APPLICATION NOTES

HEAT SINK SELECTION:

To select a heat sink for the MSK 5116, 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 5116 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.

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 125°C.

The equation may now be rearranged to solve for the required

heat sink to ambient thermal resistance (R

EXAMPLE:

An MSK 5116-3.3 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)

= 1.7 Watts

Solve for R

R

- 3.6°C/W - 0.15°C/W

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

more than 55°C/W must be used to maintain a junction tem-

perature of no more than 125°C.

DEVICE/CASE CONNECTION:

The MSK 5116 series are highly thermally conductive devices

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

junctions is very short. Since the case is electrically isolated

from the internal circuitry, the package can be directly con-

nected to a heat sink.

ENABLE PIN

The MSK 5116 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.

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.

OUTPUT CAPACITOR:

The output voltage ripple of the MSK 5116 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 10µF

is recommended for optimum performance. This capacitor need

not be an expensive low ESR type: aluminum electrolytics are

adequate. In fact, extremely low ESR capacitors may contrib-

ute to instability. Tantalum capacitors are recommended for

systems where fast load transient response is important. Tran-

sient load response can also be improved by placing a capaci-

tor directly across the load.

1.7W

3

Rev. A 1/06

=

55.07°C/W