SAA1064 flickering

40inD · Joined: 30 Jul 2007 Posts: 112 Location: Moscow, Russia

Problem is when SAA1064 drives 1.8" LED displays at max. current the image has SOMETIMES flicker (or running wave) effect, which is noticeable by naked eye. At minimum current this effect is not appearing.
The other chip on same board which drives 0.8" LEDs does not have such problem.
In both cases timing capacitors are 2.7n, decoupling caps - 0.1u and stabilized power - 5V 1A.

Perhaps, need to try to reduce timing capacity?

Ttelmah · Joined: 11 Mar 2010 Posts: 19480

Probably your supply is not actually maintaining regulation as the LED's switch.

40inD · Joined: 30 Jul 2007 Posts: 112 Location: Moscow, Russia

You suggest to add more electrolytic capacitor?

oxo · Joined: 13 Nov 2012 Posts: 219 Location: France

http://www.ccsinfo.com/forum/viewtopic.php?t=49958

This is an unresolved problem for me too.

40inD · Joined: 30 Jul 2007 Posts: 112 Location: Moscow, Russia

No, in my case I2C works ok, and i don't think that flickering is I2C problem. The second chip on same pcb works fine. And flickering also appears when there is no I2C activity with addressed chip. Also, flickering appears not always but in some very slow period.
It's look like some interference between 2 processes with close frequencies inside the chip.

temtronic · Posted: Tue Apr 22, 2014 6:26 am

'Old School' power supply rule is to build it 10X greater than the steady state current demands.
So, if your LED draws 150ma( all segments on, worst case) you need a MINIMUM of 150 * 10 = 1,150ma . Be sure to ADD whatever current the PIC and support chips draw as well !! They could easily add another 50 - 150 ma ,so in this case you need 1,150 + 150 = 1,300ma or 1.3 Amps.

hth
jay

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK

It's time to get the 'scope out and make some very careful observations.
Look for power supply drop-out, timing jitter etc.

Mike