The PCA9306, offered by HeroMicro, is a high-performance, directionless bidirectional level translator for I²C-bus and SMBus signals. It seamlessly and at high speed translates data between logic voltage domains ranging from 1.0V to 5.5V, making it the ideal bridge between low-voltage microcontrollers (e.g., 1.8V/3.3V MCUs) and higher-voltage peripherals (e.g., 5V sensors or EEPROMs).
1. Key Features Overview
Based on the datasheet provided by HeroMicro (PCA9306.pdf), key features include:
True Bidirectional Auto-Sensing Translation:
No direction control pin required: The device automatically senses the data flow direction.
Wide Voltage Range: Low-side (VREF1) supports 1.0V - 3.6V, high-side (VREF2) supports 1.8V - 5.5V. Typical applications include 1.8V↔3.3V, 1.8V↔5V, 3.3V↔5V, etc.
High Speed & Low Latency:
Maximum propagation delay of less than 1.5ns, supporting Standard-mode (100kHz), Fast-mode (400kHz), Fast-mode Plus (1MHz), and even >2MHz I²C bus speeds.
Low On-Resistance & High Compatibility:
Channel on-resistance is only ~3.5Ω, resulting in minimal signal distortion.
5V-tolerant I/O ports, allowing safe interfacing with 5V systems.
Fully compatible with open-drain I²C bus structure.
Flexible Enable Control:
EN Pin: When EN is LOW, all ports go into high-impedance state, isolating both sides. When EN is HIGH, level translation is enabled.
Package: Comes in a compact TSSOP-8 package, saving PCB space.
2. Pin Configuration & Functions
| Pin | Symbol | Function |
|---|---|---|
| 1 | GND | Ground |
| 2 | VREF1 | Low-voltage side reference supply (1.0V - 3.6V) |
| 3 | SCL1 | Low-voltage side serial clock line |
| 4 | SDA1 | Low-voltage side serial data line |
| 5 | SDA2 | High-voltage side serial data line |
| 6 | SCL2 | High-voltage side serial clock line |
| 7 | VREF2 | High-voltage side reference supply (1.8V - 5.5V) |
| 8 | EN | Enable input (referenced to VREF2) |
3. Critical Design Guidelines
(1) Pull-Up Resistors (Critical!)
Pull-up resistors MUST be present on BOTH sides of the bus! This is fundamental to I²C operation.
Low-Side Pull-Ups: SCL1 and SDA1 must be pulled up to VREF1 via resistors.
High-Side Pull-Ups: SCL2 and SDA2 must be pulled up to VREF2 via resistors.
Selecting Resistor Values: The value depends on operating frequency, bus capacitance, and drive current. Tables 1-3 in the datasheet provide recommended minimum values for different sink currents (3mA, 10mA, 15mA). For example, for 3.3V↔5V at 10mA drive, the minimum high-side (Rpu(B)) value is 1780Ω. The actual resistor chosen should be equal to or greater than the value in the table.
(2) Supply Voltage Setup
Voltage Difference Requirement: For optimal level shifting performance, it is strongly recommended that VREF2 be at least 1V higher than VREF1. For instance, if VREF1=1.8V, VREF2 should be ≥ 2.8V (typically 3.3V or 5V).
EN Pin Connection: The EN pin must be referenced to the VREF2 voltage level. For dynamic control, it can be driven by a GPIO; if always enabled, it can be tied directly to VREF2, and it's advisable to add a ~200kΩ pull-up resistor for noise immunity.
(3) Operating Modes
Enabled Mode (EN = High): The internal switch is ON, connecting SCL1/SDA1 to SCL2/SDA2 for bidirectional translation.
Disabled Mode (EN = Low): The switch is OFF, and all I/O ports are in a high-impedance state, completely isolating the two bus sides. This feature is useful for bus reset or power management.
(4) PCB Layout Recommendations
Minimize Trace Length: Place the PCA9306 as close as possible to the master controller (usually the low-voltage MCU) to minimize trace length and parasitic capacitance.
Minimize Bus Capacitance: The number of nodes, connectors, and trace length on the bus all add to the total capacitance (CL), which limits the maximum operating frequency. Optimize the layout to minimize CL.
(5) Multi-Frequency Bus Consideration
If the two sides operate at different frequencies (e.g., one at 400kHz, the other at 100kHz), the lower-speed bus must be isolated (e.g., by disabling its devices) when the high-speed bus is active. Otherwise, communication may fail due to the added delay.
4. Typical Applications
3.3V Microcontroller (MCU) communicating with 5V I²C sensors/EEPROMs
1.8V SoC/FPGA communicating with 3.3V peripheral modules
Board-level interconnects in mixed-voltage systems
Any scenario requiring bridging I²C/SMBus signals between different logic voltage domains
5. Summary
HeroMicro's PCA9306 is a simple, efficient, and reliable solution for bidirectional level translation. Its directionless operation, ultra-low latency, and wide voltage compatibility greatly simplify the design of mixed-voltage systems. The keys to successful implementation are correctly configuring pull-up resistors on both sides and adhering to the VREF2 > VREF1 + 1V power supply design rule. By following this guide, you can easily achieve seamless I²C communication across voltage domains.
