Level shifters, voltage translators: whatever you call them, these devices are very handy when interfacing 5V and 3.3V logic for devices that aren’t 5V-tolerant. The 74LVC244 has long been my go-to solution for unidirectional 5V to 3.3V level shifting, and for 3.3V to 5V I’ll typically do nothing, since the 5V inputs generally work OK without shifting. But sometimes you need bidirectional level shifting with automatic direction sensing, and you may also want to step up those 3.3V signals to a full 5V. Enter three solutions from Texas Instruments: TXB0104, TXS0104, and TXS0108. These three chips all provide 4 or 8 channels of bidirectional level shifting with auto direction sensing, and at first glance they all seem very similar. But as I recently discovered, under the hood you’ll find significant differences in how they work and the types of applications they’re best suited for.

 
TXB0104

TI describes this chip as a “4-Bit Bidirectional Voltage-Level Translator With Automatic Direction Sensing.”

This TXB0104 4-bit noninverting translator uses two separate configurable power-supply rails. The A port is designed to track VCCA. VCCA accepts any supply voltage from 1.2 V to 3.6 V. The B port is designed to track VCCB. VCCB accepts any supply voltage from 1.65 V to 5.5 V. This allows for universal low-voltage bidirectional translation between any of the 1.2-V, 1.5-V, 1.8-V, 2.5-V, 3.3-V, and 5-V voltage nodes. VCCA must not exceed VCCB.

Power VCCA with 3.3V, power VCCB with 5V, and then it just works without any further configuration. Signals on pins A1..4 are propagated to pins B1..4 and vice-versa, while performing level shifting. But how? Scroll down to page 16 of the datasheet to find this block diagram of a single level shifter channel:

It’s complicated, but the most important thing here is that when the pins are treated as outputs, they’re actively driven to a high or low voltage with a pair of inverters. The output drive current is supplied by the TXB0104, through these inverters. When the pins are treated as inputs, the input signal is supplied to another inverter. In many ways it’s like the 74LVC245 except the direction is sensed automatically.

Elsewhere in the datasheet, it mentions a maximum data rate of 100 Mbps when VCCA is at least 2.5 volts.

 
TXS0104

Change a single letter in the part name, and you get TXS0104. What’s different? TI describes it as a “4-Bit Bidirectional Voltage-Level Translator for Open-Drain and Push-Pull Applications”. That sounds awfully similar to the TXB.

This 4-bit non-inverting translator uses two separate configurable power-supply rails. The A port is designed to track VCCA. VCCA accepts any supply voltage from 1.65 V to 3.6 V. VCCA must be less