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.