APPLICATION NOTES CONT.

4

To select a heat sink for the MSK5824RH, 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 tem-

perature. The absolute maximum allowable junction tem-

perature is 150°C. The equation may now be rearranged

to solve for the required heat sink to ambient thermal

Example:

bient temperature is +25°C. The maximum desired junc-

tion temperature is +125°C.

greases

Power Dissipation=(3.3V-2.5V) x (3A)

=2.4 Watts

125°C - 25°C

2.4W

= 35.0°C/W

In this example, a heat sink with a thermal resistance

of no more than 35.0°C/W must be used to maintain a

junction temperature of no more than 125°C.

The MSK5824RH control circuitry has a thermal shut-

down temperature of approximately 150°C. This ther-

mal shutdown can be used as a protection feature, but

for continuous operation, the junction temperature of the

pass transistor must be maintained below 150°C. Proper

heat sink selection is essential to maintain these condi-

tions. Exceeding the thermal limit activates the latch fea-

ture of the MSK5824RH. Toggle the shutdown pin high then

low or cycle power to reset the latch. See shutdown pin

description and overcurrent latch description for more in-

formation.

TYPICAL APPLICATIONS CIRCUIT

- 6.5°C/W - 0.15°C/W

FIGURE 2

THERMAL LIMITING

HEAT SINK SELECTION

Radiation performance curves for TID, Neutron and

ELDRS testing have been generated for all radiation test-

ing performed by MS Kennedy. These curves show per-

formance trends throughout the TID test process and

are located in the MSK5826RH radiation test report. The

complete radiation test report is available in the RAD HARD

PRODUCTS section on the MSK website.

TOTAL DOSE RADIATION TEST

PERFORMANCE

http://www.mskennedy.com/store.asp?pid=9951&catid=19680

START UP CURRENT

The MSK5824RH sinks increased current during startup

to bring up the output voltage. Reference the "Saturated

Drive Current vs. Input Voltage graph in the typical per-

formance curves of this data sheet and the "Understand-

ing Startup Surge Current With MS Kennedy's RH1573

Based Rad Hard LDO Regulators" application note in the

application notes section of the MS Kennedy Web site

for more information.

http://www.mskennedy.com/

8548-58 Rev. H 6/14