TLC5941: Output status before power up

David Huang

Part Number: TLC5941
Other Parts Discussed in Thread: TLC5947

Hi team

Could you advice the output pin status before Vcc is ready?

By checking the past e2e post I suppose outputs will be open but I can't find any specifications which proves this in the ds.

Regards

over 1 year ago

0 Steven Li over 1 year ago

TI__Genius 14895 points

Hi David,

The datasheet does not specify the conditions before Vcc is ready.

To get a known output status before Vcc is ready, I suggest setting BLANK pin HIGH and all the current sinks should be turned off.

The GS and DC registers are set to random values that are not known just after power on. The GS and DC values must be programmed before turning on the outputs.

Best Regards,

Steven

0 David Huang over 1 year ago in reply to Steven Li

TI__Intellectual 2285 points

Hi Steven

I found the following post answered by you in the past, where you mentioned that the sequence doesn't matter for this device.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1119198/tlc5941-outputs-with-pre-bias?tisearch=e2e-sitesearch&keymatch=TLC5941#

So in short, the output status can be random, but it's fine to power the device before LED voltage?

Regards

0 Steven Li over 1 year ago in reply to David Huang

TI__Genius 14895 points

Hi David,

It is fine to power the device before LED voltage.

Make sure you hold the BLANK HIGH and do not input GSCLK before the LED voltage is ready. By doing so, the output status is known to be off, rather than random.

Best Regards,

Steven

0 David Huang over 1 year ago in reply to Steven Li

TI__Intellectual 2285 points

Hi Steven

Thanks!

What about the output status during the power off?

My understanding is that the GS and DC register wouldn't hold its value during the power off so it would be pretty much the same as the power on sequence, is it correct?(Blank H then open, Blank L or floating then random)

Regards

0 Steven Li over 1 year ago in reply to David Huang

TI__Genius 14895 points

Hi David,

Yes.

The datasheet does not specify the conditions during the power off. Again, I suggest holding BLANK HIGH and not inputting GSCLK to keep the output off during the power off.

Best Regards,

Steven

0 Steven Li over 1 year ago in reply to David Huang

TI__Genius 14895 points

Hi David,

If the controller pin for BLANK has enough drive strength, you can try to add a pull-up resistor from BLANK pin to Vcc to avoid unknown conditions during power on and power off.

You can read the below thread for reference. (TLC5941 and TLC5947 both have the BLANK pin that works in a similar manner)

TLC5947: Pin Status at Power On - Power management forum - Power management - TI E2E support forums

Best Regards,

Steven