MC34726(2008) 查看數據表（PDF） - Freescale Semiconductor

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MC34726
(Rev.:2008)

300mA High Efficiency Low Quiescent Current Synchronous Buck Regulator With Z-mode

Freescale Semiconductor 

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

MC34726 - Functional Block Diagram

Integrated Supply

Internal Regulator & Reference

Oscillator

Control

Thermal Shutdown

Soft Start

Undervoltage Lockout

Current Limit

Power MOSFET Driver

Power MOSFET

Integrated Supply Oscillator Control MOSFET

Figure 14. 34726 Functional Internal Block Diagram

INTEGRATED SUPPLY

INTERNAL REGULATOR AND REFERENCE

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.

OSCILLATOR

The oscillator block provides 2.0MHz clock signal to the

controller.

CONTROLLER

THERMAL SHUTDOWN

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.

SOFT-START

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

independent of input voltage, output voltage, or load current.

The soft-start sequence also occurs upon recovery from any

fault condition.

UVLO

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.

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.

POWER-MOSFET DRIVER

The power-MOSFET-driver block controls the phase of the

diver signals and enhances the drive capability of these

POWER-MOSFET

The power-MOSFET block contains two power

MOSFETs. One is a PMOS that passes the current from the

input to the output, and the other one is an NMOS that

provides the inductor current loop when PMOS is turned off.

Analog Integrated Circuit Device Data

Freescale Semiconductor

34726

11

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