MSK5052RH M. S Kennedy, MSK5052RH Datasheet - Page 3

• Manufacturer Part Number: MSK5052RH
• Description: Rad Hard 4.5a 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 regulator. Very high di/dt is seen at VIN during
switch on and off transitions. High frequency decoupling ca-
pacitors 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, 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 fre-
quency reduces to approximately 100KHz at VFB<=0.4V.
SIGNAL GND - The SIGNAL GND 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. Tie
the SIGNAL GND to the POWER GND as close to the case
as possible.
POWER GND- The power ground provides the high current
load return path to the MSK 5052RH's internal catch diode.
High speed switching transition occur on the power ground
with every switching cycle. The load return current commu-
tates between the input bus return and the POWER GND
pins. Place a minimum of 0.1uF to 1.0uF of high frequency
ceramic capacitance physically close to the POWER GND
and VIN pins to maximize performance.
SHDN - The SHDN (shutdown) pin has two shutdown func-
tions. 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.
BOOST- The BOOST pin connects to an internal diode-ca-
pacitor network that supplies voltage to the power switch
driver circuit. This elevated voltage level ensures the power
switch saturates. A minimum of 3V is required for proper
operation. This can be power from the input power supply,
the regulator output , or a seperate supply if desired. Overall
power dissipation increases slightly with higher BOOST volt-
ages. For a typical 5V input connect the BOOST pin to the
input source. For a 12V input to 3.3V output regulator, effi-
ciency may be improved by 1 to 2 percent by connecting the
BOOST pin to the regulator output.
VOUT - VOUT is the output of the regulator. External capaci-
tance between the VOUT pin and GND is required to main-
tain stability and minimize output ripple voltage, see "Select-
ing The Output Capacitor." Provide a low impedance path
between VOUT and the load to minimize voltage drops.
APPLICATION NOTES
3
COMP - The COMP pin is the output of the error amplifier
and the input of the peak current comparator. This pin is
typically used for frequency compensation but can also be
used as a current clamp or as an override to the internal
error amplifier control. The pin voltage is typically around 1V
at light load and 2V at heavy load. Driving the pin low will
shut down the regulator. Driving it high will increase the out-
put current. The current into the COMP pin must be limited
to 4mA when driving it high.
SYNC - The SYNC pin is used to synchronize the oscillator to
an external clock. It is logic compatible and can be driven to
any frequency between the free run frequency (500KHz nomi-
nal) and 1MHz. At frequencies greater than 700KHz the risk
of sub harmonic oscillation increases for applications with
duty cycles greater than 50%. This is the result of the mag-
nitude of the slope compensation ramp generated by the con-
trol IC being limited at higher frequencies. The duty cycle of
the input signal must be between 10% and 90% to ensure
proper synchronization. Tie the SYNC pin to GND if it is not
used.
SETTING THE OUTPUT VOLTAGE
The output voltage of the MSK 5052RH is set with a simple
resistor divider network: see Figure 1 (Typical Application
Circuit). Select the resistor values to divide the desired out-
put down to equal VFB (1.21V nominal) at the FB pin. Use a
2.5K or lower value resistor for R2 to keep output error due
to FB pin bias current less than 0.1%.
VOUT=VFB*(1+R1/R2)
R1=R2*((VOUT/VFB)-1)
Given VFB=1.21V Nominal
TYPICAL APPLICATION CIRCUIT
FIGURE 1
PRELIMINARY Rev. - 7/10