MSK5950RH M. S Kennedy, MSK5950RH Datasheet - Page 3

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

PIN FUNCTIONS
VIN A,B,C,D,E - These pins provide the input power connection
to the MSK 5950RH. This is the supply that will be regulated to
the output. All five pins must be connected for proper operation.
VBIAS - This pin provides power to all internal circuitry including
bias, start-up, thermal limit and overcurrent latch. V
range is 2.9V to 7.5V. V
equal to V
VREF - Internal general purpose 2.5V shunt regulator that will
operate over a wide current range while maintaining good stabil-
ity. This reference voltage is used along with the feedback volt-
age to configure the desired output voltage. The reference will
maintain good regulation as long as 0.4 I
shunt current is derived from a resistor tied to V
resistor must supply both the minimum shunt current of 400µA
(1mA recommended) and the current required by the output volt-
age feedback divider network, between 2 and 2.5mA total is
typically sufficient. A constant current diode (CCR) may be used
in place of the resistor to minimize variations in I
line voltage variations.
Resistor calculation example:
V
V
First determine the required current by selecting R2 in the feed
back divider, typically between 1.0 and 1.2K ; see the output
voltage selection paragraph. Using standard value 0.1% toler-
ance resistors, the nominal output will be 0.9V with R2=1.07K
and R1=316 . The current in the divider will be equal to (V
V
example.
The total current required is the sum of the worst-case divider
current plus the V
is 400µA but 1mA is recommended. Using the recommended
1mA the minimum current required in R
The maximum resistor value to source the required current is
equal to (V
The maximum current in the reference must not exceed 10mA,
the absolute maximum allowable bias voltage is
10mA*R
The designer must also consider that the feedback divider will
provide a resistive connection from the source (V
the output even when the regulator is disabled. A minimum load
resistor can be used to draw the voltage down in the event this
poses a problem. A 90
tion and pull the output well below 200mV when the regulator is
disabled in this application.
V
the circuit as long as circuit loading, shunt current and parasitics
are carefully considered.
GND1 - Internally connected to input ground, these pins should
be connected externally by the user to the circuit ground and the
GND2 pins.
VOUT A,B,C,D,E - These are the output pins for the device. All
five pins must be connected for proper operation.
GND2 - Internally connected to output ground, these pins should
be connected externally by the user to the circuit ground and the
GND1 pins.
FDBK
REF
BIAS
OUT
APPLICATION NOTES
can be used as a precision 2.5V reference for other parts of
=0.9V
=3.3V±10%
)/R2 or 1.154mA nominal and 1.2mA worst-case in this
REF
IN
BIAS
.
+V
REF
min-V
REF
(min) or 4.67V for this application.
shunt current. The minimum shunt current
REF
resistor will sink 10mA during opera-
BIAS
)/2.2mA or 218
should be kept greater than or
REF
SHUNT
is 2.2mA.
for this example.
IN
IN
SHUNT
or V
BIAS
or V
10mA. The
BIAS
BIAS
voltage
due to
. The
REF
) to
-
3
LATCH - The MSK 5950RH LATCH pin is used for both current
limit and thermal limit. A capacitor between the LATCH pin and
ground sets a time out delay in the event of an over current or
short circuit condition. The capacitor is charged to approximately
1.6V from a 7.2µA (nominal) current source. Exceeding the ther-
mal limit will charge the latch capacitor from a larger current
source for a near instant shutdown. Once the latch capacitor is
charged the device latches off until the latch is reset. Momen-
tarily pull the LATCH pin low, toggle the shutdown pin high
then low or cycle the power to reset the latch. Toggling the
shutdown pin or cycling the bias power both disable the device
during the reset operation (see SHUTDOWN pin description).
Pulling the LATCH pin low immediately enables the device for as
long as the LATCH pin is held low plus the time delay to re-
charge the latch capacitor whether or not the fault has been
corrected. Disable the latch feature by tying the LATCH pin low.
With the LATCH pin held low the thermal limit feature is dis-
abled and the current limit feature will force the output voltage
to droop but remain active if excessive current is drawn.
SHUTDOWN - There are two functions to the SHUTDOWN pin.
It may be used to disable the output voltage or to reset the
LATCH pin. To activate the shutdown/reset functions the user
must apply a voltage greater than 1.3V to the SHUTDOWN pin.
The output voltage will turn on when the SHUTDOWN pin is
pulled below the threshold voltage. If the SHUTDOWN pin is
not used, it should be connected to ground.
FB - The FB pin is the inverting input of the internal error ampli-
fier. The non-inverting input is connected to an internal 1.265V
reference. This error amplifier controls the drive to the output
transistor to force the FB pin to 1.265V. An external resistor
divider is connected to the output, FB pin, V
set the output voltage.
POWER SUPPLY BYPASSING
transients it is recommended that a 33µF minimum tantalum
capacitor is connected between VIN and ground. A 0.1µF ce-
ramic capacitor should also be used for high frequency by-
passing.
OUTPUT CAPACITOR SELECTION
linear regulator to maintain good load transient response. How-
ever, with the MSK 5950RH this is not the case. A 47µF sur-
face mount tantalum capacitor in parallel with a 0.1µF ceramic
capacitor from the output to ground should suffice under most
conditions. If the user finds that tighter voltage regulation is
needed during output transients, more capacitance may be added.
If more capacitance is added to the output, the bandwidth may
suffer. See typical gain and phase curves.
THERMAL LIMITING
temperature of approximately 150°C. This thermal shutdown
can be used as a protection feature, but for continuous opera-
tion, the junction temperature of the pass transistor must be
maintained below 150°C. Proper heat sink selection is essen-
tial to maintain these conditions. Exceeding the thermal limit
activates the latch feature of the MSK 5950RH. See LATCH pin
description for instructions to reset the latch or disable the latch
feature.
Typically, large bulk capacitance is required at the output of a
To maximize transient response and minimize power supply
The MSK 5950RH control circuitry has a thermal shutdown
PRELIMINARY
REF
Rev. A 6/08
and V
IN
to