL = 0.5 V, V_OH = 2.5 V) referenced to 5 V. Direct connection to 3.3 V microcontrollers or FPGAs risks undriven inputs or marginal VOH levels. A level-shifter or bus buffer is required for interoperability. DS8921N's design intent is compatibility with legacy 5 V disk controller architectures, not modern low-voltage systems.

What is the maximum data rate supported by DS8921N?

DS8921N supports reliable operation at up to 2 Mbps, as validated in the datasheet's typical application curves using a 1010 data pattern. This rate satisfies ST506 (5 MHz clock, ~2.5 Mbps burst), ST412 (up to 2 Mbps), and ESDI (20 MHz clock, 20 Mbps aggregate) timing requirements when used in appropriate signal conditioning roles. While not characterized beyond 2 Mbps in official test conditions, the 12 ns driver t_pd and 14 ns receiver t_pd suggest theoretical capability up to ~5 Mbps - but system-level factors like cable loss, termination accuracy, and noise margin constrain practical use to 2 Mbps for guaranteed compliance.

Is DS8921N RoHS compliant?

Yes, DS8921N/NOPB is RoHS compliant and green (halogen-free), as confirmed in TI's Packaging Information Addendum. It uses Cu-Sn lead finish and meets JEDEC J-STD-020 moisture sensitivity Level-1 (unlimited floor life). The "NOPB" suffix explicitly denotes lead-free packaging. DS8921N complies with EU RoHS Directive 2011/65/EU for all ten restricted substances, including Pb, Cd, Hg, Cr(VI), PBB, and PBDE, with concentrations below 0.1% by weight in homogeneous materials - making it suitable for environmentally regulated industrial and computing equipment.

DS8921N Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: -

Package/Case:: 8-DIP (0.300", 7.62mm)

Packaging:: Tube

Product Status:: Obsolete

Type:: Transceiver

Protocol:: RS422, RS485

Number of Drivers/Receivers:: 1/1

Duplex:: Full

Receiver Hysteresis:: 70 mV

Data Rate:: -

Voltage - Supply:: 4.5V ~ 5.5V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 8-PDIP

DS8921N FAQ

1.How can I place an order for DS8921N through Aetrix?

Please submit a Request for Quotation (RFQ) for DS8921N 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 DS8921N reliable?

The price and inventory of DS8921N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for DS8921N is usually 5 days.

3.What payment methods are accepted for DS8921N?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for DS8921N transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for DS8921N?

DS8921N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your DS8921N 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 DS8921N?

For technical support, including DS8921N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your DS8921N requirements.

6.How does Aetrix verify that DS8921N is sourced from the original manufacturer or authorized distributors?

All DS8921N 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 DS8921N meets industry standards.

7.What is the process for return or replacement of DS8921N?

All DS8921N units undergo pre-shipment inspection (PSI). If there is an issue with DS8921N, 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 DS8921N part is unused and in its original packaging.

Return procedure for DS8921N:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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