Power Delivery System in

Motherboards

In this article we will discuss Power Delivery system in Motherboards . For more in depth training , join

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Power Delivery

Power deliveryWhy & How

Why: Motherboard components need one or multiple stable and clean DC power to work

correctly

How: (1) Power Supply directly to motherboard components (2) for the power which Power

Supply can not provide directly, DC to DC power converter on the motherboard converts the

power and provide to components

Voltages type needed

Postive DC Voltage: generally between 0V to 12V, generated by DC-DC converter 0.75V,

1.5V, 1.1V or directly from power supply, like 3.3V, 5V, 12V

Negative DC Voltage: typically -12V

Motherboard voltage normally ranges from -12V to 12V

Tips: General speaking

Higher speed component=> lower voltage needed

(especially for IO function)

Current types needed

Simple answer: Power/voltage=current needed

Low power device: 50A, example: processor, high power DIMM, high end Graphic card etc

The low/medium/high is just general category, no standard

Tips: High current device has higher requirements on the PCB

Space, layers, cost, copper thickness, all in all, bigger current,

more design challenge for power designer and CAD engineer

Examples: components Voltage & Current

Processor: 1.0V to 1.5V, 50A to 150A, 130W

DIMM: 1.8V/0.9V for DDR2, 1.5V/0.75V for DDR3, 20A to 40A, 50-100W

Chipset: 1.1V, 10-20A, 5W to 30W

Onboard device: 1.5A, 1-2A, 3.3V, 0.5W to 5W

PCI slot: PCI slot: 12V, 0.5A, 3.3V, 3A, 5V, 1A, 15W, 25W, 75W or more

Fan connector: Depends on fan used, ranges from 0.1A to 5A, 5W to 50W

Tips

Normally 1 Components need multiple voltage rails

depends on what function needed, such as ICH need

1.5V, 3.3V, 1.8V, more function, more voltage rails needed

For example: ICH has more voltage rail than CPU

due to ICH has more functions

Voltage types by components function

Components may need several voltages by functions: below is general category

(CPU), VDD (DIMM), occupy most the power pin of the components

IO Voltage: Core Voltage: Main voltage for core logic, most of the power consumes on the

main voltage) for the core function, example VCCP Voltage for BUS, example: CPU Vtt

Reference Voltage: voltage used for signal sampling

Analog voltage: Some components include analog function, so analog voltage needed, such as

Video, PLL circuit, analog voltage require to be clean ! Need to be separated from normal

voltage

Components may contain 1 or more type of voltages depends on

Function needed, such as ICH need all 3 above voltages

Voltage types by power state

Some voltage are only required for certain power state

Normal Voltage: Voltage existing when the system is at S0 to S2 state, which means system is

at ON state, like CPU main power, fan power, which is main power for the system

Battery Voltage: Voltage existing when the system at AC OFF status, it is powered by onboard

battery. Example RTC clock

Standby Voltage: voltage always exists at S0 to S5 state (DC OFF), which means system at DC

off state, AC power code is plugged, it is used for board power on/off logic and wake up function

and some management function and other functions need to be functional at main power off

state, remember, when AC power cord inserted, standby voltage exists !!

Aux Voltage: Voltage switch by between Standby voltage and same Normal Voltage, the main

reason of Aux voltage is the function is needed through S0 to S5 state, but standby power can not

provide enough current at S0-S2 state due to the device consume more power at S0-S2 state then

S3-S5 state, so voltage need switch from standby voltage to normal voltage to get enough current

, example: DDR voltage 1.8V, when system is at S3, the Aux voltage comes from 1.8V standby

power to keep DIMM refresh, after power on to S0 state, Aux voltage switch to 1.8V normal

voltage to support DIMM normal read/write (which consume much more current)

Components may contain 1 or more type of voltages depends on

Function needed, such as ICH need all 4 above voltages

Let us take a look at a real sample-Chipset

G41 MCH (north bridge) function/power mapping

(not exactly correct, just for example)

Another exampleICH 10

ICH 10 has require more than 20 voltage rails !! due to lots of functions integrated in ICH 10

Refer to product EDS for pin definition and power requirement

Example 3PCI-E slot Power requirement

This voltage supply to add in PCI-e card, Card is required to design within this limit

Overall Power Delivery ExampleThurley

Overall Power Delivery Example2Romley

Motherboard Input Power

Now, we know what kind of power (voltage/Current) needed by components, but where does it

come from? Answer: from Power Supply, directly or indirectly

Power Supply Output (motherboard input)

Power Supply output type:

Multiple Output:

Power supply has multiple DC output rail (NOT connector)

Popular 12V, 5V, 3.3V, -12V, 5VSB and other voltage

12V output may have separate rails, like 12V1, 12V2, etc for 240VA protection

Single output: 12V or other voltage only

Power supply has single DC output, 12V is most popular

Battery is single output example

Power Supply output interface:

Connector: board to board or board to cable connector

PCB gold finger: PCB to mating connector

Tips:

Most of single output PSU also has standby output, like 5VSB

Power Supply Output example 1

Desktop ATX PSU : Multiple output, cable + connector

Server EPS12V : Multiple output, cable + connector

Power Supply Output example 2

Notebook Adapter:

19V Single output, connector, connect to motherboard directly

Hotswap module :

12V single output, gold finger and board to board connector

Note:

normally it also has 5VSB output

Motherboard side interface

General Rule: mate with power supply output

Connector

Gold finger mating connector

Board to Board connector

Motherboard power rails & Power supply rails

As we talked before, multiple-output power supply has multiple output, each rail will have

current limit, and each rail are separated below is example

Same for motherboard, motherboard will also have multiple rails, like 3.3V, 5V, 12V1,

12V3a, each rail has current requirement, so we need to mapping the power supply rails to

motherboard rails to make sure both power supply & motherboard rails can be met

Next page is example

Rail mapping Example

Power supply connector/rail mapping

Caution:

Power supply rail can be separate to support multiple

motherboard rail, but reverse is NOT allowed!, otherwise it will

Short power supply rails and cause protection

DC to DC converter

So far, we know how power supply provide voltage rail to motherboard, like 12V, 5V 3.3V, etc

by connectors or PCB gold finger or other method, but for the other voltage power supply can

not provide, like 1.1V, 1.5V, 0.8V, we need DC to DC converter on the motherboard to convert

the power supply voltage to the voltage we needed

DC to DC converter also called Voltage regulator (VR)

DC to DC converter (VR) types

(1) Linear voltage regulator

-Low current

-Low efficiency

-Low cost

-Simple

-Clean (little noise)

-High current

-High efficiency

-High cost

-Complex

-High noise

Linear VR

-

Simple & Clean (little noise)

-Low current

-Low voltage drop

-Low efficiency

-Low cost

(1) Why low current and low voltage drop?

vdrop on the VR= Vout-Vin, so the power loss = I x Vdrop, for example: Vin=3.3V,

Vout=1.5V, 2A, so the power loss on converter is (3.3-1.5)x2=3.6W, assume 50C/W, so the

temp rise will be 150C, which is burn the components, so only low current and low voltage is

allowed, Linear VR only support low current requirement

(2) Why low efficiency?

The efficiency= output power/input power, obvious, it is low efficiency due to the power loss on

the converter is big, the bigger difference between Vin and Vout, the lower efficiency is.

(3) Why simple & clean & low cost

It is simple & due to just a few components needed

It is clean due to no switch components, it is easier to place & layout the linear VR

Switching VR TypesSingle Phase

-High current

-High efficiency

-High cost

-Complex

-High noise

Basic working principal is by control the mosfet PWM value to adjust the output voltage,

Vout/Vin=PWM%, for example: 12V to 1.5V, PWM=12.5%

Switching VR efficiency is between 80 to 98% depends on VR design, the main power loss is

VR Mosfet switching & conduct loss

It can handle high current due to high efficiency

High cost /complex is obvious: it need chip, mosfet, inductor, capacitor

High noise: due to switching method and mosfet switching, it has much higher noise than linear

regulator

We will NOT discuss how VR works here, refer to VR training slides

if you are interested, Overall speaking, VR is a complex technology

Switching VR TypesMulti Phase

VR example

Switching VRsingle phase 12V to DDR 1.5V

Switching VRmulti phase 12V to CPU Vcore

Linear VR3.3V to IOH 1.8V

Linear VR3.3V to IOH 1.8V

VR placement & layout

CPU VCCP VR placement

CPU VCCP VR copper planar