MIC5204_02 Datasheet, PDF (4/8 Pages) Micrel Semiconductor – SCSI-II Active Terminator

MIC5204
Micrel
Applications Information
External Capacitors
A 2.2µF capacitor is recommended between the MIC5204
output and ground to prevent oscillations due to instability.
Larger values serve to improve the regulator's transient re-
sponse. Most types of tantalum or aluminum electrolytics will
be adequate; film types will work. Many aluminum electrolytics
have electrolytes that freeze at about –30°C, so solid tantalums
are recommended for operation below –25°C. The important
parameters of the capacitor are an effective series resistance
of about 5Ω or less and a resonant frequency above 500kHz.
The value of this capacitor may be increased without limit.
A 1µF capacitor should be placed from the MIC5204 input to
ground if there is more than 10 inches of wire between the
input and the AC filter capacitor or if a battery is used as the
input.
The MIC5204 will remain stable and in regulation with no load
in addition to the internal voltage divider.
Thermal Considerations
Part I. Layout
The MIC5204BM (8-pin surface mount package) has the
following thermal characteristics when mounted on a single
layer copper-clad printed circuit board.
PC Board
Dielectric
FR4
Ceramic
θ_JA
160°C/W
120°C/W
Multi-layer boards having a ground plane, wide traces near
the pads, and large supply bus lines provide better thermal
conductivity. The "worst case" value of 160°C/W assumes no
ground plane, minimum trace widths, and a FR4 material
board.
Part II. Nominal Power Dissipation and Die Temperature
The MIC5204BM at a 25°C ambient temperature will operate
reliably at up to 625mW power dissipation when mounted in
the "worst case" manner described above. At an ambient
temperature of 55°C, the device may safely dissipate 440mW.
These power levels are equivalent to a die temperature of
125°C, the recommended maximum temperature for non-
military grade silicon integrated circuits. In normal SCSI
terminator applications, the average power dissipation is very
small and this minimum geometry heat sink is suitable. The
total dissipation does not approact the 400mW to 625mW
range described above.
For MIC5204BS (SOT-223 package) heat sink characteris-
tics, please refer to Micrel Application Hint 17, “P.C. Board
Heat Sinking”. As with the SO-8, average power dissipation
in SCSI terminator applications is low and a minimum pad size
is generally adequate.
245 mil
50 mil
150 mil
February 1999
30 mil
50 mil
Minimum recommended board pad size, SO-8.
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MIC5204