SBVS211B August   2012  – April 2015

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 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Push-Button Timer Selection (TS)
      2. 7.3.2 Inputs
        1. 7.3.2.1 TPS3420 Inputs (PB1, PB2)
        2. 7.3.2.2 TPS3421 Inputs (PB1, PB2)
        3. 7.3.2.3 TPS3422 Inputs (PB1)
      3. 7.3.3 Output (RST)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation (VDD > 1.6 V)
      2. 7.4.2 Below VDD(min) (1.6 V > VDD > 1.3 V)
      3. 7.4.3 Power-On Reset (VDD < 1.3 V)
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Single Input With Fixed Reset Pulse Duration
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Dual Input Applications
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curve
      3. 8.2.3 Latched Reset Signal
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
        3. 8.2.3.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Evaluation Modules
        2. 11.1.1.2 Spice Models
      2. 11.1.2 Device Nomenclature
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Related Links
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8 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.

8.1 Application Information

The TPS342x family of devices are small, low-current, push-button reset timers. These devices use a long timing setup delay to provide the system reset signals, and avoid resets from short push-button closures. This reset configuration allows for differentiation between user inputs and hard system resets. TPS342x uses an open drain output, has an input voltage range of 1.6 V to 6.5 V, and is specified from –40°C to +125°C.

The TPS3420 and TPS3421 are used to monitor two inputs while TPS3422 is used to monitor a single input.

8.2 Typical Applications

8.2.1 Single Input With Fixed Reset Pulse Duration

If only one input must be monitored to set the state of a logic pin, such as the enable pin of a load switch, use the TPS3422. After a reset event has occurred, RST is held low for a fixed amount of time (tRST) regardless of the state of the PB1 pin.

An application diagram is shown in Figure 15.

TPS342 ai_app_dig_tps3422_bvs211.gif
A. Connect TS to VCC or ground for different PB time delays.
Figure 15. TPS3422 Application Diagram

8.2.1.1 Design Requirements

Table 3 lists the design requirements for Figure 15.

Table 3. Design Requirements and Results

DESIGN REQUIREMENTS DESIGN RESULT
Single input PB1
Does not react to input signal less than 5 s 6 s (minimum)
Reset pulse greater than 240 ms 320 ms (minimum)
ICC < 5 µA 3.3 μA (maximum)

8.2.1.2 Detailed Design Procedure

When the output switches to the high-Z state, the rise time of the RST node depends on the pullup resistance and the capacitance on that node. Choose pullup resistors that satisfy both the downstream timing requirements and the sink current required to have a VOL low enough for the application; 1-kΩ to 1-MΩ resistors are a good choice for low-capacitive loads.

8.2.1.3 Application Curve

TPS342 C004_BVS211.pngFigure 16. Reset Pulse Duration vs Temperature

8.2.2 Dual Input Applications

If two inputs must be monitored to set the state of a microprocessor reset pin, either the TPS3420 or the TPS3421 can be used. The system functionality determines which device to use. Use the TPS3420 if RST must be held low until the signal on one of the PBx pins transitions to a logic high state. Use the TPS3421 if RST should only be held low for a fixed amount of time (tRST) regardless of the state of the PBx pins.

An application diagram that is suitable for either the TPS3420 and the TPS3421 is shown in Figure 17.

TPS342 ai_app_dig_tps3420_bvs211.gif
A. Connect TS to VCC or ground for different PB time delays. Connect one PB input to ground for use as a single channel.
Figure 17. TPS3420 or TPS3421 Application Diagram

8.2.2.1 Design Requirements

Table 4 lists the design requirements for Figure 17.

Table 4. Design Requirements and Results

DESIGN REQUIREMENTS DESIGN RESULT
TPS3420 TPS3421
Dual input PB1 and PB2 PB1 and PB2
Does not react to input signal less than 5 s 6 s (minimum) 6 s (minimum)
Reset pulse greater than 140 ms Depends on PBx timing 320 ms (minimum)
Reset pulse ends after at least one input goes high True Does not depend on PBx timing

8.2.2.2 Detailed Design Procedure

Determine which version of the TPS342x family best suits the functional performance required.

When the output switches to the high-Z state, the rise time of the RST node depends on the pullup resistance and the capacitance on that node. Choose pullup resistors that satisfy both the downstream timing requirements and the sink current required to have a VOL low enough for the application; 1-kΩ to 1-MΩ resistors are a good choice for low-capacitive loads.

8.2.2.3 Application Curve

TPS342 C004_BVS211.pngFigure 18. Reset Pulse Duration vs Temperature

8.2.3 Latched Reset Signal

Some applications require the reset signal (RST) to be latched and only change state after a second low input signal is received. To achieve a latched version of the RST signal, a D-flip-flop can be used. The output of the D-flip-flop, Q, is then connected to the device to be reset.

See Figure 19 for an example of a latched reset signal configuration.

TPS342 ai_latched_application_bvs211.gifFigure 19. Latched Reset Schematic and Timing Diagram

8.2.3.1 Design Requirements

Table 5 summarizes the design requirements for Figure 19.

Table 5. Design Requirements and Results

DESIGN REQUIREMENTS DESIGN RESULT
Single input PB1
Latched output Q
Does not react to input signal less than 5 s 6 s (minimum)
Reset pulse greater than 200 ms 320 ms (minimum)
ICC < 20 µA 13.3 μA (maximum)

8.2.3.2 Detailed Design Procedure

Once a positive-edge triggered D-flip-flop is chosen, make sure the slew rate of the RST signal is fast enough to trigger the flip-flop. For the SN74LVC1G74 shown in Figure 19, TI recommends a 1-kΩ pullup resistor. The RC time constant of the delay cap (CDELAY) and delay resistor (RDELAY)should be 10 times the rise time of the input voltage to VCC so that a clear signal is sent to the D-flip-flop, to initialize it into a known state.

8.2.3.3 Application Curve

TPS342 ai_tc_scope_bvs211.gifFigure 20. Latched Reset Waveforms Using SN74LVC1G74