MIC2044/2045
Micrel
MIC2044/2045
14
January 2005
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MIC2044-1BTS
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Figure 4. Lower UVLO Setting
Power Dissipation
Power dissipation depends on several factors such as the
load, PCB layout, ambient temperature, and package type.
The following equations can be used to calculate power
dissipation and die temperature.
Calculation of power dissipation can be accomplished by the
following equation:
P
D
= R
DS(on)
×
(I
OUT
)
2
(5)
To relate this to junction temperature, the following equation
can be used:
T
J
= P
D
×
R
(
θ
J-A)
+ T
A
(6)
where T
J
= junction temperature, T
A
= ambient temperature
and R
θ
(J-A)
is the thermal resistance of the package.
Printed Circuit Board Hot Plug
The MIC2044/45 are ideal inrush current limiting power
switches suitable for hot plug applications. Due to the inte-
grated charge pump, the MIC2044/45 present a high imped-
ance when in the off state and the device slowly becomes a
low impedance as it turns on. This effectively isolates power
supplies from highly capacitive loads by reducing inrush
current during hot plug events. This same feature also can be
used for soft-start requirements.
PCB Layout Recommendations
The MIC2044 and MIC2045 have very low on-resistance,
typically 20m
Ω
, and the switches can provide up to 6A of
continuous output current. Under heavy loads, the switched
current may cause the devices to heat up considerably. The
following list contains some useful suggestions for PCB
layout design of the MIC2044/45 in order to prevent the die
from overheating under normal operating conditions.
1.
Micrel Semiconductor does not assume responsibility for the use of
this program tool in the event that any PCB assembled, tested,
produced, and/or manufactured becomes damaged and/or causes any
degradation of system performance or damage to any system
components in which the aforementioned PCB is included.
1. Supply additional copper area under the device
to remove heat away from the IC.
See
“Application Hint 17”
for a general guideline
in calculating the suggested area.
2. Provide additional pad area on the corner pins of
the MIC2044/45 IC for heat distribution.
3. Tie the common power pins (V
IN
= pins 7, 11,
13, 16 and V
OUT
= pins 9, 12, 14) together in a
manner such that the traces entering and
leaving the device have a uniform width suffi-
cient for the application’s current requirements
plus added margin (25% minimum recom-
mended).
Ex: For 4A maximum current, design traces for
5A capability.
4. For PCB trace width calculation, there are
numerous calculator programs available on the
internet and elsewhere. As a general rule of
thumb, 15-20 mils width for every 1A of current
when using 1oz. copper. However, the trace
width calculators often take into account maxi-
mum temperature increase constraints, as well
as layer arrangement, in determining the PCB
trace widths. As a reference, the following link is
suggested for trial tests in PCB trace width
calculations.
1
http://www.aracnet.com/cgi-usr/gpatrick/trace.pl
