74FCT3245QG

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74FCT3245QG Application Field and Working Principle

High speed CMOS Logic ICs are essential components when it comes to signal transmission and signal processing. They provide high noise immunity and high speed, while consuming low power and providing cost effective solutions. The 74FCT3245QG is such a high speed CMOS Logic IC, which belongs to the logic category – Buffers, Drivers, Receivers, Transceivers – and is specifically a 3.3V FCT designed for fully automated 1.5V to 3.3V bus translation applications.

The 74FCT3245QG has an auto-direction sensing capability that enables it to be used as a single IC or in multi-receiver environments without the need of complex logic. It is also an enhanced version of the 74FCT2245QG model, with improved output drive capability, higher performance and lower propagation delay, making it one of the best and most viable solutions when it comes to high speed transmissions. Its main features include:

• 15ns propagation delay
• Full TTL compatibility
• Built-in low voltage detected circuit
• Load impedance of up to 250Ω
• Low dynamic power consumption
• Fully compatible with High-Speed CMOS

The 74FCT3245QG is the ideal device of choice when demanding high-speed applications, such as hard disk drives, communications systems and high-speed digital buses and networks. It is also a suitable choice for fast microprocessor and FIFO interfaces, since it can operate in extreme temperature and process conditions with enhanced stable switching speeds.

Working Principle

The working principle of the 74FCT3245QG is based on a special Input and Output circuit design that operates with an extrinsic FET (Field Effect Transistors) level translator circuit. Generally, the Input circuit detects the logic levels present in the inputs, while the Output circuit produces an equivalent logic level in the outputs. The level translator circuit enables the 74FCT3245QG to function as a receiver in both LVCMOS and LVTTL communication systems.

The level translator circuit is composed of two P-Channel MOSFETs and two N-Channel MOSFETs. When an input is detected, one of the P-Channel FETs will be activated and a corresponding output voltage level is generated from the same FET. Moreover, the same FET will be turned off if the logic level of the input is 0. In addition, the other P-Channel FET is in series with a Pull-Down resistance and a logic level 1 is generated on its output if the input is 0.

The Output circuit includes one N-Channel FET with its gate connected to the VEN pin (Voltage Enable Pin) of the IC and its drain connected to the output buffer. The 74FCT3245QG also has a Programmable enable/disable function via the VEN pin meaning that it can be put in a low power Standby/Sleep mode. This is achieved by setting the VEN pin to its Low Voltage Enabled (LVE) state and thus no false output will be generated while consuming a low power.

The 74FCT3245QG can also be used in multi-receiver systems to auto-detect new transmitters and automatically mirror their information onto the target outputs. In such cases, the propagation delay will be determined by the increasing length of the cascaded receivers, which will result in slower switching times.

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