SLVAFE5 September   2022 TPS92610-Q1 , TPS92611-Q1 , TPS92612-Q1 , TPS92613-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2TPS9261x-Q1 Fault Detection and Discrete Fault Detection Introduction
    1. 2.1 Discrete Fault Detection
    2. 2.2 Open Load vs Short-to-Battery Detection
    3. 2.3 Short to Ground vs Overtemperature Detection
    4. 2.4 Fault Detection Logic Summary
  5. 3Discrete Fault Detection Circuit Details
    1. 3.1 Simulation
    2. 3.2 PCB Implementation
    3. 3.3 Test Setup
    4. 3.4 Thermal Testing for Overtemperature Conditions
  6. 4Conclusion
  7. 5References

2.3 Short to Ground vs Overtemperature Detection

The next faults to detect are short-to-ground (SG) and overtemperature (OT) conditions. Figure 2-5 shows the SG condition.

Figure 2-5 Short-to-Ground (SG) Condition

In both SG and OT conditions, the output is disabled and the output voltage either drops to 0 V if either fault occurs when PWM is high, or stays at 0 V when transitioning the PWM pin from low to high during either fault condition. Therefore, the output voltage comparator does not help distinguish between the SG and OT faults. However, the devices built-in detection of SG and OT detects both faults and pulls the fault pin LOW. To distinguish between a SG and OT condition, the local MCU can simply adjust the PWM pin control of the TPS9261x-Q1 output. If the fault pin is pulled low by the LED driver but the comparator output has not triggered a SB or OL condition, the MCU can logically conclude that either a SG or OT condition has occurred. Next, the MCU can hold the PWM pin low for 300 ms to 500 ms to check if the LED driver has overheated. By pulling the PWM pin low, the MCU allows the TPS9261x-Q1 time to cool off and avoid any self-heating. If an OT condition has occurred, during the 200-ms to 500-ms wait time, the LED driver clears the fault after the 15°C hysteresis has been cleared (specified in the TPS9261x-Q1 data sheet). The MCU can then drive the PWM pin high at the dedicated PWM frequency and duty cycle to monitor if the fault pin is triggered again due to the LED driver overheating. Figure 2-6 shows the logic flowchart for distinguishing between SG and OT.

Figure 2-6 Short to Ground (SG) or Overtemperature (OT) Logic Flowchart

If the PWM pin is held HIGH and the comparator output (Vcomp) is LOW while the fault pin is LOW then a SG or OT has occurred. After the MCU holds the PWM pin low for 200 ms as shown in Figure 2-6, the fault pin state can be checked to determine if an OT event has occurred. If there is a SG, the fault pin stays low unless the short has been cleared. Therefore, some simple logic and control of the PWM pin can be implemented to detect if a SG or OT condition has occurred. Testing can be performed to understand what conditions cause the TPS9261x-Q1 to overheat.
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