TMP435
SBOS495A –MARCH 2010–REVISED APRIL 2010
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n-Factor Correction Register
range from –128 to +127. Table 9 shows the n-factor
range for both 1.008 and 1.000. For the TMP435, 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.
The TMP435 allows for a different n-factor value to
be
measurements to temperature. The remote channel
uses sequential current excitation to extract
used
for
converting
remote
channel
a
differential VBE voltage measurement to determine
the temperature of the remote transistor. Equation 1
relates this voltage and temperature.
Table 9. n-Factor Range
NADJUST
BINARY
01111111
00001010
00001000
00000110
00000100
00000010
00000001
00000000
11111111
11111110
11111100
11111010
11111000
11110110
10000000
HEX
7F
0A
08
DECIMAL
n-FACTOR
1.747977
1.042759
1.035616
1.028571
1.021622
1.014765
1.011371
1.008
I2
nkT
q
V
BE2 - VBE1
=
ln
127
10
8
1
(1)
The value n in Equation 1 is a characteristic of the
particular transistor used for the remote channel.
When the beta compensation configuration is set to
'0111' (beta compensation disabled) or the sensor is
diode-connected (base shorted to collector), the
n-factor used by the TMP435 is 1.008. When the beta
compensation configuration is set to '1000' (beta
compensation enabled) and the sensor is GND
collector-connected (PNP collector to ground), the
n-factor used by the TMP435 is 1.000. If the n-factor
used for the temperature conversion does not match
the characteristic of the sensor, then temperature
offset is observed. The value in the n-Factor
Correction Register may be used to adjust the
06
6
04
4
02
2
01
1
00
0
FF
FE
FC
FA
F8
F6
80
–1
–2
–4
–6
–8
–10
–128
1.004651
1.001325
0.994737
0.988235
0.981818
0.975484
0.706542
effective n-factor according to Equation
2 and
Equation 3 for disabled beta compensation or a
diode-connected sensor. Equation 4 and Equation 5
may be used for enabled beta compensation and a
GND collector-connected sensor.
space
Software Reset
1.008 ´ 300
neff
=
300 - NADJUST
The TMP435 may be reset by writing any value to
Pointer Register FCh. This action restores the
power-on reset state to all of the TMP435 registers as
well as abort any conversion in process and clear the
ALERT and THERM pins.
(2)
(3)
(4)
(5)
300 ´ 1.008
NADJUST = 300 -
neff
1.000 ´ 300
neff
=
300 - NADJUST
The TMP435 also supports reset via the two-wire
general call address (00000000). The TMP435
acknowledges the general call address and responds
to the second byte. If the second byte is 00000110,
the TMP435 executes a software reset. The TMP435
does not respond to other values in the second byte.
300 ´ 1.000
NADJUST = 300 -
neff
The n-correction value must be stored in
twos-complement format, yielding an effective data
18
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