The LP5890 has an algorithm to distribute the blank time into each subperiod in order to prevent the black field when taking photos or video.

From Equation 3, 83.1-MHz GCLK frequency and 1.44-us line switch time, the calculated blank time is 1.0361 ms (86100 GCLK), which is too long and will bring black field.

Here are detailed steps of the algorithm:

Step1: 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 86100 and N_{sub_period} × N_{scan_line} is 960, so the distributed GCLK number in each segment is 86100/960 = 89...660. These 89 GCLKs can be used to increase PWM length or extend line switch time. If used to increase PWM length, the GCLK number in each segment will be 512 + 89 = 601, so the SEG_LENGTH (Bit9-0 in FC1 register) will be 1001011001b.

Step2: 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 600 and the distributed GCLK number in each sub-period is 600/32=18...24. The BLK_ADJ (Bit46-41 in FC1 register) is 010001b.

After distributing into each sub-period, the left GCLK number is 24, which is about 289 ns. This time is too short to bring black field.