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SN74CBTD3384CDBQR: 10-Bit FET Bus Switch with Integrated Level Shifting
10/6/2026 5:04:31 AM
SN74CBTD3384CDBQR: 10-Bit FET Bus Switch with Integrated Level Shifting
Texas Instruments' SN74CBTD3384CDBQR is a high-speed, TTL-compatible 10-bit FET bus switch in an SSOP-24 (DBQ) package. Its key value lies in an integrated 5V-to-3.3V level shifter, implemented via an on-chip series diode that eliminates external components. The device supports bidirectional data flow with near-zero propagation delay, making it ideal for bus isolation and signal gating in mixed-voltage systems.
Key Specifications at a Glance
| Parameter | Value |
|---|---|
| Number of Channels | 10-bit (configurable as two 5-bit) |
| Supply Voltage (VCC) | 4.5V to 5.5V |
| Propagation Delay (tpd) | 0.15ns at 5V, 50pF (typical) |
| ON-State Resistance (ron) | 3 Ohm (typical, VCC=5V) |
| Quiescent Current (ICC) | 1.5mA (maximum) |
| Operating Temperature | -40 degrees C to +85 degrees C |
| Package | SSOP-24-150mil |
Key Features and Operating Principle
Integrated Level Shifting: An on-chip series diode in the VCC path introduces a forward drop of approximately 0.7V, reducing the gate voltage to about 4.3V. Combined with the NMOS threshold drop of about 1V, the output is clamped to approximately 3.3V, reliably translating 5V inputs to 3.3V outputs while preserving bidirectional capability.
Active Undershoot Protection: Both A and B ports feature active undershoot-protection circuitry that senses events down to -2V and ensures the switch remains in the correct OFF state, preventing false triggering and enhancing system reliability.
Ioff Partial-Power-Down Protection: When the device is powered down (VCC=0V), the Ioff feature prevents damaging current from backflowing through the I/O ports, providing complete isolation and supporting partial-power-down system designs.
Flexible Control: The device is organized as two 5-bit switches with independent active-low output-enable pins (1OE, 2OE). A low OE connects port A to port B; a high OE places the ports in high-impedance. The two control pins can also be tied together to use the device as a single 10-bit switch.
Typical Applications
The device is widely used in memory interleaving, bus isolation, low-distortion signal gating, and logic level translation in battery-powered devices and embedded systems.
Q and A
Q1: How does the SN74CBTD3384CDBQR achieve 5V-to-3.3V level shifting?
A: An on-chip series diode in the VCC path creates a 0.7V drop, setting the MOSFET gate at about 4.3V. Subtracting the 1V gate-to-source drop limits the output to approximately 3.3V, completing the translation.
Q2: Does it support bidirectional data flow?
A: Yes. Based on an NMOS pass transistor, the switch allows bidirectional data transfer between ports A and B with minimal signal degradation.
Q3: What is the practical benefit of -2V undershoot protection?
A: When the bus switch is OFF, negative transients on I/O ports (for example, from transmission-line reflections) could falsely turn the switch on. The protection circuitry senses the event and maintains the OFF state, preventing signal contention.
Q4: In what scenarios is the Ioff feature useful?
A: In partially powered-down systems. When the device is unpowered but other active devices remain on the bus, Ioff prevents current backflow through the I/O ports, protecting the device and maintaining bus isolation.
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