MIC2595-1YM Micrel Inc, MIC2595-1YM Datasheet - Page 22

• Manufacturer Part Number: MIC2595-1YM
• Description: Negative Voltage Hot-Swap Controller -
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2595-1YM

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: -19 V ~ -80 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (0.154", 3.90mm Width)
• Family Name: MIC2595
• Package Type: SOIC
• Operating Supply Voltage (min): -19V
• Operating Supply Voltage (max): -80V
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 3.9mm
• Product Height (mm): 1.45mm
• Mounting: Surface Mount
• Pin Count: 14
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

December 2005
A 0.5W sense resistor is a good choice in this
application.
Power MOSFET Selection
Selecting the proper external MOSFET for use with
theMIC2589/MIC2595 involves three straightforward
tasks:
• Choice of a MOSFET that meets minimum voltage
• Selection of a device to handle the maximum
• Verify the selected part’s ability to withstand any
Power MOSFET Operating Voltage Requirements
The first voltage requirement for the MOSFET is that
the drain-source breakdown voltage of the MOSFET
must be greater than V
The second breakdown voltage criterion that must be
met
MIC2589/MIC2595, the gate of the external MOSFET
is driven up to a maximum of 11V above VEE. This
means that the external MOSFET must be chosen to
have a gate-source breakdown voltage of 12V or
more; 20V is recommended. Most power MOSFETs
with a 20V gate-source voltage rating have a 30V
drain-source breakdown rating or higher. For many
48V telecom applications, transient voltage spikes can
approach,
absolute maximum input voltage rating of the
MIC2589/MIC2595 is 100V; therefore, a drain-source
breakdown voltage of 100V is suggested for the
external MOSFET. Additionally, an external input
voltage
applications that do not utilize conditioned power
supplies.
Power 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 value of I
• The manufacturer’s datasheet for the candidate
• The maximum ambient temperature in which the
• Any knowledge you can get about the heat sinking
The datasheet will almost always give a value of ON
resistance for a given MOSFET at a gate-source
requirements.
continuous current (steady-state thermal issues).
peak currents (transient thermal issues).
question (see Sense Resistor Selection).
MOSFET.
device will be required to operate.
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?).
is
clamp
the
and
LOAD(CONT, MAX.)
gate-source
sometimes
is
IN(MAX)
strongly
= V
for the output in
exceed,
DD
voltage.
recommended
– V
EE
(min).
100V.
For
The
the
for
22
voltage of 4.5V and 10V. For MIC2589/MIC2595
applications, choose the gate-source ON resistance at
10V and call this value R
MOSFET acts as an ohmic (resistive) device, almost
all that’s required to determine steady-state power
dissipation is to calculate I
this is that MOSFETs have a slight increase in R
with
approximation for this value is 0.5% increase in R
per °C rise in junction temperature above the point at
which R
For instance, if the selected MOSFET has a
calculated R
junction temperature ends up at 110°C, a good first
cut at the operating value for R
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 °C/W) as that with
which the MOSFET’s performance was specified by
the manufacturer. Here are a few practical tips:
Power MOSFET Transient Thermal Issues
If the prospective MOSFET has been shown to
withstand the environmental voltage stresses and the
worst-case
addressed, the remaining task is to verify if the
MOSFET is capable of handling extreme overcurrent
load
overheating. A power MOSFET can handle a much
ON
1. The heat from a TO-263 power MOSFET
2. Airflow works. Even a few LFM (linear feet
3. The best test of a candidate MOSFET for
≈ 10mΩ[1 + (110 – 25)(0.005)] ≈14.3mΩ
flows almost entirely out of the drain tab. If
the drain tab 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.
per 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 processor’s
cooling fan.
an application (assuming the above tips
show it to be a likely fit) is an empirical one.
Check the MOSFET’s 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.
faults,
increasing
ON
was initially specified by the manufacturer.
ON
steady-state
such
of 10mΩ at T
die
as
ON
a
. Since a heavily enhanced
2
temperature.
R. The one addendum to
J
power
ON
short
= 25°C, and the actual
would be:
circuit,
dissipation
[phone]
M9999-120505
A
without
good
ON
ON
is