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參數(shù)資料
| 型號： | MAX1755-MAX1756 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | SOT23 Local Temperature Comparators with SMBus Serial Interface |
| 中文描述： | SOT23封裝本地溫度比較器，帶有SMBus串行接口 |
| 文件頁數(shù)： | 9/11頁 |
| 文件大?。?/td> | 294K |
| 代理商： | MAX1755-MAX1756 |
Applications Information
Thermal Considerations
The MAX1755/MAX1756 supply current is typically
85μA. When used to drive high-impedance loads, the
devices dissipate negligible power. Therefore, the die
temperature is essentially the same as the package
temperature. The key to accurate temperature monitor-
ing is good thermal contact between the MAX1755/
MAX1756 package and the device being monitored. In
some applications, the 6-pin SOT23 package may be
small enough to fit underneath a socketed μP, allowing
the device to monitor the μP
’
s temperature directly.
Accurate temperature monitoring depends on the ther-
mal resistance between the device being monitored
and the MAX1755/MAX1756 die. Heat flows in and out
of plastic packages primarily through the leads. Short,
wide copper traces leading to the temperature monitor
ensure that heat transfers quickly and reliably. The rise
in die temperature due to self-heating is given by the
following formula:
T
J
= P
DISSIPATION
θ
JA
where P
DISSIPATION
is the power dissipated by the
MAX1755/MAX1756, and
θ
JA
is the package
’
s thermal
resistance.
The typical thermal resistance is 110
°
C/W. To limit the
effects of self-heating, minimize the output currents. For
example, if the MAX1755 or MAX1756 sink 6mA, the
output voltage is guaranteed to be less than 0.4V.
Therefore, an additional 2.4mW of power is dissipated
within the IC. This corresponds to a 0.26
°
C shift in the
die temperature.
ALERT
Software Model Example of
Temperature Windowing
The MAX1756
ALERT
interrupt output is designed so
effective clock-throttling and/or fan-speed control can
be done by the host firmware, while keeping the com-
mands and registers of the MAX1756 very simple.
At initial power-up, T
MAX
is set to +100
°
C. The user can
modify this as needed using Send Byte. The POR state
masks undertemperature interrupts. The initial tempera-
ture is assumed to be very low, below the T
HYST
under-
temperature threshold. No
ALERT
signal is issued,
since T
HYST
interrupts are masked.
If the system heats up sufficiently to exceed T
MAX,
this
generates the first interrupt. The host reads the status
byte, determining that the T
MAX
temperature was
exceeded. The interrupt, although cleared, is immediate-
ly asserted again since the temperature still exceeds
MAX
. The host now immediately writes a new value to
the DAC register, approximately 4
°
C above the old D/A
value. This hopefully places the (T
MAX
- T
HYST
) window
centered around the current device temperature. This
new DAC value also writes a zero to the MASK bit,
enabling T
HYST
interrupts. Writing a new value clears the
status byte and
ALERT
latch. The system then takes
whatever corrective action is needed (clock throttling or
fan control).
If the temperature continues to increase, another cor-
rective action routine is done, similar to above. If the
temperature decreases below T
HYST
, an interrupt is
generated and the host can remove the corrective
action (if desired), set a new T
MAX
value, and clear sta-
tus, similar to the routine above.
If desired, the host can now mask undertemperature
interrupts to avoid nuisance interrupts as the system
cools.
Temperature Measurement Using a
Software SAR
A useful application of the MAX1755 is to determine the
ambient temperature with a successive approximation
algorithm to set the T
MAX
register. Like a successive
approximation register (SAR) analog-to-digital convert-
er, the C code routine provided in Listing 1 tests 1 bit at
a time in the T
MAX
register form MSB to LSB. Based on
the response of the
OVERT
signal, the bit is either set
or cleared. This simple set and check algorithm repeats
until all of the bits are set.
M
SOT23 Local Temperature Comparators
with SMBus Serial Interface
_______________________________________________________________________________________
9
Table 3. Slave Address Decoding (ADD Pin)
DEVICE
ADD PIN
CONNECTED TO
ADDRESS
MAX1755A
MAX1755A
MAX1755A
MAX1755B
MAX1755B
MAX1755B
MAX1756A
MAX1756A
MAX1756A
MAX1756B
MAX1756B
MAX1756B
V
CC
GND
Floating
V
CC
GND
Floating
V
CC
GND
Floating
V
CC
GND
Floating
1001 000
1001 001
0101 001
0011 000
0011 001
0101 000
1001 010
1001 011
0101 011
0011 010
0011 011
0101 010
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