MSK5010-33_15 Datasheet, PDF (3/7 Pages) M.S. Kennedy Corporation – Available in 3.3V, 5.0V and 12.0V versions

APPLICATION NOTES
MINIMIZING OUTPUT RIPPLE:
The output voltage ripple of the MSK5010 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 and is best determined by experimentation.
Transient load response can also be improved by placing a (10uF
to 20uF) capacitor directly across the load.
CASE CONNECTIONS:
The case of the MSK5010 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 between 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 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.
The same holds true for the connection from the low end of the
load to ground. For best load regulation, the low end of the load
must be connected directly to pin 2 of the MSK5010 and not to a
ground plane inches away from the hybrid.
ENABLE/SHUTDOWN PIN:
The MSK5010 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 a maximum of 5µA of quiescent current.
CHARGE 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. Approximately three times
the voltage seen on the input will appear across this capacitor.
Careful attention must be paid to capacitor voltage rating since
voltages larger than the power supply are present.
HEAT SINK SELECTION:
To select a heat sink for the MSK5010, 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
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 MSK5010-3.3 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)
= 37 Watts
Solve for Rθsa:
Rθsa = 150°C - 25°C - 0.8°C/W - 0.15°C/W
37W
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 temperature 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)
POWER DISSIPATION:
The output pass transistor in the MSK5010 is rated to dissipate near-
ly 100 watts. The limiting factor of this device is effective dissipation
of heat generated under such conditions. Careful consideration
must be paid to heat dissipation and junction temperature when
applying this device.
3
8548-149 Rev. J 2/15