TXB0104 App Note Datasheet by Adafruit Industries LLC

View All Related Products | Download PDF Datasheet
l TEXAS INSTRUMENTS
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 IIN vs VIN Curve ..................................................................................................... 4
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 Incorporated
Mimi
VCC
VCC
VCC
VCC
VCC
VCC
VOH
VIH
VT
VIL
VOL
GND
5 V
4.44 V
0.7 VCC
0.5 VCC
0.3 VCC
0.5 V
0 V
VIH
VIL
GND
VOH
VIH
VT
VIL VIL
VOL
GND
5 V
2.4 V
2 V
1.5 V
0.8 V
0.4 V
0 V
VOH
VIH
VT
VOL
GND
3.3 V
2.4 V
2 V
1.5 V
0.8 V
0.4 V
0 V
2.5 V
2.0 V
1.7 V
0.7 V
0.4 V
0 V
VOH
VIH
VIL
VOL
GND
1.8 V
VCC-0.45 V
0.65VCC
0.35VCC
0.45 V
0 V
VOH
VIH
VIL
VOL
GND
1.2 V
0.65VCC
0.35VCC
0 V
VCC
1.5 V
0.65VCC
0.35VCC
0 V
VIH
VIL
GND
5V CMOS 5V TTL 3.3V LVTTL 2.5V CMOS 1.8V CMOS 1.5V CMOS 1.2V CMOS
The 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.
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
in open-drain applications. For applications such as I2C where there is a need to connect and interface
with an open-drain driver, TI offers TXS-type (i.e., "S" 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.
2A Guide to Voltage Translation With TXB-Type Translators SCEA043March 2010
Submit Documentation Feedback
Copyright © 2010, Texas Instruments Incorporated
l TEXAS INSTRUMENTS
A-port
4 kΩ
4 kΩ
One-
shot
Translator
VCCA VCCB
B-port
T1
T2
T3
T4
Translator
One-
shot
One-
shot
One-
shot
1.8 V
3.3 V
4 kΩ
V = 3.3 V
CCB
Output
B-Port
One-
shot
1.8 V
3.3 V
Input
signal
Output
signal
4 kΩ
Output
B-Port
Time ns
T2
V = 3.3 V
CCB
One-
shot
One-
shot
One-
shot
Input
signal
Output
signal
Time ns
T2
T1T1
www.ti.com
Auto-Direction Sensing Voltage Translator Architecture
Figure 2. Basic TXB010x Architecture
The TXB translators incorporate a weak buffer with one-shot (O.S.) circuitry to improve switching speeds
for rising and falling edges. When the A-port is connected to a system driver and driven high, the weak
4-kΩbuffer drives the B-port high in conjunction with the upper one shot, which becomes active when it
senses a rising edge. The B-port is driven high by both the buffer and the T1PMOS, which lowers the
output impedance seen on the B-port while the O.S. circuit is active. On the falling edge, the lower O.S. is
triggered and the buffer, along with the T2NMOS, lowers the output impedance seen on the B-port while
the O.S. circuit is operating and the output is driven low.
Figure 3 highlights with color the active circuitry involved in a low-to-high transition and a high-to-low
transition. The weak buffer is shown in blue, and the active O.S. circuit is shown in green.
Figure 3. Active Output Rising/Falling Edge-Rate Acceleration Circuitry and DC Resistor Paths
3
SCEA043March 2010 A Guide to Voltage Translation With TXB-Type Translators
Submit Documentation Feedback
Copyright © 2010, Texas Instruments Incorporated
l TEXAS INSTRUMENTS
–(V V )/4 k
D T Ω
V /4 k
TΩ
VIN
IIN
Auto-Direction Sensing Voltage Translator Architecture
www.ti.com
The O.S. reduces the output impedance during the transition allowing the TXB device to drive a load while
maintaining fast propagation delays and edge rates. Once the transition is completed, the O.S. circuit
times out, and the buffer and the 4-kΩpullup resistor hold the B-port signal high or low.
We call the TXB-type translator "weak-buffered", because it is strong enough to hold the output port high
or low during a dc state, but weak in that the 4-kΩimpedance buffer can be easily over-driven by a
system driver connected to the A or B port when a bus direction change is desired.
Figure 4 shows a typical IIN vs VIN curve.
Figure 4. Typical IIN vs VIN Curve
Where,
VTis the input threshold voltage of the TXB010x; VTis typically VCCI/2.
VDis the supply voltage of the external system driver.
An external system driver must supply more than ±2 mA of current to reliably overdrive the hold provided
by the weak buffer.
4A Guide to Voltage Translation With TXB-Type Translators SCEA043March 2010
Submit Documentation Feedback
Copyright © 2010, Texas Instruments Incorporated
*9 TEXAS INSTRUMENTS
OL CCO CCO
4 kΩ
V = × V = 0.075 × V
50 kΩ + 4 kΩ
1.8V
Time – ns
2.6V
Input
signal
Output
signal
One-
shot
One-
shot
VCCB
Reff
T1
T2
4kΩ
www.ti.com
Driving External Loads with TXB Translators
3 Driving External Loads with TXB Translators
TXB devices were architected for driving high-impedance loads. If the application requires an external
pull-up or pull-down resistor (Rpu or Rpd), special consideration must be given to the resistor value. When
the output is in a steady high or low dc state, it is exclusively driven by the 4-kimpedance buffer. If an
external resistor is added as either a pull-up or pull-down, a resistor divider network will be formed with the
4kbuffer. If the value of the resistor is too small, the VOH or VOL will be adversely impacted. If the value is
large, (i.e. >50k), there will be very little change in the output voltage level.
Equation 1 helps to illustrate how an external pull-up resistor affects the output VOL levels. If an external
50-kresistor is connected as a pull-up and the output is in a low signal state, then:
(1)
As a result, , if an external pull-up or pull-down resistor is needed, system designers should always
choose large enough Rpu or Rpd values to ensure adequate VOH and VOL levels.
Figure 5 shows an illustration of a low-to-high, rising-edge signal for the TXB-type translators. The O.S.
circuits turn on the PMOS transistor (T1) for approximately 10 ns or 95% of the output edge, whichever
occurs first. During this acceleration phase, the output resistance (Reff) of the driver is decreased to
approximately 40 Ωto 70 Ωto increase the current-drive capability of the device. When the circuits are
active, a resulting high ac drive is realized by turning on T1and the rising-edge speeds up. The output port
is maintained at a high signal level through this 4-kinternal resistor. With no load, the one-shots remain
on for ~4.5 ns.
Figure 5. TXB Active Output Rising Edge-Rate Acceleration Illustration
During this ac drive acceleration period, the Reff associated with the PMOS (T1) and NMOS (T2) is
decreased to 40 Ω- 70 Ω. The typical output impedance varies based on output supply voltage, and is
summarized in Table 1.
Table 1. TXB010x Effective Output Impedance Values
VCCO Output Impedance Value
1.2 V to 1.8 V 70 Ω
1.8 V to 3.3 V 50 Ω
3.3 V to 5 V 40 Ω
5
SCEA043March 2010 A Guide to Voltage Translation With TXB-Type Translators
Submit Documentation Feedback
Copyright © 2010, Texas Instruments Incorporated
l TEXAS INSTRUMENTS www.1i.com
Output Enable Control
www.ti.com
With regard to capacitive loads, TXB translators are designed to drive up to 70 pF without issue. If
capacitive loading is larger than 70 pF, the O.S. will time-out after 10 ns and subsequently turn off before
the output voltage is driven fully high or low. From there, the output will continue to rise or fall based on
the RC time constant determined by the 4-kbuffer, load resistance and capacitive loading. To ensure
reliable operation, system designers should keep capacitive loading for the TXB-type devices to 70 pF or
less. With no external loading, the one-shot circuits will remain on for approximately 4.5 nsec. The
duration of the one-shots is related to the output voltage level. The output high voltage at which O.S.
switches off is approximately 95% of full scale, while the output low voltage at which O.S. switches off is
approximately 5%.
4 Output Enable Control
The TXB devices offer low power consumption of 5-mA maximum ICC when the output enable is high.
When the output enable is low, the TXB translator buffer will be disabled and the outputs are put into a
high impedance state for increased power savings. The OE input circuit is referenced to the VCCA
power-supply and when the device is disabled, the 4-kbuffer and the O.S. for both the A-port and B-Port
are also disabled. In this state, output leakage (IOZ) will be less than ±2 mA. If the application does not
require output enable control, The OE pin should be tied to the VCCA supply. One should never leave the
OE pin floating in an indeterminate state as this can cause undesirable quiescent current to flow in the
device, which subsequently increases its overall power dissipation.
Under partial power down conditions, the outputs are also disabled and put into a high-Impedance state.
This feature is referred to as VCC isolation. If VCCB = 0 V, the A-port is disabled. Likewise, if VCCA = 0V, the
B-port will be disabled. In addition, the TXB type translators are fully specified for partial-power-down
applications using the IOFF feature. This IOFF circuitry disables the outputs, preventing damaging current
backflow through the device when these devices are powered-down.
5 Conclusion
The TXB translators offer system designers a versatile solution for remedying mixed-voltage system
incompatibilities. These translators eliminate the need for provisioning a processor GPIO, since they
change the direction of the data flow automatically without the use of a direction control pin. This simplifies
system level design and allows for solutions in smaller packages.
Please visit www.ti.com for data sheets and additional information on all bit-width TXB translators along
with the full line of Texas Instruments voltage-level translators.
6A Guide to Voltage Translation With TXB-Type Translators SCEA043March 2010
Submit Documentation Feedback
Copyright © 2010, Texas Instruments Incorporated
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements,
and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should
obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are
sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard
warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where
mandated by government requirements, testing of all parameters of each product is not necessarily performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and
applications using TI components. To minimize the risks associated with customer products and applications, customers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right,
or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a
warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual
property of the third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied
by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive
business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional
restrictions.
Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all
express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not
responsible or liable for any such statements.
TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably
be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing
such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be
provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in
such safety-critical applications.
TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are
specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military
specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at
the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.
TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are
designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated
products in automotive applications, TI will not be responsible for any failure to meet such requirements.
Following are URLs where you can obtain information on other Texas Instruments products and application solutions:
Products Applications
Amplifiers amplifier.ti.com Audio www.ti.com/audio
Data Converters dataconverter.ti.com Automotive www.ti.com/automotive
DLP® Products www.dlp.com Communications and www.ti.com/communications
Telecom
DSP dsp.ti.com Computers and www.ti.com/computers
Peripherals
Clocks and Timers www.ti.com/clocks Consumer Electronics www.ti.com/consumer-apps
Interface interface.ti.com Energy www.ti.com/energy
Logic logic.ti.com Industrial www.ti.com/industrial
Power Mgmt power.ti.com Medical www.ti.com/medical
Microcontrollers microcontroller.ti.com Security www.ti.com/security
RFID www.ti-rfid.com Space, Avionics & www.ti.com/space-avionics-defense
Defense
RF/IF and ZigBee® Solutions www.ti.com/lprf Video and Imaging www.ti.com/video
Wireless www.ti.com/wireless-apps
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2010, Texas Instruments Incorporated

Products related to this Datasheet

EVAL BOARD FOR TXB0104
EVAL BOARD 8CH BI LOGIC LEVEL