TLC5955: Two Questions: GSCLK -- Can oscillator work? -- Short Detection, do outputs disable?

Some more clarity on question 1:
Do I need to align these clock edges with any signal? Like maybe SCLK or the data lines at all? or can it be out of phase and totally independent from the other inputs to the chip. 

Updated. See my next post.

Hi Daniel,

Regarding your questions,

1. Yes, you can set GSCLK by an oscillator signal (which can be independent from the other inputs) as long as you satisfy all the timing and voltage requirements as shown in "6.3 Recommended Operating Conditions" from the datasheet. But I do not suggest doing that, unless you are setting the REFRESH bit = 1 (check Figure 31 from the datasheet).

In other case, you should stop the GSCLK when you latch the GS data into the GS Data Latch (check Figure 30 and Figure 32 from the datasheet) to avoid any unwanted output of the device during the data change. See my next post.

2. No. It will not disable the output. The TLC5955 only has the LED short/open detection function, but not LED short/open removal function. You can read the LSD/LOD data and then set the grayscale data of the faulty channel to 0000h to turn off that channel.

There are some devices that do have LOD auto-removal functions. You can check TLC5946 and LP5891 / LP5890 / TLC6984 / TLC6983 (for LED matrix application).

Best Regards,

Steven

Hi Daniel,

Steven Li said:

But I do not suggest doing that, unless you are setting the REFRESH bit = 1 (check Figure 31 from the datasheet).

In other case, you should stop the GSCLK when you latch the GS data into the GS Data Latch (check Figure 30 and Figure 32 from the datasheet) to avoid any unwanted output of the device during the data change.

After I consult one of our senior experts, I get the result that from their experience, you don't need to stop the GSCLK when you latch the GS data, no matter REFRESH bit = 1 or REFRESH bit = 0. What's more, if you are cascading several TLC5955, the GSCLK for each of them can be independent from each other.

I will update my previous answer. Sorry for the inconvenience it may cause.

Best Regards,

Steven

Hi Steven,

Thank you for your very thorough help and explanation. 

If I am understanding correctly, then there is no timing relationship between GSCLK and other timing critical inputs like SIN or SCLK. i.e. SCLK and GSCLK can be running completely independently of each other? same goes for SIN and GSCLK? also what about LAT and GSCLK? 

And if GSCLK truly is independent, then there is no special programming of the chip for this to be the case? 

regards,

Daniel

Hi Daniel,

Daniel McGinley said:

If I am understanding correctly, then there is no timing relationship between GSCLK and other timing critical inputs like SIN or SCLK. i.e. SCLK and GSCLK can be running completely independently of each other? same goes for SIN and GSCLK? also what about LAT and GSCLK? 

Yes, you are right. GSCLK can be completely independent from SCLK, SIN and LAT.

Daniel McGinley said:

And if GSCLK truly is independent, then there is no special programming of the chip for this to be the case? 

Yes. There is no special programming of the chip.

Best Regards,

Steven