low noise dc to dc converters for the slhc experiments

1

Low Noise Dc to DC Converters for the sLHC

Experiments TWEPP 2010Aachen, Germany

21/9/2010

TWEPP 2010 G. Blanchot, PH/ESE

B.Allongue, G.Blanchot, F.Faccio, C.Fuentes, S.Michelis, S.Orlandi

CERN – PH-ESE

2

Outline DCDC based powering scheme. DCDC development status. Compatibility of DCDC with front-end systems. Noise optimized DCDC Plug-in-Boards. Shielding and radiated magnetic field. Performance of AMIS2-PIB using radtol ASIC. Performance of SM01B-PIB using commercial chip. Conclusions.

TWEPP 2010 G. Blanchot, PH/ESE

3TWEPP 2010 G. Blanchot, PH/ESE

Distribution scheme example (ATLAS Short Strip concept)

Identified integration issues:

Radiated magnetic field from stage 1 DC/DC. Board layout, coil topologies, shields

High noise susceptibility of modules. System tests with hybrids

Board area, material budget on stage 1 DC/DC. ASIC development, compact layout.

10-12V

2 Converter stage2 on-chip

Det

ecto

r

Intermediate voltage bus(ses)

Converter stage 1 block

Hybrid controller

SC and optoelectronics

10-12V

Module/Stave

Scheme based on 2 conversion stages:Stage 1: On Module Buck DC/DCStage 2: On Chip Switched Capacitor

Module

G. Blanchot, PH/ESE 4

DCDC Development Status

TWEPP 2010

Critical achievements: Radiation tolerant technologies have been selected. Buck converter ASIC prototypes have been produced and tested Air core inductors topology has been selected. Standard buck converter prototypes have been produced, tested and used with systems. Radiation tolerant buck converter prototypes using ASICs have been produced.

Coils optimizationD1 D1 D1 D1 D1 D1 D1

IND

IND

IND

IND

IND

D1

S2

S2

S2

S2

S2

S2

Vdd2

SUB

Enable

Enable delay

R delay

OUT

V25

V18

En_freq+S2

R_freq

VREF

Vss

Vdd

BTSTR

7 mm

7 mm

Package QFN48

5 mm

5 mm

Package QFN32

7 mm

7 mm

Package QFN48

Radiation tolerant ASICs

AMIS2

IHP1IHP2:

DCDC Prototypes

IHP Technology still under development


Buck Converter

TWEPP 2010

Identification of main noise sources: Switched voltage at node area N3 = Vin at switch frequency + harmonics. On-time switching loop “A” = uprising current. Off-time switching loop “B” = down-rising current. Transition-time loop “C” = fast current transition inside switches. Magnetic field emitted by the main coil L= triangular current.

These noise sources originate noise currents within the DCDC board that in turn radiate fields along cables and interconnections.

B

A

C


ISL6540 Proto2

Noise reduction in DC/DCs

TWEPP 2010

DCDC optimization: Voltage nodes and current loop areas have been reduced significantly. The subsequent reduction in radiated noise results in reduction of conducted noise along cables.

ISL6540 Proto3ISL6540

Proto5

The noise level is characterized on a reference test stand:

The noise level has been considerably reduced on DCDC prototypes that used an Intersil ISL6540 controller and air core coils.

Very good performance was achieved in Proto5.

Equally good performance was achieved using the AMIS2 ASIC.

This level of performance was however not enough for the sensitive trackers front-end electronics and detectors.

AMIS2 QFN48 Test Board


Proto5 with UniGe Module

TWEPP 2010

Position of hybrids

Conducted noise test

Radiated noise at corner

Radiated noise on top of hybrid

300 350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

Input Noise [ENC] @1fC

=559.7206

=32.2478

KEK Hybrid Stream 0 using Linear PS

Reference noise:ENC Average: 560ENC Sigma: 32

Measurements performed with the help of Sergio Gonzalez from the University of Geneva.

The susceptibility against radiated fields of the UniGe module was measured using the Proto5 DCDC.


Proto5 on UniGe Module

TWEPP 2010




300 350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70


=571.1318

=32.863

KEK Hybrid Stream 0 using DCDC proto5Bis

300 350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80


=582.7654

=34.6271

KEK Hybrid Stream 0 using DCDC proto5Bis close

400 600 800 1000 1200 1400 1600 1800 20000

50

100

150

200

250

300

350

400


=930.8492

=176.0532

KEK Hybrid Stream 0 using DCDC proto5Bis On Top

Proto5, shielded coil: ENC Sigma Reference: 560 32 Conducted: 571 33 Radiated Corner: 583 35 Radiated Top: 930

176 VCC and VDD powered from the same

DCDC converter, without regulator on VCC. The system is insensitive to the conducted

noise of the converters. High noise is observed when the DCDC is

very close of the hybrids: susceptibility to radiated couplings.


Radiated fields susceptibility measured at Liverpool

Shielded 3cm probe, 12 MHz, 6mA DCDC Edge Position Shielded DCDC Edge Position

Noise increases on all channels.

B field coupling only.

Noise increases on all channels (all above 1000 electrons) due to B field.

Alternating pattern due to E field.

No global increase: B field is shielded.

Alternating pattern on two first chips: some E field remains, probably due to leaking E field.

0 128 256 384 512 640 768 896 1024 1152 1280

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channel

EN

C

ROW 0

Even channelsOdd channels

0 128 256 384 512 640 768 896 1024 1152 1280

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channel

EN

C

ROW 0


0 128 256 384 512 640 768 896 1024 1152

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channel

EN

C

ROW 0


Noise Reference = 650 electrons

TWEPP 2010

Radiated fields need therefore to be mitigated further on.


Noise Optimized Plug-in-Boards

TWEPP 2010

New generation of DCDC plug-in board to be used with systems: A form factor compatible with front-end systems under development now.

More compact design. Power interface: connector or bonds. In some cases: control logic.

Better control of the noise sources for lower conducted and radiated couplings: Understanding of how electromagnetic fields are emitted from power loops and switching nodes. The reduction of radiated fields will result in reduced conducted noise.

Introduction of an electromagnetic shield: to cancel E field couplings with front-end systems. to mitigate the radiated B field down to compatible levels .

A thermal interface must be provided for cooling.

3 different DCDC-PIB have been designed and produced: AMIS2_DCDC: 2 versions with AMIS2 radiation tolerant ASIC, implementing noise cancellation techniques.

10V down to 2.5V, rated for 2A. The noise optimization method is explained by Cristian Fuentes at the Power WG.

SM01B: 1 version using a commercially available buck converter chip similar to AMIS2 10V down to 2.5V rated 5A for the 0.25um ABCN modules in use today.

Another DCDC-PIB is under design for bonding onto ATLAS Stavelets


Noise Optimized Plug-in-Boards

TWEPP 2010

Enable

Pgood

Vin

GND

Vout

PROTO5

AMIS2 SM01B

Board size reduction down to 26mmx13.5mmx9mm.

Increased switching frequency: 2 MHz on AMIS2, 3 MHz on SM01B.

A custom coil has been developped with an industrial partner : 250nH that will stand straight onto the AMIS2 ASIC.

A custom shield is under development now: it aims to replace the 200um copper foil boxes with Cu coated plastic cases to be soldered directly onto the PCBs.

Efficiencies above 80% achieved. SM01B reaches 87% at 2A, and is still at 80% for 4A load current at nominal input voltage.

0 1 2 3 4 50.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Load Current(A)

Effi

cien

cy

Efficiency vs load Current

6 7 8 9 10 11 120.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Input voltage (V)

Effi

cien

cy

Efficiency vs input voltage

Iload = 0Iload = 1Iload = 2Iload = 3Iload = 4Iload = 5

6 7 8 9 10 11 122

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

Input voltage (V)

Out

put v

olta

ge

Input voltage regulation

Iload = 0Iload = 1Iload = 2Iload = 3Iload = 4Iload = 5

0 1 2 3 4 52

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

Output current (A)

Out

put v

olta

ge

Load regulation

Vin = 6Vin = 6.5Vin = 7Vin = 7.5Vin = 8Vin = 8.5Vin = 9Vin = 9.5Vin = 10Vin = 10.5Vin = 11Vin = 11.5Vin = 12

Vin = 7.5Vin = 8.5Vin = 9Vin = 9.5Vin = 10Vin = 10.5Vin = 11Vin = 11.5Vin = 12

SM01B


Shielding: Electric field

TWEPP 2010

B

A

C

C B

A

N3

FE ASIC

Bondings

FiltersCoil

Electric field coupling

Electric field shield

Electric field is mainly radiated by node N3: square wave of 10 V at switching frequency. The field couples on the DC DC board filtered areas, on the output cables or traces and on the FE bondings. The coupling is blocked very easily with the addition of a shielding case that segregates the filtered areas from the

noisy areas on the DCDC board.

A plastic box with a very thin conductive layer is sufficient to provide E fied shielding. The shield will reduce the conducted noise and also the couplings in the bondings.


C B

A

N3

FE ASIC

Bondings

FiltersCoil

Shielding: Magnetic field

TWEPP 2010

B

A

C

Radiated Magnetic Field

Coupled Magnetic FieldCoupled Magnetic Field


Magnetic field is mainly radiated by loops A and C and by the main coil L: triangular waves of up to 8A peak to peak at switching frequency with different emission spectrums for each loop.

The field couples on the DC DC board filtered areas, on the output cables or traces and on the FE board. The coupling is mitigated with the addition of a shielding case that segregates the filtered areas from the noisy

areas on the DCDC board.

To be effective, eddy currents must develop in the shield conductor material. At 2 MHz, δ = 50 µm of copper. The shielding effectiveness for Cu thickness from 10 µm to 100 µm will be studied.

The shield will reduce the conducted noise and also the couplings in the FE board.



TWEPP 2010

12

3

12

34

5

80 85 90 95 100105110115120

X

AMIS2 not shielded

Y

dB A

/m

80

85

90

95

100

105

110

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120

12

3

12

34

5

80 85 90 95 100105110115120

X

AMIS2 shielded

Y

dB A

/m

80

85

90

95

100

105

110

115

120

12

3

12

34

5

80 85 90 95 100105110115120

X

PROTO5 with shielded PCB toroid

Y

dB A

/m

80

85

90

95

100

105

110

115

120

12

3

12

34

5

80 85 90 95 100105110115120

X

PROTO5 unshielded with toroid

Y

dB A

/m

80

85

90

95

100

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110

115

120

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3

12

34

5

80 85 90 95 100105110115120

X

SM01B without shield

Y

dB A

/m

80

85

90

95

100

105

110

115

120

12

3

12

34

5

80 85 90 95 100105110115120

X

SM01B shielded

Y

dB A

/m

80

85

90

95

100

105

110

115

120

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3

12

34

5

80 85 90 95 100105110115120

X

AMIS2 not shielded

Y

dB A

/m

80

85

90

95

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105

110

115

120

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12

34

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80 85 90 95 100105110115120

X

AMIS2 shielded

Y

dB A

/m

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85

90

95

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105

110

115

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34

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80 85 90 95 100105110115120

X

PROTO5 with shielded PCB toroid

Y dB

A/m

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110

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12

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80 85 90 95 100105110115120

X

PROTO5 unshielded with toroid

Y

dB A

/m

80

85

90

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105

110

115

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12

34

5

80 85 90 95 100105110115120

X

SM01B without shield

Y

dB A

/m

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85

90

95

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110

115

120

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80 85 90 95 100105110115120

X

SM01B shielded

Y

dB A

/m

80

85

90

95

100

105

110

115

120

The radiated magnetic field is measured along X, Y and Z axes with a 1cm loop probe over a grid. The vector magnitude is computed.

13

5

1

PROTO5

AMIS2 SM01B

Switching freq. = 1 MHz L = 350 nH Load = 1A.

[dBµA/m] Unshielded Shielded Comment

PROTO5 115 115 Shielded coil only

SM01B >120 <100 Non EMC optimized layout

AMIS2 110 <100 EMC optimized layout


AMIS2DCDC Conducted Noise

TWEPP 2010

1 10 30-30

-20

-10

0

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Frequency [MHz]

dB A

CM Comparison

CM AMIS2 10V 2AClass A (Average)Class B (Average)CM Proto5Bis 10V 2A

1 10 30-30

-20

-10

0

10

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30

40

50

Frequency [MHz]

dB A

DM Comparison

DM AMIS2 10V 2AClass A (Average)Class B (Average)DM Proto5Bis 10V 2A

3MHz peak-11.5 dBuA

Compared to Proto5: AMIS2_DCDC has more than 20dB less CM

noise, of about 300 nA at 3 MHz. Switch Frequency is now 3 MHz: there are less

harmonic peaks in the sensitive band. Now complies with Class B with more than

20dB of margin.

The DM noise has also been reduced. Barely visible. Two peaks at 3MHz and 6 MHz only, with less

than 300 nA amplitude. Now complies with Class B with more than

25dB of margin.

ATLAS Limit ATLAS Limit

Class A Limit Class A Limit

Class B Limit Class B Limit

To further mitigate the radiated fields, electric and magnetic near field couplings that take please within the DCDC board and its components were modeled. Based on this, noise cancelling routing and placement topologies were implemented onto a new generation of converters using the AMIS2 ASIC. On this, a shield is added.


Optimized AMIS2 DCDC on UniGe Module

TWEPP 2010




AMIS2_DCDC, shield: ENC Sigma Reference: 560 32 Conducted: 560 33 Radiated Corner: 558 34 Radiated Top: 614 38

VCC and VDD are each powered from two different DCDC converter, without regulator on VCC.

The AMIS2-PIB, induces 10% more noise with respect to the reference configuration, when two converters are place straight on top of the hybrids.

The improvement is very significant, and is in line with the noise reduction observed on the reference test stand (CM and DM noise).

300 350 400 450 500 550 600 650 700 750 8000

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90


=559.7042 =33.2355

KEK Hybrid Stream 0 using DCDC AMIS2

300 350 400 450 500 550 600 650 700 750 8000

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70


=558.2779 =33.894

KEK Hybrid Stream 0 using DCDC AMIS2 Close

300 350 400 450 500 550 600 650 700 750 8000

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90


=614.365 =37.9097

KEK Hybrid Stream 0 using DCDC AMIS2 On Top


1 10 30-30

-20

-10

0

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50

Frequency [MHz]

dB

A

CM SM01 #6, Vin

=10V,Iout

=2A, shield, L=250nH

CM Current output LISN 2MHzClass A (Average)Class B (Average)Proto5

1 10 30-30

-20

-10

0

10

20

30

40

50

Frequency [MHz]dB

A

DM SM01 #6, Vin

=10V,Iout

=2A, shield, L=250nH

DM Current output LISN 2MHzClass A (Average)Class B (Average)Proto5

SM01B (LT3605) Performance

TWEPP 2010

Compared to Proto5: CM of SM01B is comparable to that one of

Proto5. Beyond 10 MHz it is 10 dB lower. Switch Frequency is now 2 MHz: there are half

less harmonic peaks in the sensitive band. Complies with class B except for the 4 MHz

peak.

The DM noise has also been reduced. 15 dB reduction at 2 MHz. 10 dB attenuation beyond 10 MHz. 4 MHz peak still exceeds Class B.

ATLAS Limit ATLAS Limit

Class A Limit Class A Limit

Class B Limit Class B Limit

The LT3605 chip is used in SM01B. It integrates the switches and the control circuitry like in AMIS2. It includes two PLLs to improve the voltage tracking but that result in broader peaks. Regular layout applied, with the addition of a shield.


SM01B DCDC on UniGe Module

TWEPP 2010

SM01B shielded: ENC Sigma Reference: 560 34 3cm on bonds: 563 33 Radiated Top: 573 36

VCC and VDD are each powered from the same DCDC converter, with regulator on VCC for the analog power of the ABCN chips.

The SM01B, induces less than 2% more noise with respect to the reference configuration, when the converter is placed straight on top of the hybrids.

SM01B radiates more than AMIS2DCDC but less noise is observed:

2 AMISDCDC vs 1 SM01B. Setups are slightly different: distance from

DCDC to hybrid probably larger for SM01B. No analog regulator for the AMIS2DCDC

test. It is in both cases an excellent performance

for an extreme placement of converters.

300 350 400 450 500 550 600 650 700 750 8000

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80

90


=560.1623 =34.0556

KEK Hybrid Stream 1 using Linear PS REF1

Reference noise

300 350 400 450 500 550 600 650 700 750 8000

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90


=562.8619 =33.6686

KEK Hybrid Stream 1 using DCDC SM01 with Shield 3cm over Hybrid

3cm from bonds

300 350 400 450 500 550 600 650 700 750 8000

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80


=572.9926 =35.8624

KEK Hybrid Stream 1 using DCDC SM01 with Shield just over Hybrid



Conclusions

TWEPP 2010

The system tests performed at Liverpool and Geneva modules brought the necessary information to understand the critical noise sources and their coupling mechanisms.

As a result of this, an optimized PCB layout has been designed for the AMIS ASIC, with the addition of a shield enclosing the identified noise sources.

The noise optimized AMIS converters present a negligible level of noise on the reference test stands, with more than 20 dB improvement with respect to the previous prototype (Proto5).

The noise reduction observed on the test stand is confirmed when powering a front-end system: the noise increase in a critical placement is less than 10 % now with two AMIS2 and less than 2% using the SM01B and the ABCN regulator.

In similar conditions, the old Proto5 DCDC was inducing unacceptable levels of noise. This validates the optimization methodology applied to the design of the new prototypes. It validates the need for the shield.

The optimized design will be integrated onto supermodules, frame modules and stavelets currently under development.

low noise dc to dc converters for the slhc experiments

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