FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34727 - Functional Block Diagram
Integrated Supply
Internal Regulator & Reference
Oscillator
Control
Power MOSFET
Soft Start
Thermal Shutdown
Undervoltage Lockout
Current Limit
Power MOSFET Driver
Integrated Supply
Oscillator
Control
MOSFET
Figure 14. MC34727 Functional Internal Block Diagram
independent of input voltage, output voltage, or load current.
INTEGRATED SUPPLY
The soft-start sequence also occurs upon recovery from any
fault condition.
INTERNAL REGULATOR AND REFERENCE
UVLO
The internal regulator and reference block steps down the
high input voltage to lower voltage, to power all the internal
blocks, and provides the reference voltage for the other
internal blocks.
The UVLO block monitors the input voltage. Once the
input voltage is lower than the falling threshold voltage, this
block turns off the device, to avoid unpredictable circuit
behavior.
OSCILLATOR
CURRENT LIMIT
The current limit block monitors the inductor current. When
the peak inductor current reaches its current limit, this block
turns off the high side MOSFET, to prevent the device and
external components from damage.
The oscillator block provides 2.0MHz clock signal to the
controller.
CONTROL
POWER MOSFET DRIVER
THERMAL SHUTDOWN
The power-MOSFET driver block controls the phase of the
diver signals, and enhances the drive capability of these
signals.
The thermal shutdown block monitors the die temperature.
Once the die temperature reaches its threshold, this block
turns off the device to prevent the further die temperature
rise.
POWER-MOSFET
The power-MOSFET block contains two power
SOFT-START
MOSFETs. One is a PMOS that passes the current from the
input to the output, and the other is an NMOS that provides
the inductor current loop when PMOS is turned off.
The soft-start block controls the output voltage ramp after
the device is enabled, to limit the in-rush current. The start-up
time is internally set to approximately 2.0ms, and is
MC34727
Analog Integrated Circuit Device Data
Freescale Semiconductor
11
FREESCALE [ Freescale ]
