ZHCSP77A December   2021  – March 2022 TPS92624-Q1

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  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 Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Power Supply (SUPPLY)
        1. 7.3.1.1 Power-On Reset (POR)
        2. 7.3.1.2 Suppply Current in Fault Mode
      2. 7.3.2  Enable and Shutdown
      3. 7.3.3  Constant-Current Output and Setting (INx)
      4. 7.3.4  Thermal Sharing Resistor (OUTx and RESx)
      5. 7.3.5  PWM Control (PWMx)
      6. 7.3.6  Supply Control
      7. 7.3.7  Diagnostics
        1. 7.3.7.1 LED Short-to-GND Detection
        2. 7.3.7.2 LED Open-Circuit Detection
        3. 7.3.7.3 LED Open-Circuit Detection Enable (DIAGEN)
        4. 7.3.7.4 Overtemperature Protection
        5. 7.3.7.5 Low Dropout Operation
      8. 7.3.8  FAULT Bus Output With One-Fails-All-Fail
      9. 7.3.9  FAULT Table
      10. 7.3.10 LED Fault Summary
      11. 7.3.11 IO Pins Inner Connection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Undervoltage Lockout, V(SUPPLY) < V(POR_rising)
      2. 7.4.2 Normal Operation V(SUPPLY) ≥ 4.5 V
      3. 7.4.3 Low-Voltage Dropout Operation
      4. 7.4.4 Fault Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 BCM Controlled Rear Lamp With One-Fails-All-Fail Setup
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Independent PWM Controlled Rear Lamp By MCU
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        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 接收文档更新通知
    2. 11.2 支持资源
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 术语表
  12. 12Mechanical, Packaging, and Orderable Information

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8.2.1.2 Detailed Design Procedure

Step 1: Determine the current sensing resistor, R(SNSx), by using Equation 4.

Equation 4. GUID-20200720-CA0I-LXPB-SZP4-FLPGPC2SFHDF-low.gif

where

  • V(CS_REG) = 150 mV (typical)
  • I(OUTx_Tot) = 130 mA

According to design requirements, output current for each channel is same so that the R(SNS1) = R(SNS2) = R(SNS3) = R(SNS4) =1.15 Ω. Two resistors in parallel can be used to achieve equivalent resistance when sense resistor is not a standard decade resistance value.

Step 2: Design the current distribution between I(OUTx) and I(RESx), and calculate the current sharing resistor, R(RESx), by using Equation 5. The R(RESx) value actually decides the current distribution for I(OUTx) path and I(RESx) path. TI recommends the current sharing resistor R(RESx) to consume 50% of the total current at typical supply operating voltage.

Equation 5. GUID-FC2DB7CD-966D-4ACD-94CF-0CFB2E343442-low.gif

where

  • V(SUPPLY) = 12 V (typical)
  • I(OUTx_Tot) = 130 mA

The calculated result for R(RESx) resistor value including R(RES1), R(RES2),R(RES3) and R(RES4) is 85.4 Ω when V(OUTx) is typical 3 × 2.15 V = 6.45 V.

Step 3: Design the threshold voltage of SUPPLY to enable the LED open-circuit diagnostics, and calculate voltage divider resistor value for R1 and R2 on DIAGEN pin.

The maximum forward voltage of LED-string is 3 × 2.5 V = 7.5 V. To avoid the open-circuit fault reported in low-dropout operation conditions, additional headroom between SUPPLY and OUTx must be considered. TheTPS92624-Q1 device must disable open-circuit detection when the supply voltage is below LED-string maximum forward voltage plus V(OPEN_th_rising) and V(CS_REG). The voltage divider resistor, R1 and R2 value can be calculated by Equation 6.

Equation 6. GUID-D8EA8D12-7DB4-435B-8E16-BA4DEA31658F-low.gif

where

  • V(OPEN_th_rising) = 420 mV (maximum)
  • V(CS_REG) = 156 mV
  • VIL(DIAGEN) = 1.045 V (minimum)
  • R2 = 10 kΩ (recommended)

The calculated result for R1 is 67.3 kΩ when V(OUTx) maximum voltage is 7.5 V and V(CS_REG) is 156 mV.

Step 4: Design the threshold voltage of SUPPLY to turn on and off each channel of LED, and calculate voltage divider resistor value for R3 and R4 on PWM input pin.

The minimum forward voltage of LED string is 3 × 1.9 V = 5.7 V. To make sure the current output on each of LED-string is normal, each LED-string must be turned off when SUPPLY voltage is lower than LED minimum required forward voltage plus dropout voltage between INx to OUTx and V(CS_REG). The voltage divider resistor, R3 and R4 value can be calculated by Equation 7.

Equation 7. GUID-94EA4A54-6CE2-40C8-8D9D-1204466567D8-low.gif

where

  • V(DROPOUT) = 300 mV (typical)
  • V(CS_REG) = 156 mV (maximum)
  • VIH(PWM) = 1.26 V (maximum)
  • R4 = 10 kΩ (recommended)

The calculated result for R3 is 38.9 kΩ when V(OUTx) minimum voltage is 5.7 V and V(CS_REG) is 156 mV.
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