34716 データシートの表示（PDF） - Freescale Semiconductor

部品番号

コンポーネント説明

メーカー

34716

1.0 MHz Dual Switch-Mode DDR Power Supply

Freescale Semiconductor 

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

In modern microprocessor/memory applications, address

commands and control lines require system level termination

to a voltage (VTT) equal to 1/2 the memory supply voltage

(VDDQ). Having the termination voltage at midpoint, the power

supply insures symmetry for switching times. Also, a

reference voltage (VREF) that is free of any noise or voltage

variations is needed for the DDR SDRAM input receiver,

VREF is also equal to 1/2 VDDQ. Varying the VREF voltage will

effect the setup and hold time of the memory. To comply with

DDR requirements and to obtain best performance, VTT and

VREF need to be tightly regulated to track 1/2 VDDQ across

voltage, temperature, and noise margins. VTT should track

any variations in the DC VREF value (VTT = VREF +/- 40 mV),

(See Figure 4) for a DDR system level diagram.

The 34716 supplies the VDDQ, VTT and a buffered VREF

output. To ensure compliance with DDR specifications, the

VDDQ 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 VTT

output. The same internal voltage is also buffered to give the

VREF 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/

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 VREF output helps its immunity against noise and load

changes.

The 34716 utilizes a voltage mode synchronous buck

switching converter topology with integrated low RDS(ON)

(50 mΩ) 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

flexibility and optimization over the operating conditions and

can operate at up to 1.0 MHz to significantly reduce the

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

continuous current from the other output. It provides

protection against output overcurrent, overvoltage,

undervoltage, and overtemperature 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.

VDDQ

VTT

VDDQ

RT

RS

BUS

VREF

DDR Memory Controller

DDR Memory Input Receiver

Figure 4. DDR System Level Diagram

FUNCTIONAL PIN DESCRIPTION

BOOTSTRAP INPUT (BOOT1, BOOT2)

Bootstrap capacitor input pin. Connect a capacitor (as

discussed in Bootstrap capacitor on page 20) 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.

Analog Integrated Circuit Device Data

Freescale Semiconductor

34716

11

Share Link: