MSK5102-50_15 Datasheet, PDF (3/6 Pages) M.S. Kennedy Corporation – Extremely Compact 10 Pin Flatpack With Metal Base

APPLICATION NOTES
REGULATOR PROTECTION:
The MSK5102 series is fully protected against reversed input
polarity, overcurrent faults, overtemperature conditions (Pd) and
transient 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 MSK5102 series voltage regulators
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 recommended
for optimum performance. Transient load response can also be
improved by placing a capacitor directly across the load.
HEAT SINK SELECTION:
To select a heat sink for the MSK5102, 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
LOAD CONNECTIONS:
In voltage regulator applications where very large load currents
are present, the load connection is very important. The path con-
necting 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.
ENABLE PIN:
The MSK5102 series of voltage regulators are 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 SOLDERING/CASE CONNECTION:
The MSK5102 series are highly thermally conductive devices and
the thermal path from the package base to the internal junctions
is very short. Standard surface mount techniques should be used
when soldering the device into a circuit board. The external heat
sink/pad needs to be connected to ground because the base of
the MSK5102 is also electrically connected to ground. The user is
urged to keep this in mind when designing the printed circuit board
for the MSK5102. There should be no printed circuit traces making
contact with the base of the device except for ground. The ground
plane can be used to pull heat away from the device.
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
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 MSK5102-3.3 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 = 6°C/W and Rθcs = 0.5°C/W typically.
Power Dissipation = (5V - 3.3V) x (1A)
= 1.7 Watts
Solve for Rθsa:
Rθsa = 125°C - 25°C - 6°C/W - 0.5°C/W
1.7W
= 52.3°C/W
In this example, a heat sink with a thermal resistance of no more
than 52°C/W must be used to maintain a junction temperature of
no more than 125°C.
3
8548-36 Rev. D 5/15