TS1101 TOUCHSTONE [Touchstone Semiconductor Inc], TS1101 Datasheet - Page 10

• Manufacturer Part Number: TS1101
• Description: A 1uA, +2V to +25V Bidirectional Precision Current-Sense Amplifier
• Manufacturer: TOUCHSTONE [Touchstone Semiconductor Inc]

Figure 3: Making PCB Connections to RSENSE.
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.
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
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
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
Page 10
power
management
and
motor
the high-
control
rectification of noise signals occurs because all
amplifier
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
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.
With
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,
the TS1101 incorporates a 50-kHz (typ), 2
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
sampling capacitor can cause voltage droop at V
A 22nF to 100nF good-quality ceramic capacitor
from the OUT terminal to GND forms a low-pass
filter with the TS1101’s R
minimize voltage droop (holding V
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.
the
input
circuit,
internal
advent
stages
the
of
common-mode
OUT
monolithic
internal
are
and should be used to
constructed
track-and-hold’s
TS1101DS r1p0
current-sense
OUT
rejection
constant
nd
-order
RTFDS
with
OUT
is
.