7.3.4.2 Adjacent-Pin-Short Check

The device implements the APS check function to detect the adjacent-pin short failures during system initialization. TI recommends to do an APS check when channels are all off. The APS check can be executed by writing the APS check command.

If there is no adjacent-pin short failure, the device passes the APS check and 011b is latched into APS FLAG in the error status register. The 24-bit APS register is 0. If there are two adjacent pins shorted, 110b is latched into APS_FLAG in the error status register. The corresponding bit in the APS register is set to 1. Users can read out the 24-bit data from the APS register to check which channel has the APS failure. Table 7 shows the details of the APS_FLAG and APS register. Table 8 shows the bit arrangement of the APS register. To read this APS information, see Table 22.

APS_FLAG and the APS registers are all 0 by default. After an APS check command, APS_FLAG should be 011b or 110b. Otherwise there is a failure in the APS check circuit. If the APS check result fails, the ERR pin is pulled low, the APS_FLAG value is 110b, and the ERR pin status stays unchanged until the fault is removed and the user executes an ERROR clear command. Figure 5 and Figure 9 show more detail.

As different LEDs have different parasitic capacitance, to make sure the APS Check function is suitable for all kinds of LEDs, the device provides two configuration bits for APS current and APS time. The APS current is selected by APS_CURRENT as shown in Table 9. The APS time is selected by APS_TIME as shown in Table 10.