Datasheet

MAX4073T/F/H
Low-Cost, SC70, Voltage-Output,
High-Side Current-Sense Amplifier
8
Maxim Integrated
somewhat better, and low-inductance metal-film resis-
tors are best suited for these applications.
For V
SENSE
= 100mV, full-scale output voltage can be
2V, 5V, or 10V depending on the gain. For proper oper-
ation, ensure V
CC
exceeds the full-scale output voltage
by 1.2V (see Output High Voltage (V
CC
- V
OH
) vs.
Temperature in the Typical Operating Characteristics ).
Using a PCB Trace as R
SENSE
If the cost of R
SENSE
is an issue and accuracy is not
critical, use the alternative solution shown in Figure 2.
This solution uses copper PC board traces to create a
sense resistor. The resistivity of a 0.1-inch-wide trace of
2-ounce copper is approximately 30mΩ/ft. The resis-
tance-temperature coefficient of copper is fairly high
(approximately 0.4%/°C), so systems that experience a
wide temperature variance must compensate for this
effect. In addition, do not exceed the maximum power
dissipation of the copper trace.
For example, the MAX4073T (with a maximum load cur-
rent of 10A and an R
SENSE
of 5mΩ) creates a full-scale
V
SENSE
of 50mV that yields a maximum V
OUT
of 1V.
R
SENSE
in this case requires about 2 inches of 0.1 inch-
wide copper trace.
Output Impedance
The output of the MAX4073 is a current source driving a
12kΩ resistance. Resistive loading added to OUT
reduces the output gain of the MAX4073. To minimize
output errors for most applications, connect OUT to a
high-impedance input stage. When output buffering is
required, choose an op amp with a common-mode
input range and an output voltage swing that includes
ground when operating with a single supply. The op
amp’s supply voltage range should be at least as high
as any voltage the system may encounter.
The percent error introduced by output loading is deter-
mined with the following formula:
where R
LOAD
is the external load applied to OUT.
Current Source Circuit
Figure 3 shows a block diagram using the MAX4073
with a switching regulator to make a current source.
% 100
R
12k R
1
ERROR
LOAD
LOAD
=
Ω +
−
⎛
⎝
⎜
⎞
⎠
⎟
MAX4073T
V
SENSE
R
SENSE
+3V TO +28V
0.1µF
RS+
+
0.3in COPPER
INPUT LOAD/BATTERY
0.3in COPPER0.1in COPPER
RS-
GND
OUT
V
CC
_
Figure 2. MAX4073T Connections Showing Use of PC Board
Figure 3. Current Source
MAX4073T/F/H
R
SENSE
I
LOAD
+2V TO +28V
V
SENSE
V
CC
OUT
V
IN
GND
RS+
+3V TO +28V
0.1µF
RS-
LOAD/
BATTERY
LOW-COST
SWITCHING
REGULATOR