Technical Summary: 74373 Octal Latch with 3-State Outputs

Overview

The M54/74HC373/533 (commonly referred to as 74373) is a high-speed CMOS octal latch featuring 3-state outputs. This integrated circuit is designed to provide robust data storage and output control capabilities for digital systems. The device is part of the 74HC logic family, which combines the low power consumption of CMOS technology with the high-speed performance typically associated with bipolar logic. The 74373 is widely used in applications requiring temporary data storage, bus interfacing, and data buffering.

The octal latch architecture consists of eight transparent D-type latches with separate data inputs (D0-D7) and outputs (Q0-Q7). A latch enable (LE) input controls the data transfer from inputs to outputs, while an output enable (OE) input places the outputs in a high-impedance state, making the device suitable for bus-oriented applications.

Key Features

• High-speed operation: Typical propagation delay of 13 ns at VCC = 5V
• Low power consumption: ICC = 4 μA maximum at TA = 25°C
• Wide operating voltage range: 2V to 6V
• 3-state outputs for bus interface capability
• High noise immunity: CMOS technology provides superior noise margins
• Balanced propagation delays
• Symmetric output impedance
• ESD protection: HBM EIA/JESD22-A114-A exceeds 2000V
• Latch-up performance exceeds 250 mA per JESD78
• Available in multiple package options including DIP, SOIC, and TSSOP

Applications

The 74373 octal latch finds application in numerous digital systems, including:

• Data storage and buffering in microprocessor systems
• Bus interface and isolation circuits
• Memory address latching
• Input/output port expansion
• Data synchronization circuits
• Temporary storage in arithmetic logic units
• Bus hold circuits in communication systems
• Parallel-to-serial data conversion systems

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (VCC): -0.5V to +7V
• Input Voltage (VI): -0.5V to VCC + 0.5V
• Output Voltage (VO): -0.5V to VCC + 0.5V
• Input Diode Current (IIK): ±20 mA
• Output Diode Current (IOK): ±20 mA
• VCC or GND Current (ICC or IGND): ±50 mA
• Storage Temperature Range (TSTG): -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage (VCC): 2V to 6V
• Input Voltage (VI): 0V to VCC
• Output Voltage (VO): 0V to VCC
• Operating Temperature Range (TA): -40°C to +85°C (industrial grade)
• Input Rise/Fall Time (tr, tf): 0 to 1000 ns (VCC = 2V), 0 to 500 ns (VCC = 4.5V), 0 to 400 ns (VCC = 6V)

DC Electrical Characteristics

• High-Level Input Voltage (VIH): 70% of VCC (min)
• Low-Level Input Voltage (VIL): 30% of VCC (max)
• High-Level Output Voltage (VOH): VCC - 0.1V (min) at IOH = -4 mA
• Low-Level Output Voltage (VOL): 0.1V (max) at IOL = 4 mA
• Input Leakage Current (II): ±1 μA (max) at VCC = 6V
• 3-State Output Leakage Current (IOZ): ±5 μA (max) at VCC = 6V
• Quiescent Supply Current (ICC): 4 μA (max) at VCC = 6V

AC Electrical Characteristics

• Propagation Delay (Dn to Qn): 13 ns (typ), 26 ns (max) at VCC = 5V, CL = 50 pF
• Output Enable Time (OE to Qn): 14 ns (typ), 28 ns (max) at VCC = 5V, CL = 50 pF
• Output Disable Time (OE to Qn): 14 ns (typ), 28 ns (max) at VCC = 5V, CL = 50 pF
• Setup Time (Dn to LE): 12 ns (min) at VCC = 5V
• Hold Time (LE to Dn): 5 ns (min) at VCC = 5V
• Maximum Clock Frequency (fMAX): 50 MHz (typ) at VCC = 5V

Package Information

The 74373 is available in several industry-standard packages:

20-Pin Plastic Dual In-Line Package (PDIP)

• Package Code: 648-08
• Dimensions: 26.16 mm x 6.35 mm body
• Lead Pitch: 2.54 mm
• Operating Temperature: -40°C to +85°C

20-Pin Small Outline Integrated Circuit (SOIC)

• Package Code: 751D-05
• Dimensions: 12.8 mm x 7.5 mm body
• Lead Pitch: 1.27 mm
• Operating Temperature: -40°C to +85°C

20-Pin Thin Shrink Small Outline Package (TSSOP)

• Package Code: 948F-03
• Dimensions: 6.5 mm x 4.4 mm body
• Lead Pitch: 0.65 mm
• Operating Temperature: -40°C to +85°C

Functional Description

The 74373 octal transparent latch operates as follows: When the Latch Enable (LE) input is high, the Q outputs follow the data (D) inputs. When LE goes low, the data present at the D inputs at that time is latched and appears at the outputs until LE goes high again. The Output Enable (OE) input, when high, places the outputs in a high-impedance state regardless of the LE input state.

The truth table for the 74373 is as follows:

Where:

• L = Low voltage level
• H = High voltage level
• X = Don't care
• Z = High impedance state
• Q0 = Previous output state before LE went low

Design Considerations

When implementing the 74373 in a system design, several factors should be considered:

• Power Supply Decoupling: A 0.1 μF ceramic capacitor should be placed as close as possible between VCC and GND pins to minimize noise.
• Unused Inputs: All unused inputs should be tied to either VCC or GND to prevent floating inputs which can cause excessive power consumption and noise sensitivity.
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