Renesas QS3861QG8

Overview

QS3861QG8 from Renesas Electronics (formerly IDT) is a high-speed CMOS 10-bit bus switch with flow-through pinout, designed for bidirectional signal routing in TTL-compatible digital systems. It features 5 Ω ON resistance, zero propagation delay, undershoot clamp diodes on all I/O and control pins, and operates across –40°C to +85°C for industrial hot-swap and voltage translation applications.

For engineers reviewing the QS3861QG8 datasheet, QS3861QG8 pinout, QS3861QG8 application, or QS3861QG8 equivalent, key selection criteria include its 5 Ω bidirectional switch resistance, flow-through pinout enabling minimal trace skew, industrial temperature rating, undervoltage-tolerant input clamping, and compatibility with 5V/3.3V mixed-voltage bus isolation.

Technical Context

The QS3861QG8 implements ten independent N-channel FET switches with no inherent body diode to V_CC, eliminating parasitic conduction paths during voltage translation. Its control logic uses a single Bus Enable (BE) input to simultaneously connect or isolate all A–B channels in either direction.

Switching is characterized by t_PZL ≤ 6.5 ns (BE-to-output turn-on) and t_PLZ ≤ 5.5 ns (BE-to-output turn-off), with input capacitance of 3–7 pF per channel and guaranteed OFF-state leakage ≤ ±1 μA at full operating range.

Key Specifications

Pinout & Package

QS3861QG8 is packaged in a 24-pin QSOP (Quarter Size Outline Package), green RoHS-compliant, with 0.65 mm pitch and flow-through pinout optimized for PCB layout symmetry and signal integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus switch applications.

Compared with SN74CBT3384APW and 74LVC1G3157GW, the QS3861QG8 uniquely combines industrial temperature range, integrated undershoot clamping, flow-through pinout, and sub-6 Ω R_ON in a single 24-pin package-making it optimal for robust, high-integrity bus isolation where layout efficiency and ESD resilience matter.

Availability

QS3861QG8 is available at Aetrix Electronics and suitable for hot-swapping systems, voltage translation interfaces, and power-gated subsystems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for QS3861QG8 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 QS3861QG8 belongs to Renesas' legacy QuickSwitch® bus switch family, originally developed by IDT to solve high-speed signal integrity challenges in mixed-voltage computing and communications systems.

FAQ

What is the maximum allowable undershoot voltage on QS3861QG8 inputs?

The QS3861QG8 features built-in undershoot clamp diodes on all A, B, and BE pins rated for –3 V (pulse width ≤20 ns). This protects against negative transients during hot-plug events. Exceeding –3 V may damage the device. The QS3861QG8 datasheet specifies this absolute limit under AC Input Voltage (V_AC) in Absolute Maximum Ratings, and it applies regardless of V_CC level or operating temperature.

Does QS3861QG8 support bidirectional signal flow between Bus A and Bus B?

Yes, the QS3861QG8 provides fully bidirectional signal routing: when BE is LOW, signals pass transparently from A0–A9 to B0–B9 and vice versa with identical 5 Ω ON resistance in both directions. No direction control pin is needed. This behavior is confirmed in the Functional Description and Function Table sections of the QS3861QG8 datasheet, and is fundamental to its use in bus isolation and hot-swap applications.

What is the recommended PCB layout practice for QS3861QG8's NC pin (Pin 22)?

Pin 22 of the QS3861QG8 is designated NC (No Connect) and must not be tied to V_CC, GND, or any signal. Per the manufacturer's guidance, it should remain electrically floating-unrouted and unconnected on the PCB. Solder mask coverage is acceptable, but intentional grounding or powering violates the QS3861QG8 design specification and may compromise parametric performance or reliability.

Can QS3861QG8 operate reliably at 3.3V supply voltage?

No, the QS3861QG8 is specified only for 5 V ±5% operation (4.75 V to 5.25 V). Its DC Electrical Characteristics-including VIH (2 V min), VIL (0.8 V max), and R_ON (5 Ω typ)-are guaranteed only at V_CC = 5 V. Operation at 3.3 V is outside datasheet specifications and may result in undefined logic thresholds, increased R_ON, or functional failure. For 3.3V systems, consider dedicated low-voltage bus switches instead of the QS3861QG8.

How does QS3861QG8 achieve zero propagation delay?

The QS3861QG8 achieves zero added propagation delay by using passive FET switches with no internal logic gates or amplifiers. Signal delay arises only from the RC time constant of its 5 Ω R_ON and load capacitance-typically <0.25 ns at 50 pF-which is negligible compared to driver rise/fall times. This is explicitly stated in the Switching Characteristics note: "The bus switch contributes no propagation delay other than the RC delay… adds very little propagation delay to the system." The QS3861QG8 thus preserves timing integrity in high-speed parallel buses.