MSK5950RH M. S Kennedy, MSK5950RH Datasheet - Page 4

• Manufacturer Part Number: MSK5950RH
• Description: Rad Hard Ultra Low Voltage Adjustable Positive Linear Regulator
• Manufacturer: M. S Kennedy

OVERCURRENT LATCH-OFF/LATCH PIN
CAPACITOR SELECTION
output short circuit protection with a timed latch-off circuit. Refer-
ence the LATCH pin description note. The latch off time out is
determined with an external capacitor connected from the LATCH
pin to ground. The time-out period is equal to the time it takes to
charge this external capacitor from 0V to 1.6V. The latch charging
current is provided by an internal current source. This current is a
function of bias voltage and temperature (see latch charging current
curve). For instance, at 25°C, the latch charging current is 7.2µA
at VBIAS=3V and 8µA at VBIAS=7V.
the bias supply. This additional latching current is also a function
of bias voltage and temperature (see typical performance curves).
the input and output voltages. Custom current limit is available;
contact the factory for more information.
when VBIAS and VIN are applied simultaneously. Applying VBIAS
before VIN starts the MSK 5950RH up in a disabled or latched
state. When starting in a latched state the device output can be
enabled either by pulling the latch pin low to drain the latch capaci-
tor or pulsing the shutdown pin high. The shutdown pulse dura-
tion is partially dependent upon the size of the latch capacitor and
should be characterized for each application; 30uS is typically ad-
equate for a 1uF latch capacitor at 25°C. A momentary high pulse
on the shutdown pin can be achieved using the RC circuit below if
VIN rises rapidly. The resistor and capacitor must be selected based
on the required pulse duration, the rise characteristic of VIN and
the shutdown pin threshold (see shutdown pin threshold and cur-
rent curves).
The shutdown pin can be held high and pulled low after VIN comes
up or the latch pin held low and released after VIN comes up to
ensure automatic startup when applying VBIAS before VIN. Either
of the basic circuits below can be adapted to a variety of applica-
tions for automatic start up when VBIAS rises before VIN.
START UP OPTIONS
In the latch-off mode, some additional current will be drawn from
As previously mentioned, the LATCH pin provides over current/
The MSK 5950RH current limit function is directly affected by
The MSK 5950RH starts up and begins regulating immediately
APPLICATION NOTES CONT.
4
HEAT SINK SELECTION
ing formula for convective heat flow may be used.
Governing Equation:
Where
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 re-
sistance (R
Example:
V
bient temperature is +25°C. The maximum desired junc-
tion temperature is +125°C.
R
greases
Solve for R
of no more than 39°C/W must be used to maintain a junc-
tion temperature of no more than 125°C.
TOTAL DOSE RADIATION TEST
PERFORMANCE
generated for all radiation testing performed by MS
Kennedy. These curves will show performance trends
throughout the TID test process and will be located in the
MSK 5950RH radiation test report. The complete radia-
tion test report will be available in the RAD HARD PROD-
UCTS section on the MSK website.
To select a heat sink for the MSK 5950RH, the follow-
OUT
In this example, a heat sink with a thermal resistance
Next, the user must select a maximum junction tem-
JC
Radiation performance curves for TID testing will be
An MSK 5950RH is connected for V
R
T
P
R
R
R
T
=8.4°C/W and R
=+1.2V. I
SA
J
A
D
JC
CS
SA
=
= 39°C/W
Power Dissipation=(3.3V-1.2V) x (1A)
T
Power Dissipation=(V
J
= Junction Temperature
= Total Power Dissipation
= Junction to Case Thermal Resistance
= Case to Heat Sink Thermal Resistance
= Heat Sink to Ambient Thermal Resistance
= Ambient Temperature
SA
SA:
=
125°C - 25°C
).
P
D
OUT
X (R
2.1W
is a continuous 1A DC level. The am-
CS
JC
=0.15°C/W for most thermal
+ R
=2.1Watts
PRELIMINARY
CS
-8.4°C/W - 0.15°C/W
IN
+ R
-V
OUT
SA
) x I
) + T
IN
=+3.3V and
OUT
Rev. A 6/08
A