below illustrates the connections between the current-sense amplifier and the current-sense resistor. The PCB layout should be bal-

Current-shunt resistors are available in metal film, metal strip, and wire-wound constructions. Wire-wound current-shunt resistors con-

sist of a wire spirally wound onto a core. As a result, these types of current shunt resistors exhibit the largest self inductance. In applica-

tions where the load current contains high-frequency transients, metal film or metal strip current-sense resistors are recommended.

2.4.7 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 introduced into the circuit inductively or

ly-generated, common-mode noise is the high-frequency output ripple of a switching regulator that can result in the injection of com-

mon-mode noise 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 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 P–N junction diodes were

used as RF envelope detectors in early radio designs. The amplifier’s internal common-mode rejection is usually sufficient to defeat

injected common-mode noise.

To counter the effects of externally-injected noise, it has always been good engineering practice to add external low-pass filters in ser-

ies 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 to compensate for any input-bias-current-generated offset voltage and

gain errors.

With the advent of monolithic current-sense amplifiers, the addition of external low-pass filters in series with the current-sense amplifi-

er’s inputs only introduces additional offset voltage and gain errors. To minimize or altogether eliminate the need for external low-pass

filters and to maintain low input offset voltage and gain errors, the current-sense amplifiers incorporate a 50 kHz (typ) 2nd-order differ-

ential low-pass filter as shown in the Block Diagrams.

2.4.8 Output Filter Capacitor

If the current-sense amplifiers are a part of a signal acquisition system in which their 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

the OUT terminal will also reduce the small-signal bandwidth as well as band-limiting amplifier noise.

2.4.9 PC Board Layout and Power Supply Bypassing

For optimal circuit performance, the current-sense amplifiers should be in very close proximity to the external current-sense resistor,

ground plane and surface mount resistors and capacitors.

TS1100/01/02/03 Data Sheet

System Overview

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