Integrated Circuits For Seamless Bidirectional Voltage Translation

As electronic systems grow more complex, seamlessly communicating across different voltage domains becomes increasingly important. Integrated circuits with built-in bidirectional translation capabilities can greatly simplify mixed-voltage interface design.

Enabling Seamless Communication Across Different Voltage Domains

With proliferating power domains in today’s electronics, seamless voltage translation enables critical system connectivity. Careful interface design is necessary for robust operation.

Importance of voltage translation in mixed-voltage systems

Bidirectional voltage translation bridges connections between circuitry operating at different voltage levels. This facilitates interoperation, modular system design, and integration of components regardless of supply voltage.

Table of Contents

For example, voltage translation allows a microcontroller on a 1.8V power domain to interface with peripherals powered at 3.3V or 5V. I/O signals can traverse between domains without level shifting external to the translator device.

Key requirements for bidirectional translation

Bidirectional translators must reliably convert voltages in both directions without introducing excess delays or glitches during domain transitions. Additional key parameters include:

Propagation delay to maintain signal integrity, especially for high-speed serial interfaces
Current drive capability to avoid distortion of signals that load down during translation
Voltage translation range between specified minimum and maximum I/O voltages
Low-power operation based on the application power budget
Compact package options for space-constrained PCB designs

Leveraging Integrated Circuits to Simplify Design

Integrated bidirectional voltage translator circuits greatly ease implementation compared to discrete solutions. Circuit protection, timing control, and reduced BOM provide advantages.

Integrated circuits with bidirectional translation capabilities

Bidirectional translator ICs integrate level shifting diodes, FETs, timing logic, and protective circuitry within compact, dedicated packages. Translators specifially designed for dual-supply translation applicatons include:

TXS0102 – Fast 2.5V to 5.5V bidirectional translator in tiny SOT-23 package
ADUM3160 – 3.0V to 5.5V translator with propagation delays down to 3.5ns
SN74AVC4T774 – 4-bit translator targeting vacuum fluorescent display interfaces

Example part numbers and key parameters

The TXS0102 from Texas Instruments provides fast translation between voltages up to 5.5V in either direction:

Maximum VCC voltage: 5.5V
Maximum VO voltage on outputs: VCC
VO/VI voltage translation range: 2.5V to 5.5V
Bidirectional propagation delay: 9ns
Available in SOT-23-6 package

Reference circuit showing integrated circuit implementation

The TXS0102 enables a dual-supply interface between a microcontroller and peripheral device:

The microcontroller operates from a 1.8V supply while the peripheral requires a 5V input. The TXS0102 translates bidirectionally with minimal delays.

Achieving Robust Level Shifting Using Integrated FET Arrays

Integrated arrays with back-to-back NMOS and PMOS FETs achieve reliable bidirectional level shifting for mixed-voltage interfaces.

Dual NMOS/PMOS FET arrays for bidirectional translation

Paired NMOS and PMOS transistors configured in arrays enable bidirectional voltage translation functionality. The FETs effectively transform voltages bidirectionally based on their gate-source relationships.

When interfaces operate within the FET array design range, the PMOS transistors activate to pull translated signal voltages high while the NMOS transistors pull low.

Example schematic with FET array implementation

The SN74AVC4T774 4-bit translator from Texas Instruments leverages NMOS/PMOS FET arrays:

The chip translates control signals for vacuum fluorescent display segments bidirectionally between 2.5V and 5V supplies.

Key design considerations for noise immunity

For robust operation, additional components help filter noise, prevent latch-up, and protect against overvoltages across the FET arrays:

Small series resistors with capacitors aid power supply decoupling
Zener diodes help clamp transients beyond FET maximums
Careful PCB layout places components minimizing coupling/ground noise

Verifying Bidirectional Translation Functionality

Thorough testing across operating conditions ensures the translator design achieves reliable bidirectional voltage shifting.

Recommended test setup

The test setup should generate signals across the translator’s expected interface voltage range. Connect oscilloscope probes monitoring both translator input and output pins during evaluation.

Checking voltage translation in both directions

Apply low frequency signals first in one translation direction, then the other. Observe oscilloscope waveforms translating between different voltage levels without distortion.

Probe both translator terminals to verify level shifting behaviour into the connected logic families.

Example oscilloscope captures showing correct operation

The captured waveform shows a 1MHz input signal transitioning from 3.3V logic high to 0V properly translating to the 5V domain output.

Meeting High-Speed Communication Requirements

While many voltage translators focus on control/interface applications, high throughput bidirectional translation up to hundreds of megabits/second is achievable.

Impact of propagation delay through voltage translator

Excess propagation delays as signals traverse the translator can distort high-rate serial bus waveforms. Violating interface timing budgets may result.

Selecting translator devices with guaranteed maximum propagation delays ensures signal integrity for a given communication standard.

Techniques to preserve signal integrity at high data rates

Integrated translators targeting high-speed serial applications incorporate methods to prevent waveform distortion. Common techniques include:

Aggressive propagation delay minimization
Output slew rate control
Low-jitter timing elements
Integrated series termination resistors
Small form factor packaging to reduce parasitic capacitance

Example simulation plots demonstrating signal performance

The simulated eye diagram of a 100MHz data signal traversing the translator shows minimal noise and temporal closure, meeting interface integrity requirements.

Overcoming Voltage Translation Issues During Development

While highly reliable when designed properly, voltage translation circuits may still encounter problems. Understanding troubleshooting techniques accelerates debugging.

Common problems and troubleshooting tips

Basic voltage translator issues include:

Distorted output levels – Measure translator power pin voltages to ensure within spec range
Excess propagation delays – Reduce signal frequency, minimize capacitive loading
Unidirectional translation – Check translator power connections and enable control signals if available

Example failure modes and mitigation strategies

Overvoltage events may disrupt bidirectional translators:

Use clamping diodes and TVS diodes to protect translators against transients exceeding absolute maximum ratings
Insert series resistors on connections to vulnerable translator terminals to help limit current
Select translators specified to tolerate higher voltages or implement voltage regulators

Next Steps for Seamless Voltage Translation

Additional resources and design tools further assist in developing robust multi-voltage interfaces.

Additional resources for further learning

Refer to device manufacturer websites for voltage translator reference designs, application notes, selection tools, and related technical documentation to refine implementations.

Industry conferences also provide leading-edge advancements in mixed-voltage interface solutions as system complexity increases.

Extending concepts to other mixed-voltage interfaces

While the article focuses on digital voltage translation, the concepts apply equally to translating analogue signals between different domains. Simply substitute analogue translator devices in the example circuits.