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that also utilize an analog OUT/ comparator SIGN
arrangement exhibit a SIGN transition band that can
range up to 2mV (or 40mA referred to a 50mΩ sense
resistor). Low-transition band, bi-directional CSAs can
be 200 times more sensitive on this attribute alone.
Internal Noise Filters
It’s always been good engineering practice to add
external low-pass filters (LPFs) in series with the CSA’s
inputs to counter the effects of externally-injected
differential and common-mode noise prevalent in any
load current measurement scheme. Resistors used in
the external LPFs in the design of discrete CSAs were
incorporated into the circuit’s overall design so errors
because of any input-bias current-generated voltage
and gain errors were compensated.
Utilizing external LPFs in series with the CSA’s inputs
only introduces additional offset voltage and gain
errors with the advent of monolithic CSAs. Higherperformance
uni-directional and bi-directional CSAs
incorporate internal LPFs to further save system cost
and improve overall system performance, thereby
minimizing/eliminating the need for external LPFs and
to maintain low offset voltage and gain errors.
Additional Applications Tips
All parasitic pcb track resistances to the sense
resistor should be minimized for optimal VSENSE
accuracy. Strongly recommended are Kelvin-sense pcb
connections between RSENSE and the CSAs’ RS+
and RS- terminals. The pcb layout should be balanced
and symmetrical to minimize wiring-induced errors.
Also, the pcb layout for RSENSE should include good
thermal management techniques for optimal RSENSE
power dissipation.
To form an LPF with the CSAs’ ROUT, a 22nF to 100nF
good-quality ceramic capacitor should be connected
from the OUT terminal to GND. The use of a capacitor
at this terminal minimizes voltage droop (holding VOUT
constant during the sample interval). Using a capacitor
on the OUT terminal will also reduce the CSAs’ smallsignal
bandwidth as well as band-limiting amplifier
noise.
A new state of the art in CSA technology has been
redefined. These new CSAs can resolve charging or
discharging currents with 12-bit or better resolution,
exhibit very low VOS and gain match errors, are
extremely easy to use, are self-powered, and consume
very little supply current. These higher-performance
30 EEWeb | Electrical Engineering Community
CSAs are specified to operate over wide or extended
industrial temperature ranges, can operate from
2V to 25V (and higher) power supplies, and mate
their electrical performance with pcb-space saving
packages (such as SOT23-5 and SOT23-6).
About the Author
Adolfo Garcia has over 30 years of experience in the
analog IC business. He has held design, applications,
marketing, and product line/business unit management
positions of increasing responsibility at Analog Devices,
Linear Technology, Micrel, Advanced Analogic
Technologies, and Leadis Technology. His technical and
market knowledge spans a broad spectrum of analog
products and applications, including amplifiers, data
converters, and power management functions. This
expertise has led to the definition and market launch
of over 65 high-performance analog IC products. He
holds three US Patents and is an accomplished author
with over 60 publications to his credit.