output driver - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: March 16, 2017, 05:41:35 pm
content: I'm looking for an IC that will act as a level shifter and signal driver from 5V inputs to 24V automotive outputs (32V). I have never been able to find stuff like this on the usual distributor websites as they don't know what they are selling half the time or I don't know what it's called.I'd need to drive no more than a few mA and it would be nice to have short circuit protection.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 05:45:23 pm
content: Would something like the ULN2003 work?Do you need high side or low side (open collector) outputs?

author: BrianHG
author_rank: Super Contributor
timestamp: March 16, 2017, 05:46:51 pm
content: A R-R opamp here will be your friend. Supply voltage will range your output. Tie the - input to 2 resistors creating your switch voltage. IE VCC & GND for these, not the 24/32v. This ensures the logic switch point for the + input. Swap the +and- if you want an inverted output. The output of most opamps are current limited & short circuit protected already.Hope this helps.Note that high voltage drivers, high and low side, NPN/PNP transistor arrays do exist, but their input voltage threshold cant necessarily be set.

author: Simon
author_rank: Unknown
timestamp: March 16, 2017, 05:49:15 pm
content: Quote from: james_s on March 16, 2017, 05:45:23 pmThese are just transistors in a single package, I was looking for something a bit more polished. Half bridge output required.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 05:53:08 pm
content: Ah ok, that wasn't clear from your post. Might want to clarify precisely what your requirements are as that will help narrow down the search.

author: MagicSmoker
author_rank: Super Contributor
timestamp: March 16, 2017, 06:16:08 pm
content: Quote from: Simon on March 16, 2017, 05:41:35 pmI've used gate drivers for this purpose before, protected with a 100mA PTC fuse. For example, IXDD604, which is dual 4A peak driver, so it has a chance of surviving a short on the output with a 100mA PTC fuse.

author: Zero999
author_rank: Super Contributor
timestamp: March 16, 2017, 07:15:56 pm
content: Quote from: Simon on March 16, 2017, 05:41:35 pmFour channels only but what about the 754410?http://www.ti.com/lit/ds/symlink/sn754410.pdfIf you need eight channels, then there are high side, rather than low side, drivers:MIC2981http://ww1.microchip.com/downloads/en/DeviceDoc/mic2981.pdfTD62783http://acg.media.mit.edu/people/simong/hotpants/tech/media/TD62783AF.pdfTBD62783Ahttps://toshiba.semicon-storage.com/info/docget.jsp?did=30523M54563Phttps://www.mitsubishielectric-mesh.com/products/pdf/m54563p_e.pdf

author: BrianHG
author_rank: Super Contributor
timestamp: March 16, 2017, 07:34:38 pm
content: Quote from: MagicSmoker on March 16, 2017, 06:16:08 pmWow, a low side gate driver with 35v support. I didn't think they existed since the largest mosfet gate voltage I've seen was 20v, maybe a really old one with 25v, but, 35v???

author: Monkeh
author_rank: Super Contributor
timestamp: March 16, 2017, 07:49:29 pm
content: Because half-bridge drivers are rareIf you want something pathetically small, grab some transistors..

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2017, 08:32:03 pm
content: Ah, but, if this is for automotive applications, do you not then need short circuit current limiting, and perhaps crossed wire and crossed polarity protection as well? What about load dump?Tim

author: Zero999
author_rank: Super Contributor
timestamp: March 16, 2017, 08:49:58 pm
content: Does it really need to output 24V?Lots of 24V logic circuits such as PLCs will trigger at much lower voltages. You might be able to get away with 18V, in which case, you can use the CD4504 and suitable voltage regulator.

author: MagicSmoker
author_rank: Super Contributor
timestamp: March 16, 2017, 09:35:21 pm
content: Quote from: BrianHG on March 16, 2017, 07:34:38 pmYep, that was why I picked it - I needed push-pull 24V I/O drivers that were faster than the venerable L293/SN754410 and could be put into a high impedance state (so the same external connector pin could be used as an input or an output, software-selectable). It was a bit kludgy, but worked great and was very tolerant of the usual abuses as long as you were willing to forego a lot of the current rating (or use active current limiting circuits on each output, but if you need to do that then you might as well roll your own driver).

author: Simon
author_rank: Unknown
timestamp: March 16, 2017, 10:05:44 pm
content: Quote from: Hero999 on March 16, 2017, 08:49:58 pmIt would be for automotive and ideally it needs to pull to Vbatt+ as although genericly I'd use a push pull driver often inputs have pull up resistors.

author: Simon
author_rank: Unknown
timestamp: March 16, 2017, 10:06:42 pm
content: Quote from: T3sl4co1l on March 16, 2017, 08:32:03 pmReverse polarity and load dump will be dealt with by the circuit itself, the idea is to have an output that while only driving signals is still robust.

author: BrianHG
author_rank: Super Contributor
timestamp: March 17, 2017, 12:40:24 am
content: Every IC mentioned in this thread should work for you except for the CD4045 with it's 18v limit.I would add a series resistor on the output of the IXDD604 as it's outputs will drive 4 amps which sounds like overkill for you, but, I do like it's sturdiness and that it consumes almost no power since it is a CMOS circuit.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2017, 01:08:20 am
content: OK, so what about shorts and crosses?Gate drivers are great when you need power in a hurry (10s of ns), they're not so great for signals that have softer constraints, like EMI (a gate driver will easily excite standing waves in a modest length of wiring!), current limiting and fault protection.Tim

author: MagicSmoker
author_rank: Super Contributor
timestamp: March 17, 2017, 12:36:38 pm
content: Yes, gate driver ICs tend to not be protected against reverse voltage, shorts, etc., and their high transition speed can induce some pretty nasty EMI on long wires but a ferrite bead, plus shunt clamping or TVS diodes and a series PTC fuse will often provide enough damping along with a modicum of protection from abuse. No, it won't necessarily protect against a short to ground when the output is high, or to V+ when the output is low, but in the real world we often have to allow for bad consequences if the end-user doesn't wire things up correctly rather than add to board cost and area consumed in fancy protection circuits.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2017, 05:39:53 pm
content: Quote from: MagicSmoker on March 17, 2017, 12:36:38 pmAll of which can be avoided by simply choosing an appropriate switch device.Also, a ferrite bead won't do much at this voltage and edge rate, or may even make things worse (it's a saturable reactor, which can sharpen the edge under extreme conditions -- which a fast gate driver is adept at producing!).And yeah, you can always add more filtering -- a bigger FB or inductor, and series resistance, and a bit of filter capacitance, and so on, will get you there. But now you're stacking up added parts, that you wouldn't need otherwise.FYI, polyfuses are nearly useless with semiconductor switches. The transistor dies in 100us, then the fuse opens 99.9ms later.On the upside, I wouldn't be too concerned about ESD here; the output pin driver of something this size should be beefy enough to handle that kind of treatment. (Do refer to MFG's ESD ratings though, of course!) Schottky diodes can be added for peace of mind.I don't know offhand of a device which handles everything, but I've seen protected switch devices with high side or low side action, and there's probably one with both. A nice, smooth, controlled edge, with current protection inside, will do a perfect job here -- at least until below-GND / overvoltage output tolerance is required (but at that point, maybe some big beefy diodes, and a polyfuse, would be good enough?).(I know there are single (HS/LS) switches with that kind of voltage tolerance/protection, but I don't know if there are half bridge style pairs with that kind of protection.)TLDR: OP should do due diligence and search frikken Digikey firstTim

author: MagicSmoker
author_rank: Super Contributor
timestamp: March 17, 2017, 06:21:35 pm
content: Quote from: T3sl4co1l on March 17, 2017, 05:39:53 pmThat's the problem in a nutshell... The aforementioned L293 and SN754410 are half-bridge driver ICs (4 outputs) good for up to 35V with overtemperature protection built-in, but not overcurrent, and they are slow as molasses.Quote from: T3sl4co1l on March 17, 2017, 05:39:53 pmThat's an interesting point which I have, admittedly, not looked into much, but my working assumption is that ferrite beads - in contrast to, say, similarly sized "inductors" - intentionally use very lossy core materials in a gapped or open-ended structure to avoid sharp saturation at the expense of raw inductance.Quote from: T3sl4co1l on March 17, 2017, 05:39:53 pmThat was the point I was making, just from a different direction - ie, that it is sometimes ok to accept the occasional field failure from a ham-fisted/clueless tech wiring things wrong than to add all these extra parts to protect against such.Quote from: T3sl4co1l on March 17, 2017, 05:39:53 pmYes, that's usually the case, but note the specific recommendation I made: use a 100mA PTC fuse on a 4A gate driver. The 100mA PTC fuse should have sufficient resistance when cold to limit short circuit current to something the driver IC can tolerate for the (yes, relatively long) time it takes to trip. That's been my practical experience, anyway.

author: BrianHG
author_rank: Super Contributor
timestamp: March 17, 2017, 07:47:34 pm
content: The OP said he only needs a few ma. A series resistor would limit current & emi and for long term short, it will blow.

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2017, 08:30:45 pm
content: Quote from: Simon on March 16, 2017, 10:05:44 pmWhy bother with push-pull if the inputs have pull-ups anyway?How fast does it need to be?

author: Simon
author_rank: Unknown
timestamp: March 17, 2017, 08:43:13 pm
content: it's a case of a one size fits all. I can use a TLE5205 but for having all the required features its a relatively expensive driver.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2017, 09:08:50 pm
content: Quote from: MagicSmoker on March 17, 2017, 06:21:35 pmThe slowness is probably helpful, really, and at least they can be harnessed for current limiting (L293 + L297 being the classic case for steppers), but no, it's not going to be elegant, it's not built in.Large voltage drop, too, though probably not a concern in this application, and at this current level.QuoteNope-- quite the opposite! Inductors are designed to store energy, ferrite beads are designed to present impedance.Largely the same materials and construction are used, too (well, among multilayer parts; obviously, wound inductors differ!).The one is done at the expense of the other: a gapped core reduces permeability, reduces relative core loss, increases magnetizing current (while saturation flux remains ~constant), and reduces the relative severity of saturation -- proportionally (more or less).And obviously, multilayer parts aren'tidenticalmaterials. They probably use a filler (e.g., clay?) to reduce permeability, much as the permeability of a powdered iron core is limited by the packing density of the powder, and the amount of resin used to bond it.The "relative severity of saturation" means, L(sat) / L(zero-bias). With high initial permeability, you have more to lose, so to speak. In the extreme, "square" materials (permalloy and nanocrystalline being the best examples) have so much inductance that they "switch" from "off" to "on" in a very meaningful way (>10^4 on/off ratio)! So, aninductorwon't "switch" hard, it just sucks down current a lot faster.Ferrite beads are probably still lossy enough that the edge rate won't be much accelerated, or, after a couple in series (as an LCLC.. filter), it's attenuated enough that things are playing in the linear range again.It's an effect which can be helpful at times: FBs are actually fantastic for driving MOSFET gates! At first, the driver edge begins ramping across the ferrite bead; after a little delay, it saturates, suddenly delivering full drive current to the gate. During the transition, DCR (of driver, FB and transistor Rg) sets risetime. When the transition is complete and current falls, the FB slowly comes out of saturation, again presenting a high impedance. The gate voltage is able to float a little at AC, preventing a grounded-gate or tuned-gate type oscillation. (Oscillation can still occur during the Miller plateau; the intent is to make it short enough in duration to avoid breaking into oscillation.)Alternately, you can use a chain of ferrite beads (maybe not the EMI type, but a lower loss ferrite) and capacitors to build a nonlinear transmission line. When driven with a tall enough step to cause the line's components to saturate, the wavefront accelerates forward, pushing into itself, piling up, becoming sharpened. An electromagnetic shock wave!(The same principle is used in the world's fastest DSOs, though using linear inductors (planar transmission lines) and nonlinear capacitors (schottky junctions) on InP or something like that. Single digit picosecond speeds are achieved!)Anyway, I digress; nonlinear materials are fun.QuoteAhh, right, gotcha!Tim

author: capt bullshot
author_rank: Super Contributor
timestamp: March 17, 2017, 09:10:04 pm
content: Quote from: Simon on March 16, 2017, 10:05:44 pmLook for smart or intelligent high side Edit: switches, not drivers. Infineon, STM, OnSemi have plenty of them in all sizes, colours and number of channels.Usually these are fully protected N-Channel Mosfets with integrated driver to operate from 3.3V to 5V logic inputs. Some of them offer serial input and/or isolation between logic and power.

author: BrianHG
author_rank: Super Contributor
timestamp: March 17, 2017, 09:25:11 pm
content: Quote from: Simon on March 17, 2017, 08:43:13 pmThat's a few more orders of magnitude than just a few ma....A 2 channel op-amp, with a 50ma drive is 0.85$us vs the equiv 2 channel TLE5205 5.67$us for 5 amp drive.

author: Simon
author_rank: Unknown
timestamp: March 17, 2017, 09:33:55 pm
content: quite, i'd want a lower power version with more drivers in one package

author: BrianHG
author_rank: Super Contributor
timestamp: March 17, 2017, 09:49:58 pm
content: 4x 50ma drivers for $1.02us. << They don't guarantee short circuit conditions.http://www.digikey.com/product-detail/en/on-semiconductor/NCS20074DR2G/NCS20074DR2GOSCT-ND/58017444x 1amp drivers for $2.43us. <<< This is your closest one. And it does have thermal shutdown if too much current is being drawn.http://www.digikey.com/product-detail/en/texas-instruments/SN754410NE/296-9911-5-ND/380180

author: Zero999
author_rank: Super Contributor
timestamp: March 19, 2017, 12:51:32 am
content: Quote from: Simon on March 17, 2017, 09:33:55 pmYou still haven't said how fast it needs to be?Does it matter if it's inverted?Why not use discrete components?Try this. Current limiting is implemented with potential dividers (R3 & R4 and R1 & R6) on the bases and emitter resistors (R2 and R5).Note that, in the attached schematic, CL represents a capacitive load, not part of the circuit.

author: Simon
author_rank: Unknown
timestamp: March 19, 2017, 09:27:50 am
content: Well the other option was to go descreet and use emitter resistors. I was hoping for one mutichannel chip. I only need a few KHz.

author: Zero999
author_rank: Super Contributor
timestamp: March 19, 2017, 10:53:31 pm
content: How near to either supply rail does the output have to go?The previous example I posted will only go to within 0.7V of either rail. Lots of the ICs mentioned have Darlington output stages and will only reach 1.2V at low currents.Here's an example for a driver which will go to within 100mV of either rail.Note that in both of the above schematics, the IC at the input needs to be able to sink all the current, as the lower transistor is in common base configuration.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 20, 2017, 02:50:57 am
content: This works, but as mentioned, it does require some current capacity to operate the input. I "created" that years ago, here for example,In this case, using both polarities of transistor "gain stage", to get complementary outputs. Rather than driving the high side, a CCS load is used; using common bias means the CCS is really only active during transition, and doesn't consume much current once one or the other output is saturated (near +V).Tim

author: Simon
author_rank: Unknown
timestamp: March 20, 2017, 07:42:54 am
content: strict rail to rail is not neccessary, but 18V is not enough on a 24+V system.

author: Zero999
author_rank: Super Contributor
timestamp: March 22, 2017, 07:35:13 pm
content: What about the ADG3123? It's pricey but may be economical, in small volumes, especially if you're building them by hand, as less time will be spent placing parts.http://uk.rs-online.com/web/p/voltage-translators/7097657/?searchTerm=ADG3123&relevancy-data=636F3D3126696E3D4931384E4B6E6F776E41734D504E266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E5B5C707B4C7D5C707B4E647D2D2C2F255C2E5D2B2426706F3D313326736E3D592673743D4B4559574F52445F53494E474C455F414C5048415F4E554D455249432677633D424F5448267573743D41444733313233267374613D4144473331323326