SLVS037O September   1989  – December 2020 TL7702B , TL7705B , TL7733B

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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: TL77xxBC, TL77xxBI, and TL7705BQ
    6. 6.6 Switching Characteristics: TL77xxBC, TL77xxBI, and TL7705BQ
    7. 6.7 Timing Diagrams
    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 Wide Supply-Voltage Range
      2. 8.3.2 Adjustable Pulse Duration
    4. 8.4 Device Functional Modes
  9. 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 Related Links
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|8
  • P|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

10 Power Supply Recommendations

GUID-7E26BF41-0845-4470-AE31-B7159DC0FB88-low.gif Figure 10-1 System Reset Controller With Undervoltage Sensing

When the TL770xB SENSE terminal is used to monitor VCC, TI recommends a current-limiting resistor in series with CT. During normal operation, the timing capacitor is charged by the onboard current source to approximately VCC or an internal voltage clamp (≈7.1-V Zener), whichever is less. When the circuit then is subjected to an undervoltage condition during which VCC is rapidly slewed down, the voltage on CT exceeds that on VCC. This forward biases a secondary path internally, which falsely activates the outputs. A fault is indicated when VCC drops below V(CT), not when VSENSE falls below VT–.

Adding the external resistor, RT, prevents false triggering. Its value is calculated as follows:

Equation 1. (V(CT) – VT-) / RT

where

  • V(CT) = VCC or 7.1 V, whichever is less
  • VT– = 4.55 V (nom)
  • RT = value of series resistor required

For VCC = 5 V

Equation 2. (5 – 4.55) / RT < 1 mA

Therefore,

Equation 3. RT > 450 Ω

Using a 20%-tolerance resistor, RT should be greater than 560 Ω.

Adding this series resistor changes the duration of the reset pulse by no more than 10%. RT extends the discharge of CT, but also skews the V(CT) threshold. These effects tend to cancel one another. The precise percentage change can be derived theoretically, but the equation is complicated by this interaction and is dependent upon the duration of the supply-voltage fault condition.

Both outputs of the TL770xB must be terminated with similar value resistors, even when only one is being used. This prevents unwanted plateauing in either output waveform during switching, which may be interpreted as an undefined state or delay system reset.