Detailed Description
The MAX4073 high-side current-sense amplifier fea-
tures a +2V to +28V input common-mode range that is
independent of supply voltage. This feature allows the
monitoring of current out of a battery as low as +2V and
also enables high-side current sensing at voltages
greater than the supply voltage (V
CC
).
The MAX4073 operates as follows: current from the
source flows through R
SENSE
to the load (Figure 1). Since
the internal-sense amplifier’s inverting input has high
impedance, negligible current flows through RG2
(neglecting the input bias current). Therefore, the
sense amplifier’s inverting-input voltage equals
V
SOURCE
- (I
LOAD
)(R
SENSE
). The amplifier’s open-loop
gain forces its noninverting input to the same voltage as
the inverting input. Therefore, the drop across RG1
equals (I
LOAD
)(R
SENSE
). Since I
RG1
flows through RG1,
I
RG1
= (I
LOAD
)(R
SENSE
) / RG1. The internal current mirror
multiplies I
RG1
by a current gain factor, β, to give
I
RGD
= β
✕
I
RG1
. Solving I
RGD
= β
✕
(I
LOAD
)(R
SENSE
)/
RG1. Assuming infinite output impedance, V
OUT
= (I
RGD
)
(RGD). Substituting in for I
RGD
and rearranging, V
OUT
=
β
✕
(RGD/RG1)(R
SENSE
✕
I
LOAD
). The parts gain equals
β
✕
RGD/RG1. Therefore, V
OUT
= (GAIN) (R
SENSE
)
(I
LOAD
), where GAIN = 20V/V for MAX4073T, GAIN =
50V/V for MAX4073F, and GAIN = 100V/V for MAX4073H.
Set the full-scale output range by selecting R
SENSE
and
the appropriate gain version of the MAX4073.
Applications Information
Recommended Component Values
The MAX4073 senses a wide variety of currents with
different sense resistor values. Table 1 lists common
resistor values for typical operation of the MAX4073.
Choosing R
SENSE
To measure lower currents more accurately, use a
large value for R
SENSE
. The larger value develops a
higher-sense voltage that reduces offset voltage errors
of the internal op amp. Typical sense voltages range
between 10mV and 150mV.
In applications monitoring very high currents, R
SENSE
must be able to dissipate the I
2
R losses. If the resistor’s
rated power dissipation is exceeded, its value may drift
or it may fail altogether, causing a differential voltage
across the terminals in excess of the absolute maxi-
mum ratings (±5V).
If I
SENSE
has a large high-frequency component, mini-
mize the inductance of R
SENSE
. Wire-wound resistors
have the highest inductance, metal-film resistors are
MAX4073T/F/H
Low-Cost, SC70, Voltage-Output,
High-Side Current-Sense Amplifier
7
Maxim Integrated
Pin Description
Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.
Voltage Output. V
. Output impedance is approximately
