MC34164-3 Datasheet, PDF (13/23 Pages) Freescale Semiconductor, Inc – 3.0 A 1.0 MHz Fully Integrated DDR Switch-Mode Power Supply

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 V_REF and
V_TT voltages to track 1/2 V_DDQ and assures that none of them
will be higher than V_DDQ 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 V_TT and V_REF 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.
Analog Integrated Circuit Device Data
Freescale Semiconductor
34712
13