VPG’s Bulk Metal® Foil Current Sensing Resistors Offer Accuracy and
Stability for Li-ion Batteries in Avionics
MALVERN, Pa. -- August 29, 2013
Vishay Precision Group, Inc. (NYSE: VPG) today announced that it has completed
tests showing that its Bulk Metal^® Foil current sensing resistors meet the
accuracy and stability required by its aircraft customers for charging of
Li-ion batteries in avionics applications. VFR resistors provide a variety of
device configurations and ultra-high-precision specifications to help ensure
the efficient and safe charging of Li-ion batteries. They include the
surface-mount Z-Foil VCS1610Z and VCS1625ZP and the high-power VCS331Z and
CSNG (offering 3- or 6-chip constructions).
The Li-ion battery charging process goes through several critical phases to
ensure the battery is charged to its maximum capacity, while at the same time
following certain safety rules to avoid explosion or fire. Li-ion battery
chargers require accurate current and voltage settings and monitoring, as well
as a constant current and constant voltage. If these accuracy requirements are
not met, the charger will undercharge or overcharge the battery. A failure to
completely charge the battery results in reduced battery life, while
overcharging can cause batteries to fail due to overheating.
Precision current sensing resistors are required to charge and monitor the
Li-ion battery at a known current level until it reaches its final voltage. At
this point, the charger circuitry switches over to constant voltage mode,
providing the current necessary to hold the battery at this final voltage. For
both phases, Bulk Metal Foil resistors provide higher accuracy than other
technologies, such as thin film, thick film, and wirewound resistors.
“Li-ion batteries are well established in portable consumer electronics and
are now becoming more popular in military and advanced civilian avionics. As
the scope of their applications has expanded, so have the stringent
requirements they must meet, especially in terms of cell safety and lifetime.
For designers, the main challenge in meeting these requirements is in finding
the optimal point between undercharging and overcharging through continuous
accurate and stable monitoring of input and output current,” said Yuval
Hernik, senior director of application engineering for VFR.
Hernik added, “The need for safety was emphasized in the latest
near-catastrophic incident involving the charging of Li-ion batteries, in
which a Dreamliner caught fire while parked at Heathrow. Luckily, no
passengers were on board. In our opinion, designers in the avionics industry
have every motivation to look for more precise and reliable
commercial-off-the-shelf (COTS) resistors to accurately monitor the battery
voltage when connected to the charger. Bulk Metal Foil current sensing
resistors provide the low TCR and thermal EMF required to meet this need. They
also provide wide resistance ranges, and unlike most COTS resistors, any
resistance value within their given range is available with no additional cost
or lead time effect.”
There are five important phases that need to be considered when choosing a
current sense or shunt resistor for any application: connection errors,
external and Internal temperature errors, frequency, drift over time, load
life stability and thermal EMF. VFR's Bulk Metal Foil current sense resistors
offer a four-terminal Kelvin connection for increased accuracy. They feature
an ultra-low TCR of ±0.05 ppm/°C typical (0°C to +60°C) and ±0.2 ppm/°C
typical (-55°C to +125°C, +25°C ref.). The surface-mount VCS1610Z and
VCS1625ZP offer load-life stability of ±0.015% at 70°C for 2,000 hours at
rated power while the VCS331Z power resistor features load-life stability down
to ±0.005% (50 ppm) typical at 3 W and +25°C for 2,000 hours (mounted on a
heatsink) and thermal EMF of 0.05 μV/°C typical.
Featuring a non-inductive (<0.08 μH), non-capacitive design, Bulk Metal Foil
resistors offer a rise time of 1.0 ns with effectively no ringing, a thermal
stabilization time of < 1 s to within 10 ppm of steady state value, current
noise of 0.010 µVrms per volt of applied voltage (<-40 dB), voltage
coefficient of <0.1 ppm/V, and resistance tolerance down to ±0.01%.
Samples and production quantities of the Z-Foil resistors are available now,
with lead times of five days for prototypesamples and fromtwo days to five
weeks for standard orders at the catalog houses, depending on their shelf
Further information about Vishay Foil Resistors products is available at
www.vishayfoilresistors.com. Follow Vishay Foil Resistors at
About Vishay Precision Group
Vishay Precision Group (VPG) is an internationally recognized designer,
manufacturer and marketer of: components based on its resistive foil
technology; sensors; and sensor-based systems specializing in the growing
markets of stress, force, weight, pressure, and current measurements. VPG is a
market leader of Foil Technology Products, providing ongoing technology
innovations in precision foil resistors and foil strain gages, which are the
foundation of the Company’s Force Sensors Products and its Weighing and
Control Systems. The product portfolio consists of a variety of
well-established brand names recognized for precision and quality in the
marketplace. To learn more, visit VPG at www.vishaypg.com.
About VPG Foil Resistors
VPG Foil Resistors, a part of Vishay Precision Group (VPG), produces the most
precise and stable resistors available. Distinguished by the premier brands
Vishay Foil Resistors, Powertron, and Alpha Electronics, the VPG Foil
Resistors portfolio includes discrete resistors and resistor networks in
surface mount and through-hole (fixed-lead) configurations; customized chip
resistor networks; precision trimming potentiometers; and discrete chips for
use in hybrid circuits. These devices are used in applications requiring a
high degree of precision and stability, such as in medical testing equipment,
semiconductor equipment, precision measuring instruments, aerospace, and
military applications. To learn more, visit www.vishayfoilresistors.com.
Bulk Metal is a registered trademark of Vishay Precision Group, Inc.
Links to featured product datasheets:
http://www.vishaypg.com/ppg?63240 (VCS331Z, CSNG et al)
Link to product image:
Vishay Precision Group, Inc.
Marti Spalding, +1 919-374-5515
Director, Global MarCom
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