MSK5010-12HTU datasheet(3/5 Pages) MSK

3 / 5 page

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 5010-3.3 is configured for Vin = +7V and Vout =

+3.3V. Iout is a continuous 10A DC level. The ambient tem-

perature is +25°C. The maximum desired junction tempera-

ture is 150°C. Rθjc = 0.8°C/W and Rθcs = 0.15°C/W typi-

cally.

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)

APPLICATION NOTES

HEAT SINK SELECTION:

MINIMIZING OUTPUT RIPPLE:

To select a heat sink for the MSK 5010, 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

The output voltage ripple of the MSK 5010 series voltage regu-

lators 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.

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.

37W

CASE CONNECTIONS:

The case of the MSK 5010 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

currents 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 regulation, the low end of the load must be con-

nected directly to pin 2 of the MSK 5010 and not to a

ground plane inches away from the hybrid.

ENABLE/SHUTDOWN PIN:

The MSK 5010 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.

POWER DISSIPATION:

The output pass transistor in the MSK 5010 is rated to

dissipate nearly 100 watts. The limiting factor of this device

is effective dissipation of heat generated under such condi-

tions. For example, to dissipate 100 watts, calculations

show that the MSK 5010 would have to be bolted to the

underbelly of a submarine submerged in the Arctic Ocean!

Careful consideration must be paid to heat dissipation and

junction temperature when applying this device.

= 37 Watts

Rev. H 10/02

MSK5010-12HTU Datasheet(PDF) 3 Page - M.S. Kennedy Corporation

MSK5010-12HTU Datasheet(HTML) 3 Page - M.S. Kennedy Corporation

Html Pages

1 2 3 4 5

Datasheet Download

Link URL