參數(shù)資料
型號(hào): MIC184BMM
廠商: MICREL INC
元件分類(lèi): 模擬信號(hào)調(diào)理
英文描述: Local/Remote Thermal Supervisor Advance Information
中文描述: SPECIALTY ANALOG CIRCUIT, PDSO8
封裝: MSOP-8
文件頁(yè)數(shù): 16/21頁(yè)
文件大?。?/td> 140K
代理商: MIC184BMM
MIC184
Micrel
MIC184
16
November 2000
{START Polling-Based Test and Initialization
Routine}
1. Temporarily disable the host
s interrupt input
from the device under test.
2. Write 0000 0010b (02h) to the CONFIG register.
3. Write 1100 1000 1000 0000b = C880h to T_SET
and T_HYST. This corresponds to -55.5
°
C.
4. Wait t
conv
(160ms max.) for the part to finish at
least one A/D conversion.
5. Read the contents of the CONFIG register:
a)
If the part is an MIC184, the MSB will be set
to one (CONFIG = 82h).
b)
If the part is a conventional LM75-type part,
the MSB will be zero (CONFIG = 02h).
6. Write 0111 1111 1000 0000b = 7F80h to T_SET
and T_HYST. This corresponds to +127.5
°
C.
7. Wait an additional t
conv
for the part to finish a
second conversion.
8. Read CONFIG again, to clear the interrupt
request from step (7). This will also clear STS, if
the part under test is an MIC184.
9. Based on the results of the test in step (4), do
the following four steps within 50ms total:
a)
Set the CONFIG register as required.
b)
Load T_HYST with its operational value.
c)
Load T_SET with its operational value.
d)
Re-enable the host
s interrupt handling input
from the part under test.
{END}
These routines force the device under test to generate an
overtemperature fault (steps 3 and 4), followed by an
undertemperature fault (steps 6 through 8). This sequence
causes the device under test to exit the routine prepared to
respond to an overtemperature condition. If being immedi-
ately prepared to detect an undertemperature condition upon
exit is desired, swap steps 3 and 6 in each routine.
Remote Diode Selection
Most small-signal PNP transistors with characteristics similar
to the JEDEC 2N3906 will perform well as remote tempera-
ture sensors. Table 3 lists several examples of such parts.
Micrel has tested those marked with a bullet for use with the
MIC184.
Vendor
Fairchild
On Semiconductor
Phillips Semiconductor
Rohm Semiconductor
Samsung
Zetex
Table 5. Transistors Suitable for Remote Temperature Sensing Use
Part Number
MMBT3906
MMBT3906L
PMBT3906
SST3906
KST3906-TF
FMMT3906
Package
SOT-23
SOT-23
SOT-23
SOT-23
SOT-23
SOT-23
Tested
Minimizing Errors
Self-Heating
One concern when using a part with the temperature accu-
racy and resolution of the MIC184 is to avoid errors induced
by self-heating (V
DD
×
I
DD
). In order to understand what level
of error this might represent, and how to reduce that error, the
dissipation in the MIC184 must be calculated, and its effects
examined as a temperature error.
In most applications, the INT output will be low for at most a
few milliseconds before the host sets it back to the high state,
making its duty cycle low enough that its contribution to self-
heating of the MIC184 is negligible. Similarly, the DATA pin
will in all likelihood have a duty cycle of substantially below
25% in the low state. These considerations, combined with
more typical device and application parameters, allow the
following calculation of typical device self-heating in interrupt-
mode:
P
D
= (I
DD(typ.)
3.3V + 25% I
OL(data)
0.3V +
1% I
OL(int)
0.3V)
P
D
= (0.3mA
×
3.3V + 25%
×
1.5mA
×
0.3V +
1%
×
1.5mA
×
0.3V)
T
J
= 1.11mW
×
206
°
C/W
T
J
relative to T
A
is 0.23
°
C
If the part is to be used in comparator mode, calculations
similar to those shown above (accounting for the expected
value and duty cycle of I
OL(int)
) will give a good estimate of the
device
s self-heating error.
In any application, the best test is to verify performance
against calculation in the final application environment. This
is especially true when dealing with systems for which some
of the thermal data, (for example, PC board thermal conduc-
tivity and/or ambient temperature), may be poorly defined or
unavailable except by empirical means.
Series Resistance
The operation of the MIC184 depends upon sensing the
V
CB-E
of a diode-connected PNP transistor ("diode") at two
different current levels. For remote temperature measure-
ments, this is done using an external diode connected be-
tween A2/T1 and ground.
Since this technique relies upon measuring the relatively
small voltage difference resulting from two levels of current
through the external diode, any resistance in series with the
external diode will cause an error in the temperature reading
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