MAX4172 Maxim, MAX4172 Datasheet - Page 7

• Manufacturer Part Number: MAX4172
• Description: The MAX4172 is a low-cost, precision, high-side current-sense amplifier for portable PCs, telephones, and other systems where battery/DC power-line monitoring is critical
• Manufacturer: Maxim

• Accuracy: A high R
• Efficiency and Power Dissipation: At high current
• Inductance: Keep inductance low if I
• Cost: If the cost of R
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 R
50mV drop at full scale. This resistor requires about 2
inches of 0.1-inch-wide copper trace.
Table 1. Suggested Component Values
LOAD CURRENT
rents to be measured more accurately. This is
because offsets become less significant when the
sense voltage is larger. For best performance,
select R
sense voltage for the full-scale current in each
application.
levels, the I
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.
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.
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).
FULL-SCALE
(A)
0.1
10
1
5
SENSE
2
R losses in R
_______________________________________________________________________________________
to provide approximately 100mV of
CURRENT-SENSE
SENSE
SENSE
R
RESISTOR,
SENSE
SENSE
1000
100
20
10
value allows lower cur-
is an issue, you might
(mΩ)
SENSE
can be significant.
Low-Cost, Precision, High-Side
SENSE
= 5mΩ for a
RESISTOR, R
has a
OUTPUT
(kΩ)
3.48
3.48
3.48
3.48
Current-Sense Amplifier
Choose R
obtain the full-scale voltage you require, given the full-
scale I
ance permits using R
minimal error. OUT’s load impedance (e.g., the input of
an op amp or ADC) must be much greater than R
(e.g., 100 x R
accuracy.
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.
OUT
Figure 2. MAX4172 Connections Showing Use of PC Board
O.3 in. COPPER
OUT
INPUT
OUT
VOLTAGE, V
determined by R
FULL-SCALE
(Resistor Range, Output Adjust)
OUT
after selecting R
OUTPUT
3.48
3.48
3.48
3.48
1
2
) to avoid degrading measurement
High-Current Measurement
Current-Sense Adjustment
RS+
RS-
OUT
O.1 in. COPPER
OUT
MAX4172
R
V
(V)
SENSE
SENSE
SENSE
values up to 200kΩ with
SENSE
GND
OUT
V+
. OUT’s high imped-
V
SCALE FACTOR,
8
6
5
OUT
. Choose R
O.3 in. COPPER
LOAD/BATTERY
/I
SENSE
0.696
0.348
34.8
3.48
3V TO 32V
V
R
SUPPLY
OUT
(V/A)
OUT
OUT
to
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