Signal
Level Shifter
Bidirectional voltage-domain translation for mixed-voltage systems.
What is it?
A level shifter translates logic signals between two different voltage domains — e.g., a 1.8 V SoC talking to a 3.3 V peripheral, or a 5 V sensor feeding a 3.3 V MCU. Modern automatic-direction level shifters use small MOSFETs to handle bidirectional signalling without explicit direction control — both sides can drive the line, and the shifter passes either edge.
When do you need it?
- MCU at 3.3 V talking to legacy 5 V peripherals (or vice versa).
- Application processor at 1.8 V talking to 3.3 V SD card / I²C devices.
- Mixed-voltage I²C bus (one side 1.8 V, other 3.3 V or 5 V).
- SPI / UART / GPIO domain bridging on multi-rail boards.
- ESD-protected port translation (some level shifters add I/O ESD protection).
How to pick the right one
- Number of channels
- 1, 2, 4, 8 — match to your bus width.
- Bidirectional or unidirectional
- Auto-direction-sensing for I²C-like buses; explicit-direction (DIR pin) for SPI/UART where you know the signal flow.
- VA and VB ranges
- Voltages each side can swing to. Common: 1.65-5.5 V on each side.
- Speed
- Slow (100 kHz I²C), fast (>10 MHz SPI), or very fast (USB / SDIO).
- Output drive / fanout
- Match to load capacitance — long traces or multiple inputs need stronger drive.
What Magnias offers
Magnias level-shifting solutions include single-gate translators (ML74LV1T08 / ML74LV1T126) for unidirectional signals, and dedicated bidirectional translators in SOT-23-6 / SOT-363 / TSSOP packages for I²C and SPI.
Common questions
Auto-direction or fixed-direction?
Auto-direction (FET-based) is simpler and works for I²C / open-drain buses. Fixed-direction (buffer-based) gives sharper edges and faster speed for SPI / clock signals.
Why does I²C need a special level shifter?
I²C is bidirectional open-drain. A simple unidirectional buffer would lock the bus in one direction. Use a FET-based bidirectional translator for I²C.
Can I just use resistor dividers to shift down?
Only for unidirectional 5 V → 3.3 V signal. Doesn't work for bidirectional signals or 3.3 V → 5 V shift. Real level shifters are needed for everything else.