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 TPS9261x-Q1 Fault Detection and Discrete Fault Detection Introduction

Before covering discrete fault detections, the device behavior during each fault condition must be understood.

Table 2-1 as published in the TPS92611-Q1 Automotive Single-Channel Linear LED Driver data sheet shows the expected behavior of the device during the four different fault conditions (OL,SB, SG, and OT).

Table 2-1 Fault Table With DIAGEN = HIGH
FAULT BUS STATUS FAULT TYPE DETECTION MECHANISM CHANNEL STATE DEGLITCH TIME FAULT BUS FAULT HANDLING ROUTINE FAULT RECOVERY
FAULT floating or externally pulled up Open-circuit or short-to-supply V(IN) – V(OUT) < V(OPEN_th_rising) On t(OPEN_deg) Constant-current pulldown Device works normally with FAULT pin pulled low. Device sources I(retry) current when PWM is LOW. Device keeps output normal when PWＭ is HIGH. Auto recover
Short-to-ground V(OUT) < V(SG_th_rising) On t(SG_deg) Constant-current pulldown Device turns output off and retries with constant current I(retry), ignoring the PWM input. Auto recover
Over-
temperature		 TJ > T(TSD) On or off t(TSD_deg) Constant-current pulldown Devices turns output off. Auto recover
Externally pulled low Device turns output off

When the device PWM pin input is high (output is on) during an open load or short to battery condition, the TPS9261x-Q1 detects an open load or short to battery has occurred and pull the fault pin low. The device continues to try and source the set current to the output every time PWM is set high. However, little to no current flows through the device due to the output voltage being equal to the input voltage (battery). In a short to battery condition, it is clear that the output voltage equals the battery but during an open load condition, the output also equals battery due to the constant current control of the TPS9261x-Q1. With a high impedance on the output, the TPS92611x tries to source the designed output current but because the output has infinite impedance, the output voltage is limited to the input voltage of the device. When PWM is set low and DIAG EN pin is high, the device sources a 1-mA I(retry) current to check if the open load or short to battery condition has been removed.

During a short to ground condition, when the PMW pin is high, the TPS9261x-Q1 detects a short to ground and pull the fault pin low. Before the fault is reported, the output voltage drops to approximately 0 V due to the TPS9261x-Q1 output sourcing the designed current into ground or close to 0 Ω. The output then is disabled once the fault is detected after t(SG_deg) and the device tries to source the 1-mA I(retry) current, regardless of the PWM pin, to detect if the short to GND has been removed.

Lastly, for an overtemperature condition, the device simply shuts off the output regardless of the state of the PWM pin. In this case, the output is disabled and there is no voltage on the output due to no current flowing from the device.