TMP451
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SBOS686 –JUNE 2013
η-Factor Correction Register
The TMP451 allows for a different η-factor value to be used for converting remote channel measurements to
temperature. The remote channel uses sequential current excitation to extract a differential VBE voltage
measurement to determine the temperature of the remote transistor. Equation 1 describes this voltage and
temperature.
hkT
I2
I1
VBE2 - VBE1
=
ln
q
(1)
The value η in Equation 1 is a characteristic of the particular transistor used for the remote channel. The power-
on reset value for the TMP451 is η = 1.008. The value in the η-factor correction register may be used to adjust
the effective η-factor according to Equation 2 and Equation 3.
≈
∆
«
’
÷
◊
1.008 ì 2088
2088 + NADJUST
ꢀeff
=
(2)
≈
∆
«
’
÷
◊
1.008 ì 2088
NADJUST
=
- 2088
ꢀeff
(3)
The η-factor correction value must be stored in twos complement format, yielding an effective data range from
–128 to +127. The η-factor correction value is written to and read from pointer address 23h. The register power-
on reset value is 00h, thus having no effect unless a different value is written to it.
Table 7. η-Factor Range
NADJUST
BINARY
HEX
7F
0A
08
DECIMAL
η
0111 1111
0000 1010
0000 1000
0000 0110
0000 0100
0000 0010
0000 0001
0000 0000
1111 1111
1111 1110
1111 1100
1111 1010
1111 1000
1111 0110
1000 0000
127
10
8
0.950198
1.003195
1.004152
1.005111
1.006072
1.007035
1.007517
1.008
06
6
04
4
02
2
01
1
00
0
FF
FE
FC
FA
F8
F6
80
–1
–2
–4
–6
–8
–10
–128
1.008483
1.008967
1.009935
1.010905
1.011877
1.012851
1.073837
Offset Register
The offset register allows the TMP451 to store any system offset compensation value that might be observed
from precision calibration. The value in the register is stored in the same format as the temperature result, and is
added to the remote temperature result upon every conversion. Combined with the η-factor correction, this
function allows for very accurate system calibration over the entire temperature range.
Copyright © 2013, Texas Instruments Incorporated
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