Octal D-type Transparent Latches with 3-state Outputs# Technical Documentation: HD74LVC373ATELL Octal D-Type Latch with 3-State Outputs
Manufacturer : HIT (Hitachi, Ltd.)
Component Type : Octal Transparent Latch with 3-State Outputs
Technology : Low-Voltage CMOS (LVC)
Package : TSSOP-20 (Tape and Reel)
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## 1. Application Scenarios
### Typical Use Cases
The HD74LVC373ATELL is an octal transparent latch designed for temporary data storage and bus interfacing in digital systems. Its primary function is to capture and hold data present at its inputs (D0-D7) when the Latch Enable (LE) signal is high, and present this data at its outputs (Q0-Q7) when the Output Enable (OE) signal is low. When OE is high, the outputs enter a high-impedance state, allowing multiple devices to share a common bus without contention.
Key operational modes:
- Data Latching : When LE is high, Q outputs follow D inputs transparently. When LE transitions from high to low, the data present at D inputs at that moment is latched and maintained at Q outputs regardless of subsequent changes at D inputs.
- Bus Driving : With OE active low, the latched data drives the connected bus lines. With OE high, outputs are disabled (high-Z), making the device effectively invisible to the bus.
- Buffer/Isolation : The device can isolate subsystems while allowing controlled data transfer between them.
### Industry Applications
1. Microprocessor/Microcontroller Systems
- Address/Data Bus Buffering : Frequently used in 8-bit systems to demultiplex address/data buses, latch addresses during the first part of a bus cycle, and free the bus for data transfer.
- I/O Port Expansion : Latches output data for peripheral devices like displays (LED, LCD), keypad scanners, or relay drivers.
- Memory Interface : In memory subsystems to hold row/column addresses or chip select signals.
2. Communication Equipment
- Data Packet Buffering : Temporarily stores data packets in networking equipment (routers, switches) during processing or routing decisions.
- Signal Conditioning : In serial-to-parallel or parallel-to-serial conversion circuits.
3. Industrial Control Systems
- Process Control : Latches sensor data or control signals for actuators in PLCs (Programmable Logic Controllers).
- Machine Control : Holds step sequences or state information in automated machinery.
4. Automotive Electronics
- Body Control Modules : Controls lighting, window lifts, or seat positioning where multiple outputs need to be set simultaneously and held.
- Instrument Clusters : Drives discrete indicators or segments of displays.
5. Consumer Electronics
- Display Drivers : Latches data for multi-digit LED displays or LCD panels.
- Gaming Consoles : Interfaces between processors and input/output devices.
### Practical Advantages and Limitations
Advantages:
- Wide Voltage Range : Operates from 1.65V to 3.6V, compatible with modern low-voltage logic (1.8V, 2.5V, 3.3V) while tolerating 5V inputs, enabling mixed-voltage system design.
- High-Speed Operation : Typical propagation delay of 4.3 ns at 3.3V, supporting bus frequencies up to 100+ MHz.
- Low Power Consumption : CMOS technology provides very low static power dissipation (typically <10 µA ICC).
- High Drive Capability : Can sink/sink up to 24 mA per output, sufficient to drive multiple CMOS inputs or LEDs directly.
- 3-State Outputs : Allows direct connection to bidirectional buses.
- Bus-Hold Function : Optional feature on inputs eliminates need for external pull-up/pull-down resistors in floating input
