34712 datasheet(13/23 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34712

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

occurred by releasing the drive on the PG pin high,

allowing the signal/pin to be pulled high by the external

pull-up resistor.

TRACKING AND SEQUENCING

This block allows the output of the 34712 to track 1/2 the

voltage applied at the VREFIN pin. This allows the VREF and

VTT voltages to track 1/2 VDDQ and assures that none of them

will be higher than VDDQ at any point during normal operating

conditions. For power down during a shutdown (S5) mode,

the 34712 uses internal discharge MOSFETs (M5 and M6 on

Figure 2) to discharge VTT and VREF respectively. These

discharge MOSFETs are only active during shutdown mode.

Using this block along with controlling the SD and STBY pins

can offer the user power sequencing capabilities by

controlling when to turn the 34712 outputs on or off.

BUCK CONVERTER

This block provides the main function of the 34712: 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 45 mΩ N-channel

power MOSFETs saving board space and enhancing

efficiency. The switching regulator output voltage is

adjustable with an accuracy of less than ±2.0 % to meet DDR

requirements. Its output has the ability to track 1/2 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 34712 is designed to address DDR memory power

supplies. The integrated converter has the ability to both sink

and source up to 3.0 A of continuous current, making it

suitable for bus termination power supplies.

34712 Datasheet(PDF) 13 Page - Freescale Semiconductor, Inc

34712 Datasheet(HTML) 13 Page - Freescale Semiconductor, Inc

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