TS1101
the current-sense amplifier and the current-sense
resistor. The pcb layout should be balanced and
symmetrical to minimize wiring-induced errors. In
addition, the pcb layout for RSENSE should include
good thermal management techniques for optimal
RSENSE power dissipation.
rectification of noise signals occurs because all
amplifier input stages are constructed with
transistors that can behave as high-frequency signal
detectors in the same way pn-junction diodes were
used as RF envelope detectors in early radio
designs. Against common-mode injected noise, the
amplifier’s internal common-mode rejection is
usually sufficient.
To counter the effects of externally-injected noise, it
has always been good engineering practice to add
external low-pass filters in series with the inputs of a
current-sense amplifier. In the design of discrete
current-sense amplifiers, resistors used in the
external low-pass filters were incorporated into the
circuit’s overall design so errors because of any
input-bias current-generated offset voltage errors
and gain errors were compensated.
Figure 3:
Making PCB Connections to RSENSE.
With the advent of monolithic current-sense
amplifiers, like the TS1101, the addition of external
low-pass filters in series with the current-sense
amplifier’s inputs only introduces additional offset
voltage and gain errors. To minimize or eliminate
altogether the need for external low-pass filters and
to maintain low input offset voltage and gain errors,
nd
the TS1101 incorporates a 50-kHz (typ), 2 -order
differential low-pass filter as shown in the TS1101’s
Block Diagram.
Output Filter Capacitor
If the TS1101 is part of a signal acquisition system
where its OUT terminal is connected to the input of
an ADC with an internal, switched-capacitor track-
and-hold circuit, the internal track-and-hold’s
sampling capacitor can cause voltage droop at V
OUT
.
A 22nF to 100nF good-quality ceramic capacitor
from the OUT terminal to GND forms a low-pass
filter with the TS1101’s R
OUT
and should be used to
minimize voltage droop (holding V
OUT
constant
during the sample interval. Using a capacitor on the
OUT terminal will also reduce the TS1101’s small-
signal bandwidth as well as band-limiting amplifier
noise.
PC Board Layout and Power-Supply Bypassing
For optimal circuit performance, the TS1101 should
be in very close proximity to the external current-
sense resistor and the pcb tracks from RSENSE to
the RS+ and the RS- input terminals of the TS1101
should be short and symmetric. Also recommended
are a ground plane and surface mount resistors and
capacitors.
6) RSENSE Composition
Current-shunt resistors are available in metal film,
metal strip, and wire-wound constructions. Wire-
wound current-shunt resistors are constructed with
wire spirally wound onto a core. As a result, these
types of current shunt resistors exhibit the largest
self inductance. In applications where the load
current contains high-frequency transients, metal
film or metal strip current sense resistors are
recommended.
Internal Noise Filter
In power management and motor control
applications, current-sense amplifiers are required to
measure load currents accurately in the presence of
both externally-generated differential and common-
mode noise. An example of differential-mode noise
that can appear at the inputs of a current-sense
amplifier is high-frequency ripple. High-frequency
ripple – whether injected into the circuit inductively
or capacitively - can produce a differential-mode
voltage drop across the external current-shunt
resistor (RSENSE). An example of externally-
generated, common-mode noise is the high-
frequency output ripple of a switching regulator that
can result in common-mode noise injection into both
inputs of a current-sense amplifier.
Even though the load current signal bandwidth is
DC, the input stage of any current-sense amplifier
can rectify unwanted, out-of-band noise that can
result in an apparent error voltage at its output. This
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TS1101DS r1p0
RTFDS
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