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What is the difference between level-shifting bus switches and bus buffers?

A bus switch uses a MOSFET as a switch and pull-up resistors to level-shift the High-level voltage.
Being a simple switch, the bus switch does not provide any current drive capability.
The following describes the operation of a bus switch. Suppose that a signal is applied to input A.
When a voltage equal to or higher than VIH is applied to the Output Enable (OE) input, the bus switch transfers the input signal (High or Low) to the output.
The signal transfer operations depend on whether the input voltage is higher than the VOHU (input/output characteristics for up translation) specified in the datasheet.

  • 0V ≤ input voltage < VOHU: The internal switch is on and transfers a signal from A to B without changing its voltage.
  • Input voltage ≥ VOHU: The internal switch is off. The external pull-up resistor on the VCCB side pulls up the input voltage to the VCCB level.

In this way, the input signal is level-shifted and transferred to the output.

Equivalent circuit for a bus switch and its input and output waveforms  (VCCA < VCCB)
Equivalent circuit for a bus switch and its input and output waveforms (VCCA < VCCB)
VOHU and VOHD characteristics  shown in the datasheet ( TC7SPB9306TU )

VOHU and VOHD characteristics  shown in the datasheet ( TC7SPB9306TU )

Note 1: The Input/Output Characateristics for up translation indicate the input voltages required to provide. VCCA + 0.5 V on the outputs when measured using the test circuitry shown in Figure 7.
Note 2: The Input/Output Characateristics for down translation indicate the voltages that cause the output voltages to saturate when measured using the test circuitry shown in Figure 9.

A bus buffer uses a CMOS circuit for level-shifting. Therefore, it has an inherent drive capability and provides a digital output. For the drive capability, see the output current value shown in the Operating Ranges table in the datasheet.

Equivalent circuit for a bus buffer and its input and output waveforms
Equivalent circuit for a bus buffer and its input and output waveforms
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