MIC184 Micrel Semiconductor, MIC184 Datasheet - Page 16

• Manufacturer Part Number: MIC184
• Description: Local/Remote Thermal Supervisor Advance Information
• Manufacturer: Micrel Semiconductor

MIC184
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.
MIC184
{START Polling-Based Test and Initialization
1. Temporarily disable the host’s interrupt input
2. Write 0000 0010b (02h) to the CONFIG register.
3. Write 1100 1000 1000 0000b = C880h to T_SET
4. Wait t
5. Read the contents of the CONFIG register:
6. Write 0111 1111 1000 0000b = 7F80h to T_SET
7. Wait an additional t
8. Read CONFIG again, to clear the interrupt
9. Based on the results of the test in step (4), do
{END}
Routine}
from the device under test.
and T_HYST. This corresponds to -55.5 C.
least one A/D conversion.
a) If the part is an MIC184, the MSB will be set
b) If the part is a conventional LM75-type part,
and T_HYST. This corresponds to +127.5 C.
second conversion.
request from step (7). This will also clear STS, if
the part under test is an MIC184.
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
to one (CONFIG = 82h).
the MSB will be zero (CONFIG = 02h).
from the part under test.
conv
(160ms max.) for the part to finish at
Table 5. Transistors Suitable for Remote Temperature Sensing Use
conv
Vendor
Fairchild
On Semiconductor
Phillips Semiconductor
Rohm Semiconductor
Samsung
Zetex
for the part to finish a
Part Number
MMBT3906
MMBT3906L
PMBT3906
SST3906
KST3906-TF
FMMT3906
16
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
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:
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
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
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
V
CB-E
P
P
T
T
D
D
of a diode-connected PNP transistor ("diode") at two
J
J
1% I
1%
= (I
= (0.3mA
= 1.11mW
relative to T
Package
SOT-23
SOT-23
SOT-23
SOT-23
SOT-23
SOT-23
DD(typ.)
OL(int)
1.5mA
DD
0.3V)
3.3V + 25% I
3.3V + 25%
I
DD
A
206 C/W
OL(int)
Tested
0.3V)
is 0.23 C
). In order to understand what level
) will give a good estimate of the
OL(data)
1.5mA
0.3V +
November 2000
0.3V +
Micrel