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FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
In modern microprocessor/memory applications, address
commands and control lines require system level termination
to a voltage (V TT ) equal to 1/2 the memory supply voltage
(V DDQ ). Having the termination voltage at midpoint, the power
supply insures symmetry for switching times. Also, a
reference voltage (V REF ) that is free of any noise or voltage
variations is needed for the DDR SDRAM input receiver,
V REF is also equal to 1/2 V DDQ . Varying the V REF voltage will
effect the setup and hold time of the memory. To comply with
DDR requirements and to obtain best performance, V TT and
V REF need to be tightly regulated to track 1/2 V DDQ across
voltage, temperature, and noise margins. V TT should track
any variations in the DC V REF value (V TT = V REF +/- 40 mV),
(See Figure 6 ) for a DDR system level diagram.
The 34716 supplies the V DDQ , V TT and a buffered V REF
output. To ensure compliance with DDR specifications, the
V DDQ line is applied to the VREFIN pin and divided by 2
internally through a precision resistor divider. This internal
voltage is then used as the reference voltage for the V TT
output. The same internal voltage is also buffered to give the
continuous current from the other output. It provides
protection against output over-current, over-voltage, under-
voltage, and over-temperature conditions. It also protects the
system from short-circuit events. It incorporates a power
good output signal to alert the host when a fault occurs.
For boards that support the Suspend-To-RAM (S3) and
the Suspend-To-Disk (S5) states, the 34716 offers the STBY
and the SD pins respectively. Pulling any of these pins low,
puts the IC in the corresponding state.
By integrating the control/supervisory circuitry along with
the Power MOSFET switches for the buck converter into a
space-efficient package, the 34716 offers a complete, small-
size, cost-effective, and simple solution to satisfy the needs
of DDR memory applications.
Besides DDR memory termination, the 34716 can be used
to supply termination for other active buses and graphics card
memory. It can be used in Netcom/Telecom applications like
servers. It can also be used in desktop motherboards, game
consoles, set top boxes, and high end high definition TVs.
V REF voltage at the VREFOUT pin for the application to use
without the need for an external resistor divider. The 34716
provides the tight voltage regulation and power sequencing/
V D DQ
V TT
V DD Q
tracking required along with handling the DDR peak transient
current requirements. It gives the user a complete DDR
power supply solution with optimum performance. Buffering
the V REF output helps its immunity against noise and load
changes.
The 34716 utilizes a voltage mode synchronous buck
R S
BUS
R T
V REF
switching converter topology with integrated low R DS(ON)
(50 m ? ) N-channel power MOSFETs to provide an output
voltage with an accuracy of less than ±2.0% output voltage.
It has a programmable switching frequency that allows for
DDR Memory Controller
DDR Memory Input Receiver
flexibility and optimization over the operating conditions and
can operate at up to 1.0 MHz to significantly reduce the
Figure 6. DDR System Level Diagram
external components size and cost. The 34716 can supply up
to 5.0 A from one output and sink and source up to 3.0 A of
FUNCTIONAL PIN DESCRIPTION
BOOTSTRAP INPUT (BOOT1, BOOT2)
Bootstrap capacitor input pin. Connect a capacitor (as
discussed in Bootstrap capacitor on page 21 ) between this
pin and the SW pin of the respective channel to enhance the
gate of the high-side Power MOSFET during switching.
POWER INPUT VOLTAGE (PVIN1, PVIN2)
Buck converter power input voltage. This is the drain of the
buck converter high side power MOSFET.
SWITCHING NODE (SW1, SW2)
Buck converter switching node. This pin is connected to
the output inductor.
POWER GROUND (PGND1, PGND2)
Buck converter and discharge MOSFETs power ground. It
is the source of the buck converter low side power MOSFET.
COMPENSATION INPUT (COMP1, COMP2)
Buck converter external compensation network connects
to this pin. Use a type III compensation network.
34716
Analog Integrated Circuit Device Data ?
12
Freescale Semiconductor
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