Datasheet

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SBOS383C − DECEMBER 2006 − REVISED MAY 2008
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14
N-FACTOR CORRECTION REGISTER
The TMP411 allows for a different n-factor value to be used
for converting remote channel measurements to
temperature. The remote channel uses sequential current
excitation to extract a differential V
BE
voltage
measurement to determine the temperature of the remote
transistor. Equation 1 relates this voltage and temperature.
V
BE2
* V
BE1
+
nkT
q
ln
ǒ
I
2
I
1
Ǔ
The value n in Equation 1 is a characteristic of the
particular transistor used for the remote channel. The
default value for the TMP411 is n = 1.008. The value in the
N-Factor Correction Register may be used to adjust the
effective n-factor according to Equation 2 and Equation 3.
n
eff
+
1.008 @ 300
ǒ
300*N
ADJUST
Ǔ
N
ADJUST
+ 300*
ǒ
300 @ 1.008
n
eff
Ǔ
The n-correction value must be stored in
two’s-complement format, yielding an effective data range
from −128 to +127, as shown in Table 8. The n-correction
value may be written to and read from pointer address 18h.
The register power-on reset value is 00h, thus having no
effect unless written to.
Table 8. N-Factor Range
N
ADJUST
BINARY HEX DECIMAL
N
01111111 7F 127 1.747977
00001010 0A 10 1.042759
00001000 08 8 1.035616
00000110 06 6 1.028571
00000100 04 4 1.021622
00000010 02 2 1.014765
00000001 01 1 1.011371
00000000 00 0 1.008
11111111 FF −1 1.004651
11111110 FE −2 1.001325
11111100 FC −4 0.994737
11111010 FA −6 0.988235
11111000 F8 −8 0.981818
11110110 F6 −10 0.975484
10000000 80 −128 0.706542
MINIMUM AND MAXIMUM REGISTERS
The TMP411 stores the minimum and maximum
temperature measured since power-on, chip-reset, or
minimum and maximum register reset for both the local
and remote channels. The Local Temperature Minimum
Register may be read by reading the high byte from pointer
address 30h and the low byte from pointer address 31h.
The Local Temperature Minimum Register may also be
read by using a two-byte read command from pointer
address 30h. The Local Temperature Minimum Register is
reset at power-on, by executing the chip-reset command,
or by writing any value to any of pointer addresses 30h
through 37h. The reset value for these registers is
FFh/F0h.
The Local Temperature Maximum Register may be read
by reading the high byte from pointer address 32h and the
low byte from pointer address 33h. The Local Temperature
Maximum Register may also be read by using a two-byte
read command from pointer address 32h. The Local
Temperature Maximum Register is reset at power-on by
executing the chip reset command, or by writing any value
to any of pointer addresses 30h through 37h. The reset
value for these registers is 00h/00h.
The Remote Temperature Minimum Register may be read
by reading the high byte from pointer address 34h and the
low byte from pointer address 35h. The Remote
Temperature Minimum Register may also be read by using
a two-byte read command from pointer address 34h. The
Remote Temperature Minimum Register is reset at
power-on by executing the chip reset command, or by
writing any value to any of pointer addresses 30h through
37h. The reset value for these registers is FFh/F0h.
The Remote Temperature Maximum Register may be read
by reading the high byte from pointer address 36h and the
low byte from pointer address 37h. The Remote
Temperature Maximum Register may also be read by
using a two-byte read command from pointer address 36h.
The Remote Temperature Maximum Register is reset at
power-on by executing the chip reset command, or by
writing any value to any of pointer addresses 30h through
37h. The reset value for these registers is 00h/00h.
(1)
(2)
(3)