MIC2042/2043
Micrel
V
DD
2.5V
V
IN
0.8V
C3
10
m
F
R2
95.3k
W
1%
R3
59k
W
1%
R1
47k
W
MIC2042-1BTS
C2
0.1
m
F
C1
0.1
m
F
7
8, 12
2
4
9
6
VBIAS
VIN
EN
UVLOIN
SLEW
ILIM
VOUT
PGREF
10,11,14
13
R6
47k
W
PWRGD
1
3
R4
75k
W
1%
R5
36.5k
W
1%
R7
47k
W
C
LOAD
22
m
F
V
OUT
0.8V @1.5A
R
SET
200
W
/FAULT
GND
5
Digital
Output
Signals
Note:
All V
IN
pins (8, 12) must be externally tied together.
All V
OUT
pins (10, 11, 14) must be externally tied together.
Undervoltage Lockout = 0.6V.
Output Power-Good = 0.7V.
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
×
Rθ
JA
+ T
A
(6)
where T
J
= junction temperature, T
A
= ambient temperature
and Rθ
JA
is the thermal resistance of the package.
Printed Circuit Board Hot-Plug
The MIC2042/43 are ideal inrush current limiting power
switches suitable for hot-plug applications. Due to the inte-
grated charge pump, the MIC2042/43 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 MIC2042 and MIC2043 have very low on-resistance,
typically 40mΩ, and the switches can provide up to 3A of
continuous output current. Under such heavy loads, the
power consumed by the devices may cause the devices to
heat up considerably. The following list contains some useful
suggestions for PCB layout design of the MIC2042/43 in
order to prevent the die from overheating under normal
operating conditions:
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 MIC2042/43 IC for heat distribution.
3. Tie the common power pins (VIN = pins 8 and
12 and VOUT = pins 10, 11, 14 for the 14-pin
TSSOP, VIN = pins 5 and 7 and VOUT = pins 6
and 8 for the 8-pin SOP) together in a manner
such that the traces entering and leaving the
device have a uniform width sufficient for the
application’s current requirements plus added
margin (25% minimum recommended).
Ex: For 2A maximum current, design traces for
2.5A 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 for every 1A of current when
using 1oz. copper. However, the trace width
calculators often take into account maximum
temperature increase constraints, as well as
layer arrangement, in determining the PCB trace
widths.
M0512-112603
14
January 2005
MICREL [ MICREL SEMICONDUCTOR ]
