ZHCSPI8D November 2021 – July 2022 TLC6984
PRODUCTION DATA
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 Nsub_period × Nscan_line, it can be distributed into each segment.
In this application, the blank GCLK number is 88280, and Nsub_period × Nscan_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 Nsub_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.