Hot Links: Freedom Edition

This Inde­pen­dence Day, I’m going to start a new series called Hot Links, in which I go full neck­beard (read: offer my unin­vited and under­in­formed opin­ions) on stuff I find on the Inter­net.

Today’s theme is all about that good Amer­i­can stuff.

Texas Instruments (TI) wireless modules

As a hobby­ist who will soon start a career in creat­ing hard­ware, I see TI as folks who “get it.” They’re already at the top of most engi­neers’ lists just by having great prod­ucts with (more impor­tantly) excel­lent docu­men­ta­tion. But it’s more than that. They really go the extra mile to make the designer’s life easier; they’ll cut down on exter­nal parts for their inte­grated circuits (ICs) when­ever possi­ble and try to use fewer pins to get the job done. They even try to make the pinouts on their chips easy to lay out a printed circuit board (PCB) for.

So I wasn’t surprised to find a TI Blue­tooth module cater­ing to my “lazy bum” use case of lever­ag­ing the Blue­tooth Serial Port Profile (BT SPP) to emulate a connec­tion between a micro­con­troller UART¹ and a desk­top serial connec­tion: the LMX9838. My lack of surprise lacked harder when I discov­ered that it’s smaller (10 mm × 17 mm × 2 mm) and not cost­lier than what I had been using due to its single-mind­ed­ness of purpose in doing only that. It’s got that perfect “no-frills” prod­uct feel. I mean just look at the appli­ca­tion diagram:

This part is a brutally simple “by-engi­neers-for-engi­neers” prod­uct that also happens to be perfectly conveyed by their tech­ni­cal writers/illustrators. Compare that schematic to the current hobby­ist-favored² Roving Networks RN42:

Here’s the thing, guys: the folks who look at some­thing like that and think, “hmm, I’d like to incor­po­rate that stuff into my prod­uct” are not the fuck­ing customers for modules like this because they’re design­ing a prod­uct. It’s noobs like me who use an LMX9838 or an RN42. Unless your “prod­uct” is “hand­made” by “produc­tors” in “Brook­lyn³,” you’re not using some off-the-shelf plug’n’play module like this in it. It’s not just a Blue­tooth radio; it’s a Blue­tooth radio on its own board with an antenna and a micro­con­troller running a whole BT stack and it connects to comput­ers all on its own. Engi­neer­ing teams⁴ design­ing prod­ucts are perfectly capa­ble laying a simple BT radio down, rout­ing RF fron­tends to anten­nae, drop­ping some vendor’s yucky Blue­tooth stack on their own micro­con­troller, and then getting it FCC certi­fied. Every­one else just wants a dongle that hooks her “data device with sensor” to her MacBook.

Now, tinker­ers and profes­sional engi­neers would prob­a­bly recog­nize that the LMX9838 part number doesn’t look very TI-ish, and they’d be right: this is orig­i­nally a National Semi­con­duc­tor part. However, it got discon­tin­ued in 2010 and TI wisely brought it back, prob­a­bly as part of their SimpleLink move. However, the only “every­thing onboard” Blue­tooth solu­tion that’s actu­ally part of the SimpleLink family, the CC2564-BLUEBRIDGE, is from two (?) 3rd-party devel­op­ers (???) and suffers from pretty much the same immense feature-creepi­ness I just whined about. It’s also bigger and more expen­sive.

Texas Instruments Half-Bridge Modules

Along another branch of TI’s awesome “shove many great­nesses into one module” path of prod­uct evolu­tion, I’m really digging how they packed a half-bridge driver and a half-bridge into a 5 mm × 6 mm pack­age (think SON-8 except not 8) I normally asso­ciate with power MOSFETs.

Every­one had already been cram­ming two N-chan­nel Field-Effect Tran­sis­tors (N-FETs) into one 5×6 block for a few years now, but now we can have it with dead­time-matched drivers built in? This is hard­core Amer­i­can patri­o­tism right here.

Sadly for motor control fans⁵, this is designed for multi­phase buck DC-DC convert­ers in comput­ers, where a bank of these help drop 12V down what­ever your CPU uses. That means that the FETs inside are highly asym­met­ri­cal, as the high-side FET is pass­ing current much less of the time than the low-side FET does. For exam­ple, the r_{DS (on)} of the high-side FET on this dual FET (no driver) is more than 3 times that of its low-side FET. So this is no bueno for control­ling motors on a robot, where all the FETs are engaged for basi­cally the same frac­tion of the time. Not only that, these modules are rated to only 16V input—not enough for many.

I can only hope that TI can bring this minia­tur­iza­tion and ultra-low r_{DS (on)} tech to their motor control power stages, which are currently utter shit.

Intersil Full-Bridge Drivers

Moving on to another Amer­i­can semi­con­duc­tor company, Inter­sil in good ol’ Sili­con Valley. They’ve got three differ­ent dual half-bridge drivers in itty-bitty 16-pad 4 mm × 4 mm QFN. If judg­ing only by pad count, they’re even better at the “simple is better” thing than TI is: just think, you need at least

• Four pads for each of two half bridges
• Two pads for each of logic and power supplies
• Two pads for the inputs

Oh wait, that’s it. The other two pads on the ISL6610 and ISL6614B are both No Connects (NCs). Heck, the ISL6610 datasheet even says that it’s two 6609 single half-bridge drivers crammed together with enable func­tion removed. The PWM inputs are three-state (high/low/disable for 1/0/Hi-Z), the boot­strap diodes are built-in, the shoot-through protec­tion is auto­matic (?!), and the only exter­nal compo­nents are two boot­strap capac­i­tors for the high-side drivers (whose values, of course, depend on what FETs you drive).

It’s so Amer­i­can, it’s as if Apple designed and sold inte­grated circuits and this were one of their three semi­con­duc­tor prod­ucts.

At any rate, either of these would be really nifty drivers for brushed DC motor control in robots. I’d use the ISL6614B for the bigger FETs that require more than 5V to fully enhance (it does require a sepa­rate supply though) and the ISL6610 when 5V gate drive would suffice. Now the caveat here is their absolute maxi­mum volt­age rating (no recom­mended is given) of 15V, with 30V for 100 ns spikes. I think that rules out both chips for a lot of robot folks. Those folks should then look at the ISL6210, which has double the volt­age rating and some features you might actu­ally want (I don’t know what diode emula­tion is, but appar­ently that pad doubles as a dead­time set resis­tor).

The final catch? I can’t find any vari­ety of the ISL6210 in stock anywhere, and the other two only as 14-SOICs, which are massive. Rawr.

Maxim Integrated Charge Pumps

Speak­ing of using higher gate drive volt­ages, where were you about to get that gate drive volt­age? For smart but small analog solu­tions where the condi­tions aren’t extreme, I look to another Valley company, Maxim. I’ve known them as the company that sounds like a machine gun and the men’s maga­zine, and which has the best samples policy for hobby­ist engi­neers, hands down. I’ve been grub­bing free chips off of them in little acrylic cases lined with anti-static foam bedding since middle school (I can hear the geezer engi­neers scoff­ing already :P).

Side­note: they recently rebranded à la Microsoft (nice butter­fly logo) and retooled their website in such a way that changed zero func­tion­al­ity. Wat.

For gener­at­ing gate drive volt­ages, how about a MAX1680/1 or even a smaller MAX680/1? Both are charge pumps. The former handle 125mA and the latter 50mA, and both use just three exter­nal capac­i­tors to double volt­age input volt­age for compact, simple DC-DC conver­sion. Nifty.

Sneak Peak

Hmm, I defi­nitely didn’t intend to do the whole thing on just elec­tron­ics, but oh well. Happens. Here’s what I’m work­ing on right now:

1. A hard­ware periph­eral or subsys­tem on most micro­con­trollers that handles asyn­chro­nous and synchro­nous serial commu­ni­ca­tion. Other periph­er­als can talk on the SPI or I²C buses, gener­ate PWM, etc. [▲]
2. And by that I mean sold carried by Spark­Fun, one of the self-appointed tastemak­ers of the “maker” commu­nity. [▲]
3. Since when was Williams­burg ever repre­sen­ta­tive of Brook­lyn? Since when was it even part of Brook­lyn? [▲]
4. So again, we’re drop­ping Williams­burg from the race here. [▲]
5. As in people who like motor control, such as a Fan, not fans designed for… control­ling motors…? [▲]