APPLICATION NOTES

HEAT SINK SELECTION:

To select a heat sink for the MSK 5100, the following formula

for convective heat flow may be used.

Governing Equation:

Tj = Pd x (R

WHERE:

Tj = Junction Temperature

Pd = Total Power Dissipation

R

R

R

Ta = Ambient Temperature

REGULATOR PROTECTION:

The MSK 5100 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 MSK 5100 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, but a minimum of 33µF is

recommended for optimum performance. 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 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 MSK 5100 series requires a mini-

mum of 10mA of load current to stay in regulation.

ENABLE PIN:

The MSK 5100 series of voltage regulators are equipped with a

TTL compatible ENABLE pin. A TTL high level on this pin acti-

vates 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.

FLAG OUTPUT PIN:

All of the fixed output voltage versions of the MSK 5100 series

are equipped with a flag output pin. Since the flag pin is an

open collector configuration it can be pulled up to any voltage

between 3V and 26V. This feature allows direct interfacing to

practically any logic. This active low output has a typical level

of 0.22V when the flag comparator detects an "out of regula-

tion" condition.

Flag states include low input voltage,

overtemperature shutdown and output current limit. Extremely

high level input voltage transients will also cause the flag out-

put pin to activate.

MSK5100-00 OUTPUT ADJUSTMENT:

The MSK 5100-00 is an adjustable version in the series of high

performance regulators. The diagram below illustrates proper

adjustment technique for the output voltage. The series resis-

tance of R1+R2 should be selected to pass the minimum regu-

lator output current requirement of 10mA.

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 (R

EXAMPLE:

An MSK 5100-3.3 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 tem-

perature is 125°C.

R

Power Dissipation = (5V - 3.3V) x (1A)

Solve for R

R

In this example, a heat sink with a thermal resistance of no more

than 56°C/W must be used to maintain a junction temperature

of no more than 125°C.

1.7W

= 1.7 Watts

DEVICE SOLDERING/CASE CONNECTION:

The MSK 5100 series are highly thermally conductive devices

and the thermal path from the package heat sink to the internal

junctions is very short.

Standard surface mount techniques

should be used when soldering the device into a circuit board.

A hole can be cut in the printed circuit board to allow the heat

sink of the package to be thermally bonded to an external heat

sink for very high power applications. The external heat sink

needs to be connected to ground because the heat sink and lid

of the MSK 5100 are also electrically connected to ground.

The user is urged to keep this in mind when designing the printed

circuit board for the MSK 5100. There should be no printed

circuit traces making contact with the case or lid of the device

except for ground. The ground plane can be used to pull heat

away from the device.

Rev. F 1/06

3

= 56.32°C/W