JAJSBT4D August   2011  – April 2021 TPS53353

PRODUCTION DATA  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings (1)
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 5-V LDO and VREG Start-Up
      2. 7.3.2 Adaptive On-Time D-CAP™ Control and Frequency Selection
      3. 7.3.3 Ramp Signal
      4. 7.3.4 Adaptive Zero Crossing
      5. 7.3.5 Power-Good
      6. 7.3.6 Current Sense, Overcurrent and Short Circuit Protection
      7. 7.3.7 Overvoltage and Undervoltage Protection
      8. 7.3.8 UVLO Protection
      9. 7.3.9 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Small Signal Model
      2. 7.4.2 Enable, Soft Start, and Mode Selection
      3. 7.4.3 Auto-Skip Eco-mode™ Light Load Operation
      4. 7.4.4 Forced Continuous Conduction Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Application Circuit Diagram
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 External Component Selection
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Typical Application Circuit Diagram With Ceramic Output Capacitors
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 External Component Selection
          2. 8.2.2.2.2 External Component Selection Using All Ceramic Output Capacitors
        3. 8.2.2.3 Application Curves
  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 Third-Party Products Disclaimer
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 サポート・リソース
    4. 11.4 Trademarks
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 用語集

7.3.6 Current Sense, Overcurrent and Short Circuit Protection

TPS53353 has cycle-by-cycle overcurrent limiting control. The inductor current is monitored during the OFF state and the controller maintains the OFF state during the period in that the inductor current is larger than the overcurrent trip level. In order to provide both good accuracy and cost effective solution, TPS53353 supports temperature compensated MOSFET RDS(on) sensing. The TRIP pin should be connected to GND through the trip voltage setting resistor, RTRIP. The TRIP terminal sources current (ITRIP) which is 10 μA typically at room temperature, and the trip level is set to the OCL trip voltage VTRIP as shown in Equation 1.

Equation 1. GUID-859C3607-A801-4083-84E6-DCC5A44B71A4-low.gif

The inductor current is monitored by the LL pin. The GND pin is used as the positive current sensing node and the LL pin is used as the negative current sense node. The trip current, ITRIP has 4700ppm/°C temperature slope to compensate the temperature dependency of the RDS(on).

As the comparison is made during the OFF state, VTRIP sets the valley level of the inductor current. Thus, the load current at the overcurrent threshold, IOCP, can be calculated as shown in Equation 2.

Equation 2. GUID-73F6571B-883F-4364-B7AE-2E7B24FEA1CC-low.gif

In an overcurrent or short circuit condition, the current to the load exceeds the current to the output capacitor thus the output voltage tends to decrease. Eventually, it crosses the undervoltage protection threshold and shuts down. After a hiccup delay (16 ms with 0.7 ms sort-start), the controller restarts. If the overcurrent condition remains, the procedure is repeated and the device enters hiccup mode.

Hiccup time calculation:

Equation 3. tHIC(wait) = (2n + 257) × 4 μs

where

  • N = 8, 9, 10, or 11 depending on soft start time selection
Equation 4. tHIC(dly) = 7 × (2n + 257) × 4 μs
Table 7-2 Hiccup Time Calculation
SELECTED SOFT-START TIME (tSS) (ms)nHICCUP WAIT TIME (tHIC(wait)) (ms)HICCUP DELAY TIME (tHIC(dly)) (ms)
0.782.05214.364
1.493.07621.532
2.8105.12435.868
5.6119.2264.54