SCES727A June   2008  – December 2014 TXB0104-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Electrical Characteristics
    6. 6.6  Timing Requirements: VCCA = 1.2 V
    7. 6.7  Timing Requirements: VCCA = 1.5 V ± 0.1 V
    8. 6.8  Timing Requirements: VCCA = 1.8 V ± 0.15 V
    9. 6.9  Timing Requirements: VCCA = 2.5 V ± 0.2 V
    10. 6.10 Timing Requirements: VCCA = 3.3 V ± 0.3 V
    11. 6.11 Switching Characteristics: VCCA = 1.2 V
    12. 6.12 Switching Characteristics: VCCA = 1.5 V ± 0.1 V
    13. 6.13 Switching Characteristics: VCCA = 1.8 V ± 0.15 V
    14. 6.14 Switching Characteristics: VCCA = 2.5 V ± 0.2 V
    15. 6.15 Switching Characteristics: VCCA = 3.3 V ± 0.3 V
    16. 6.16 Operating Characteristics
    17. 6.17 Typical Characteristics
  7. Parameter Measurement Information
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Architecture
      2. 8.3.2 Input Driver Requirements
      3. 8.3.3 Output Load Considerations
      4. 8.3.4 Enable and Disable
      5. 8.3.5 Pullup or Pulldown Resistors on I/O Lines
    4. 8.4 Device Functional Modes
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Trademarks
    2. 12.2 Electrostatic Discharge Caution
    3. 12.3 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Detailed Description

8.1 Overview

The TXB0104 device is a 4-bit, bi-directional voltage-level translator specifically designed for translating logic voltage levels. The A port is able to accept I/O voltages ranging from 1.2 V to 3.6 V, while the B port can accept I/O voltages from 1.65 V to 5.5 V. The device is a buffered architecture with edge-rate accelerators (one-shots) to improve the overall data rate. This device can only translate push-pull CMOS logic outputs. If for open-drain signal translation, please refer to TI’s TXS010X products.

8.2 Functional Block Diagram

FBD_TXB0104.gif

8.3 Feature Description

8.3.1 Architecture

The TXB0104 architecture (see Functional Block Diagram) does not require a direction-control signal to control the direction of data flow from A to B or from B to A. In a DC state, the output drivers of the TXB0104 can maintain a high or low, but are designed to be weak, so that they can be overdriven by an external driver when data on the bus starts flowing the opposite direction.

The output one-shots detect rising or falling edges on the A or B ports. During a rising edge, the one-shot turns on the PMOS transistors (T1, T3) for a short duration, which speeds up the low-to-high transition. Similarly, during a falling edge, the one-shot turns on the NMOS transistors (T2, T4) for a short duration which speeds up the high-to-low transition. The typical output impedance during output transition is 70 Ω at VCCO = 1.2 V to 1.8 V, 50 Ω at VCCO = 1.8 V to 3.3 V, and 40 Ω at VCCO = 3.3 V to 5 V.

arch_t55_ces650.gifFigure 5. Architecture of TXB0104 I/O Cell

8.3.2 Input Driver Requirements

Typical IIN vs VIN characteristics of the TXB0104 are shown in Figure 6. For proper operation, the device driving the data I/Os of the TXB0104 must have drive strength of at least ±2 mA.

typ_curve_ces650.gifFigure 6. Typical IIN vs VIN Curve

8.3.3 Output Load Considerations

TI recommends careful PCB layout practices with short PCB trace lengths to avoid excessive capacitive loading and to ensure that proper one shot (O.S.) triggering takes place. PCB signal trace-lengths should be kept short enough such that the round trip delay of any reflection is less than the one-shot duration. This improves signal integrity by ensuring that any reflection sees a low impedance at the driver. The O.S. circuits have been designed to stay on for approximately 10 ns. The maximum capacitance of the lumped load that can be driven also depends directly on the one-shot duration. With very heavy capacitive loads, the one-shot can time-out before the signal is driven fully to the positive rail. The O.S. duration has been set to best optimize trade-offs between dynamic ICC, load driving capability, and maximum bit-rate considerations. Both PCB trace length and connectors add to the capacitance that the TXB0104 output sees, so it is recommended that this lumped-load capacitance be considered to avoid O.S. retriggering, bus contention, output signal oscillations, or other adverse system-level affects.

8.3.4 Enable and Disable

The TXB0104 has an OE input that is used to disable the device by setting OE = low, which places all I/Os in the high-impedance (Hi-Z) state. The disable time (tdis) indicates the delay between when OE goes low and when the outputs actually get disabled (Hi-Z). The enable time (ten) indicates the amount of time the user must allow for the one-shot circuitry to become operational after OE is taken high.

8.3.5 Pullup or Pulldown Resistors on I/O Lines

The TXB0104 is designed to drive capacitive loads of up to 70 pF. The output drivers of the TXB0104 have low DC drive strength. If pullup or pulldown resistors are connected externally to the data I/Os, their values must be kept higher than 50 kΩ to ensure that they do not contend with the output drivers of the TXB0104.

For the same reason, the TXB0104 should not be used in applications such as I2C or 1-Wire where an open-drain driver is connected on the bidirectional data I/O. For these applications, use a device from the TI TXS01xx series of level translators.

8.4 Device Functional Modes

The TXB0104 device has two functional modes, enabled and disabled. To disable the device, set the OE input to low, which places all I/Os in a high impedance state. Setting the OE input to high will enable the device.