AN840 Datasheet, PDF (1/4 Pages) Silicon Laboratories – Redefining a New State-of-the-Art in Microampere Current-Sense Amplifiers

AN840
Redefining a New State-of-the-Art in Microampere Current-Sense Amplifiers
1. Introduction
Sensing and controlling supply current flow are a fundamental requirement in most all electronic systems from
battery-operated, portable equipment to mobile or fixed-platform power management and dc motor control. High-
side current-sense amplifiers (or “CSAs”) are useful in these applications especially where power consumption is
an important design parameter. New CSA developments offer even greater benefits in allowing engineers to save
power without sacrificing performance.
With the right combination of small form factor, low supply-current operation, wide operating supply-voltage range,
low input offset voltage (VOS) and gain errors, and fixed gain options, design engineers now have even more
options high-side current-sensing amplification. As a result, new CSA enhancements enable the next generation of
battery-powered, hand-held portable instruments addressing power management, motor control, and fixed-
platform applications.
2. Unidirectional Current Sense Amplifiers
The internal configuration of some unidirectional CSAs is based on a commonly-used operational amplifier (op
amp) circuit for measuring load currents in the presence of high-common-mode voltages. In the general case, a
CSA monitors the voltage across an external sense and generates an output voltage as a function of load current.
Referring to the typical application circuit in Figure 1, featuring the TS1100, the inputs of the op-amp-based circuit
are connected across an external RSENSE. At the RS- terminal, the applied voltage is ILOAD x RSENSE.
Figure 1. Typical Application for a High-Precision Unidirectional Current-Sense Amplifier
(TS1100)
Since the RS- terminal is the non-inverting input of the internal op amp, op-amp feedback action forces the
inverting input of the internal op amp to the same potential (I LOAD x RSENSE). Therefore, the voltage drop across
RSENSE (VSENSE) and the voltage drop across RGAIN (at the RS+ terminal) are equal. To minimize any
additional error because of op-amp input bias current mismatch, both RGAIN resistors are the same value.
Rev. 1.0 7/14
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AN840