Datasheet

A high R
SENSE
value allows lower currents to be mea-
sured more accurately because offsets are less significant
when the sense voltage is larger. Note that the toler-
ance and temperature coefficient of the chosen resistors
directly affect the precision of any measurement sys-
tem. For best performance, select R
SENSE
to provide
approximately maximum input differential sense voltage of
110mV (MAX44284F) or 55mV (MAX44284H) or 27.5mV
(MAX44284W) or 11mV (MAX44284E) of sense voltage for
the full-scale current in each application. Sense resistors of
5mΩ to 100mΩ are available with 1% accuracy or better.
Efciency and Power Dissipation
At high current levels, the I
2
R losses in R
SENSE
can be
significant. This should be taken into consideration when
choosing the resistor value and its power dissipation
(wattage) rating. The sense resistor’s value will drift if it
is allowed to heat up excessively. The precision V
OS
of
the MAX44284 allows the use of small sense resistors to
reduce power dissipation and reduce hot spots.
Kelvin Connections
Because of the high currents that may flow through
R
SENSE
based on the application, take care to eliminate
solder and parasitic trace resistance from causing errors
in the sense voltage. Either use a four-terminal current-
sense resistor or use Kelvin (force and sense) PCB layout
techniques.
Input Filtering
Some applications of current-sense amplifiers need to
measure currents accurately even in the presence of both
differential and common-mode ripple, as well as a wide
variety of input transient conditions.
The MAX44284 allows two methods of filtering to help
improve performance in the presence of input common-
mode voltage and input differential voltage transients.
Figure 1 shows a differential input filter. The capacitor
C
IN
across RS+ and RS- along with the resistor R
IN
helps
filter against input differential voltages and prevents them
from reaching the MAX44284. The corner frequency of
this filter is determined by the choice of R
IN
, C
IN
. Figure 2
shows a common-mode input filter. The choice of capaci-
tance depends on corner frequency after R
IN
is chosen.
In case of mismatch or error in application design, an
additional DC error is accumulated as offset voltage and
increased gain error.
( ) ( )
OS IN OFFSET IN BIAS
V R I DR I=× +×
DR
IN
is the resistance mismatch in R
IN
at RS+ and RS-.
If DR
IN
is too small, its effect can be neglected. Since
I
OFFSET
of the MAX44284 is smaller than 2nA, and if we
want to make sure V
OS
is lesser than 1µV range, choosing
( )
IN OS OFFSET
RVI<÷
Figure 1. Differential Input Filtering
Figure 2. Input Common-Mode Filtering
GND
C
IN
R
IN
R
IN
LOAD
R
SENSE
C
IN
OUT
MAX44284
RS-RS+
GND
R
IN
R
IN
LOAD
R
SENSE
OUT
MAX44284
RS-RS+
C
IN
MAX44284 36V, Input Common-Mode, High-Precision,
Low-Power Current-Sense Amplier
www.maximintegrated.com
Maxim Integrated │ 11