SLUS970C March   2011  – November 2023 TPS40170

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 Handling Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  LDO Linear Regulators and Enable
      2. 6.3.2  Input Undervoltage Lockout (UVLO)
        1. 6.3.2.1 Equations for Programming the Input UVLO:
      3. 6.3.3  Oscillator and Voltage Feed-Forward
        1. 6.3.3.1 Calculating the Timing Resistance (RRT)
      4. 6.3.4  Overcurrent Protection and Short-Circuit Protection (OCP and SCP)
      5. 6.3.5  Soft-Start and Fault-Logic
        1. 6.3.5.1 Soft Start During Overcurrent Fault
        2. 6.3.5.2 Equations for Soft Start and Restart Time
      6. 6.3.6  Overtemperature Fault
      7. 6.3.7  Tracking
      8. 6.3.8  Adaptive Drivers
      9. 6.3.9  Start-Up into Pre-Biased Output
      10. 6.3.10 Power Good (PGOOD)
      11. 6.3.11 PGND and AGND
    4. 6.4 Device Functional Modes
      1. 6.4.1 Frequency Synchronization
      2. 6.4.2 Operation Near Minimum VIN (VVIN ≤ 4.5 V)
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Bootstrap Resistor
      2. 7.1.2 SW Node Snubber Capacitor
      3. 7.1.3 Input Resistor
      4. 7.1.4 LDRV Gate Capacitor
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Custom Design with WEBENCH® Tools
        2. 7.2.2.2  List of Materials
        3. 7.2.2.3  Select a Switching Frequency
        4. 7.2.2.4  Inductor Selection (L1)
        5. 7.2.2.5  Output Capacitor Selection (C9)
        6. 7.2.2.6  Peak Current Rating of Inductor
        7. 7.2.2.7  Input Capacitor Selection (C1, C6)
        8. 7.2.2.8  MOSFET Switch Selection (Q1, Q2)
        9. 7.2.2.9  Timing Resistor (R7)
        10. 7.2.2.10 UVLO Programming Resistors (R2, R6)
        11. 7.2.2.11 Boot-Strap Capacitor (C7)
        12. 7.2.2.12 VIN Bypass Capacitor (C18)
        13. 7.2.2.13 VBP Bypass Capacitor (C19)
        14. 7.2.2.14 VDD Bypass Capacitor (C16)
        15. 7.2.2.15 SS Timing Capacitor (C15)
        16. 7.2.2.16 ILIM Resistor (R9, C17)
        17. 7.2.2.17 SCP Multiplier Selection (R5)
        18. 7.2.2.18 Feedback Divider (R10, R11)
        19. 7.2.2.19 Compensation: (R4, R13, C13, C14, C21)
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 Custom Design with WEBENCH® Tools
      3. 8.1.3 Related Devices
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.3.4 Overcurrent Protection and Short-Circuit Protection (OCP and SCP)

The TPS40170 has the capability to set a two-level overcurrent protection. The first level of overcurrent protection (OCP) is the normal overload setting based on low-side MOSFET voltage sensing. The second level of protection is the heavy overload setting such as short-circuit based on the high-side MOSFET voltage sensing. This protection takes effect immediately. The second level is termed short-circuit protection (SCP).

The OCP level is set by the ILIM pin voltage. A current (IILIM) is sourced into the ILIM pin from which a resistor RILIM is connected to GND. Resistor RILIM sets the first level of overcurrent limit. The OCP is based on the low-side FET voltage at the switch-node (SW pin) when the LDRV is ON after a blanking time, which is the product of inductor current and low-side FET turn-on resistance RDS(on). The voltage is inverted and compared to ILIM pin voltage. If it is greater than the ILIM pin voltage, then a 3-bit counter inside the device increments the fault-count by 1 at the start of the next switching cycle. Alternatively, if it is less than the ILIM pin voltage, then the counter inside the device decrements the fault-count by 1. When the fault-count reaches 7, an overcurrent fault (OC_FAULT) is declared and both the HDRV and LDRV are turned OFF. The resistor RILIM can be calculated by the following Equation 6.

Equation 6. GUID-52F35DF7-FAC7-4E20-9687-C4C115479E38-low.gif

The SCP level is set by a multiple of the ILIM pin voltage. The multiplier has three discrete values, 3, 7 or 15 times, which can be selected by respectively choosing a 10-kΩ, open circuit, or 20 kΩ resistor from LDRV pin to GND. This multiplier AOC information is translated during the tCAL time, which starts after the enable and UVLO conditions are met.

The SCP is based on sensing the high-side FET voltage drop from VVIN to VSW when the HDRV is ON after a blanking time, which is product of inductor current and high-side FET turn-on resistance RDS(on). The voltage is compared to the product of multiplier and the ILIM pin voltage. If it exceeds the product, then the fault-count is immediately set to 7 and the OC_FAULT is declared. The HDRV is terminated immediately without waiting for the duty cycle to end. When an OC_FAULT is declared, both the HDRV and LDRV are turned OFF. The appropriate multiplier (A), can be selected using Equation 7.

Equation 7. GUID-4FE1E03D-7A09-4EF3-83C7-1CB9BB0E24BD-low.gif

Figure 6-4 shows the functional block of the two-level overcurrent protection.

GUID-5C8513A3-00C2-47E9-ACFB-5E9A2A11EC01-low.gif Figure 6-4 OCP and SCP Protection Functional Block Diagram
Note:

Both OCP and SCP are based on low-side and high-side MOSFET voltage sensing at the SW node. Excessive ringing on the SW node can have negative impact on the accuracy of OCP and SCP. Adding an RC snubber from the SW node to GND helps minimize the potential impact.