Datasheet

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ISNS
+
6
ILIM
L
20
19
VO
UDG−04148
V
OUT
C
OUT
C
FLT
R
F1
V
IN
R
F2
R
F3
R
NTC
R
THE
R
LDG
R
ILIM
−2000 ppm/°C
a ^ 0.8
R
THE
R
THE
) R
F1
(dimensionless)
(11)
R
THE
+ R
F2
)
R
F3
R
NTC
R
F3
) R
NTC
(W)
(12)
TPS40100
SLUS601–MAY 2005
APPLICATION INFORMATION (continued)
Figure 4. Compensation for Temperature Coefficient of the Inductor Resistance
The first step is to determine an attenuation ratio α. This ratio should be near to 1 but not too close. If it is too
close to 1, the circuit requires large impedances and thermistor values too high. If α is too low, the current signal
is attenuated unnecessarily. A suggested value is 0.8.
R
THE
is the equivalent resistance of the R
F2
-R
F3
-R
NTC
network:
The base temperature (T
BASE
) should be selected to be the lowest temperature of interest for the thermal
matching – the lowest ambient expected. The resistance of the inductor at this base temperature should be used
to calculate effective resistance. The expected current sense amplifier gain at T
BASE
should be used for
calculating over current components (R
ILIM
).
The next step is to decide at what two temperatures the compensation is matched to the response of the
deviceand inductor copper, T1 and T2. Once these are chosen, an NTC thermistor can be chosen and its value
found from its data sheet at these two temperatures: R
NTC(T1)
and R
NTC(T2)
. The component values in the network
can be calculated using the following equations:
13