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MSK5012BTU Datasheet(PDF) 3 Page - M.S. Kennedy Corporation

Part No. MSK5012BTU
Description  HIGH CURRENT, SUPER LOW DROPOUT ADJUSTABLE VOLTAGE REGULATOR
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Maker  MSK [M.S. Kennedy Corporation]
Homepage  http://www.mskennedy.com
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MSK5012BTU Datasheet(HTML) 3 Page - M.S. Kennedy Corporation

   
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APPLICATION NOTES
MINIMIZING OUTPUT RIPPLE:
The output voltage ripple of the MSK 5012 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 and is best determined by
experimentation. Transient load response can also be improved
by placing a capacitor directly across the load. Typically a
10µF capacitor is a good starting point.
CASE CONNECTIONS:
The case of the MSK 5012 is electrically isolated from the
internal circuitry so that a direct connection can be made to
the heat sink for most efficient heat dissipation. However, it
may be necessary in some applications to connect the case to
ground. Grounding the case will help eliminate oscillations and
produce a clean, noise free output.
LOAD REGULATION:
For best results, the ground pin should be connected directly to
the load (see next note). This effectively reduces the ground
loop effect and eliminates excessive voltage drop in the sense
leg. It is also important to keep the output connection be-
tween the regulator and the load as short as possible since this
directly affects the load regulation. For example, if 20 gauge
wire were used which has a resistance of about .008 ohms per
foot, this would result in a drop of 8mV/ft at a load current of
1 amp.
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 same holds true for the connection
from the low end of the load to ground. For best load regula-
tion, the low end of the load must be connected directly to pin
2 of the MSK 5012 and not to a ground plane inches away
from the hybrid.
FILTER CAPACITOR:
For all applications, the user must connect a 1.0uF capacitor
from pin 5 directly to ground. This capacitor is part of the
circuit which drives the gate of the internal MOSFET. Approxi-
mately three times the voltage seen on the input will appear
across this capacitor. Careful attention must be paid to capaci-
tor voltage rating since voltages larger than the power supply
are present.
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 175°C.
The equation may now be rearranged to solve for the required
heat sink to ambient thermal resistance (Rθsa).
EXAMPLE:
An MSK 5012 is configured for Vin = +7V and Vout = +3.3V.
Iout is a continuous 10A DC level. The ambient temperature is
+25°C. The maximum desired junction temperature is 150°C.
Rθjc = 0.8°C/W and Rθcs = 0.15°C/W typically.
Power Dissipation = (7V - 3.3V) x (10A)
Solve for Rθsa:
Rθsa = 150°C - 25°C - 0.8°C/W - 0.15°C/W
In this example, a heat sink with a thermal resistance of no
more than 2.43°C/W must be used to maintain a junction tem-
perature of no more than 150°C. The Thermalloy Corporation
makes a heat sink with a thermal resistance of 2.2°C/W that
would work well for this application.
(See Thermalloy part number 7023)
HEAT SINK SELECTION:
To select a heat sink for the MSK 5012, the following formula
for convective heat flow must 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
37W
POWER DISSIPATION:
The output pass transistor in the MSK 5012 is rated to dissi-
pate nearly 100 watts. The limiting factor of this device is
effective dissipation of heat generated under such conditions.
For example, to dissipate 100 watts, calculations show that
the MSK 5012 would have to be bolted to the underbelly of a
submarine submerged in the Arctic Ocean! Careful consider-
ation must be paid to heat dissipation and junction temperature
when applying this device.
= 37 Watts
OUTPUT VOLTAGE ADJUSTMENT
The output voltage of the MSK 5012 can be adjusted from
+1.3 volts to +36 volts. Refer to the following formula for
resistor divider selection. R2 should be 10KΩ for all applica-
tions.
R1 = R2 ((VOUT / 1.235) -1)
Figure one below illustrates proper resistor divider connection.
3
Rev. H 10/02


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