SBVS250 April   2015 TPS3779 , TPS3780

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Feature Description
      1. 8.3.1 Inputs (SENSE1, SENSE2)
      2. 8.3.2 Outputs (OUT1, OUT2)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation (VDD ≥ VDD(min))
      2. 8.4.2 Power-On Reset (VDD < V(POR))
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Threshold Overdrive
      2. 9.1.2 Sense Resistor Divider
    2. 9.2 Typical Applications
    3. 9.3 Monitoring Two Separate Rails
      1. 9.3.1 Design Requirements
      2. 9.3.2 Detailed Design Procedure
      3. 9.3.3 Application Curve
    4. 9.4 Early Warning Detection
      1. 9.4.1 Design Requirements
      2. 9.4.2 Detailed Design Procedure
      3. 9.4.3 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 Device Support
      1. 12.1.1 Development Support
        1. 12.1.1.1 Evaluation Modules
        2. 12.1.1.2 Spice Models
      2. 12.1.2 Device Nomenclature
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
        1. 12.2.1.1 Related Documentation
    3. 12.3 Related Links
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9 Application and Implementation

9.1 Application Information

The TPS3779 and TPS3780 are used as precision dual-voltage detectors. The monitored voltage, VDD voltage, and output pullup voltage (TPS3780 only) can be independent voltages or connected in any configuration.

9.1.1 Threshold Overdrive

Threshold overdrive is how much VDD exceeds the specified threshold, and is important to know because smaller overdrive results in slower OUTx response. Threshold overdrive is calculated as a percent of the threshold in question, as shown in Equation 1:

Equation 1. Overdrive = | (VDD / VIT – 1) × 100% |

where

  • VIT is either VIT– or VIT+, depending on whether calculating the overdrive for the negative-going threshold or the positive-going threshold, respectively.

Figure 16 illustrates the VDD minimum detectable pulse versus overdrive, and is used to visualize the relationship overdrive has on tPD(f) for negative-going events.

9.1.2 Sense Resistor Divider

The resistor divider values and target threshold voltage can be calculated by using Equation 2 and Equation 3 to determine VMON(UV) and VMON(PG), respectively.

Equation 2. TPS3779 TPS3780 uv_sbvs250.gif
Equation 3. TPS3779 TPS3780 pg_sbvs250.gif

where

  • R1 and R2 are the resistor values for the resistor divider on the SENSEx pins,
  • VMON(UV) is the target voltage at which an undervoltage condition is detected, and
  • VMON(PG) is the target voltage at which the output goes high when VMONx rises.

Choose RTOTAL ( = R1 + R2) so that the current through the divider is approximately 100 times higher than the input current at the SENSEx pins. The resistors can have high values to minimize current consumption as a result of low input bias current without adding significant error to the resistive divider. For details on sizing input resistors, refer to application report SLVA450, Optimizing Resistor Dividers at a Comparator Input, available for download from www.ti.com.

9.2 Typical Applications

9.3 Monitoring Two Separate Rails

TPS3779 TPS3780 two_rail_sbvs250.gifFigure 22. Monitoring Two Separate Rails Schematic

9.3.1 Design Requirements

Table 2. Design Parameters

PARAMETER DESIGN REQUIREMENT DESIGN RESULT
VDD 5 V 5 V
Hysteresis 10% 10%
Monitored voltage 1 3.3 V nominal, VMON(PG) = 2.9 V, VMON(UV) = 2.6 V VMON(PG) = 2.908 V, VMON(UV) = 2.618 V
Monitored voltage 2 3 V nominal, VMON(PG) = 2.6 V, VMON(UV) = 2.4 V VMON(PG) = 2.606 V, VMON(UV) = 2.371 V
Output logic voltage 3.3-V CMOS 3.3-V CMOS

9.3.2 Detailed Design Procedure

  1. Select the TPS3780C. The C version is selected to satisfy the hysteresis requirement. The TPS3780 is selected for the output logic requirement. An open-drain output allows for the output to be pulled up to a voltage other than VDD.
  2. The resistor divider values are calculated by using Equation 2 and Equation 3. For SENSE1, R1 = 1.13 MΩ and R2 = 787 kΩ. For SENSE2, R3 (R1) = 681 kΩ and R4 (R2) = 576 kΩ.

9.3.3 Application Curve

TPS3779 TPS3780 two_curve_sbvs250.gifFigure 23. Monitoring Two Separate Rails Curve

9.4 Early Warning Detection

TPS3779 TPS3780 early_sbvs250.gifFigure 24. Early Warning Detection Schematic

9.4.1 Design Requirements

Table 3. Design Parameters

PARAMETER DESIGN REQUIREMENT DESIGN RESULT
VDD VMON VMON
Hysteresis 10% 10%
Monitored voltage 1 VMON(PG) = 3.3 V, VMON(UV) = 3 V VMON(PG) = 3.330 V, VMON(UV) = 2.997 V
Monitored voltage 2 VMON(PG) = 3.9 V, VMON(UV) = 3.5 V VMON(PG) = 3.921 V, VMON(UV) = 3.529 V

9.4.2 Detailed Design Procedure

  1. Select the TPS3779C. The C version is selected to satisfy the hysteresis requirement. The TPS3779 is selected to save on component count and board space.
  2. Use Equation 4 to calculate the total resistance for the resistor divider. Determine the minimum total resistance of the resistor network necessary to achieve the current consumption specification. For this example, the current flow through the resistor network is chosen to be 1.41 µA. Use the key transition point for VMON2. For this example, the low-to-high transition, VMON(PG), is considered more important.
    3. Equation 4. TPS3779 TPS3780 rtot_sbvs250.gif

    where

    • VMON(PG_2) is the target voltage at which OUT2 goes high when VMON2 rises, and
    • I is the current flowing through the resistor network.
  3. After RTOTAL is determined, R3 can be calculated using Equation 5. Select the nearest 1% resistor value for R3. In this case, 845 kΩ is the closest value.
    4. Equation 5. TPS3779 TPS3780 r3_sbvs250.gif
  4. Use Equation 6 to calculate R2. Select the nearest 1% resistor value for R2. In this case, 150 kΩ is the closest value. Use the key transition point for VMON1. For this example, the low-to-high transition, VMON(UV), is considered more important.
    5. Equation 6. TPS3779 TPS3780 r2_sbvs250.gif

    where

    • VMON(UV_1) is the target voltage at which OUT1 goes low when VMON1 falls.
  5. Use Equation 7 to calculate R1. Select the nearest 1% resistor value for R1. In this case, 1.78 MΩ is a 1% resistor.
    6. Equation 7. TPS3779 TPS3780 r1_sbvs250.gif

9.4.3 Application Curve

TPS3779 TPS3780 early_curve_sbvs250.gifFigure 25. Early Warning Detection Curve