Sensirion’s “World’s Smallest Flow Sensor” for Taking Accurate Differential Pressure Measurements

Sensirion announces their new SDP3x series of "the world's smallest differential pressure sensors," which allow for more integration and application possibilities.

Sensirion recently announced their new SDP3x series of differential pressure sensors.

A rather unique and specialized-looking pressure sensor. From the SDP3x datasheet (PDF).

As of the writing of this article, there are four IC versions within this series: two digital (I2C) sensors, and two analog output sensors. See the image below. And instead of cramming both the digital and analog sensor information into a single datasheet, Sensirion has made it a bit easier, at least in my opinion, by providing standalone documents of the digital version datasheet and the analog version datasheet. Keep in mind, however, that this article will focus only on the digital part.

 

Depending upon your application's needs, you can choose from either two digital (I2C) or two analog flavors. Information courtesy of Sensirion.com

This "world's smallest differential pressure sensor" is well-suited for applications such as smart inhalers (see image below), medical home care applications, and appliances.

 

The SDP3x allows for numerous new application possibilities, such as this smart inhaler. Image courtesy of Sensirion.com

CMOSens Technology

Like all other Sensirion products, the SDP3x series of pressure sensors use Sensirion's CMOSens Technology for fusing together the sensor element and the digital signal processing on a single CMOS chip. This technology approach, according to Sensirion, is what allows the SDP3x series sensors to provide both high reliability and long-term stability (see the image below). By the way, this pressure sensor also provides temperature readings. A nice add-on!

 

It's Sensirion's CMOSens Technology that allows for stable, reliable, and repeatable measurements (for both pressure and temperature). Table taken from the SDP3x datasheet (PDF).

Device Pinout

If, at first, you find yourself a bit intimidated when viewing the sixteen pins of this sensor (see image below), hopefully your apprehension will be diminished by the fact that five of these pins are no-connects and that six pins are for GND connections, leaving a mere five pins for routing.
The die pad is internally connected to ground and can be soldered to increase mechanical stability. However, and this is real important: be mindful that the hole in the middle of the die pad (center pad) must stay open during and after the soldering process. For more information on this topic, check out Section 3.6 (entitled Die Pad (Center Pad)) of the datasheet.

 

Only five of the sixteen pins, not counting GND, need to be routed. From the SDP3x datasheet (PDF).

I2C Interface, and Multiple I2C Addresses using a Single ADDR Pin

These digital pressure sensors are designed to operate at I2C clock speeds of up to 1 MHz (see image below), which may be very handy in some design circumstances. But, what I find to be most intriguing, is that a single I2C ADDR pin can select multiple I2C devices. For more information on the IC's I2C commands and registers, review Section 5 in the datasheet (entitled, Digital Interface Description).

This digital pressure sensor series can operate at I2C clock speeds of up to 1MHz. Table from the SDP3x datasheet (PDF).

Do you have any experience (good or bad) with this single-pin I2C-address-setting design approach? If so, please share your experiences in the comments section below.

A single I2C ADDR pin, along with different resistor values, is used for selecting multiple I2C addresses. Information taken from the SDP3x datasheet (PDF).

Layout Assistance and Other Information

Due to the rather unique physical attributes of this sensor, Sensirion has been forward thinking by providing plenty of package outline information as well as soldering and layout guidance (see the following image). Thanks, Sensirion, for not making us ask for it!

 

Sensirion provides, within the datasheet, detailed information on the IC's package and layout requirements. Click to enlarge.

And if you're in need of additional information related to this IC, in terms of application notes, sample code, and a selection guide for differential pressure sensors (see the image below), then be sure to checkout Sensirion's Download Center (website).

 

Sensirion has made available plenty of pressure-sensor-related documentation. Screenshot from Sensirion's Download Center (website).

An Evaluation Kit Is Available

Apparently, to help designers more easily and cheaply test these new super-small pressure sensors—meaning, designers won't need to design their own pressure sensor PCBs, Sensirion makes available the EK-P4 Evaluation Kit for the SDP3x series. Within this eval kit, you'll find a USB stick attached to a PCB, of which utilizes an SDP31 sensor, and a flow element (see the image below). Sensirion, by providing their EK-P4 viewer software together with their quick start guide, obviously hopes that users of this eval kit will have an enjoyable and easy experience, all with the self-serving goal of getting the SDP3x series included in new designs. Who can blame them, right?

 

An apparently easy-to-use evaluation kit, the EK-P4.

Have you had a chance to use any of Sensirion's differential pressure sensors from their SDP3x series? Or, have you had an opportunity to evaluate (play around with) their evaluation kit? If so, leave a comment and tell us about your experiences.