MSK5044RH M. S Kennedy, MSK5044RH Datasheet - Page 3

• Manufacturer Part Number: MSK5044RH
• Description: Rad Hard 3.5a Switching Regulator
• Manufacturer: M. S Kennedy

PIN FUNCTIONS
VIN - VIN connects to the collector of the internal power switch and
provides power to the internal control circuitry and internal regula-
tor. Very high di/dt is seen at VIN during switch on and off transi-
tions. High frequency decoupling capacitors are recommended to
minimize voltage spikes. VIN should be connected to a low impedence
source for best operation.
FB - The FB (feedback) pin's primary function is to set the output
voltage to the desired level. Use a single resistor between VOUT
and FB to form a feedback divider network with the internal 2.49K
resistor. Select the external resistor value to set the voltage at the
FB pin to 1.21V when the output is at the desired level, see "Setting
The Output Voltage."The FB pin provides two additional functions. If
the voltage at the FB pin drops below 0.8V the switch current limit
is reduced. When the voltage at the FB pin drops below 0.7V the
switching frequency is reduced. The switching frequency reduces to
approximately 100KHz at V
GND - The GND pin provides a return path for all internal control
current and acts as a reference to the error amplifier. It is important
that it is at the same voltage potential as the load return to ensure
proper regulation. Keep current on the ground between the load and
the MSK 5044RH to a minimum and use heavy copper traces to
minimize voltage drops and regulation error.
SHDN - The SHDN (shutdown) pin has two shutdown functions. The
first function disables switching when the voltage on the pin drops
below 2.38V (nominal). The second forces a complete shutdown
minimizing power consumption when the voltage drops below 0.4V
(nominal). Pull this pin high or leave open for normal operation. The
2.38V threshold can be used for UVLO functions by configuring a
resistive divider to VIN and GND that holds the pin voltage below
2.38V until VIN rises to the minimum desired voltage.
VOUT - VOUT is the output of the regulator. External capacitance
between the VOUT pin and GND is required to maintain stability and
minimize output ripple voltage, see "Selecting The Output Capaci-
tor." Provide a low impedance path between VOUT and the load to
minimize voltage drops.
SETTING THE OUTPUT VOLTAGE
The output voltage of the MSK 5044RH is set with a single resistor,
see Figure 1 (Typical Application Circuit). Select the value of R
using the formulas below.
VOUT=VFB*(1+R
R
Given V
TYPICAL APPLICATION CIRCUIT
FB
=2490*((VOUT/V
APPLICATION NOTES
FB
=1.21V Nominal
FB
/2490)
FB
)-1)
FB
FIGURE 1
<=0.4V.
FB
3
SELECTING THE OUTPUT CAPACITOR
The output capacitor filters the ripple current from the internal induc-
tor to an acceptable ripple voltage seen by the load. The primary
factor in determining voltage ripple is the ESR of the output capaci-
tor. The voltage ripple can be approximated as follows:
V
Where I
The typical ESR range for an MSK 5044RH application is between
0.05 and 0.20 ohm. Capacitors within these ESR ranges typically
have enough capacitance value to make the capacitive term of the
ripple equation insignificant. The capacitive term of the output volt-
age ripple lags the ESR term by 90° and can be calculated as fol-
lows:
V
Where:
Select a capacitor or combination of capacitors that can tolerate the
worst-case ripple current with sufficient de-rating. When using mul-
tiple capacitors in parallel to achieve ESR and/or total capacitance,
sharing of ripple current between capacitors will be approximately
equal if all of the capacitors are the same type and preferably from
the same lot. Low ESR tantalum capacitors are recommended over
aluminum electrolytic. The zero created by the ESR of the capacitor
is necessary for loop stabilty. A small amount of ceramic capaci-
tance close to the load to decouple high frequency is acceptable but
it should not cancel the ESR zero.
TYPICAL EFFICIENCY
TOTAL DOSE RADIATION TEST
PERFORMANCE
Radiation performance curves for TID testing will be generated for
all radiation testing performed by MS Kennedy. These curves show
performance trends throughout the TID test process and are located
in the MSK 5044RH radiation test report. The complete radiation
test report will be available in the RAD HARD PRODUCTS section on
the MSK website.
http://www.mskennedy.com/store.asp?pid=9951&catid=19680
P
P
F=Switching Frequency in Hertz
C=output capacitance in Farads
-
-
P
P
=I
(CAP)=I
P
-
P
P
-
*ESR
P
=VOUT*(VIN-VOUT)/(1.65*VIN)
P
-
P
/(8*F*C)
PRELIMINARY Rev. - 1/10