Datasheet

T
ERR
=
1.004 1.008
1.008
-
(
(
´ °273.15+100 C
)
)
T =1.48 C
ERR
°
T
ERR
=
n 1.008
1.008
-
(
(
´ °273.15+T( C)
TMP512
TMP513
www.ti.com SBOS491A –JUNE 2010– REVISED MAY 2011
between 100pF and 1nF. Some applications attain Where:
better overall accuracy with additional series
n = ideality factor of remote temperature sensor.
resistance; however, this increased accuracy is
T(°C) = actual temperature.
application-specific. When series resistance is added,
T
ERR
= error in TMP512/13 because n ≠ 1.008.
the total value should not be greater than 3kΩ. If
Degree delta is the same for °C and K.
filtering is needed, suggested component values are
100pF and 50Ω on each input; exact values are
For n = 1.004 and T(°C) = 100°C:
application-specific.
GENERAL CALL RESET
The TMP512/13 support reset via the two-wire
General Call address 00h (0000 0000b). The
(5)
TMP512/13 acknowledge the General Call address
If a discrete transistor is used as the remote
and respond to the second byte. If the second byte is
temperature sensor with the TMP512/13, the best
06h (0000 0110b), the TMP512/13 execute a
accuracy can be achieved by selecting the transistor
software reset state to all TMP512/13 registers, and
according to the following criteria:
abort any conversion in progress. The TMP512/13
1. Base-emitter voltage > 0.25V at 6μA, at the
take no action in response to other values in the
highest sensed temperature.
second byte.
2. Base-emitter voltage < 0.95V at 120μA, at the
REMOTE SENSING
lowest sensed temperature.
3. Base resistance < 100Ω.
The TMP512/13 are designed to be used with either
discrete transistors or substrate transistors built into
4. Tight control of V
BE
characteristics indicated by
processor chips and ASICs. Either NPN or PNP
small variations in h
FE
(that is, 50 to 150).
transistors can be used, as long as the base-emitter
Based on these criteria, two recommended
junction is used as the remote temperature sense.
small-signal transistors are the 2N3904 (NPN) or
NPN transistors must be diode-connected. PNP
2N3906 (PNP).
transistors can either be transistor- or
diode-connected, as Figure 19 and Figure 21 show.
BASIC ADC FUNCTIONS
Errors in remote temperature sensor readings are
The two analog inputs to the TMP512/13, V
IN+
and
typically the consequence of the ideality factor and
V
IN–
, connect to a shunt resistor in the bus of interest.
current excitation used by the TMP512/13 versus the
The TMP512/13 are powered by an internal
manufacturer-specified operating current for a given
subregulator, which has a typical output of 3.3V. The
transistor. Some manufacturers specify a high-level
bus being sensed can vary from 0V to 26V. There are
and low-level current for the temperature-sensing
no special considerations for power-supply
substrate transistors. The TMP512/13 use 6μA for
sequencing (for example, a bus voltage can be
I
LOW
and 120μA for I
HIGH
.
present with the supply voltage off, and vice-versa).
The ideality factor (n) is a measured characteristic of
The TMP512/13 sense the small drop across the
a remote temperature sensor diode as compared to
shunt for shunt voltage, and sense the voltage with
an ideal diode. The TMP512/13 allow for different
respect to ground from V
IN–
for the bus voltage. See
n-factor values; see the n-Factor Correction Register
Figure 29 for an illustration of this operation.
section.
When the TMP512/13 are in the normal operating
The ideality factor for the TMP512/13 is trimmed to
mode (that is, MODE bits of Configuration Register 1
be 1.008. For transistors that have an ideality factor
are set to '111'), the devices continuously convert the
that does not match the TMP512/13, Equation 4 can
shunt voltage up to the number set in the shunt
be used to calculate the temperature error. Note that
voltage averaging function (Configuration Register 1,
for the equation to be used correctly, actual
SADC bits). The devices then convert the bus voltage
temperature (°C) must be converted to kelvins (K).
up to the number set in the bus voltage averaging
(Configuration Register 1, BADC bits). The Mode
control in Configuration Register 1 also permits
(4)
selecting modes to convert only voltage or current,
either continuously or in response to a two-wire
space
command.
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