Lo Vce Equivalent replacement for ULN2003

[whizgeek]

Hi All. First off, I'm new registered to post but longtime lurker.

A 5v application, uses one of these 2003 open collector drivers for a bunch of relays.
New design puts a green(ish) smps to power the whole circuit.

But the 2003 has a Vce Sat of >0.85V in this application, add in a drop for power filtering etc, and the resulting drop  is too high to reliably drive the relays.

So ideally need a pin-pin compatible 7channel lo side driver/switch with low Rds/Vsat

Have looked at TPL7407 - 5v is too low. TBD62003 has similar Vds to 2003..

Anyone any other suggestions?

[helge]

Mildly disappointed by TPL7407 and its "internal LDO".
TPL7407: 8.5V minimum VCOM (misnomer, should be VCC) with an LDO to 7V which turns out dying when subjected to >0.5V/µs, so don't use the internal freewheeling diodes. Oh lord...

Now evaluating TPL7407LA (starting at 6.5V and with internal regulation to 5.3V) vs. ULN2003LV.

[exe]

Why not using a logic-level mosfets (descrete or arrays)? Just don't forget protection diodes, etc.

[bson]

You can always use a dual switching MOSFET, like Diodes Inc DMG6898LSD.  At Vgs=2.5V  and Id=8.9A, Rds<=23mohm.  Since Rds is PTC at smaller currents the max channel resistance will be lower and Vds lower as well; fig1 in the datasheet suggests Vds<<100mV @ Id<1A currents.  The drawback of the DMG6898LSD is the rather large 50mil SO package, but you could probably fit 3 of these within the real estate of one ULN2003, and get other benefits like placement closer to the relays and more distributed heat dissipation if you need significant switching currents.  If you switch using GPIO pins on a µC this combined with pin swapping can simplify layout.

Or maybe a quad/hex/octal common-source variety - if you can find one with high channel on-conductance (~>25S).  If you do, let me know!  With independent S pins you can use a source resistor to set the driving current and reduce noise and glitch sensitivity (always a good habit when dealing with relays, even with flywheel diodes), but may not need this if the coil supply voltage is a good match for the relay.

There are also low-Vce(sat) BJTs, but I'm only aware of discrete devices, not any sort of array, but this may be your best bet if you need TH.  You could easily make a small adapter board with a few of these that is pin compatible with a ULN2003.  (But if you do this you might as well use modern SMD parts IMO.)