MIC2583-LBQS Micrel Inc, MIC2583-LBQS Datasheet - Page 20

• Manufacturer Part Number: MIC2583-LBQS
• Description: IC,Power Control/Management,CMOS,SSOP,16PIN,PLASTIC
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2583-LBQS

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 2.3 V ~ 13.2 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

MOSFET Steady-State Thermal Issues
The selection of a MOSFET to meet the maximum
continuous current is a fairly straightforward exercise.
First, arm yourself with the following data:
The data sheet will almost always give a value of on
resistance given for the MOSFET at a gate-source
voltage of 4.5V, and another value at a gate-source
voltage of 10V. As a first approximation, add the two
values together and divide by two to get the on-
resistance of the part with 8V of enhancement.
Call this value R
acts as an ohmic (resistive) device, almost all that’s
required to determine steady-state power dissipation is
to calculate I
The one addendum to this is that MOSFETs have a
slight increase in R
good approximation for this value is 0.5% increase in
R
at which R
For instance, if the selected MOSFET has a calculated
R
temperature ends up at 110ºC, a good first cut at the
operating value for R
The final step is to make sure that the heat sinking
available to the MOSFET is capable of dissipating at
least as much power (rated in ºC/W) as that with which
the MOSFETs performance was specified by the
manufacturer. Here are a few practical tips:
Micrel, Inc.
April 2009
ON
ON
R
• The value of I
• The
• The maximum ambient temperature in which
• Any knowledge you can get about the heat
1. The heat from a surface-mount device such as
2. Airflow works. Even a few LFM (linear feet per
ON
per ºC rise in junction temperature above the point
of 10mΩ  a t a T
question (see Sense Resistor Selection).
candidate MOSFET.
the device will be required to operate.
sinking available to the device (e.g., can heat
be dissipated into the ground plane or power
plane, if using a surface-mount part? Is any
airflow available?).
an SOIC-8 MOSFET flows almost entirely out
of the drain leads. If the drain leads can be
soldered down to one square inch or more, the
copper will act as the heat sink for the part.
This copper must be on the same layer of the
board as the MOSFET drain.
minute) of air will cool a MOSFET down
substantially.
If you can, position the MOSFET(s) near the
inlet of a power supply’s fan, or the outlet of a
≅
10
ON
m
2
manufacturer’s
R.
was initially specified by the manufacturer.
Ω
[
ON
1
+
. Since a heavily enhanced MOSFET
ON
(
110
ON
LOAD(CONT, MAX.)
J
with increasing die temperature. A
= 25ºC, and the actual junction
would be:
−
25
)(
data
. 0
005
for the output in
)
]
sheet
≅
14
3 .
m
for
Ω
the
(13)
20
MOSFET Transient Thermal Issues
Having chosen a MOSFET that will withstand the
imposed
continuous I
remains only to verify the MOSFETs ability to handle
short-term
overheating. A MOSFET can handle a much higher
pulsed power without damage than its continuous
dissipation ratings would imply. The reason for this is
that, like everything else, thermal devices (silicon die,
lead frames, etc.) have thermal inertia.
In terms related directly to the specification and use of
power MOSFETs, this is known as “transient thermal
impedance,” or Z
sheets give a Transient Thermal Impedance Curve. For
example, take the following case: V
been set to 100msec, I
trip threshold is 50mV nominal, and the fast-trip
threshold is 100mV. If the output is accidentally
connected to a 3Ω load, the output current from the
MOSFET will be regulated to 2.5A for 100ms (t
before the part trips. During that time, the dissipation in
the MOSFET is given by:
At first glance, it would appear that a really hefty
MOSFET is required to withstand this sort of fault
condition. This is where the transient thermal impedance
curves become very useful. Figure 10 shows the curve
for the Vishay (Siliconix) Si4410DY, a commonly used
SOIC-8 power MOSFET.
Taking the simplest case first, we’ll assume that once a
fault event such as the one in question occurs, it will be
a long time– 10 minutes or more– before the fault is
isolated and the channel is reset. In such a case, we can
approximate this as a “single pulse” event, that is to say,
there’s no significant duty cycle. Then, reading up from
the X-axis at the point where “Square Wave Pulse
Duration” is equal to 0.1sec (=100msec), we see that the
Z
duration is only 8% of its continuous R
This particular part is specified as having an R
50°C/W for intervals of 10 seconds or less.
θ(JA)
3. The best test of a surface-mount MOSFET for
of this MOSFET to a highly infrequent event of this
processor’s cooling fan.
an application (assuming the above tips show
it to be a likely fit) is an empirical one. Check
the MOSFETs temperature in the actual layout
of the expected final circuit, at full operating
current. The use of a thermocouple on the
drain leads, or infrared pyrometer on the
package, will then give a reasonable idea of
the device’s junction temperature.
P = E x I; E
P
MOSFET
voltage
2
R power dissipation which it will see, it
overload
= (4.5V x 2.5A) = 11.25W for 100msec.
θ(JA)
MOSFET
stresses,
. Almost all power MOSFET data
LOAD(CONT. MAX)
power
= [12V-(2.5A)(3Ω)] = 4.5V
and
dissipation
IN
MIC2582/MIC2583
= 12V, t
the
θ(JA)
is 2.5A, the slow-
M9999-043009-C
.
worse
OCSLOW
OCSLOW
without
θ(JA)
case
has
of
)