SN74LVC2G74DCUR

The SN74LVC2G74 is a single positive-edge-triggered D-type flip-flop from TI’s 74LVC logic family, offering asynchronous preset (PRE) and clear (CLR) inputs with complementary Q and Q-bar outputs. Despite the ‘2G’ prefix (indicating a 2-gate device in the LVC family), this part contains a single flip-flop element with both preset and clear — the ‘2G’ refers to the approximate gate count, not the number of flip-flops.

The device operates across a wide voltage range of 1.65 V to 5.5 V, making it suitable for mixed-voltage systems. At 5 V, the maximum propagation delay is 4.4 ns with a 50-pF load, and the maximum clock frequency reaches 200 MHz. The setup time is only 1.1 ns and hold time is 500 ps at 5 V, enabling high-speed synchronous designs.

The asynchronous preset input (PRE, active low) sets Q high regardless of clock and data inputs. The asynchronous clear input (CLR, active low) sets Q low regardless of other inputs. When both PRE and CLR are inactive (high), data at the D input is transferred to Q on the rising edge of CLK. This independent preset/clear capability is useful for power-on initialization, manual reset, and handshake circuits.

The Ioff feature disables outputs when VCC is at 0 V, preventing damaging backflow current in partial-power-down and live-insertion applications. The ±24-mA output drive at 3.3 V (±32 mA at 5 V) can directly drive LED indicators or interface with TTL-level inputs. The 10-µA maximum ICC makes the device suitable for always-on logic circuits.

The VSSOP-8 (DCU) package occupies only 4.6 mm² of board area, approximately half the size of the SSOP-8 (DCT) alternative. TI also offers a DSBGA (chip-scale) package (YZP suffix) at 1.91×0.91 mm for ultra-compact designs. The -40°C to +125°C operating range (DCUR suffix) supports automotive and industrial applications.

**D Flip-Flop Core:** The SN74LVC2G74 uses CMOS transmission-gate and inverter-based master-slave latch architecture. On the low phase of CLK, the master latch is transparent and tracks the D input. On the rising edge of CLK, the master latch closes and the slave latch opens, transferring the captured D value to the Q output. This edge-triggered behavior ensures that Q changes only once per clock cycle.

**Asynchronous Preset and Clear:** The PRE and CLR inputs bypass the clocked path. When PRE is low, an internal pull-up path forces Q high regardless of CLK and D. When CLR is low, an internal pull-down path forces Q low. Both inputs are level-sensitive and active-low. If both PRE and CLR are asserted simultaneously, both Q and Q-bar go high (invalid state); the last one released determines the final output.

**Ioff Partial Power-Down:** When VCC = 0 V, the Ioff circuitry places all I/O pins in a high-impedance state. This prevents current from flowing from an external signal (e.g., from a powered device on the same bus) through the SN74LVC2G74’s internal ESD diodes to the unpowered VCC rail. This is critical for hot-swap and battery-backup systems where some devices may be powered while others are not.

**Wide-Voltage Operation:** The LVC architecture uses a thin-oxide CMOS process that supports 1.65-V to 5.5-V operation. Input pins accept voltages up to 5.5 V independently of VCC, allowing the device to translate between voltage domains (e.g., 3.3-V input signals with 1.8-V VCC).