Low-Cost, SC70, Voltage-Output,

High-Side Current-Sense Amplifier

8

_______________________________________________________________________________________

somewhat better, and low-inductance metal-film resis-

tors are best suited for these applications.

2V, 5V, or 10V depending on the gain. For proper oper-

Temperature in the Typical Operating Characteristics).

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 30m

Ω/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-

Ω) creates a full-scale

wide copper trace.

Output Impedance

The output of the MAX4073 is a current source driving a

12k

Ω 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:

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

+3V TO +28V

0.1

µF

RS+

+

0.3in COPPER

INPUT

LOAD/BATTERY

0.3in COPPER

0.1in COPPER

RS-

GND

OUT

_

Figure 2. MAX4073T Connections Showing Use of PC Board

Figure 3. Current Source

MAX4073T/F/H

+2V TO +28V

OUT

GND

RS+

+3V TO +28V

0.1

µF

RS-

LOAD/

BATTERY

LOW-COST

SWITCHING

REGULATOR