74HC573D

The 74HC573D is an octal D-type transparent latch from Nexperia’s 74HC high-speed CMOS logic family, designed for general-purpose data storage and bus interface applications. This 8-bit latch features eight individual D-type data inputs and eight 3-state non-inverting outputs, all controlled by common latch enable (LE) and output enable (OE) signals. When the latch enable (LE) input is HIGH, the latch operates in transparent mode where the Q outputs directly follow the D inputs – any change on a D input immediately appears on the corresponding Q output. When LE transitions from HIGH to LOW, the data present at the D inputs at that moment is captured and held in the latch, regardless of subsequent changes on the inputs. The output enable (OE) controls the 3-state output buffers independently of the latch state. When OE is LOW, the latched data is presented at the outputs. When OE is HIGH, all outputs enter a high-impedance state, disconnecting from the bus but preserving the stored latch data. This allows multiple devices to share a common data bus without conflict. The flow-through pin arrangement (inputs on one side, outputs on the other) simplifies PCB layout, particularly for microprocessor bus interface designs. Operating from a 2.0V to 6.0V supply range with CMOS input levels, the 74HC573D offers typical propagation delays of 14ns (D to Q) at 4.5V supply. The device features input clamp diodes, latch-up immunity exceeding 100mA, and ESD protection greater than 2000V HBM. Packaged in the standard SO20 (SOT163-1) surface-mount package with 1.27mm pitch, the device is specified over the extended industrial temperature range of -40°C to +125°C and is fully compliant with JEDEC standards JESD8C and JESD7A. The 74HC573D is functionally identical to the 74HC373 but features a different pin configuration that is often preferred for bus-oriented designs.

The 74HC573D is a CMOS-based transparent latch, meaning that when the latch enable (LE) signal is HIGH, the output Q follows the input D (the latch is ‘transparent’). When LE goes LOW, the value of D at that moment is captured and held at the output, even if D subsequently changes. Each of the eight latch channels consists of a master latch stage that accepts the D input data when LE is HIGH, and a slave/output stage that drives the Q output. In transparent mode (LE=HIGH), the master latch is open and continuously passes the D input through to the slave stage, so Q=D. When LE goes LOW, the master latch closes and holds the last value, isolating the output from further input changes. The 3-state output buffer is controlled by the output enable (OE) signal. When OE is LOW, the output buffer is enabled and drives the latched data onto the output pin. When OE is HIGH, the output buffer is disabled and enters a high-impedance state where the pin is effectively floating, allowing bus sharing with other devices. Importantly, the OE signal does not affect the internal latch state – data remains latched and stored even when OE is HIGH. The CMOS implementation provides very low static power consumption, with quiescent current in the microamp range. The output stage uses complementary PMOS/NMOS transistors for rail-to-rail output swing and balanced sourcing/sinking capability. Setup and hold times define the timing requirements around the LE falling edge: the D input must be stable for at least the setup time before LE falls, and must remain stable for at least the hold time after LE falls, to ensure reliable latching. The device is designed to be robust with input protection diodes, latch-up immunity, and extensive ESD protection.

• Microprocessor and microcomputer data bus interface latches
• I/O port expansion for microcontroller and embedded systems
• Address latching in memory and peripheral decoding circuits
• Bus-oriented data storage and parallel data transfer
• Data acquisition systems holding sampled data
• Industrial control and automation systems
• Consumer electronics: TVs, set-top boxes, audio equipment
• General-purpose parallel data storage and register applications