power integrity

7/29/2019 power integrity

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Power Integrity analysis techniques toget the best system performance at

the cheapest cost.

Power Integrity analysis techniques toget the best system performance at

the cheapest cost.

Sigrity, Inc.Sigrity, Inc.

EDAPS2009 Shenzhen, ChinaEDAPS2009 Shenzhen, China

Dec 2Dec 2ndnd, 2009, 2009

Tanit Virutchapunt

[email protected]

Power Integrity Specialist


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2

What is the best power plane performance?

What is bestDCpower plane performance? Devices see voltage closet to nominal voltage

Low IR dropWell balanced DC voltages among devices on the same rail

Low Temperature Rise on Metal Low Current Density

Power Efficiency Low Power Loss

What is bestDCpower plane performance? Devices see voltage closet to nominal voltage

Low IR dropWell balanced DC voltages among devices on the same rail

Low Temperature Rise on Metal Low Current Density

Power Efficiency Low Power Loss

What is best AC power plane performance? Low noise Low loop inductance Low and Flat impedance

What is best AC power plane performance? Low noise Low loop inductance Low and Flat impedance


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3

Best Performance VS Cost

$$

BESTBEST

Best power plane performance comes with a price. How to get the best powerplane without adding extra cost to the design is challenging to designer.


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4

What to look for in DC analysis?What to look for in DC analysis?


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IR drop target

Poor design

Total

margin

AC noise

margin

IR drop

AC noise margin

IR drop

Totalmargin

Good design

How to budget IR drop and AC noise margin?

IR drop margin should be less than AC noise margin since the AC

noise usually a lot harder to be controlled in the margin.


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6SIGRITY Confidential

Excessive IR drop due to narrow and long traces

criteria 66mV (2%)Voltage refdes Breif description Max current (A) IR drop (mV)

+3.3VCS U3_CP1 P6 0.250 -160U2_CP0 P6 0.250 -115

J23_GX1 GX CARD 0.218 -113

J24_GX2 GX CARD 0.218 -111J54_DASD DASD backplane 0.006 -29J49_RAID RAID card 0.006 -13U18_FSP1 FSP1 chip 0.51 -2.0J25_ENET0 ENET card 0.006 -1.4U31_HMC0 HMC chip 0.012 -1.2

U30_HMC0 HMC chip 0.012 -1.0

IR drop target is 66mVIR drop target is 66mV

159% over the target159% over the target

Functional problem can becaused by too much IRdrop

even in the low power .


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Excessive IR drop due to DC resistance on passive

components

There is no such thing as zero ohm resistor.


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Excessive IR drop on vias

10mV drop

2.4A flows into each via

5mV drop on each via

VRM

IC


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Understand Temperature Rise on coppercaused by current flow on the copper

Thickness = 0.5oz

Current VS AreaCurrent Density VS Width

IPC-2152 spec gives relationshipbetween Temperature Rise VS

Cross-session of copper.

Trace has an uniform cross-session thusIPC spec is straight forward.Shape has different cross-sessions atdifferent locations, IPC spec is no longerstraight forward.


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Same Current

5A 5A

100 sq.mil30c

500sq.mil

5c

With the same current flow on the plane, narrower plane will cause more heat.


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SameTemperature

5A 12A

100sq.mil

30c

500 sq.mil30c

To keep the same temperature rise on copper, wider plane can have more current.


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Same CurrentDensity

30mA/mil^

2

30mA/mil^

2

100 mil9c

500 mil32c

With the same current density flowing on the plane at different width,the wider plane will cause more heat on the copper since there is less

area heat can dissipate.

heat

heat


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Same Temperature

28mA/mil^2

100 mil

30c

500 mil

30c

56mA/mil^2

To keep the same temperature rise on copper, narrower plane can have highercurrent density.


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Smoke or Fire is number#1 concern,

what would happen if this design were built?

Temperature Rise = 300c


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Localize Heat in low power netThis low power rail can cause excessivecurrent density on the copper plane becauseof the narrow shape.


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Power Loss

High power loss area

Power Loss is important in all designsespecially products that use battery.


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Devices should see voltage closet to a nominal voltage

1A

2A

4A

5A

0.5A

10A1A

1A

1A 2A

4A

0.5A 0.5A 0.5A

0.5A 0.5A 0.5A 0.5A

VRM

With DC resistance on the plane that causes IR drop from power source to

devices, actual voltages at the devices will be less than the nominal voltage.


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Power Source location and voltage output setting

are important

1A200mV drop

1.5V1)

200mV drop

1A2)

1.7V

1A 1A

1A

52mV on each directionFrom regulator

1.552V

6)

1A

150mV drop 100mV

1A3)1.75V

3L/4 L/4

1A1A

75mV drop4)1.575V

75mV drop

L/2 L/2

Power Source

Device

60mV on each directionFrom regulator

1A 1A

2A

1.56V

7)

Current Flow

5) I2R1R2

L2 L1

I1

1.3V

1.5V

1.5V

1.5V 1.5V

VRM is at a location where R2*I2 = R1*I1

1.5V 1.5V

1.5V

1.5V 1.5V

1.5V

1.65V


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Impossible to place power source in the best

location for all devices

Mechanical requirement forcesconnectors to this place


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How to improve the power planeperformance without adding extra cost?

How to improve the power planeperformance without adding extra cost?


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How to identify copper areas that need to be

improved when DC voltage is failing?

Plane Current Density PlotPlane Current Density Plot

1st

2nd

3rd

VRM

Sink 1

Sink 0Sink 3

Sink 4Sink 5

Sink 2

5.25 V

4.75V

Plane Voltage Distribution PlotPlane Voltage Distribution Plot

Underflow color, Voltage below 4.75V

Improving high current density area can help three things:Improving high current density area can help three things:1. Reduce Resistance in this area2. Reduce current density which will make copper cooler

3. Cooler copper will make copper resistivity lower which will make evenless resistance in this area

Current density plot is used to identify areas

that should be used to add copper toimprove IRdrop.


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How to improve Power Efficiency?

Top L1 L2 Bottom Total %Trace 15.75 0 0 0 15.75 2Via 8.48 0.3 0 0 8.78 1Plane 73.94 45.78 666.06 47.67 833.45 97

Total power loss 857.98 mW

1A each

5A3A

RegulatorHigh Power Loss area

Identify high power loss areas in the design.Power Loss plot can be used to pinpoint high power loss area.


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How to find the via that will trigger field failure?


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Highest current vias from Thousand of vias

5A

Identify vias that have high current flow.Via Current plot can be used to pinpoint vias with high current flow.


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Optimize VRM sense line

to get the best DC voltage balance


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VRM

10A

Load sees 100mV belownominal voltage (1V)

Without feedback voltage sense to VRM

VR

M10A

Voltage Senselocation

Load now seesnominal voltage (1V)

With feedback voltage sense to VRM

Remote Sense Line is needed when the power

source cant be placed in the desired location


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VRM10A


1A

This device sees too highvoltage

This device sees perfect

voltage

1A

VRM

10A


This device sees too lowvoltage

This device sees perfectvoltage

Where to place the Sense Line when there are

more than one device on the power rail?

1V 1V1.08V

0.93V


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Chip1(10A)

Chip2(1A)

Chip1

Chip2

A typical way to find the optimal sense location


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A better way to find the optimal senselocations

[Patent Pending - U.S. Patent Application No. 12/468,807]


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Objective = minimizing voltage differences between actual voltage at devices and nominal voltage

With this example, Objective = min{ (Vdevice1 - Vnominal1)2+(Vdevice2 - Vnominal2)

2+(VdeviceN - VnominalN)2}

1) Start without any sense line

2) Determine the optimal output voltage level of VRM that meets the objective

3) With using the VRM output voltage level from (2) search meshes that have the nominal voltage.

4) The meshes that have the nominal voltage is the optimal sense locations.

5) Optimal Sense Location Tolerance maybe used to display sub-optimal sense locations.

Note that the rectangular meshes are used in the picture above to simplify the drawing and explanation.

Device1

VRM Device2

Vnominal

Vdevice1

Vdevice2

Vout_VRM

Optimal VRMOutput Voltage

Voltage Level

[Patent Pending - U.S. Patent Application No. 12/468,807]


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Optimal Sense Locations (Green)

1A10A


0.965V

1.035V

35mV

35mV


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Example

VRM connector 11 devices, 1A each

Where are the Optimal Sense Locations ?


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No sense line

Sense at U1

Optimal Sense Location

Sense here

Sense here


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34What to look for in AC analysis?What to look for in AC analysis?


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Flat and Low Power Plane Impedance

Regulator

BulkCapacitors

BoardDecaps

P

kgdecaps

Frequency (Log scale)PowerplaneImpedan

ce

On-chip capacitance

~1KHz

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power integrity