34717 datasheet(13/25 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34717

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

PROTECTION FUNCTIONS

This block contains the following circuits:

• Over Current Limit and Short Circuit Detection: This

block monitors the output of the buck converters for

over current conditions and short circuit events and

alerts the system control for further command.

• Thermal Limit Detection: This block monitors the

temperature of the device for overheating events. If the

temperature rises above the thermal shutdown

threshold, this block will alert the system control for

further commands.

• Output Overvoltage and Undervoltage Monitoring: This

block monitors the buck converters output voltages to

ensure they are within regulation boundaries. If not, this

block alerts the system control for further commands.

CONTROL AND SUPERVISORY FUNCTIONS

This block is used to interface with an outside host. It

contains the following circuits.

• Shutdown Control Input: An outside host can put the

34717 device into shutdown mode by sending a logic

“0” to the SD pin.

• Power Good Output Signal: The 34717 can

communicate to an outside host that a fault has

occurred by pulling the voltage on the PG pin high.

TRACKING AND SEQUENCING

This block allows the second output of the 34717 to track

the voltage applied at the VREFIN pin in different tracking

configurations. This will be discussed in further details later in

this document. For power down during a shutdown mode, the

34717 uses internal discharge MOSFETs (M8 and M9 on

Figure 2, page 2) to discharge the first and second output

respectively. The discharge MOSFETs are only active during

shutdown mode. Using this block along with controlling the

SD pin can offer the user power sequencing capabilities by

controlling when to turn the 34717 outputs on or off.

BUCK CONVERTER

This block provides the main function of the 34717: DC to

DC conversion from an un-regulated input voltage to a

regulated output voltage used by the loads for reliable

operation. The buck converter is a high performance, fixed

frequency (externally adjustable), synchronous buck PWM

voltage-mode control. It drives integrated 50 mΩ N-channel

power MOSFETs saving board space and enhancing

efficiency. The switching regulator output voltage is

adjustable with an accuracy of less than ±2 % to meet today’s

requirements. The second channel’s output has the ability to

track the voltage applied at the VREFIN pin. The regulator's

voltage control loop is compensated using a type III

compensation network, with external components to allow for

optimizing the loop compensation, for a wide range of

operating conditions. A typical Bootstrap circuit with an

internal PMOS switch is used to provide the voltage

necessary to properly enhance the high-side MOSFET gate.

The 34717 has the ability to supply up to 5.0 A of

continuous current from each channel, making it suitable for

many high current applications.

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