Power Delivery System In Motherboards

Power Delivery System in Motherboards In this article we will discuss Power Delivery system in Motherboards . For more in depth training , join PCLR Course of chiptroniks or you can also buy our course materials with online support.

Power Delivery Power delivery—Why & 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: <2A, example: Clock chip, LAN… Medium power device : between 2A to 50A: example: Fan, DIMM, Chipset High 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 example—ICH 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 3—PCI-E slot Power requirement

This voltage supply to add in PCI-e card, Card is required to design within this limit Overall Power Delivery Example–Thurley

Overall Power Delivery Example2—Romley

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 Types—Single 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 Types—Multi Phase

VR example Switching VR—single phase 12V to DDR 1.5V

Switching VR—multi phase 12V to CPU Vcore

Linear VR–3.3V to IOH 1.8V

Linear VR–3.3V to IOH 1.8V

VR placement & layout CPU VCCP VR placement

CPU VCCP VR copper planar