Datasheet

k +
RNTC
S
RNTC
C
R1
C
+ R
THE
(25)
ƪǒ
(
1 * k
)
) k R1
R
Ǔƫ
T
A
- Ambient Temperature - °C
10
10
20 40 60 80 100 120
20
30
40
CURRENT SENSE IMPEDANCE
vs
AMBIENT TEMPERATURE
R
THE
(T
5
C)
- Current Sense Impedance - kΩ
r
r
r
r
Measured
Acquired
TPS40090
TPS40091
www.ti.com SLUS578B –OCTOBER 2003– REVISED MAY 2006
For the given example R1
R
= 0.281, R2
R
= 2.079, and RNTC
R
= 1.1.
8. Calculate the absolute value of the NTC resistor as R
THE
(25). In given example R
NTC
= 244.3 kΩ.
9. Find a standard value for the NTC resistor with chosen curve type. In case the close value does not exist in a
desired form factor or curve type. Chose a different type of the NTC resistor and repeat steps 6 to 9. In the
example, the NTC resistor with the part number NTHS0402N17N2503J with R
NTCS
(25) = 250 kΩ is close
enough to the calculated value.
10. Calculate a scaling factor for the chosen NTC resistor as a ratio between selected and calculated NTC value
and. In the example k = 1.023.
(24)
11. Calculate values of the remaining network resistors.
(25)
For the given example, R1
C
= 58.7 kΩ and R2
C
= 472.8 kΩ. Pick the closest available 1% standard values:
R1 = 39.2 kΩ, and R2 = 475 kΩ, thus completing the design of the thermally compensated network for the
DCR current sensor.
Figure 12 illustrates the fit of the designed network to the required function.
Figure 12.
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