LED Driver Problem (STP16C596)

[Deebo]

I am using an STP16C596 as a constant current LED driver. I am not interested in using any logic, I just want the device to turn on all channels all the time. I used a similar device in the past, a Toshiba TB62701AN. I simply set SDI (serial data input) and OE (output enable) high on the device and it turned on all the channels without a CLK signal. On the STP16C596, it seems like I need to set SDI high, send 16 pulses on CLK, set LE (latch) high, and then set OE high. This prevents me from using the STP16C596 as a stand alone LED driver. Is there a state I can set on all these inputs to simply turn all channels on all the time? Your help is much appreciated.

Deebo

 

[hentai]

Hi, from what i see from the truth table i reckon u should set OE to low instead of high... give it a try and post the results.
Good luck!

 

[Deebo]

Sorry, I had a typo. OE was set low, not high. Thanks for the correction hentai.

However, I still have the problem.

 

[hentai]

i see... well try seting LE low too and see what happens...
also have u looked at this application from datasheet?

 

[Deebo]

I tried it but I get no output.

I only get an output if I set SDI high, pulse the clock, set LE high, and then set OE low.

 

[hentai]

hmm tricky chip... from the datasheet internal layout i would have guessed it only needed OE acitve (low) and the leds would be on...
Have u tried it like this, leaving sdi,le and clk unconnected thus high, and OE set low?... i mean with these settings already made at power on not making them in a sequence...

 

[Deebo]

I ended up using two 555 timers to make it work: one for a simple square wave into the CLK, the other to delay the latch (OE) by approximately one second after powering the board up. So the drawbacks are more components and a one second delay to turn the LEDs on on initial powerup. Thanks for the advice Hentai.

Deebo

 

[Blueteeth]

You could replace those 555's with a small 8-pin (or even 6-pin) PIC. Very cheap, and for your purpose, a snap to program. No external components needed as most of the smaller ones have internal oscillators. It would also provide the option of 'future upgrades', seeing as how you'll have some intelligence in there. If PIC's aren't your bag, I blieve atmel do some 8-pin avr's, that only require a very simple programmer (parallel port + resistors). Just a thought, I've got these little bad boys doing all sorts of things

Blueteeth

 

[Deebo]

It sounds like a great suggestion Blueteeth. I will look into it.

 

[hentai]

why do u want to use that particular ic?

 

[justDIY]

why do u want to use that particular ic?

it does seem a bit odd that the OP would chose a rather complicated SPI / serial led driver, just to light up a string of leds all at once. how about just wiring all the leds in parallel and switch their low side with a 2n7000?

 

[mneary]

Built in current regulation?

 

[hentai]

as sugested he can make a constant current source with a transistor pretty easily

 

[Deebo]

I used this IC because it is a constant current source and because I can adjust the current of 80 LEDs with one pot (each channel has 5 LEDs in series and the IC has 16 channels). I used a Toshiba device in the past that was much simpler to implement. I had to switch to a different device because the Toshiba model could only handle 50mA.