LED Open Detection

The LP5866 includes LED open detection (LOD) for the fault caused by any opened LED dot. The threshold for LED open is 0.25V typical. LED open detection is only performed when PWM ≥ 25 (Mode 1 and Mode 2) or PWM ≥ 6400 (Mode 3) and voltage on CSn is detected lower than open threshold for continuously 4 sub-periods.

Figure 7-11 shows the detection circuit of LOD function. When open fault is detected, 'Global_LOD' bit in Fault_state register is set to 1 and detailed fault state for each LED is also monitored in register Dot_lodx (x = 0, 1, … , 17). All open fault indicator bits can be cleared by setting LOD_clear = 0Fh after the open condition is removed.

LOD removal function can be enabled by setting 'LOD_removal' bit in Dev_config2 register to 1. This function turns off the current sink of the open channel when scanning to the line where the opened LED is included.

Figure 7-11 LOD Circuits

The LP5866 includes LED short detection (LSD) for the fault caused by any shorted LED. Threshold for channel short is (VLED – 1) V typical. LED short detection only performed when PWM ≥ 25 (Mode 1 and Mode 2) or PWM ≥ 6400 (Mode 3) and voltage on CSn is detected higher than short threshold for continuously 4 sub-periods. As there is parasitic capacitance for the current sink, to make sure the LSD result is correct, TI recommends to set the LED current higher than 0.5mA.

Figure 7-12 shows the detection circuit of LSD function. When short fault is detected, 'Global_LSD bit' in Fault_state register is set to 1 and detailed fault state for every channel can also be monitored in register Dot_lsdx (x = 0, 1, … , 17). All short fault indicator bits can be cleared by setting LSD_clear = 0Fh after the short condition is removed.

LSD removal function can be enabled by setting 'LSD_removal' bit in Dev_config2 register to 1. This function turns off the upside deghosting function of the scan line where short LED is included.

Figure 7-12 LSD Circuit

Thermal Shutdown

The LP5866 device implements thermal shutdown mechanism to protect the device from damage due to overheating. When the junction temperature rises to 160°C (typical) and above, the device switches into shutdown mode. The LP5866 exits thermal shutdown when the junction temperature of the device drops to 145°C (typical) and below.

UVLO (Undervoltage Lockout)

The LP5866 has an internal comparator that monitors the voltage at VCC. When VCC is below V_UVF, reset is active and the LP5866 enters INITIALIZATION state.