The TLC6984 has an algorithm to distribute the blank time into each subperiod to prevent the black field when taking photos or video.

From Equation 3, 83.4-MHz GCLK frequency and 1.44-us line switch time, the calculated blank time is 1.059 ms ( 88280 GCLK ), which is too long and brings black field.

Here are detailed steps of the algorithm.

Step 1: Distribute blank time into each segment

When the blank GCLK number is larger than N_{sub_period} × N_{scan_line}, it can be distributed into each segment.

In this application, the blank GCLK number is 88280, and N_{sub_period} × N_{scan_line} is 960, so the distributed GCLK number in each segment is 88280/960 = 91...920. These 91GCLKs can be used to increase PWM length or extend line switch time. If used to increase PWM length, the GCLK number in each segment is 512 + 91= 603, so the SEG_LENGTH ( Bit9-0 in FC1 register) is 1001011010b.

Step 2: Distribute blank time into each sub-period

If the left GCLK number is larger than N_{sub_period}, it can be distributed into each sub-period.

In this application, the left GCLK is 697, the distributed GCLK number in each sub-period is 920/32=28...24. The BLK_ADJ (Bit46-41 in FC1 register) is 011100b.

After distributing into each sub-period, the left GCLK number is 24, which is about 300 ns, this time is too short to bring black field.