Re: ULN2803 or equivalent in SMD package? TI's???

From: Lewin Edwards (larwe_at_larwe.com)
Date: 07/24/04 

Date: Sat, 24 Jul 2004 02:01:56 GMT

> You could always do both a 150 and 300mil patterns. I have not seen
> std SO packages not on 50mil pitch, but there are offerings in both
> 150 and 300 mils width - mainly for thermal reasons.

The only thing that worries me is pinouts. I don't feel comfortable
assuming things. Chip mfrs do weird things for no apparent reason.

This is also a "mature" design that is just being respun for lower
production cost, so I don't want to change it any more than necessary.
I'm going to take a chance on rework and order a 250-piece run of
boards. This component is the single item I'm not happy about;
everything else, I have checked datasheets for all important
characteristics, and I've physically checked components on a 1:1
printout of the artwork.

> You could also look at SMD MOSFETS, they are lower loss than
> darlingtons, and so can give a smaller thermal layout ?

I don't really have a thermal problem though. The package does not
become noticeably warmer than ambient during normal operation of the
appliance. I'm actually using paired channels to drive four outputs,
each output only needs to sink 120mA continuous at most (more typically,
60mA), and the switching speeds are low. There *are* some transient
current spikes that can get up pretty high, which is why I want plenty
of margin. But they are rare and don't significantly contribute to chip
heating.

The other part I'm going to be looking for soon is an H-bridge IC
equivalent to the LMD18200 or 18201 (the next thing I'm costing-down is
the DC motor controller). That should be fun. I bet it will be some odd
package with big heatsink tabs. OBTW, these are submarine modules in
case you didn't guess :)