Capacitors & Resistors
mechanical isolation technology, which provides the most advanced mechanical and thermal stress performance capable of withstanding deflections of up to 10mm as the board flexes.
Kemet has developed a number of flex- mitigation technologies which are used throughout product ranges such as Open- Mode and Floating-Electrode devices with Fail-open technology capable of withstanding 2mm of flexing. The latest C0G and Ultra-Stable X8R capacitors feature FT-CAP flexible termination technology (Figure 3) , which directs circuit board stress away from the ceramic body and into the termination area allowing the devices to withstand flexing up to 5mm.
FT-CAP C0G capacitors have an enhanced high-temperature dielectric rated for operation up to 125°C, while the X8R
Figure 3: FT-CAP technology saves MLCC failure due to flex cracking
series maintains stable capacitance values at temperatures up to 150°C.
Automotive-qualified versions of X7R and C0G capacitors provide the high- temperature capability required for controlling High-Intensity Discharge (HID) headlamps. High-temperature capability is particularly needed in advanced controllers that integrate both the igniter and ballast circuits, which can expose the boost capacitor to temperatures of up to 150°C. Advanced film capacitors may also be used for this application.
Tantalum capacitors
Figure 2: Leadframe-mounted stacked capacitors deliver high capacitance in a small footprint
Hybrid FO-CAP Fail-Open/Flexible- termination and FF-CAP Floating- Electrode/Flexible Termination devices are also available.
Another development among today’s advanced capacitor families is the arrival of true fail-open tantalum fused capacitors for use in high-reliability applications where a short-circuit capacitor failure will disrupt the overall operation of the system. Such applications include decoupling and filtering in computing, telecommunications and defence electronics, and industrial
applications such as filtering for point-of- load and switched-mode power supplies requiring a built-in fuse capability. These are often high-current applications where high fault currents can occur and little or no series resistance is present to protect the capacitor. The T496 MnO2 tantalum Commercial Off The Shelf (COTS) family addresses these types of applications by including an internal fuse that opens within one second when a fault current is detected, to ensure the capacitor is isolated from the circuit. Tantalum capacitors are also in demand for applications such as Solid-State Drives (SSD), wireless cards and GPS systems, which benefit from the very high capacitance, low ESR and small case sizes that are characteristics of these devices. The latest families combine improvements in capacitance and ESR performance with low
mounted height and all solid-state construction.
Another innovation is Tantalum Stack Polymer (TSP) technology, which features a cathode plate of organic conductive polymer and stack two, three, four, or six discrete components into one device as shown in Figure 4. These devices combine high capacitance with very low ESR and high ripple-current capability for power- supply applications.
Polymer-film capacitors
New polymer capacitor technologies allow designers to reduce the number of capacitors used, and therefore to reduce Bill-of-Materials (BOM) costs, in applications such as radar pulse capacitors, and point- of-load DC/DC and switched-mode power supplies in the computer, industrial, defence and telecom sectors. These devices also have low ESR and high power dissipation resulting in higher ripple current capability than comparable MnO2 devices. Kemet’s polymer COTS T543 series capacitors combine the latest commercial polymer technologies with up-screening comprising at least 24 hours of voltage conditioning and surge-current options at +25°C and -55°C/+85°C. The devices also have a benign failure mode. The assurance of long-term reliability allows designers to use up to 90% fewer capacitors in new power-management designs.
Kemet |
www.kemet.com
Figure 4: Tantalum Stack Polymer technology delivers high capacitance with the low-ESR and robust characteristics of tantalum capacitors
Geoff Imlach, Product Manager Film and Electrolytic Business Group Americas, KEMET
www.cieonline.co.uk
Components in Electronics
May 2013 17
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