8.1 Overview

The SN74CB3Q3125 device is a high-bandwidth FET bus switch utilizing a charge pump to elevate the gate voltage of the pass transistor, providing a low and flat ON-state resistance (r_on). The low and flat ON-state resistance allows for minimal propagation delay and supports rail-to-rail switching on the data input/output (I/O) ports. The SN74CB3Q3125 device also features low data I/O capacitance to minimize capacitive loading and signal distortion on the data bus. Specifically designed to support high-bandwidth applications, the SN74CB3Q3125 device provides an optimized interface solution ideally suited for broadband communications, networking, and data-intensive computing systems.

The SN74CB3Q3125 device is organized as four 1-bit bus switches with separate output-enable (1OE, 2OE, 3OE, 4OE) inputs. It can be used as four 1-bit bus switches or as one 4-bit bus switch. When OE is low, the associated 1-bit bus switch is ON, and the A port is connected to the B port, allowing bidirectional data flow between ports. When OE is high, the associated 1-bit bus switch is OFF, and a high-impedance state exists between the A and B ports.

This device is fully specified for partial-power-down applications using I_off. The I_off circuitry prevents damaging current backflow through the device when it is powered down. The device has isolation during power off.

To ensure the high-impedance state during power up or power down, OE should be tied to V_CC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.

Figure 4. Simplified Schematic, Each FET Switch (SW)

8.2 Functional Block Diagram

8.3 Feature Description

The SN74CB3Q3125 device has a high-bandwidth data path (up to 500 MHz) and has 5-V tolerant I/Os with the device powered up or powered down. It also has low and flat ON-state resistance (r_on) characteristics over operating range (r_on = 4-Ω Typ).

The SN74CB3Q3125 device has rail-to-rail switching on data I/O ports for 0-V to 5-V switching with
3.3-V V_CCand 0-V to 3.3-V switching with 2.5-V V_CC as well as bidirectional data flow with near-zero propagation delay and low input/output capacitance that minimizes loading and signal distortion (C_io(OFF) = 3.5-pF Typ).

The SN74CB3Q3125 device also provides a fast switching frequency (f_OE = 20-MHz Max) with data and control inputs that provide undershoot clamp diodes as well as low power consumption (I_CC = 0.6-mA Typ).

The V_CC operating range is from 2.3 V to 3.6 V and the data I/Os support 0-V to 5-V signal levels of
(0.8 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3.3 V, 5 V).

The control inputs can be driven by TTL or 5-V or 3.3-V CMOS outputs, and I_off supports partial-power-down mode operation.

8.4 Device Functional Modes

Table 1 lists the functional modes for the SN74CB3Q3125 device.