FEATURES
· Operate From 1.65 V to 3.6 V
· Inputs Accept Voltages to 5.5 V
· Max tpd of 7.4 ns at 3.3 V
· Typical V OLP (Output Ground Bounce)
<0.8 at VCC = 3.3 V, TA = 25°C
· Typical V OHV (Output VOH Undershoot)
>2 V at VCC = 3.3 V, TA = 25°C
· Support Mixed-Mode Signal Operation on All
Ports (5-V Input/Output Voltage With
3.3-V VCC)
· Ioff Supports Partial-Power-Down Mode
Operation
· Latch-Up Performance Exceeds 250 mA Per
JESD 17
· ESD Protection Exceeds JESD 22
– 2000-V Human-Body Model (A114-A)
– 200-V Machine Model (A115-A)
– 1000-V Charged-Device Model (C101)

DESCRIPTION/ORDERING INFORMATION
The SN54LVC646A octal bus transceiver and register is designed for 2.7-V to 3.6-V VCC operation, and the
SN74LVC646A octal bus transceiver and register is designed for 1.65-V to 3.6-V VCC operation.
These devices consist of bus-transceiver circuits, D-type flip-flops, and control circuitry arranged for multiplexed
transmission of data directly from the input bus or from the internal registers. Data on the A or B bus is clocked
into the registers on the low-to-high transition of the appropriate clock (CLKAB or CLKBA) input. Figure 1
illustrates the four fundamental bus-management functions that are performed with the 'LVC646A devices.
Output-enable (OE) and direction-control (DIR) inputs control the transceiver functions. In the transceiver mode,
data present at the high-impedance port is stored in either register or in both.
The select-control (SAB and SBA) inputs can multiplex stored and real-time (transparent mode) data. DIR
determines which bus receives data when OE is low. In the isolation mode (OE high), A data is stored in one
register and B data can be stored in the other register.
When an output function is disabled, the input function still is enabled and can be used to store and transmit
data. Only one of the two buses, A or B, can be driven at a time.
Inputs can be driven from either 3.3-V or 5-V devices. This feature allows the use of these devices as translators
in a mixed 3.3-V/5-V system environment.
These devices are fully specified for partial-power-down applications using Ioff. The Ioff circuitry disables the
outputs, preventing damaging current backflow through the device when it is powered down.
To ensure the high-impedance state during power up or power down, OE should be tied to VCC through a pullup
resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.