SLVSE03B April   2019  – February 2021 TPS929120-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  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 Device Bias and Power
        1. 7.3.1.1 Power Supply (SUPPLY)
        2. 7.3.1.2 5-V Low-Drop-Out Linear Regulator (VLDO)
        3. 7.3.1.3 Undervoltage Lockout (UVLO) and Power-On-Reset (POR)
        4. 7.3.1.4 Programmable Low Supply Warning
      2. 7.3.2 Constant Current Output
        1. 7.3.2.1 Reference Current With External Resistor (REF)
        2. 7.3.2.2 64-Step Programmable High-Side Constant-Current Output
      3. 7.3.3 PWM Dimming
        1. 7.3.3.1 PWM Dimming Frequency
        2. 7.3.3.2 PWM Generator
        3. 7.3.3.3 Linear Brightness Control
        4. 7.3.3.4 Exponential Brightness Control
        5. 7.3.3.5 External Clock Input for PWM Generator (CLK)
        6. 7.3.3.6 External PWM Input ( PWM0 and PWM1)
      4. 7.3.4 On-chip 8-bit Analog-to-Digital Converter (ADC)
      5. 7.3.5 Diagnostic and Protection in Normal State
        1. 7.3.5.1  Fault Masking
        2. 7.3.5.2  Supply Undervoltage Lockout Diagnostics in Normal State
        3. 7.3.5.3  Low-Supply Warning Diagnostics in Normal State
        4. 7.3.5.4  Reference Diagnostics in Normal State
        5. 7.3.5.5  Pre-Thermal Warning and Overtemperature Protection in Normal State
        6. 7.3.5.6  Communication Loss Diagnostic in Normal State
        7. 7.3.5.7  LED Open-Circuit Diagnostics in Normal State
        8. 7.3.5.8  LED Short-circuit Diagnostics in Normal State
        9. 7.3.5.9  On-Demand Off-State Invisible Diagnostics
        10. 7.3.5.10 On-Demand Off-State Single-LED Short-Circuit (SS) Diagnostics
        11. 7.3.5.11 Automatic Single-LED Short-Circuit (AutoSS) Detection in Normal State
        12. 7.3.5.12 EEPROM CRC Error in Normal State
        13.       47
      6. 7.3.6 Diagnostic and Protection in Fail-Safe States
        1. 7.3.6.1 Fault Masking
        2. 7.3.6.2 Supply UVLO Diagnostics in Fail-Safe States
        3. 7.3.6.3 Low-supply Warning Diagnostics in Fail-Safe states
        4. 7.3.6.4 Reference Diagnostics at Fail-Safe States
        5. 7.3.6.5 Overtemperature Protection in Fail-Safe State
        6. 7.3.6.6 LED Open-circuit Diagnostics in Fail-Safe State
        7. 7.3.6.7 LED Short-circuit Diagnostics in Fail-safe State
        8. 7.3.6.8 EEPROM CRC Error in Fail-safe State
        9.       57
    4. 7.4 Device Functional Modes
      1. 7.4.1 POR State
      2. 7.4.2 Initialization State
      3. 7.4.3 Normal State
      4. 7.4.4 Fail-Safe States
      5. 7.4.5 Program State
      6. 7.4.6 Programmable Output Failure State
      7. 7.4.7 ERR Output
      8. 7.4.8 Register Default Data
    5. 7.5 Programming
      1. 7.5.1 FlexWire Protocol
        1. 7.5.1.1 Protocol Overview
        2. 7.5.1.2 UART Interface Address Setting
        3. 7.5.1.3 Status Response
        4. 7.5.1.4 Synchronization Byte
        5. 7.5.1.5 Device Address Byte
        6. 7.5.1.6 Register Address Byte
        7. 7.5.1.7 Data Frame
        8.       76
        9. 7.5.1.8 CRC Frame
        10. 7.5.1.9 Burst Mode
      2. 7.5.2 Registers Lock
      3. 7.5.3 All Registers CRC Check
      4. 7.5.4 EEPROM Programming
        1. 7.5.4.1 Chip Selection by Pulling REF Pin High
        2. 7.5.4.2 Chip Selection by ADDR Pins configuration
        3. 7.5.4.3 EEPROM Register Access and Burn
        4. 7.5.4.4 EEPROM Program State Exit
        5. 7.5.4.5 Reading Back EEPROM
    6. 7.6 Register Maps
      1. 7.6.1 FullMap Registers
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Smart Rear Lamp With Distributed LED drivers
      2. 8.2.2 Design Requirements
      3. 8.2.3 Detailed Design Procedure
      4. 8.2.4 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 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7.3.6.6 LED Open-circuit Diagnostics in Fail-Safe State

The TPS929120-Q1 integrates LED open-circuit diagnostics to allow users to monitor LED status in real time. The device monitors voltage difference between SUPPLY and OUTx to detect if there is any open-circuit failure. The SUPPLY voltage is also monitored by on-chip ADC with programmable threshold to detect if supply voltage is high enough for open-circuit diagnostics.

The open-circuit monitor is only enabled during PWM-ON state with minimal pulse width greater than T(ODPW) + T(OPEN_deg). If PWM on-time is less than T(ODPW) + T(OPEN_deg), the device does not report any open-circuit fault. T(ODPW) is programmable by register CONF_ODPW.

When the voltage difference V(SUPPLY) – V(OUTx) is below threshold V(OPEN_th_rising) with duration longer than T(ODPW) + T(OPEN_deg) and the device supply voltage V(SUPPLY) is above the threshold V(ADCLOWSUPTH) set by register CONF_ADCLOWSUPTH, the TPS929120-Q1 turns off the current output on the open-circuit channel, pulls ERR pin down with constant current sink to report fault and sets the flag registers including FLAG_OPENCHx, FLAG_OUT and FLAG_ERR to 1. If the device supply voltage V(SUPPLY) is below the threshold V(ADCLOWSUPTH) set by register CONF_ADCLOWSUPTH, open-circuit fault are not detected and reported. If any channel is disabled by CONF_ENCHx to 0, the LED open-circuit diagnostics skip the channel. If one-fails-all-fail protection is enabled by setting EEPROM register EEP_OFAF to 1, all the used output channels are turned off even though the LED open-circuit is only detected on one channel. If one-fails-all-fail protection is disabled by setting EEPROM register EEP_OFAF to 0, only failed channels are turned off.

In fail-safe states, the TPS929120-Q1 retries the failed channel with low-current retry pulses every 10 ms. The pulse width T(ODPW) is programmable by CONF_ODPW, and the retry current is set by CONF_ODIOUT. If the retry is succeed, the device automatically releases the ERR pin and clear the flag registers. If the CONF_DIAGENCHx is set to 0, the open-circuit fault is ignored.

Possible user case:

1. Supply voltage dip below threshold, triggering false open-circuit fault.

2. Real LED open-circuit and recover

3. Extra capacitance caused false open-circuit.

4. Dutycycle too short to detect

5. Sequential Turn Error Detection. Only on-time diagnostics only.

6. Off-state diagnostics?