Texas Instruments SN75478P

Overview

SN75478P from Texas Instruments is a dual OR peripheral driver IC designed for high-voltage, high-current switching in electromechanical systems. It delivers 300 mA continuous output per channel, supports 100 V typical output breakdown voltage, features integrated output clamp diodes (70 V, 300 mA), TTL/MOS-compatible diode-clamped inputs, and operates across 0°C to 70°C - enabling use in solenoid, relay, and hammer-driver interfaces.

For engineers reviewing the SN75478P datasheet, SN75478P pinout, SN75478P application, or SN75478P equivalent, key selection considerations include its OR logic function per channel, 5 V nominal supply operation, 350 ns max propagation delay, latch-up immunity at 55 V, and PDIP-8 package with copper-lead frame for thermal reliability.

Technical Context

The SN75478P implements two independent OR-gate drivers with pnp transistor input stages that reduce input current demand and enable direct TTL/MOS interfacing. Each channel includes internal clamp diodes rated for 300 mA transient suppression at up to 70 V reverse voltage.

It operates from a single 4.5–5.5 V supply, exhibits low-level output voltage of ≤0.6 V at 300 mA load, and maintains output breakdown voltage ≥70 V - supporting safe switching of inductive loads such as print hammers and relays without external protection components.

Key Specifications

Pinout & Package

SN75478P uses an 8-pin plastic DIP (PDIP) package with copper-lead frame for improved thermal performance and reliability. Pin 1 is located at the top-left corner when viewed from the top with the notch or dot oriented upward.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual high-voltage OR driver applications.

Compared with ULN2003A and SN75477P, the SN75478P uniquely combines dual OR logic, 70 V output clamping, and a dedicated CLAMP pin - making it the only option among the three qualified for 55 V inductive load switching without external components while preserving positive-logic enable timing.

Availability

SN75478P is available at Aetrix Electronics and suitable for impact printer design, industrial relay interface, thermal print head control, and stepper motor phase switching requiring stable component supply and long-term obsolescence management.

Supply support for SN75478P 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN75478P belongs to TI's legacy peripheral driver family designed specifically for electromechanical interface applications - emphasizing latch-up immunity, integrated transient protection, and direct logic compatibility in cost-sensitive industrial systems.

FAQ

What logic function does the SN75478P implement per channel?

The SN75478P implements a dual OR gate function: Y = A + S for each channel. When either input A or the strobe input S is high, the corresponding output Y is driven low (active-low open-collector). This behavior is confirmed in the function table on page 1 of the SLRS025A datasheet and distinguishes SN75478P from SN75476 (AND) and SN75477 (NAND). The OR logic enables flexible enable-based control in printer hammer and relay driver applications.

Does the SN75478P require external flyback diodes when driving inductive loads?

No, the SN75478P does not require external flyback diodes. It integrates high-current clamp diodes on each output with a rated reverse voltage of 70 V and forward current capacity of 300 mA - sufficient to suppress transients from typical solenoids, relays, and print hammers. The CLAMP pin (Pin 4) serves as the common anode connection, and proper grounding of this pin completes the protection path. This integration reduces BOM count and improves reliability over discrete solutions.

What is the maximum continuous output current rating for the SN75478P?

The SN75478P is characterized for 300 mA continuous output current per channel under recommended operating conditions (VCC = 4.5–5.5 V, TA = 0°C to 70°C). Absolute maximum ratings allow 400 mA continuous, but the 300 mA value reflects the tested, guaranteed performance level with thermal margin. At TA = 70°C, the PDIP package supports 640 mW total power dissipation, limiting practical sustained current based on load voltage and duty cycle.

Is the SN75478P pin-compatible with other devices in the SN75476–SN75478 family?

Yes, the SN75478P is pin-compatible with SN75476P and SN75477P - all share identical PDIP-8 packaging, pin numbering, and terminal functions (1A, 1Y, GND, CLAMP, VCC, 2A, 2Y, S). The only functional difference lies in internal logic: AND, NAND, or OR. This allows board-level substitution between family members without layout changes, provided the logic function matches system requirements. The CLAMP pin and thermal design remain fully interchangeable.

What is the purpose of the CLAMP pin (Pin 4) on the SN75478P?

The CLAMP pin (Pin 4) on the SN75478P is the common anode connection for the internal output clamp diodes. It must be connected to the positive rail of the inductive load (e.g., +55 V for relay coils) to provide a path for transient energy during switch-off. This configuration enables bidirectional clamping: when the output transistor turns off, stored inductive energy flows through the internal diode into the CLAMP rail, preventing voltage overshoot beyond the diode's reverse breakdown rating (70 V min). Proper CLAMP pin routing is essential for latch-up immunity.