Specifications

Sensors
Current, light, and proximity sensing
www.digikey.com/maxim-industrial 75
Overview
Current sensing is important in many
applications and can be categorized
into two popular approaches.
• In one approach current sensing
is commonly used with higher
currents and often in power-supply
monitoring. Typical applications
include short-circuit detection,
transient detection, and reverse-
battery detection.
• Current sensing is also used in
applications that require much
lower levels of current detection
(down in the micro-amps), such as
photodiodes that generate a small
amount of current when exposed
to light. Common applications are
ambient light sensing, proximity
detection, and light absorption-/
reflection-based chemical process
monitoring.
These current-sensing techniques
employ current-sense amplifiers
which are available in multiple
configurations, or transimpedance
amplifiers (TIAs). Each type
of current-sensing amplifier is
discussed below.
Current sensing using
current-sense amplifiers
A variety of techniques are used
to measure current, but by far the
most popular is with a current-sense
resistor. The basic principle of this
approach is to amplify the voltage
drop across the current-sense resistor
by using an op-amp-based differential
gain stage, and then to measure
the resulting voltage. While discrete
components can be used to build the
amplifier circuit, integrated current-
sense amplifiers have significant
advantages over discrete implemen-
tations: better temperature drift,
smaller PC-board (PCB) area, and
the ability to handle wide common-
mode ranges.
Most current-sensing applica-
tions employ either the low-side
or the high-side principle. In the
low-side technique the sense
resistor connects in series with the
ground path. The circuit deals with
Current, light, and proximity sensing
μC
SENSOR AND
NETWORK
AFE FILTER ADC DIGITAL DOMAIN
ADC
Reference
CURRENT-
SENSE AMP
TRANSCONDUCTANCE
AMPLIFIERS
= MAXIM SOLUTION
FILTERS
OP AMPS
PRECISION
RESISTORS
REFERENCE
LEVEL
TRANSLATOR
TOUCH
SCREEN
ISOLATION
ADC
SOURCE
LOAD
Block diagram of the signal chain in a current-sensing application. For a list of Maxim’s recommended current-sensing solutions, please go to: www.maxim-ic.com/detect.