SCPS199D August   2014  – October 2016 TCA9538


  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 I2C Interface Timing Requirements
    7. 6.7 RESET Timing Requirements
    8. 6.8 Switching Characteristics
    9. 6.9 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 I/O Port
      2. 8.3.2 Interrupt Output (INT)
      3. 8.3.3 RESET Input
    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 Map
      1. 8.6.1 Device Address
      2. 8.6.2 Control Register and Command Byte
      3. 8.6.3 Register Descriptions
        1. Bus Transactions
          1. Writes
          2. Reads
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 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



9 Application and Implementation


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

Figure 24 shows an application in which the TCA9538 can be used.

9.2 Typical Application

TCA9538 typ_app_cps199.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 could be powered on while VCC is powered off, then the supply current, ICC, increases as a result.
B. Device address is configured as 1110000 for this example.
C. P0, P2, and P3 are configured as outputs.
D. P1, P4, and P5 are configured as inputs.
E. P6 and P7 are not used and must be configured as outputs.
Figure 24. Application Schematic

9.2.1 Design Requirements 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 24. 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 25 shows a high-value resistor in parallel with the LED. Figure 26 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.

TCA9538 app_hival_r_cps126.gif Figure 25. High-Value Resistor in Parallel with LED
TCA9538 app_lowval_r_cps126.gif Figure 26. 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 1:

Equation 1. TCA9538 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 2:

Equation 2. TCA9538 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 TCA9538, 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

TCA9538 D008_SCPS204.gif
(fSCL = 100 kHz, tr = 1 µs)
(fSCL = 400 kHz, tr = 300 ns)
Figure 27. Maximum Pull-Up Resistance (Rp(max)) vs Bus Capacitance (Cb)
TCA9538 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 28. Minimum Pull-Up Resistance (Rp(min)) vs Pull-Up Reference Voltage (VCC)