I met with an engineering team at Texas Instruments while I was attending DesignCon in Santa Clara, Calif. The engineers showed me a new analog front end (AFE) IC they have released. More semiconductor manufacturers are starting to turn out AFE ICs. This one is intended for use with three-terminal electrochemical gas sensors.
The AFE device looks pretty straightforward.
The TI LMP91000 AFE.
What makes this one unique is the Eval platform the apps guys there put together. Except for the gas sensor cell and the 3V lithium coin cell to power it, all the important parts are from TI. There's the LMP91000 device (shown above), a TPS61220 boost converter, an LM4120 LDO, and the CC2541 Bluetooth IC. The Eval module also has two circuit boards and the usual small number of connectors or headers, resistors, and capacitors.
The complete coin cell-powered, Bluetooth-linked AFE module.
The boost converter is needed just to give the AFE and chemical cell sufficient voltage over the life of the battery. It's a very high-efficiency device, which it must be for a battery-operated device. Also, the LDO is the right part for battery apps. The input-to-output differential is very low, and so is the quiescent current.
What makes this device even more special is the time it took the apps team to put this together. From the initial concept through schematic capture, PCB layout, writing the software, and assembling the first prototype, the total elapsed time was 11 days. The implications for anyone working on a similar design (the companies in western Pennsylvania come immediately to mind) are obvious.
The unit I saw had an O2 sensor, but the same AFE can work with sensors for H2S, CO, and CO2. The total current draw is around 40uA, so it can run more than six months on the coin cell. TI demonstrated the sensor with an iPad app to show O2 concentration in the air. Fortunately, it was around 20 percent, so everyone in the room could breathe easy.
Gas sensors like this will see use at oil refineries and by firefighters and mine workers. Portable blood analyzers can also benefit from the technology. For all these applications, the threat of toxic or life-threatening gases is extremely serious, so the work TI's engineers are doing is especially good humanitarian work.
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