false switching in LED board Problem..

[peeyushsigma]

hi..everyone..
i have designed a Dual Layer PCB for LED display board ...it contains 512 LEDs in each Board ...i have used STP16DO05TTR ic for driving the LED .....clock freq is 5Mhz and ...and Data is transferred serially..
but when some pattern is displayed on the board then some LEDs are blinking automatically ...and some sectors glows for a relatively long time....please give some solution to this problem ...



thanks in advance..:smile:

 

[chuckey]

Can't find your STP16DO05TTR with google have you got the number correct? You say that some sectors "glow", are they on a a low level with DC or are being pulsed for a short duration?
Frank

 

[peeyushsigma]

sorry The IC number is STP16DP05TTR..

but the glowing sectors ..are being switched on properly only the problem is ,they retain charge for a relatively long time ...after that they disappears.

 

[chuckey]

It sounds as though the output stages of the driver chip are faulty. From the data sheet the chip has only 16 outputs, how come you have 512 LEDs?
Frank

 

[peeyushsigma]

thanks chuckey ....you r right that it has only 16 outputs...i have 32 such drivers that makes possible to connect 512 LEDs .....i have made only two such boards both r having same problem...today i have connected some more decoupling capacitors of 0.1 uf but no improvements..on the performance...

 

[chuckey]

There is one current setting resistor per chip, so this device is OK?, have you tried to measure the voltage drop across it when the LEDs are on properly and when they glow? The output transistors must come on properly to make the LEDs come on, if the LEDs then "glow", it would mean that there is a leakage path either in or outside the chip, draining current through the LED. You have two boards that do this,is there a problem with the track layout? i.e. have you any boards that do not do this? If you run two boards in parallel,and stop the signal both should show the same output on or off, have you tried this?
Frank