Texas Instruments SN74HCS251QPWRQ1

Overview

SN74HCS251QPWRQ1 from Texas Instruments is an automotive-grade 8-to-1 CMOS multiplexer with Schmitt-trigger inputs and complementary 3-state outputs (Y and W). It operates from 2 V to 6 V, delivers ±7.8 mA output drive at 6 V, features 100 nA typical supply current, and supports –40°C to +125°C ambient operation for engine control and body electronics data routing.

For engineers reviewing the SN74HCS251QPWRQ1 datasheet, SN74HCS251QPWRQ1 pinout, SN74HCS251QPWRQ1 application, or SN74HCS251QPWRQ1 equivalent, key selection criteria include AEC-Q100 Grade 1 qualification, hysteresis-enabled noise immunity on all address/data inputs, dual active-low 3-state control via OE, and TSSOP-16 package compatibility with high-density automotive PCB layouts.

Technical Context

The SN74HCS251QPWRQ1 implements full binary decoding of three address lines (A, B, C) to select one of eight data inputs (D0–D7), with simultaneous complementary outputs Y (non-inverted) and W (inverted). Its Schmitt-trigger inputs provide 0.6 V minimum hysteresis at 6 V supply, enabling robust operation with slow-rising signals or EMI-prone wiring harnesses.

All outputs are controlled by a single active-low output-enable (OE) input, placing both Y and W into high-impedance state when asserted. The device uses balanced CMOS 3-state drivers capable of sourcing/sinking up to ±7.8 mA at 6 V while maintaining VOL ≤ 0.33 V and VOH ≥ 5.4 V under load.

Key Specifications

Pinout & Package

TSSOP-16 package (5.00 mm × 4.40 mm), lead-free, RoHS-compliant, moisture sensitivity level MSL-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-to-1 multiplexer applications.

Compared with SN74HCS251QPWRQ1, SN74HCS151QPWRQ1 offers identical functionality without input hysteresis-making it unsuitable for unconditioned harness signals-while MC74HC251ADTR2G provides pin-compatible redundancy but omits published CDM ESD data, requiring additional qualification effort for safety-critical nodes.

Availability

SN74HCS251QPWRQ1 is available at Aetrix Electronics and suitable for engine control units, body control modules, ADAS camera interfaces, and infotainment display switching requiring stable component supply across automotive production lifecycles.

Supply support for SN74HCS251QPWRQ1 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 specializing in analog and embedded processing solutions, with leadership in automotive electronics, power management, and precision signal chain products.

The SN74HCS251QPWRQ1 belongs to TI's HCS logic family designed specifically for automotive applications requiring AEC-Q100 qualification, low power consumption, and robust noise immunity in harsh electrical environments.

FAQ

What is the maximum capacitive load the SN74HCS251QPWRQ1 can drive while meeting datasheet timing specifications?

The SN74HCS251QPWRQ1 is characterized for CL = 50 pF in its switching characteristics table. Propagation delay (tpd), enable time (ten), and transition time (tt) values are guaranteed only up to this load. Driving larger capacitances increases delay and may cause timing violations in high-speed applications. For loads exceeding 50 pF, verify performance empirically or add buffer stages. The SN74HCS251QPWRQ1 datasheet explicitly states "The SN74HCS251-Q1 can drive a load with a total capacitance less than or equal to 50 pF while still meeting all of the datasheet specifications."

Does the SN74HCS251QPWRQ1 support true 3-state operation on both Y and W outputs simultaneously?

Yes. Both Y and W outputs are controlled by the same active-low OE input. When OE is high, both outputs enter high-impedance (3-state) mode independently of address or data inputs. This behavior is confirmed in the Function Table (Table 8-1) and Functional Block Diagram (Figure 8-1) of the SN74HCS251QPWRQ1 datasheet. No internal logic forces either output active during OE assertion - both are fully disabled.

How does the Schmitt-trigger input architecture improve noise immunity in the SN74HCS251QPWRQ1?

The SN74HCS251QPWRQ1 Schmitt-trigger inputs provide hysteresis (ΔVT) of 0.6 V minimum at 6 V supply, meaning the positive switching threshold (VT+) and negative switching threshold (VT−) differ by that amount. This prevents multiple output transitions when input signals cross the threshold slowly or contain noise spikes smaller than ΔVT. As stated in the datasheet, this "allows for slow or noisy input signals" and makes the SN74HCS251QPWRQ1 tolerant to >600 mV peak-to-peak interference on address or data lines.

Can unused address inputs (A, B, C) on the SN74HCS251QPWRQ1 be left floating?

No. All unused inputs-including A, B, and C-must be terminated to a defined logic level (VCC or GND) per TI's Layout Guidelines and Application Information. Floating CMOS inputs cause undefined internal node voltages, increased supply current, and potential oscillation. The SN74HCS251QPWRQ1 datasheet explicitly states: "Unused inputs must be terminated to either VCC or ground" and recommends 10-kΩ pull-up/down resistors where appropriate. Leaving them unconnected violates AEC-Q100 reliability requirements.

What is the recommended decoupling strategy for the SN74HCS251QPWRQ1 in automotive PCB layouts?

Texas Instruments specifies a 0.1 µF ceramic capacitor placed physically and electrically close to the VCC and GND pins of the SN74HCS251QPWRQ1. This is documented in Section 10 (Power Supply Recommendations) and Figure 11-1 (Layout Example). The capacitor must be mounted adjacent to the device with short, direct traces to minimize inductance. TI further notes that paralleling a 1 µF capacitor is acceptable to suppress broader frequency noise, but the 0.1 µF unit is mandatory for high-frequency transient suppression critical in automotive EMI environments.