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 Ã— 17 mm Ã— 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 Ã— 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 5Ã—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 rDS (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 inputâ€”not enough for many.
I can only hope that TI can bring this miniaturization and ultra-low rDS (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 Ã— 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 Ã 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.
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:
- A hardware peripheral or subsystem on most microcontrollers that handles asynchronous and synchronous serial communication. Other peripherals can talk on the SPI or IÂ²C buses, generate PWM, etc. [▲]
- And by that I mean sold carried by SparkFun, one of the self-appointed tastemakers of the “maker” community. [▲]
- Since when was Williamsburg ever representative of Brooklyn? Since when was it even part of Brooklyn? [▲]
- So again, we’re dropping Williamsburg from the race here. [▲]
- As in people who like motor control, such as a Fan, not fans designed for… controlling motors…? [▲]