Adding Intelligence to Fixed Function ICs: Q&A with TI



A low-cost entry point approach to simple sensing applications

Editor’s Note: The announcement  that Texas Instruments (TI) now offers its ultra-low-power MSP430™ microcontrollers (MCUs) at around 25 cents in high volume made for a good occasion to speak with Dave Smith. Smith is the Product Marketing Manager for TI’s MSP430 FRAM-based microcontrollers and argued that there are Big Reasons for Small MCUs in an earlier article. Now, Smith explains that reasons for designer interest in the MSP430 line go beyond just the low-price entry point. Edited excerpts from our conversation follow:

EECatalog:  What comprises the MSP430 Value Line Sensing MCU family?

Dave Smith, Texas Instruments

Dave Smith, TI: This is a collection of application reports complete with code libraries aimed at adding a little bit of intelligence to fixed function ICs—that is, some of the common things found on a PCB: comparators; real-time clocks; EEPROMs; supply voltage supervisors; reset controllers—some of the simple functions that many PCBs have.

EECatalog: What goes into the decision to use a microcontroller rather than an off-the-shelf product?

Smith, TI: When thinking about the decision to use a microcontroller as compared to an off-the-shelf product you’re often looking at a situation where there is not an exact fit for one of the off-the-shelf products. In those cases, using a microcontroller can enable an engineer to tailor the functionality, whether a simple timing parameter or a particular sequence of wake up events, for example, to their application needs. However, we are not trying to go head-to-head with an off-the-shelf whatever-type IC, but rather adding to that.

Figure 1: Smith notes the applicability of microcontrollers that allow the customization of system-level functions to markets such as Smart Home. (Courtesy TI)

EECatalog: Could you offer an example?

Smith, TI: Yes. Things like a real-time clock or a system wake up controller is where we are targeting some of these applications or these functional blocks. So, while I can buy an off-the-shelf real-time clock, what I can’t buy is something that really fits in with the system needs that I have. In this case we are using the FRAM nonvolatile memory along with the real-time clock and allowing them to use that as a combination of real-time clock and EEPROM.

Another example is a programmable system wake up controller. Yes, I can buy an external chip that is going to trigger a wake up every 100 milliseconds, two hundred milliseconds, whatever is hard-wired into that part. With the MSP430 based solution we can adjust the sleep interval and wake up schedule by simply sending a command over the UART, this added flexibility can help to extend system battery life.

Or say I have an RF chip, Bluetooth, Wi-Fi or whatever, but I want it in a battery-powered system, some home security product or network product. I may not want that to be active all the time because I want the battery to last more than six months, 12 months. With this type of device, I can program it so that it only wakes up that RF chip when something relevant happens—that could be monitoring an ADC for example.

In the low-power MSP430 we can monitor an ADC or use the window comparator to significantly drive down the power consumption of that overall system. Many of those functions could be incorporated into the main logic processor, but it is often very inefficient to do that. So, it may be a part that may have low-power modes and may be able to go into some of the shut-down modes but may be limited or use even more power when it is in those modes, than the MSP would.

EECatalog: So designers can hew a bit closer to their application’s demands than they might be able to with an off-the-shelf IC?

Smith, TI: Yes, we see a lot of customers that are trying to develop energy harvesting or maybe scavenging applications where the ability to do very low power stores, or nonvolatile stores, or operate for longer with a very limited power supply. Whether that’s a rechargeable battery that is charged by solar panels or just a conventional battery, lasting longer between service intervals will help to reduce maintenance costs and overall system ownership costs.

A couple of other examples: On the PWM one of the example code snippets creates a dual 8-bit DAC, so in a standalone situation this could be a simple sounder. Maybe it gets a push button or some other trigger from an ADC or a comparator and then it plays a tone or a series of tones to indicate that something has happened. Everything from a simple doorbell to a simple timer.

Or it could be incorporated into a larger system, where you are going to send some communication data, some serial data, to trigger that signal. So that’s a little dual DAC. It could be as simple as controlling color blending on an RGB LED.

One of the areas that we have really seen this being taken up by our customers is where they are looking to do very low power nonvolatile writes. With an energy-harvesting solution or with a small coin cell battery, if you need to write data in a conventional flash or EEPROM memory the mA’s of current required will quickly deplete the available stored energy. Conventional EEPROM and Flash technologies include a charge pump within the device that is required to boost the supply voltage to a higher voltage. It takes timing to do that and, more critically, it takes a significant amount of energy to do that.

If you want to store something in a system whether sensor data or whatever data it is—and want to store it frequently—that can quickly deplete the battery. The FRAM technology we’re using with the MSP430 Value Line is very, very low power. We don’t have the charge pump involved, which also makes it faster.

It’s also very high erase/write endurance, with 1015 cycles as compared to the typical 100K or 1M cycles of EEPROM or Flash.

EECatalog: What are you seeing in the ecosystem of folks coming up with interesting sensors?

Smith, TI: We see a lot of activity in and around the connected home. Yes, there is a lot of activity going on in office and factory automation as well, but the home automation that is going on at the moment and is driven by cloud services and the big names rolling out the personal assistants stands out.

The automation being built into homes is going into places that I don’t think even a couple of years ago we would have expected to see that level of intelligence, whether through some of the simple applications we have been talking about here, or things that use capacitive touch to program thermostats or to operate a voice assistant just to trigger something. I think where we are going to see explosive growth is in the home automation, small appliance, and personal assistant areas, and these parts can definitely play roles in that because many of these are battery-powered. Longer battery life makes battery changes less frequent and helps the environment.

EECatalog: Are there some additional things our readers should know before we wrap up?

Smith, TI: These half-a-kilobyte to 1-kilobyte in FRAM devices also have half a kilobyte in SRAM, and this is one of the characteristics which sets them apart from competitive devices. Usually if you have a small program memory, you will have a very small data memory. With the competitions’ 512-byte program memory, you might get 64 or 128 bytes of data memory.

In our parts, if you get 512 bytes of program memory, you actually get 512 bytes of data memory as well, so that makes it a little more programmer friendly; it allows you to do more with the device.

 

 

 

 

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