High current switching

Hi AdamCSL,

Great that you're looking at Analog Devices for this, but our product lineup in this category is limited. Under "Solenoid Drivers" there are a couple of devices that are more targeted at stepper motor applications:

https://www.analog.com/en/product-category/solenoid-driver.html

If those are overkill, the L293D from other manufacturers might be a simple solution. This chip is popular on Arduino and other maker-style motor driver boards.

-Mark

Thanks for the response but it's not the kind of solenoid that needs a stepper motor. It's actually a mechanical 7 segment digit display and the solenoids turn each segment either yellow or black, depending which one of the pairs of cathodes you connect. A single timed pulse is all that's required so a fast switch is actually ideal.

The L293D might be useful for a completely different project where I need to reverse the polarity instead of routing to a different cathode so thanks for that!

cheers,

Adam

Is something like the ULN2003 what you're after for driving the low sides of the coils? It's only 7 channels, but they're fairly inexpensive and you can probably find similar with 8. Again this isn't in ADI's product line, just giving some hints on where to look. For the high side drivers, you could implement this discretely - do a search on "high side coil driver" or "high side solenoid driver" and a bunch of circuits will pop up.

And after another quick search, it does look like there are a few more options in ADI's lineup, but again, likely overkill: https://www.analog.com/en/product-category/dc-motor-driver.html 

It sounds like you need independent control of high-side and low-side drivers, rather than half-bridge - which can be made to work by enabling one of the drivers or disabling  both, but there's probably a more elegant solution. 

Also re: anode / cathode, I assume you're referring to a frewheeling diode wired in parallel to the solenoid? A napkin sketch of your circuit would help.

-Mark

Hi Mark,

Yes I'm currently using ULN2803 darlington array to test the devices and logic etc. but it doesn't solve the issue of switching between the yellow and black segments and if I have to add another component to do that I figured I could just replace the darlington with a SPDT switch and that would kill two birds with one stone. Here is the current test setup showing just the yellows and just one display. I could probably still use a darlington for the anode switching in the final circuit.

Gotcha - I guess the choice is yours - if you can find a PNP darlington and make an inverter out of an NPN to drive its base, that would work.

The main apprehension with the MAX4660 is not exceeding abs max when the solenoids switch - the ULN2803 has internal clamp diodes, you'd want to add these externally when using the MAX4660. While the MAX4660 LOOKS like it has these diodes already - see datasheet Figure 1 and associated text - they are for ESD protection during handling, not intended for absorbing inductive "kick".

-Mark

Thanks Mark... so something like this which would cover all 14 channels? It says it's primarily for ESD but also mentions clamping...

uk.rs-online.com/.../1714298P

So the only answer I can give is to follow all datasheet abs max values verbatim. There is a note in the MAX4660 datasheet:

Signals on NO, NC, COM, or INexceeding V+ or V- are clamped by internal diodes. Limit forward-diode current to maximum current rating.

with currents listed in the tables. The Littlefuse clamp has a forward drop of:

"The SCR structures are designed for fast triggering at a threshold of one +VBE diode threshold above V+ (Pin 16) or a -VBE diode threshold below V- (Pin 8)"

This is about 0.7 V, so what this means is that the MAX4660 internal diode may end up absorbing all of the current, before the Littlefuse clamp turns on.

In summary - it would be better to use external Schottky diode clamps, which have a lower forward drop. You may be able to find a Schottky diode array, similar to the Littlefuse part.

-Mark