SCPS196E December   2010  – February 2017 TCA9554A

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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 I2C Interface Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 I/O Port
      2. 8.3.2 Interrupt Output (INT)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-On Reset
    5. 8.5 Programming
      1. 8.5.1 I2C Interface
    6. 8.6 Register Maps
      1. 8.6.1 Device Address
      2. 8.6.2 Control Register and Command Byte
      3. 8.6.3 Register Descriptions
        1. 8.6.3.1 Bus Transactions
          1. 8.6.3.1.1 Writes
          2. 8.6.3.1.2 Reads
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Calculating Junction Temperature and Power Dissipation
        2. 9.2.1.2 Minimizing ICC When I/Os Control LEDs
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Power-On Reset Requirements
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

Applications of the TCA9554A has this device connected as a slave to an I2C master (processor), and the I2C bus may contain any number of other slave devices. The TCA9554A is typically in a remote location from the master, placed close to the GPIOs to which the master must monitor or control. IO Expanders such as the TCA9554A are typically used for controlling LEDs (for feedback or status lights), controlling enable or reset signals of other devices, and even reading the outputs of other devices or buttons.

9.2 Typical Application

Figure 26 shows an application in which the TCA9554A can be used.

TCA9554A typ_app_SCPS196.gif
1. The SCL and SDA pins must be tied directly to VCC because if SCL and SDA are tied to an auxiliary power supply that can be powered on while VCC is powered off, then the supply current, ICC, increases as a result.
2. Device address is configured as 0111000 for this example.
3. P0, P2, and P3 are configured as outputs.
4. P1, P4, and P5 are configured as inputs.
5. P6 and P7 are not used and have internal 100-kΩ pullup resistors to protect them from floating.
Figure 26. Application Schematic

9.2.1 Design Requirements

9.2.1.1 Calculating Junction Temperature and Power Dissipation

When designing with this device, it is important that the Recommended Operating Conditions not be violated. Many of the parameters of this device are rated based on junction temperature. So junction temperature must be calculated in order to verify that safe operation of the device is met. The basic equation for junction temperature is shown in Equation 1.

Equation 1. TCA9554A Equation_01_SCPS254.gif

θJA is the standard junction to ambient thermal resistance measurement of the package, as seen in Thermal Information table. Pd is the total power dissipation of the device, and the approximation is shown in Equation 2.

Equation 2. TCA9554A Equation_02_SCPS254.gif

Equation 2 is the approximation of power dissipation in the device. The equation is the static power plus the summation of power dissipated by each port (with a different equation based on if the port is outputting high, or outputting low. If the port is set as an input, then power dissipation is the input leakage of the pin multiplied by the voltage on the pin). Note that this ignores power dissipation in the INT and SDA pins, assuming these transients to be small. They can easily be included in the power dissipation calculation by using Equation 3 to calculate the power dissipation in INT or SDA while they are pulling low, and this gives maximum power dissipation.

Equation 3. TCA9554A Equation_03_SCPS254.gif

Equation 3 shows the power dissipation for a single port which is set to output low. The power dissipated by the port is the VOL of the port multiplied by the current it is sinking.

Equation 4. TCA9554A Equation_04_SCPS254.gif

Equation 4 shows the power dissipation for a single port which is set to output high. The power dissipated by the port is the current sourced by the port multiplied by the voltage drop across the device (difference between VCC and the output voltage).

9.2.1.2 Minimizing ICC When I/Os Control LEDs

When the I/Os are used to control LEDs, normally they are connected to VCC through a resistor as shown in Figure 26. For a P-port configured as an input, ICC increases as VI becomes lower than VCC. The LED is a diode, with threshold voltage VT, and when a P-port is configured as an input the LED is off but VI is a VT drop below VCC.

For battery-powered applications, it is essential that the voltage of P-ports controlling LEDs is greater than or equal to VCC when the P-ports are configured as input to minimize current consumption. Figure 27 shows a high-value resistor in parallel with the LED. Figure 28 shows VCC less than the LED supply voltage by at least VT. Both of these methods maintain the I/O VI at or above VCC and prevents additional supply current consumption when the P-port is configured as an input and the LED is off.

The TCA9554A has an integrated 100-kΩ pull-up resistor, so there is no need for an external pull-up.

TCA9554A app_hival_r_cps126.gif Figure 27. High-Value Resistor in Parallel With LED
TCA9554A app_lowval_r_cps126.gif Figure 28. Device Supplied by a Lower Voltage

9.2.2 Detailed Design Procedure

The pull-up resistors, RP, for the SCL and SDA lines need to be selected appropriately and take into consideration the total capacitance of all slaves on the I2C bus. The minimum pull-up resistance is a function of VCC, VOL,(max), and IOL as shown in Equation 5.

Equation 5. TCA9554A desc_eq1_scps199.gif

The maximum pull-up resistance is a function of the maximum rise time, tr (300 ns for fast-mode operation,
fSCL = 400 kHz) and bus capacitance, Cb as shown in Equation 6.

Equation 6. TCA9554A desc_eq2_scps204.gif

The maximum bus capacitance for an I2C bus must not exceed 400 pF for standard-mode or fast-mode operation. The bus capacitance can be approximated by adding the capacitance of the TCA9554A, Ci for SCL or Cio for SDA, the capacitance of wires, connections, traces, and the capacitance of additional slaves on the bus.

9.2.3 Application Curves

TCA9554A D008_SCPS204.gif
Standard-mode Fast-mode
(fSCL = 100 kHz, tr = 1 µs) (fSCL = 400 kHz, tr = 300 ns)
Figure 29. Maximum Pull-Up Resistance (Rp(max)) vs Bus Capacitance (Cb)
TCA9554A D009_SCPS199.gif
VOL = 0.2*VCC, IOL = 2 mA when VCC ≤ 2 V
VOL = 0.4 V, IOL = 3 mA when VCC > 2 V
Figure 30. Minimum Pull-Up Resistance (Rp(min)) vs Pull-Up Reference Voltage (VCC)