Renesas QS3251QG8

Overview

QS3251QG8 from Renesas Electronics is a high-speed CMOS 8:1 multiplexer/demultiplexer with TTL-compatible control inputs, 5 Ω typical ON resistance, zero propagation delay, and operation across –40°C to +85°C. It serves as a bidirectional logic-level switch in signal routing applications requiring low ground bounce and voltage translation between 5V and 3.3V domains.

For engineers reviewing the QS3251QG8 datasheet, QS3251QG8 pinout, QS3251QG8 application, or QS3251QG8 equivalent, key selection considerations include its 5 Ω switch resistance, 0.25 ns max propagation delay, 3-state output enable, undershoot clamp diodes on all I/O, and compatibility with 74F251/74FCT251 logic families.

Technical Context

The QS3251QG8 implements an enhanced N-channel FET architecture with no inherent body diode to V_CC, enabling true bidirectional signal flow without forward voltage drop or latch-up risk. Its control logic accepts standard TTL voltage levels (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and drives three select lines (S0–S2) plus active-low enable (E) to route one of eight inputs (I0–I7) to the Y output.

When disabled, the Y output enters high-impedance state with ±1 μA off-state leakage; when enabled, the switch exhibits <7 Ω max ON resistance at V_CC = 4.75 V and supports DC switching up to ±120 mA per channel. Pass voltage remains ≥3.7 V at V_CC = 5 V, confirming robust 5V-to-3.3V level-shifting capability.

Key Specifications

Pinout & Package

QS3251QG8 is housed in a 16-pin QSOP (Quarter Size Outline Package) with green RoHS-compliant finish. Pin spacing is 0.65 mm, body width 3.9 mm, and total package dimensions 9.9 mm × 3.9 mm × 1.4 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8:1 analog/digital multiplexer applications.

Compared with 74FCT251QSC and SN74CBT3251PWR, the QS3251QG8 uniquely combines pin compatibility, zero-delay switching, built-in undershoot protection, and guaranteed 5 V → 3.3 V translation-making it optimal for industrial hot-swap and mixed-voltage signal routing where reliability and timing precision are critical.

Availability

QS3251QG8 is available at Aetrix Electronics and suitable for industrial automation interfaces, video matrix switching, and embedded test access multiplexing requiring stable component supply and long-term lifecycle support.

Supply support for QS3251QG8 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

Renesas Electronics Corporation is a global semiconductor leader delivering microcontrollers, analog, power, and connectivity solutions for automotive, industrial, infrastructure, and IoT applications.

The QS3251QG8 belongs to Renesas' QuickSwitch® bus switch product line, designed specifically for high-speed, low-distortion signal routing in mixed-voltage, hot-pluggable, and noise-sensitive digital systems.

FAQ

What is the maximum operating voltage for QS3251QG8?

The QS3251QG8 supports a supply voltage range of –0.5 V to +7 V on all pins except V_CC, where V_CC is rated for 4.75 V to 5.25 V nominal operation. This extended absolute maximum rating allows tolerance of transient overvoltages up to +7 V on I/O pins, enhancing system robustness in electrically noisy environments. The QS3251QG8 must be operated within its specified 5 V ±5% supply range for guaranteed functional performance.

Does QS3251QG8 support bidirectional signal flow?

Yes, the QS3251QG8 supports fully bidirectional signal flow between any Ix pin and the Y pin due to its enhanced N-channel FET architecture with no inherent body diode to V_CC. This enables use in both multiplexer (I→Y) and demultiplexer (Y→I) configurations without signal polarity restrictions. The 5 Ω typical ON resistance applies equally in either direction, and voltage translation works symmetrically across 5 V and 3.3 V domains.

Is QS3251QG8 pin-compatible with standard logic multiplexers?

Yes, the QS3251QG8 is explicitly pin-compatible with the 74F251, 74FCT251, and 74FCT251T 8:1 multiplexers. Its 16-pin QSOP footprint matches those devices exactly, including identical placement of I0–I7, S0–S2, E, Y, V_CC, and GND. This allows direct replacement in existing designs without PCB modification, provided thermal and signal-integrity requirements are verified for the lower R_ON and faster switching.

What is the purpose of the undershoot clamp diodes in QS3251QG8?

The undershoot clamp diodes in QS3251QG8 protect all switch and control inputs from negative voltage transients down to –3 V for pulses ≤20 ns. These integrated diodes eliminate the need for external TVS devices in many hot-swap, cable-disconnect, or electrostatic discharge scenarios. They conduct transient energy to GND before it reaches sensitive gate oxides, preserving long-term reliability in industrial and field-deployed equipment using the QS3251QG8.

Can QS3251QG8 be used for 5 V to 3.3 V level translation?

Yes, the QS3251QG8 is specified for 5 V to 3.3 V level translation with a guaranteed minimum pass voltage of 3.7 V at V_CC = 5 V and I_OUT = –5 μA. This ensures that a logic HIGH from a 5 V source remains above the VIH threshold of typical 3.3 V CMOS receivers. Unlike active translators, the QS3251QG8 achieves this passively via its low R_ON and controlled threshold behavior, with no additional power supply or direction control required.