VOUT

1.265

VOUT=1.265(1+R1/R2)

OUTPUT VOLTAGE SELECTION

As noted in the above typical applications circuit, the formula

for output voltage selection is

A good starting point for this output voltage selection is to set

R2=1K. By rearranging the formula it is simple to calculate

the final R1 value.

- 7.5°C/W - 0.15°C/W

APPLICATION NOTES CONT'D

4

R1

R2

1+

VOUT=1.265

-1

R1=R2

TYPICAL APPLICATIONS CIRCUIT

THERMAL LIMITING

The MSK5805RH control circuitry has a thermal shutdown

temperature of approximately 150°C. This thermal shutdown

can be used as a protection feature, but for continuous op-

eration, the junction temperature of the pass transistor must

be maintained below 150°C. Proper heat sink selection is

essential to maintain these conditions. Exceeding the ther-

mal limit activates the latch feature of the MSK5805RH. See

LATCH pin description for instructions to reset the latch or

disable the latch feature.

Radiation performance curves for TID testing will be gener-

ated for all radiation testing performed by MSK. These curves

show performance trends throughout the TID test process

and can be located in the MSK5805RH radiation test report.

The complete radiation test report will be available in the RAD

HARD PRODUCTS section on the MSK website.

TOTAL DOSE RADIATION TEST

PERFORMANCE

The MSK5805RH requires less starup current than other

RH1573 based regulators in this series. LDO regulators sink

increased current during startup to bring up the output volt-

age. The MSK5805RH was designed to require less starup

current making it ideal for lower current applications. The

startup current can be further reduced by placing a resistor

the current limit of the device. Reference the "Current Limit

Volatge" graph in the typical performance curves section of

this data sheet. See AN 024 "Understanding Start Up Surge

Current With MS Kennedy's RH1573 based Rad Hard LDO

Regulators" in the application notes section of MSK's web

site for additional information.

http://www.anaren.com/msk

START UP CURRENT

8548-111 Rev. F 5/15

HEAT SINK SELECTION

To select a heat sink for the MSK5805RH, the following

formula for convective heat flow may be used.

Governing Equation:

Where

= Junction Temperature

= Total Power Dissipation

= Ambient Temperature

Next, the user must select a maximum junction tempera-

ture. The absolute maximum allowable junction temperature

is 150°C. The equation may now be rearranged to solve for

Example:

An MSK5805RH is connected for VIN=+5V and VOUT-

temperature is +25°C. The maximum desired junction tem-

perature is +125°C.

greases

Power Dissipation=(5V-3.3V) x (0.5A)

=0.85Watts

125°C - 25°C

0.85W

= 110°C/W

In this example, a heat sink with a thermal resistance of

no more than 110°C/W must be used to maintain a junction

temperature of no more than 125°C.