SN74LVC8T245PWR

The SN74LVC8T245PWR is an 8-bit dual-supply bus transceiver with configurable voltage-level shifting and three-state outputs, manufactured by Texas Instruments. It belongs to the 74LVC family of low-voltage CMOS logic devices and is designed for bidirectional voltage-level translation between two independently powered data buses.

The device features two independent supply rails: VCCA (1.65V to 5.5V) for the A port and VCCB (1.65V to 5.5V) for the B port. This fully configurable dual-rail architecture allows translation between any two voltage nodes in the 1.65V to 5.5V range, including common combinations such as 1.8V to 3.3V, 2.5V to 3.3V, 3.3V to 5V, and any other valid pairing. The direction of data flow is controlled by the DIR (direction) input pin, and the outputs can be placed in a high-impedance state using the OE (output enable, active-low) input pin.

The SN74LVC8T245 supports a maximum data rate of 200 Mbps, making it suitable for high-speed digital interfaces including SPI, UART, I2S, JTAG, GPIO, and PCM. The propagation delay is typically 6.6 ns. The device provides ±32 mA output drive current on both ports, ensuring robust signal integrity across a wide range of load conditions.

A key feature is the VCC isolation function: when either VCCA or VCCB is grounded, all outputs are placed in the high-impedance state, preventing back-drive current from the active supply rail into the disabled side. The Ioff circuitry supports partial-power-down operation, ensuring that no destructive current flows back through the device when one or both supply rails are de-energized. This makes the SN74LVC8T245 suitable for hot-swap and live-insertion applications.

The device provides excellent ESD protection: 4000V HBM (Human Body Model), 100V MM (Machine Model), and 1000V CDM (Charged Device Model). Latch-up performance exceeds 100 mA per JESD 78 Class II. The control inputs (DIR and OE) reference VCCA for their VIH/VIL thresholds.

The PWR suffix denotes the TSSOP-24 (PW) package with tape and reel packaging (2,000 units per reel). The TSSOP-24 package measures 7.8 × 4.4 mm with a maximum height of 1.05 mm, making it suitable for space-constrained PCB layouts. Operating temperature range is -40°C to +85°C.

The SN74LVC8T245PWR operates as an 8-bit non-inverting bidirectional bus transceiver with configurable voltage-level translation between two independently powered bus domains.

Dual-Supply Architecture: The device has two independent power supply rails: VCCA powers the A port (pins A1-A8) and VCCB powers the B port (pins B1-B8). Each supply can be set independently within the 1.65V to 5.5V range. The A port I/O pins have input thresholds and output levels referenced to VCCA, while the B port I/O pins are referenced to VCCB. This dual-rail design is the fundamental mechanism that enables voltage-level translation: when data passes from the A port to the B port (or vice versa), the input signal is received at one voltage domain and the output is driven at the other voltage domain.

Direction Control (DIR): The DIR pin determines the direction of data flow between the A and B ports. When DIR is HIGH (referenced to VCCA thresholds), data flows from the A port to the B port: A1-A8 are configured as inputs, and B1-B8 are configured as outputs that follow the A port logic levels translated to the VCCB domain. When DIR is LOW, the direction reverses: B1-B8 become inputs and A1-A8 become outputs translated to the VCCA domain. This direction control is a global setting that applies to all 8 bits simultaneously; the SN74LVC8T245 does not support bit-wise independent direction control.

Output Enable (OE): The OE pin is an active-low output enable referenced to VCCA logic thresholds. When OE is LOW, the transceiver is active and data flows according to the DIR setting. When OE is HIGH, all outputs (both A port and B port) are placed in the high-impedance (three-state) state. This allows multiple SN74LVC8T245 devices or other bus drivers to share the same bus without contention, as only one device drives the bus at any given time.

Voltage-Level Translation Mechanism: The translation process occurs through the devices internal CMOS circuitry that is powered by both VCCA and VCCB simultaneously. When an input signal arrives at the A port, the internal logic detects the signal level using VCCA-referenced comparators. The detected logic state is then propagated to the B port output driver, which drives the output at VCCB-referenced levels. This ensures that a 1.8V logic HIGH on the A port (when VCCA = 1.8V) is correctly translated to a 3.3V logic HIGH on the B port (when VCCB = 3.3V), and vice versa. The translation is non-inverting: the logic state is preserved, only the voltage levels are changed.

VCC Isolation and Ioff: When either VCCA or VCCB is grounded or falls below the minimum operating voltage, the VCC isolation circuitry activates and places all I/O pins in the high-impedance state. This prevents current from flowing from the active supply through the device to the inactive supply, which could damage the device or the connected circuitry. The Ioff circuitry further ensures that during partial power-down, the input and I/O pins do not source or sink current, preventing destructive latch-up or back-drive conditions. This feature is critical for applications where different voltage domains may be powered up and down independently.

ESD and Latch-Up Protection: The device incorporates robust ESD protection clamps on all pins, rated at 4000V HBM, 100V MM, and 1000V CDM. The latch-up performance exceeds 100 mA per JESD 78 Class II, ensuring reliable operation in electrically harsh environments such as hot-plug backplanes and industrial control systems.