IEEE Power Electronics Magazine - March 2022 - 71

However, these resistors offer other
benefits, such as high power handling
capability, an extended resistance
value range, rapid frequency
response, and the ability to withstand
higher surges. Moreover, the
high resistance density of thick-film
resistors provide greater versatility,
while their glassy protective coatings
make them resistant to environmental
impact.
On the other hand, this resistor
type is plagued by low precision, high
noise, and low stability. The glass
matrix particle-to-particle contactbased
resistance track of thick-film
resistors reduces stability. Similarly,
their low metal content granular
structure causes greater noise susceptibility.
Fortunately, recent advances
in thick-film resistor technologies
by leading manufacturers
such as ROHM are addressing these
challenges and limitations, leading
to greater adoption in more sophisticated
circuits.
Thick-film resistors have evolved
throughout the years into higher performing
semiconductor electronic
components. To meet the increasing
energy-saving needs of industrial
and consumer applications, designers
are developing thick-film resistor
solutions that offer high power
ratings with significantly lower TCR
characteristics. For instance, ROHM
recently expanded its LTR series with
the LTR100L thick-film shunt resistor
that provides industry-leading
rated power for high power current
detection applications. Leveraging an
original approach involving resistor
material revision and terminal temperature
derating led to a higher-performing
thick-film resistor solution.
As a result, in addition to favorably
competing with existing metal shunt
resistors, significant improvements
were achieved over conventional thickfilm
resistors.
This allows customers to switch
from metal shunt resistors to cheaper
thick-film resistors. Lower TCR
enables higher current detection accuracy
compared to existing thickfilm
resistors. Figure 3 shows a comparison
between ROHM's LTR100L
and conventional thick-film resistors.
The higher TCR values of conventional
thick-film resistors translate
to comparatively lower current
detection accuracy of up to 12% Err.
Conversely, the LTR100L, with Err ≤
7%, ensures higher current detection
accuracy by significantly reducing
TCR values below 300 ppm/°C.
In addition to lower TCR values,
ROHM thick-film resistors deliver a
high power rating ideal for high power-intensive
applications-achieved
by configuring the electrodes on the
long sides of the substrate. This approach
increases heat dissipation,
ramping up the rated power to up to
4 W. Designers can achieve further
improvements by replacing two general-purpose
resistors with a single
LTR100L, saving space while ensuring
adequate heat dissipation in industrial
and consumer applications.
Key Applications
Thick-film resistors are widely adopted
for current detection in motor drive
and battery protection circuits for a
broad range of industrial and consumer
applications. For industrial sets,
thick-film resistors are essential in
power supplies, motor-peripheral circuits,
high-pressure pumps, and factory
automation. Many engineers incorporate
them into consumer appliances
as well, such as vacuum cleaners, air
conditioners, refrigerators, and washers.
Thick-film resistors are even
adopted in automotive applications
Difference in Current Detection
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Accuracy Due to Difference in ∆VSHUNT Voltage
Conditions
LTR100L
10 mΩ
Operational Amplifier Offset Voltage VOS=
450 µV Tolerance of Gain Setting Resistor
and Shunt Resistor in Typ.
Company B
Not OK
Specification Range
OK
≤ Due to high temperature coefficient
of resistance, detection accuracy
is not enough.
≤ Low temperature coefficient of
resistance enables high-precision
detection.
ILoad_max = 20 A Design
Simulation Results
02468 10 12 14 16 18 20 22 24 26
Detected Current Value ILOAD (A)
FIG 3 LTR100L vs conventional thick-film resistor.
March 2022 z IEEE POWER ELECTRONICS MAGAZINE 71
Current Detection Accuracy Err
IEEE Power Electronics Magazine - March 2022

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