New ams current-sensing solution for battery management systems needs no shunt resistor
April 23 2014 - 7:49AM
Business Wire
Design breakthrough achieves accurate, linear current
measurement up to 100A by monitoring voltage drop across a PCB’s
copper track
ams AG (SIX: AMS), a leading provider of high performance analog
ICs and sensors, has introduced a reference design board which
measures current to an accuracy of ±1% by monitoring the voltage
drop across a copper track on a PCB.
The development of the new technique, which uses the ams AS8510
data-acquisition front end, enables designers of Battery Management
Systems (BMS) to reduce bill-of-materials cost by eliminating the
precision shunt resistor normally used in current-sensing
applications. A precision resistor with low temperature drift can
typically cost as much as $1.50 in volume.
Accurate current measurement is an essential function in a BMS,
which provides functions including monitoring of a battery’s state
of charge and state of health. The new reference design board from
ams provides a blueprint for the current measurement function in a
BMS, and can be applied in e-bikes, pedelecs and other applications
drawing current of up to 40A. The same design can also readily be
adapted to measure currents of up to 100A using only the resistance
of a PCB’s copper track.
The new ams reference design takes advantage of the very high
sensitivity and precision of the AS8510, an integrated data
acquisition front end which provides two measurement channels.
One channel is used to measure current by sensing the voltage
drop over a 10mm section of a PCB track with a known resistance
value and temperature co-efficient. The other, matched channel
measures the temperature of the copper track. This temperature
measurement can be performed either internally by the AS8510, or by
an external temperature sensor.
By applying a compensation algorithm developed by ams, the
AS8510 can eliminate the effect of the variation in the resistance
of the copper track over temperature. This means that it can
produce current measurements accurate to ±1% over its entire
operating temperature range (-40°C to +125°C) without the normal
requirement for a precision shunt resistor with a low temperature
co-efficient.
‘When paired with a precision 100µΩ resistor, the AS8510
provides extremely high accuracy of ±0.5% over a current range from
a few mA up to several kA,’ said Bernd Gessner, Vice-President and
General Manager of the automotive business unit at ams. ‘This new
reference design from ams shows how the same device can be used to
capture measurements almost as accurately while completely
eliminating the resistor.
‘For designers of BMS for use in pedelecs and electrics scooter,
for instance, which are subject to very wide swings in ambient
temperature, the technique for temperature compensation implemented
in this design is a valuable breakthrough, enabling a worthwhile
reduction in component cost while meeting many applications’
requirement for measurement accuracy.’
For further information on the AS8510 reference design please
visitwww.ams.com/AS8510/CopperShunt
Download Press Picture or Block Diagram at
http://www.ams.com/eng/Press/Press-Releases/AS8510_refdesign
Patricia MoosburgerMedia Relationsphone: +43 (0) 3136 500
31235press@ams.comwww.ams.com
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