Medical Electronics
the skin is not only their greatest strength, but also a potential weakness. The reason is that they will inevitably be exposed to user-generated static electricity, which can render them inoperable without the
Figure 2: Wristbands will soon be able to communicate important information on blood sugar levels, blood pressure, cholesterol, heart rate, nutrition, pulse oximetry, sleep, and other relevant health matters to a user's smartphone for easy transfer to a doctor
proper protection. It might sound surprising, but a simple human touch can be all it takes to initiate an electrostatic discharge (ESD) transient because any of the sensor circuits, buttons, battery- charging interfaces, or data I/Os could provide a path for ESD to enter the device.
Fortunately, manufacturers of semiconductor-based ESD protection components are working hard to improve the capabilities of these solutions. Littelfuse, Inc., for instance, continually invests in developing new processes that enhance their protection products. Recent component innovations include: • Lower clamping voltage to protect even the most sensitive circuits: During an ESD event, the main job of the ESD protector is to divert and dissipate as much of the ESD transient as possible. This characteristic is improved by reducing the on-state resistance (often called "dynamic resistance"). By reducing the dynamic resistance, the ESD protector carries significantly more of the surge current than the circuit being protected. In doing so, it reduces the electrical stress on the integrated circuit and ensures that it survives. The SP3014 Series TVS Diode Array from Littelfuse, for example, has a dynamic resistance value of less than 0.1 to provide best-in-class performance. • Lower capacitance to avoid interfering with high speed data transfer: Although circuit protection is crucial to an ESD protection device's purpose, it is important to remember that it has to perform this role without interfering with the day-to-day functioning of the circuit it protects. For instance, on an RF interface (Bluetooth, ZigBee, etc.) or wired port like USB 2.0, the ESD protector must be prevented from causing distortion or loss of strength of the data signals. To ensure signal integrity, the capacitance of the ESD protector must be minimized without compromising protection levels. The SP3022 Series TVS Diode from Littelfuse features a capacitance value of 0.35pF,
www.cieonline.co.uk
ensuring that it will remain "invisible" to high speed signals. • Smaller form factors to fit the limited board space available in the wearable devices: No matter how well a protection device performs, it won't be that useful if it can't fit into the application it is intended to protect. Wearable medical devices such as watches, wristbands, and chest bands will gradually get thinner and smaller or be incorporated directly into clothing so that the circuit boards will have minimal space available for the ESD protection solutions. Discrete diodes are ideal for giving design engineers exceptional board layout flexibility; and the SP1020 (30pF) and SP1021 (6pF) Series are packaged in the 01005 package outline to minimize the amount of space they take up. Furthermore, the SP1012 Series (Figure 3) packs five bi-directional channels of protection in a compact 0.94mm x 0.61mm package outline for applications that demand reducing part counts and protection device footprint.
In summary, although it is quite clear that upcoming wearable technologies will help advance users' quality of life, they will continue to pose challenges for designers. Making sure that they also provide long- lasting reliability is therefore extremely important. In fact, they must allow for
Figure 3: SP1012 Series five-channel bidirectional TVS Diode Arrays provide reliable protection against highly destructive electrostatic discharges. Their bidirectional configuration provides symmetrical protection when AC signals are present
accurate measurements to be made no matter how active the lifestyle or how often they are subjected to potentially damaging ESD events. Manufacturers of ESD protection devices are committed to working hard to provide protection for these devices while not interfering with their core functionality.
Littelfuse |
www.littelfuse.com
James Colby is Manager, Business and Technology Development for the Semiconductor Business Unit at Littelfuse
Components in Electronics October 2014 29
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70