Application Report SCEA043March 2010 A Guide to Voltage Translation With TXB-Type Translators Susan Curtis, Dave Moon ....................................................................................... High Volume Linear ABSTRACT Modern trends are driving the need for lower supply voltages across many system-level designs. As most processor voltage levels continue to decrease in the interest of achieving the lowest possible power consumption, peripheral devices maintain a need for higher voltage levels, creating potential for voltage discontinuities within a system. To remedy this mixed voltage system incompatibility, a voltage translator can be used. Texas Instruments High Volume Linear group offers a wide range of voltage level translators. A variety of architectures provide solutions for different application environments including dual-supply direction-controlled, auto-direction sensing, and application-specific memory card interface translators. The information in this application report is intended to help system designers understand the architecture and operation of the TXB-type auto-direction sensing translator family. Contents 1 The Need For Voltage-Level Translation ................................................................................ 2 2 Auto-Direction Sensing Voltage Translator Architecture ............................................................... 2 3 Driving External Loads with TXB Translators ........................................................................... 5 4 Output Enable Control ...................................................................................................... 6 5 Conclusion ................................................................................................................... 6 List of Figures 1 Digital Switching Levels.................................................................................................... 2 2 Basic TXB010x Architecture............................................................................................... 3 3 Active Output Rising/Falling Edge-Rate Acceleration Circuitry and DC Resistor Paths........................... 3 4 Typical I vs V Curve ..................................................................................................... 4 IN IN 5 TXB Active Output Rising Edge-Rate Acceleration Illustration ....................................................... 5 1 SCEA043March 2010 A Guide to Voltage Translation With TXB-Type Translators Submit Documentation Feedback Copyright 2010, Texas Instruments IncorporatedThe Need For Voltage-Level Translation www.ti.com 1 The Need For Voltage-Level Translation The need for voltage level translation is becoming increasingly significant in today s electronic systems. As the digital switching level standards have continued to progress toward lower voltage levels, system incompatibilities have arisen. Figure 1 illustrates the trend toward lower system voltage levels and demonstrates the incompatibilities that mixed voltage systems can face. 5 V V 5 V V CC CC V 4.44 V OH 0.7V V CC IH 3.3 V V CC 2.4 V 2.5 V V 0.5V V 2.4 V V V CC CC OH OH T 2 V V 2.0 V V 2 V V IH IH OH 1.8 V V CC 1.7 V V IH V 1.5 V V V -0.45V CC OH CC 0.3V V 1.5 V V 1.5 V V V CC IL T T 1.2 V CC 0.65V V CC IH 0.65V V CC IH V 0.65V CC IH 0.8 V V 0.8 V V IL IL 0.7 V V IL 0.35V V CC IL 0.35V V IL 0.5 V V CC OL 0.4 V V 0.4 V V OL 0.4 V V 0.45 V V OL V 0.35V OL OL IL CC GND 0 V 0 V 0 V GND 0 V 0 V GND GND 0 V GND GND 0 V GND 2.5V CMOS 1.8V CMOS 1.5V CMOS 1.2V CMOS 5V CMOS 5V TTL 3.3V LVTTL Figure 1. Digital Switching Levels For two devices to interface reliably, the output driver voltages must be compatible with receiver input thresholds. For this condition to be met in mixed voltage systems, a voltage translator is often required. Texas Instruments offers several unique device architectures for addressing voltage translation needs. The most familiar to system designers is probably a direction controlled buffer translator, such as the SN74AVC8T245. These translators can help remedy many problems in system voltage compatibility but do require DIR (direction) control pins. If the system environment does not provide a programmable GPIO to control the direction pin, an auto-direction sensing translator architecture can provide an alternative translation solution. 2 Auto-Direction Sensing Voltage Translator Architecture If a processer GPIO input direction-control signal is not available or if one is not desired, an auto-direction sensing voltage translator can provide a robust solution. As the name implies, this type of translator does not require the use of a direction control signal, and each channel supports independent transmission or reception of data. This eliminates the need for a processor GPIO to control a DIR input, resulting in simplified software driver development as well as smaller device packaging due to reduced pin-count. The TXB push-pull buffered type architecture does not require a DIR control signal to establish the direction of data flow. This architecture is designed to exclusively be connected and interfaced with a push-pull CMOS driver and is capable of driving a capacitive or high impedance loads in applications such as Secure Digital (SD) or Serial Peripheral Interface (SPI). The TXB010x devices are not intended for use 2 in open-drain applications. For applications such as I C where there is a need to connect and interface with an open-drain driver, TI offers TXS-type (i.e., for Switch-type) translators. Please refer to TI application report, A Guide to Voltage Translation With TXS-Type Translators, literature number SCEA044 for more information on the TXS-type voltage translators. Figure 2 shows the basic architecture of a single-bit (or channel) of the TXB010x device. 2 A Guide to Voltage Translation With TXB-Type Translators SCEA043March 2010 Submit Documentation Feedback Copyright 2010, Texas Instruments Incorporated