MAX4172(1996) データシートの表示（PDF） - Maxim Integrated
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MAX4172 Datasheet PDF : 8 Pages
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Low-Cost, Precision, High-Side
Current-Sense Amplifier
Table 1. Suggested Component Values
FULL-SCALE
LOAD CURRENT
(A)
0.1
1
5
10
CURRENT-SENSE
RESISTOR,
RSENSE (mΩ)
1000
100
20
10
OUTPUT
RESISTOR, ROUT
(kΩ)
3.48
3.48
3.48
3.48
FULL-SCALE
OUTPUT
VOLTAGE, VOUT (V)
3.48
3.48
3.48
3.48
SCALE FACTOR,
VOUT/ISENSE (V/A)
34.8
3.48
0.696
0.348
• Accuracy: A high RSENSE value allows lower cur-
rents to be measured more accurately. This is
because offsets become less significant when the
sense voltage is larger. For best performance,
select RSENSE to provide approximately 100mV of
sense voltage for the full-scale current in each
application.
• Efficiency and Power Dissipation: At high current
levels, the I2R losses in RSENSE can be significant.
Take this into consideration when choosing the
resistor value and its power dissipation (wattage)
rating. Also, the sense resistor’s value might drift if it
is allowed to heat up excessively.
• Inductance: Keep inductance low if ISENSE has a
large high-frequency component. Wire-wound resis-
tors have the highest inductance, while metal film is
somewhat better. Low-inductance metal-film resis-
tors are also available. Instead of being spiral
wrapped around a core, as in metal-film or wire-
wound resistors, they are a straight band of metal
and are available in values under 1Ω.
• Cost: If the cost of RSENSE is an issue, you might
want to use an alternative solution, as shown in
Figure 2. This solution uses the PC board traces to
create a sense resistor. Because of the inaccura-
cies of the copper resistor, the full-scale current
value must be adjusted with a potentiometer. Also,
copper’s resistance temperature coefficient is fairly
high (approximately 0.4%/°C).
In Figure 2, assume that the load current to be mea-
sured is 10A, and that you have determined a 0.3-inch-
wide, 2-ounce copper to be appropriate. The resistivity
of 0.1-inch-wide, 2-ounce (70µm thickness) copper is
30mΩ/ft. For 10A, you might want RSENSE = 5mΩ for a
50mV drop at full scale. This resistor requires about 2
inches of 0.1-inch-wide copper trace.
INPUT
O.3 in. COPPER
RSENSE
O.1 in. COPPER
LOAD/BATTERY
O.3 in. COPPER
VSENSE
1 RS+ MAX4172 V+ 8
2 RS-
OUT 6
GND 5
VSUPPLY
3V TO 32V
ROUT
Figure 2. MAX4172 Connections Showing Use of PC Board
Current-Sense Adjustment
(Resistor Range, Output Adjust)
Choose ROUT after selecting RSENSE. Choose ROUT to
obtain the full-scale voltage you require, given the full-
scale IOUT determined by RSENSE. OUT’s high imped-
ance permits using ROUT values up to 200kΩ with
minimal error. OUT’s load impedance (e.g., the input of
an op amp or ADC) must be much greater than ROUT
(e.g., 100 x ROUT) to avoid degrading measurement
accuracy.
High-Current Measurement
The MAX4172 can achieve high-current measurements
by using low-value sense resistors, which can be paral-
leled to further increase the current-sense limit. As an
alternative, PC board traces can be adjusted over a
wide range.
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