MAX4173FESA 查看數據表（PDF） - Maxim Integrated
零件编号
产品描述 (功能)
生产厂家
MAX4173FESA Datasheet PDF : 10 Pages
| |||
Low-Cost, SOT23, Voltage-Output,
High-Side Current-Sense Amplifier
Detailed Description
The MAX4173 high-side current-sense amplifier fea-
tures a 0 to +28V input common-mode range that is
independent of supply voltage. This feature allows the
monitoring of current out of a battery in deep discharge
and also enables high-side current sensing at voltages
greater than the supply voltage (VCC).
The MAX4173 operates as follows: Current from the
source flows through RSENSE 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
VSOURCE - (ILOAD)(RSENSE). The amplifier’s open-loop
gain forces its noninverting input to the same voltage as
the inverting input. Therefore, the drop across RG1
equals (ILOAD)(RSENSE). Since IRG1 flows through RG1,
IRG1 = (ILOAD)(RSENSE) / RG1. The internal current mirror
multiplies IRG1 by a current gain factor, β, to give
IRGD = β · IRG1. Solving IRGD = β · (ILOAD)(RSENSE) /
RG1. Assuming infinite output impedance, VOUT = (IRGD)
(RGD). Substituting in for IRGD and rearranging, VOUT =
β · (RGD / RG1)(RSENSE · ILOAD). The parts gain equals
β · RGD / RG1. Therefore, VOUT = (GAIN) (RSENSE)
(ILOAD), where GAIN = 20 for MAX4173T, GAIN = 50 for
MAX4173F, and GAIN = 100 for MAX4173H.
VSOURCE
0 TO +28V
+3V TO +28V
VCC
RSENSE
RS+
IRG1
RG1
ILOAD
TO LOAD BATTERY
RS-
RG2
A1
MAX4173
CURRENT
OUT
VOUT
MIRROR
IRGD
RGD = 12k
GND
Figure 1. Functional Diagram
Set the full-scale output range by selecting RSENSE and
the appropriate gain version of the MAX4173.
Applications Information
Recommended Component Values
The MAX4173 senses a wide variety of currents with
different sense resistor values. Table 1 lists common
resistor values for typical operation of the MAX4173.
Choosing RSENSE
To measure lower currents more accurately, use a high
value for RSENSE. The high value develops a higher
sense voltage that reduces offset voltage errors of the
internal op amp.
In applications monitoring very high currents, RSENSE
must be able to dissipate the I2R 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.
If ISENSE has a large high-frequency component, mini-
mize the inductance of RSENSE. Wire-wound resistors
have the highest inductance, metal-film resistors are
somewhat better, and low-inductance metal-film resis-
tors are best suited for these applications.
Using a PCB Trace as RSENSE
If the cost of RSENSE 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 MAX4173T (with a maximum load cur-
rent of 10A and an RSENSE of 5mΩ) creates a full-scale
VSENSE of 50mV that yields a maximum VOUT of 1V.
RSENSE in this case requires about 2 inches of 0.1 inch-
wide copper trace.
Output Impedance
The output of the MAX4173 is a current source driving a
12kΩ resistance. Resistive loading added to OUT
reduces the output gain of the MAX4173. 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
_______________________________________________________________________________________ 7
Share Link: 