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Module Flow 11.1 Circuit Protection Overview Module Flow 11.1 Circuit Protection Overview

Module Flow 11.1 Circuit Protection Overview - PowerPoint Presentation

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Module Flow 11.1 Circuit Protection Overview - PPT Presentation

112 Circuit Protection Device Features and Options 113 Common Design Errors 114 Common Test Errors 115 eFuses 115a eFuse Overview 115b eFuse vs Fuse 115c eFuse vs Polyfuse 1 Circuit Protection Fundamentals ID: 675652

power fet load protection fet power protection load limit current circuit soa efuse supply fuse trip ilimit limiting design

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Slide1

Module Flow

11.1 Circuit Protection Overview 11.2 Circuit Protection Device Features and Options11.3 Common Design Errors11.4 Common Test Errors11.5 eFuses11.5a eFuse Overview11.5b eFuse vs. Fuse11.5c eFuse vs. Polyfuse

1Slide2

Circuit Protection Fundamentals

11.1 Circuit Protection OverviewSlide3

Circuit Protection – What is it ?

Many things with many namesInrush ControlHotswapHotplugCurrent LimitingElectronic Circuit BreakerShort Circuit ProtectionSoft StartOver Voltage Protection (OVP)

eFuse

Load Power Limiting

FET SOA Limiting ( Protecting the Protector ! )

Reverse Current Protection (ORing)

Often Required for Agency RatingUL, CSA – North AmericaEN, IEC, (CENELEC) – EuropeCCC Mark (CNCA) - China

~ the same functions

3Slide4

Circuit Protection – What is it ?

Circuits designed specifically to….Prevent Fire ! --“Keep the smoke in!”Keep small problems from growing bigMinimize damage by quickly isolating failuresPrevent potentially disruptive power bus disturbancesOne small transient can take down/reset an entire system

What Gets Protected ?

LOAD

POWER FET

CONNECTORS

SUPPLY

4Slide5

Circuit Protection – Where Is It Used ?

Telecom Equipment

Datacenters / Servers

Storage / HDD, SSD, Midplanes

Industrial Control

24 or 48 V typically

Tower Mounted Antennas

Merchant Power

5Slide6

Circuit Protection – The Basic Parts

Most Common ElementsLocation..Sometimes on the Load Side of the Connector

Sometimes on the Supply Side of the Connector

LOAD BOARD

BACKPLANE

Element

for controlling the FET

Element

for sensing

current

Element for modulating

current

6Slide7

Thank you!

7Slide8

Circuit Protection Fundamentals

11.2 Device Features and OptionsSlide9

9

“End customers can’t make you design in protection circuits but they can make you wish you had.”

– Design review wisdom Slide10

Device Features/Options

Some of the ChoicesFETInternal or ExternalInrush controldV/dT, or di/dTCurrent LimitAlways, Never, or just at startupFault responseLatch off or RetryShort Circuit Response

Latch Off or Retry

Control

I2C or Analog Control

Outputs

Power Good, Fault, FET Fault

ILIMIT Accuracy20% Standard, 10% Pretty Good, 5% Very GoodFET SOA protection.. Or notAllows use of smaller FET and provides very high survivabilityCurrent Indicator Output (IMON)Analog or Digital Output ?Digital Output requires internal ADC and typically includes PIV MonitoringORing ControlLinear or Hysteretic10Slide11

Device Features/OptionsInternal FET vs. External

FET11Internal FET

External FET

Highly Integrated

Few External Parts

Internal sense FET

Built it Power Limiting

Extremely well protected Compromises are madeFET process vs. Analog processFET package vs. Analog packageRequire careful thermal design

Generally not found in app > 5 A

Flexible R

DSON

(Designers Choice)

More feature options

No limit on upper current limit

Generally more accurate

More external parts

R

SENSE, FETRS, CS for configurationLarger foot printSlide12

Device Features/Options

FET SOA Protection

One of the least understood but most appreciated features

Allows use of smaller, less expensive FETs

Analog multiplier calculates P

DIS_FET

in real time and compares result to PROG pin

If PLOAD > PROG then gate drive reduced to lower ILOAD and PFETTI is now the ONLY manufacturer to offer true Power Limiting !12Slide13

Device Features/Options

FET SOA ProtectionDynamically adjusts ILIMIT to be approximately proportional to 1/(VDS)2Limits PDIS of FET

to programmed

limit

TPS2420 Startup into 15 Ω, 700 μF

I

LOAD

V

OUT

TPS2420 Limits FET P

DIS

< 5 Watts

P

DIS

V

OUT

I

LOAD

Orange

=

Violet

x

(V

IN

– Blue)

P

DIS

=

I

LOAD

x

V

DS

13Slide14

Device Features/Options Power Limiting – Startup into overload

responseSOA protection keeps FET safe even when starting up into a severe overloadFault timer limits T(ime) factor of SOASome competitive devices will reduce ILIMIT over a limited range and with limited protection.

ONLY TI has true FET SOA Power Limiting built into the Hotswap Controller !!

!

P

DIS

V

OUT

I

LOAD

C

T

TPS2420 Startup into overload

14Slide15

Positive Low Voltage Protection

TI Device Portfolio Sample

PART

Input Range

Package

V

THRESH

(mV)

I

LIMIT

Int. FET

SOA

OV

I2C

PG

Imon Acc.

TPS2420

3 to 20

QFN16 (4x4mm)

Internal FET

R

DSON

= 30 m

W

I

LIMIT

= ±10% @ 2 A

Always

Yes

Yes

No

No

Lo

17%@2A

TPS2590

QFN16 (4x4mm)

-

N/A

TPS2421-1/2

SOIC8

Lo

TPS24720

2.5 to 18

QFN16 (3x3)

Prog

Startup Only

No

Yes

Yes

No

Lo

Prog

TPS24710/1/2/3

MSOP10

25 ± 10%

Yes

No

l/l/h/h

N/A

TPS24700/1

MSOP8

No

No

Lo

LM25066/A

2.9 to 17

LLP24 (4x5mm)

25 ± 10%

46.5 ± 11.8%

Always

No

Yes

Yes

Yes

Hi

2.40%

LM25066I/AI

LLP24 (4x5mm)

1.00%

LM25069-1/2

MSOP10

50 ± 10%

No

N/A

LM25061-1/2

MSOP10

50 ± 10%

No

TPS2480/1

9 to 26

PW20

50 ± 10%

Yes

0.5%

TPS2482/3

9 to 36

0.5%

15Slide16

Typical Inrush/OCP Design Steps

Select RSENSE to set ILIMIT and IFASTTRIP

I

LIMIT

= V

TH

/RSENSE - VTH typically 25 – 50 mVSimplest controllers have fixed VTH

High VTH → Better Accuracy but Higher I2R LossesFast trip – (Short Circuit) threshold usually 1.5x -3x ILIMIT Level Select CFAULT to get desired TFAULT Set TFAULT long enough to allow all downstream caps to charge (TCHARGE)before time outTCHARGE ~ CV/I (C = Bulk Cap, V = VOUT, I= ILIMIT )Set TFAULT as short as reasonable to minimize FET stress during overcurrent eventsEnsure that TFAULT x VIN X I

LIMIT is within SOA curveSelect FET that can withstand TFAULT x V

IN

x I

LIMIT

x ~1.5 …..SOA !!

Set FET SOA Power Limit on devices so equipped

Design tools available for some devices - check webpage

TPS24700/10/20, TPS2490/1/2/3, TPS2480/1, LM5064/6/7/9, LM25061/6/9

16Slide17

Questions To Ask During Design

Will a load get plugged into a live socket?Will a load get unplugged from a live socket?Is it OK for supply to collapse if one load shorts?Are multiple loads connected to a common supply?OK for all loads to shut off if one load shorts?

Do loads need ability to ride through transients?

Do loads needs protection from voltage surges?

Do loads have large capacitance on the inputs?

Are multiple supplies powering the load or bus?

17Slide18

Thank you!

18Slide19

Circuit Protection Fundamentals

11.3 Common Design ErrorsSlide20

Common Design Errors

SOA of FET too SmallLayout IssuesInadequate Transient Protection20Slide21

SOA of FET Too Small

I

DS

Drain to Source Current

10

3

10

2

10

1

10

0

10

-1

10

-2

10

-2

10-1 100 101 10

2V

DS

Drain to Source Voltage

V

DS_MAX

I

D_MAX

R

DSON

1 ms

10 ms

100 ms

1 s

DC

SOA = Safe Operating Area

SOA Chart – Every FET has one

Defines Bounds of FET Operation

V

DS_MAX

= Vertical Limit

I

D_MAX

= Horizontal Limit

R

DSON

limits I

D

at lower voltages

Theoretical

P

MAX

= 3000 W

Fault Time Is Critical

Longer Fault time means bigger FET

Shorter Fault Time allows higher peak power

Most Stressful FET Events

Startup into short

Shorted load while under full load

Putting FETs in parallel does NOT improve dynamic SOA !!!

21Slide22

SOA of FET Too Small

Example - 12 V, 50 A Server

10

3

10

2

10

1

10010-1

10

-2

10

-2

10

-1

10

0

101 102

VDS Drain to Source Voltage

IDS Drain to Source Current

1 ms

10 ms

100 ms

1 s

DC

Without Power Limiting

P

MAX

= I

LIMIT

x V

SUPPLY

= 600 W

T

SOA_MAX

= ~800 us

With Power Limiting

P

MAX_LIMITED

= 50 W

As V

DS

increases I

LIMIT

is reduced

T

SOA_MAX

= 10 ms

Smaller FET can be used

@ 50 A will start limiting when

V

DS

> 1V

Common Error to Pick FET Too Small

12 V

50 A

22Slide23

Layout Issues - A Little Stray R Can

Make a Big ErrorCritical Kelvin ConnectionsSense Runs Critical Short RunGroundGateHigh Current RunsPoor Kelvin Runs…Inaccurate/variable ILIMIT

Poor High Current Runs

Voltage droop

Power loss

Overheating

23Slide24

Inadequate Transient Protection

All wires are inductiveInductance stores energyWhen the FET turns off, voltage spikes occur

LOAD CURRENT

LOAD VOLTAGE

Positive Spikes at Input to Switch/FET

Negative Spikes at Output of Switch/FET

24Slide25

Inadequate Transient Protection

To squelch inductive spikes from supply / load leadsCaps and/or TVS at UUT Input to clamp positive spikeSchottky Clamp across output to clamp negative spikeShort, Wide Leads and Runs

25Slide26

Thank you!

26Slide27

Circuit Protection Fundamentals

11.4 Common Test ErrorsSlide28

Common Test Error Sources

Current Probes

Electronic Loads

Transients From Long Supply Leads

Supply ILIMIT Too Low

28Slide29

Current Probes

Current Probe Behavior

↑ Great For Observing Waveform Shapes

↑ Don

t have to be

In The Loop”…Nice !!Simply Clamps around feed or RTN wire↓ Need Frequent Degaussing/Cal↓ Not So Great for Precise MeasurementsLimited Bandwidth1% Accuracy at Best

29Slide30

Current Probes

For precise DC current measurements If ILOAD < 10 Amps use Multimeter on Current ScaleIf ILOAD > 10 Amps Use Shunt and MultimeterPick RSENSE so VRSENSE

@ I

LIMIT

= 50-100 mV

Note….Now V

OUT_SUPPLY ≠ VIN_LOAD...so measure VLOAD at The Load!

30Slide31

Electronic Loads

Good for DC Loading and Automated TestsProper Setup Very ImportantEx. - Constant Current, Constant Power, Constant ResistanceBut…often Have Switch Transients When Stepping LoadTransients Can Cause Premature Trip When Measuring ILIMITSo What Do We DO ??

31Slide32

Electronic Loads

For Minimal Transients While Adjusting Load32

Method 1: Use Power Resistors as Loads

Method 2: Use Power FET as Load

A bit tedious and Old School… but accurate

A collection of fixed and variable resistors is best

Apply “Last Half Amp” With Small Wire Rheostat

Can be effective with eLoads alsoConnect FET and Series Resistor as LoadAdjust Potentiometer to vary CurrentMake Sure the FET can Handle the power !!!!Slide33

Long Supply Leads

All wires are inductive

Long Supply Leads can have significant L

Lab Test Environment Usually Worse Than Final Application!

Reason for TVS and diodes on most TI EVMs

When the FET turns off, voltage spikes occur

To counter inductive spikes from supply / load leadsCaps and/or TVS at UUT Input to clamp positive spikeSchottky Clamp across output to clamp negative spike

Twisted Supply leads

33Slide34

Supply ILIMIT

Too Low Lab Supply Limit Sometimes Set Slightly Above ILIMIT_LOADVSUPPLY can sag due to I limiting during overload / short circuit testingSagging VSUPPLY can cause UV shutdown before ILOAD reaches I

FASTTRIP

UV Shutdown is typically much slower than Fast trip (SC) Shutdown

Slow shut down can violate FET SOA, resulting in dead FETs

Fix 1

: Ensure PS set to supply currents ABOVE fast trip levelFix 2

: Attach bulk caps at input of UUT before test is run34Slide35

Trends in Circuit Protection

AccuracyCurrent limit, power limit, monitoringEfficiencyLow RDSON, low IQHigh levels of integrationi.e. bring FET, RSENSE into the package

I

2

C, PMBus for control and monitoring

Especially PMBus with Intel Grantley processors

eFuses replacing/augmenting fuses & polyfusesHigh Power POE Systems (25-100 Watts)

35Slide36

Thank you!

36Slide37

Circuit Protection Fundamentals

11.5a eFuse OverviewSlide38

Integrated Circuit Protection Types

Power controlling element contained therein

好运

Initial $

Level

of

Protection

Wishful Thinking

Fuse

eFuse

Polyfuse (PTC)

38Slide39

What is an eFuse?

An active circuit protection device that…Will:Limit current at inrushPrevent load or source damage due to OC eventsHave an internal FET to control the load currentMight:Provide OVP (none, fixed, adjustable)

H

ave adjustable fault time and/or current limit

H

ave indicator outputs (Fault, PG, etc.)

Be able to control turn on slew rateHave a load current indicator outputBe on source side of a connector or load side or..

Be nowhere near a connector39Slide40

Typical Applications for eFuse

Enterprise Class SSD

SAS HDD

Storage Server

Chassis

Set-Top Box

DVD Player

Internet TV

m-SATA SSD

Appliances

40Slide41

Brand Damage – A

Hidden CostIt’

s not fair and that won

t change

Most end users don’

t know or care how a product worksEven fewer know or care about circuit protectionA good fuse design in a bad system can still get the blame

Dirty power, poor transient control, can cause a fuse to blowA load with a blown fuse is viewed as the problem…not the faulty sourceBlame should go to the source of “bad” power...but rarely doesEND CUSTOMER DOESN’T CARE about power specs !!! Your board died….now fix it!!!Replacement board likely to blow a fuse, tooCustomer not happy – switches to competitive brandControl your products’ destiny !!Don’t rely on other systems to “do the right thing”Protect the product, the brand, the profit, your career !Someone will pay….don’t let it be you!

41Slide42

Backend costs of

fuse only

designs

Tangible costs

Replacement of nonfunctional product

RMA admin costs / timeShipping broken/new devices from/to customerTruck rolls, service personnelIntangible backend costsUnhappy retailersBrand damageLoss of customer(s)In the end, we all want happy customersIt’s that simple, it’s that complicated

42Slide43

Thank you!

43Slide44

Circuit Protection Fundamentals

11.5b eFuse vs. FuseSlide45

Why Not U

se a Fuse?SlowInaccurateLossyLeave a load unpowered after event45Slide46

“Fast Blo Fuse” Trip T

ime vs. Current eFuse vs. FuseTime and trip limit inaccuracies mean bigger power supplies

eFuse Limit !

Fusible fuse trip range

 

eFuse trip range

Time (sec.)

46Slide47

Fuses Are Slow…E

ven the Fast Ones

eFuse Performance

I

LIMIT

is programmable, predictable, and stable over temp

Bus droop and supply stress reduced by tight over current tolerance

47Slide48

Fuses are Lossy

Higher resistance -> more energy -> more heat -> higher OPEX13x more power lost with fuse!800 mV/2A = 400 mΩ vs. eFuse @ 30 m

Ω

Lifetime cost of 1 Watt = $2 to $18 ( customer supplied numbers)

Includes energy cost, distribution infrastructure, HVAC, product life

Little Fuse 231Series

0.12

0.19

0.30

0.48

0.75

1.19

Lower Losses using TPS2590 ( 30 m

W

)

48Slide49

Fuses are Inaccurate

Fuse makers recommend the INOMINAL< 75% IFUSE_RATEDPower supplies must be overspec’dAccommodate fuse derating, fuse tolerance, PFUSE Bigger supplies = more CAPEX, more OPEX

Seconds

 

49Slide50

Fuse’s Behavior

is Sloppy and Stressful50

During Overload

After Overload

Much slower than eFuse

No active current limiting

Uncontrolled turn off time

Bus droop likelyMore stress on supplies & loadHigh I2R losses10x+ nom. trip current for 3 ms

No auto reset

Inoperative system

Module, fuse, or system must be replaced

Repair costs

Field returns

Unhappy

CustomersSlide51

Fuse Summary

51Challenges

Benefits

Slow

Lossy

Inaccurate

Load unpowered after event

Low CostCan provide Safety Compliance

UL, IEC, CSASlide52

Fuses DO Excel in Some Apps!

52Slide53

Thank you!

53Slide54

Circuit Protection Fundamentals

11.5c eFuse vs. PolyfuseSlide55

eFuse vs. Polyfuse

55eFuse (USB Power Switch)

Polyfuse

Current based I

LIMIT

Stable, accurate (20% - 30%) I

LIMIT

Fixed or Programmable ILIMITRepeatable ILIMIT0Fast ( < 1.5 us typ)Wide temp range-40° to +

125° C

Temp based I

LIMIT

Sloppy, variable I

LIMIT

No Programmable I

LIMIT

R

ON Increases with each eventSlow to trip (several ms)Not usable above

85° CAuto-resets after trip eventSlide56

Polyfuses (PTC Devices)

Require Derating

Curve D

TPS2420/21, TPS2590/910

D

DSlide57

eFuse vs. Polyfuse

Brand conscious Tier 1, 2, 3s use USB Power SwitchLow cost “

bottom end

apps may use Polyfuse

True story #2

Major ODM experiencing Power supply resets during STB short testing. TPS2066C with faster response got designed in and no more resets.True story #1 – Low end desktop maker melted wireless datacard during a short condition. Three times. Now using USB switches.Slide58

Polyfuse Summary

58Challenges

Benefits

Slow

Lossy – 2x regular fuse

Inaccurate

Each OC event increases resistance

Not suitable for high temp.R increases with Temp.-Resets after OC eventLow Cost

Can provide Safety Agency compliance UL, IEC, CSASlide59

Thank you!

59