MIC284_05 Datasheet, PDF (19/20 Pages) Micrel Semiconductor – Two-Zone Thermal Supervisor

MIC284
1. Place the MIC284 as close to the remote diode
as possible, while taking care to avoid severe
noise sources such as high frequency power
transformers, CRTs, memory and data busses,
and the like.
2. Since any conductance from the various volt-
ages on the PC Board and the T1 line can in-
duce serious errors, it is good practice to guard
the remote diode’s emitter trace with a pair of
ground traces. These ground traces should be
returned to the MIC284’s own ground pin. They
should not be grounded at any other part of their
run. However, it is highly desirable to use these
guard traces to carry the diode’s own ground
return back to the ground pin of the MIC284,
thereby providing a Kelvin connection for the
base of the diode. See Figure 6.
3. When using the MIC284 to sense the tempera-
ture of a processor or other device which has an
integral thermal diode, e.g., Intel’s Pentium III,
connect the emitter and base of the remote sen-
sor to the MIC284 using the guard traces and
Kelvin return shown in Figure 6. The collector
of the remote diode is typically inaccessible to
the user on these devices. To allow for this, the
MIC284 has superb rejection of noise appearing
from collector to GND, as long as the base to
ground connection is relatively quiet.
4. Due to the small currents involved in the mea-
surement of the remote diode’s ΔV_BE, it is
important to adequately clean the PC board after
soldering to prevent current leakage. This is
Micrel, Inc.
most likely to show up as an issue in situations
where water-soluble soldering fluxes are used.
5. In general, wider traces for the ground and T1
lines will help reduce susceptibility to radiated
noise (wider traces are less inductive). Use
trace widths and spacing of 10 mils wherever
possible and provide a ground plane under
the MIC284 and under the connections from
the MIC284 to the remote diode. This will help
guard against stray noise pickup.
6. Always place a good quality power supply
bypass capacitor directly adjacent to, or un-
derneath, the MIC284. This should be a 0.1µF
ceramic capacitor. Surface-mount parts provide
the best bypassing because of their low induc-
tance.
7. When the MIC284 is being powered from par-
ticularly noisy power supplies, or from supplies
which may have sudden high-amplitude spikes
appearing on them, it can be helpful to add ad-
ditional power supply filtering. This should be
implemented as a 100Ω resistor in series with
the part’s VDD pin, and a 4.7µF, 6.3V electrolytic
capacitor from VDD to GND. See Figure 7.
MIC284
1 DATA
2 CLK
3 /INT
4 GND
VDD 8
A0 7
T1 6
/CRIT 5
GUARD/RETURN
REMOTE DIODE (T1)
GUARD/RETURN
3.3V
10k pull-ups
FROM
SERIAL BUS
HOST
OVER-TEMP
SHUTDOWN
Figure 6. Guard Traces/Kelvin Ground Returns
100
MIC284
DATA
VDD
CLK
T1
/INT
A0
/CRIT
GND
0.1F
4.7F
2200pF
Figure 7. V_DD Decoupling for Very Noisy Supplies
Remote
Diode
September 2005
19
MIC284