Need advise - Screwed up on my PCB - Need replacement part

[Jouellet]

Hi Folks,

I just received a bunch of PCBs that I ordered. When I tried to assemble the first unit, I realised that I've screwed up with my design.

NO, I did not test it before, as it was "so simple" ...call it being dumb, overconfident, cocky, etc ...Mea Culpa !

Here's the deal: I have a microcontroller that feeds into a ULN2003 (Darlington array). the output of that array, feeds 7 x 3 LEDS. So far so good...

Here's what the circuit should have looked like (with the ULN2003):



But when I did my schematic/board, I've connected the diode as if the ULN2003 was going to source, rather than sink:



Now, I'm not too excited about having my PCBs (25X) re-done...

I found a chip, that I believe, could be a direct replacement, without any modification on my board. I need a second (third, fourth...) opinion.

The chip is M54580P. The datasheet is included in this post.

Please, have a look at it, and tell me if you also think that it should work with my current board.

My other solution, would be to take something like a UDN2981, which is a 8-bit source version of the ULN2003, and mount it on a small transition PCB, that would ignore the 8th channel, flip GND and VCC, while providing the "footprint" of a DIP16. That solution would be cheaper than having all the board re-done.(My actual board is slightly longer than 100 mm, which triggers a totally different price range with most PCB makers...)

 

[Minder]

Simple, cut the trace for pin 9, you do not need it with LED's as a load, only inductive loads.
Pin 9 is just reversed biased diodes.
Edit: oops I see you mean you did not source the lED's from +ve
M.

 

[Jouellet]

Simple, cut the trace for pin 9, you do not need it with LED's as a load, only inductive loads.
Pin 9 is just reversed biased diodes.
Edit: oops I see you mean you did not source the lED's from +ve
M.

yep... the LEDs would still be connected reverse, to ground !

That's why I think the M54580P might work...

 

[Minder]

The IC sources so it should work and it does not include reverse diodes which you don't need.
M.

 

[duke37]

You need R1 or R8, not both. That would make things a bit simpler.
If you have populated only one board, you could turn the leds round. Cut the track from Vcc to the leds and connect them to GND.

 

[Jouellet]

You need R1 or R8, not both. That would make things a bit simpler.
If you have populated only one board, you could turn the leds round. Cut the track from Vcc to the leds and connect them to GND.

I have 2 resistors, to get the exact value...not that it matters that much. Since these are 1206 SMD, it allows me to minimize the wattage for each, by using a smaller value ...

BTW, LEDS are connected to ground, that's part of the problem. Cutting them is not that easy, as the bottom side is all a ground plane.....and I have 25 of these ....

 

[CDRIVE]

You do realize that the M54580P's input logic is opposite of the ULN series? The ULN's Collector (output) goes low when the input goes high. The M54580P's Collector (output) goes high when the input goes low.

Chris

 

[Jouellet]

You do realize that the M54580P's input logic is opposite of the ULN series? The ULN's Collector (output) goes low when the input goes high. The M54580P's Collector (output) goes high when the input goes low.

Chris

Yes, and they are driven by an Arduino, so it's an easy fix.

 

[CDRIVE]

Ah, that's the best part of working with μC's. Changing logic via code is soooo easy!

Chris