MSK5115-00BTU(2013) Ver la hoja de datos (PDF) - M.S. Kennedy Corporation
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MSK5115-00BTU Datasheet PDF : 5 Pages
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APPLICATION NOTES
REGULATOR PROTECTION:
The MSK 5115 is fully protected against reversed input polar-
ity, overcurrent faults, overtemperature conditions (Pd) and tran-
sient voltage spikes of up to 60V. If the regulator is used in
dual supply systems where the load is returned to a negative
supply, the output voltage must be diode clamped to ground.
OUTPUT CAPACITOR:
The output voltage ripple of the MSK 5115 voltage regulator
can be minimized by placing a filter capacitor from the output to
ground. The optimum value for this capacitor may vary from
one application to the next, but a minimum of 10μF is recom-
mended for optimum performance. This capacitor need not be
an expensive low ESR type: aluminum electrolytics are adequate.
In fact, extremely low ESR capacitors may contribute to instabil-
ity. Tantalum capacitors are recommended for systems where
fast load transient response is important. Transient load response
can also be improved by placing a capacitor directly across the
load.
LOAD CONNECTIONS
In voltage regulator applications where very large load cur-
rents are present, the load connection is very important. The
path connecting the output of the regulator to the load must be
extremely low impedance to avoid affecting the load regulation
specifications. Any impedance in this path will form a voltage
divider with the load. The MSK 5115 requires a minimum of
10mA of load current to stay in regulation.
ENABLE PIN
The MSK 5115 of voltage regulator is equipped with a TTL
compatible ENABLE pin. A TTL high level on this pin activates
the internal bias circuit and powers up the device. A TTL low
level on this pin places the controller in shutdown mode and the
device draws approximately 10μA of quiescent current. If the
enable function is not used, simply connect the enable pin to
the input.
DEVICE/CASE CONNECTION:
The MSK 5115 is a highly thermally conductive device, and the
thermal path from the package heat sink to the internal junction
is very short. Since the case is electrically isolated from the
internal circuitry, the package can be directly connected to a
heat sink.
HEAT SINK SELECTION:
To select a heat sink for the MSK 5115, the following formula
for convective heat flow may be used.
Governing Equation:
Tj = Pd x (Rθjc + Rθcs + Rθsa) + Ta
WHERE:
Tj = Junction Temperature
Pd = Total Power Dissipation
Rθjc = Junction to Case Thermal Resistance
Rθcs = Case to Heat Sink Thermal Resistance
Rθsa = Heat Sink to Ambient Thermal Resistance
Ta = Ambient Temperature
First, the power dissipation must be calculated as follows:
Power Dissipation = (VIN - VOUT) x Iout
Next, the user must select a maximum junction temperature.
The absolute maximum allowable junction temperature is 125°C.
The equation may now be rearranged to solve for the required
heat sink to ambient thermal resistance (Rθsa).
EXAMPLE:
An MSK 5115 is configured for VIN=+5V and VOUT=+3.3V.
Iout is a continuous 1A DC level. The ambient temperature is
+25°C. The maximum desired junction temperature is 125°C.
Rθjc = 3.6°C/W and Rθcs = 0.15°C/W for most thermal greases
Power Dissipation = (5V - 3.3V) x (1A)
= 1.7 Watts
Solve for Rθsa:
Rθsa = 125°C - 25°C - 3.6°C/W - 0.15°C/W
1.7W
= 55.07°C/W
In this example, a heat sink with a thermal resistance of no
more than 55°C/W must be used to maintain a junction tem-
perature of no more than 125°C.
MSK5115-00 OUTPUT ADJUSTMENT:
The diagram below illustrates proper adjustment technique for
the output voltage. The series resistance of R1+R2 should be
selected to pass the minimum regulator output current require-
ment of 10mA.
3
8548-37 Rev. J 2/13
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