Integration Aspects of DC-DC Converters

Katja Klein

1. Physikalisches Institut B RWTH Aachen University

TUPO, June 10

th

, 2009

Outline

• Conversion ratio & output current • Dimensions and weight of buck converters • Material budget • Cooling requirements • Shielding requirements • Should the DC-DC converter be part of the module?

• Possibility of integration for various module proposals • Provision of two operation voltages for CBC • Discussion of four options • Conclusion & recommendation

Assumption: GBT powered from outside of sensitive volume

Katja Klein 2

Comparison of Layouts

Layout Long barrel double

stack (Marcello)

Hybrid

layout § (Duccio) tracking trigger

Cluster width

Fabrizio; barrel only Duccio; full outer tr.

FE Power

100kW 12.5kW 2.9kW & 12kW 56.5kW

Link-Power

25kW $ 15.6kW & 20.9kW 2.3 – 14.1kW ° 23.2 – 35.0kW

~ 20kW

Total Power

125kW 43kW ~ 75kW

# of Modules

20 000 10 040 1 568 * 14 037 13 008

All power numbers include a DC-DC efficiency of 80%

§ Variant with 2 long barrel p T layers and tracking-only endcaps $ assuming 10Gb/s GBT-like link, 2W per link & with 2W/GBT ° depends on optical module (GBT vs. MZM), larger number for GBT (3W per GBT) * for A = 85cm 2 # depends strongly on module proposal Katja Klein

FE-Power per module

4 - 9W 0.94 - 1.9W

1.3 – 9W # 1.25W

1.1 – 9.4W

3

Total Power Consumption

• Total power consumption limited by heating up of water-cooled cable channels • Today the total current in cable channels is 15kA • Upper limit would have to be determined by measurements on mock-ups of hot spots in cable channel (Hans Postema) • 10-20% more might be possible, but probably not more? (Hans Postema) • Can calculate maximum power consumption for certain

convertion ratio r = I in / I out

: E.g. for r = 1/10 and 80% efficiency: P max = 150kA x 1.2V x 0.8 = 144kW • Can estimate the necessary conversion ratio for a given power consumption: r = 15kA / I out P = U out x I out (includes already converter efficiency of 80%) r = 15kA x U out /P

Layout Long barrel double stack Hybrid strawman Total Power

125kW 43kW

Operating voltage

0.9V

Conversion Ratio 1/10

1.2V

0.4

Katja Klein 4

Conversion Ratio from Cable Specs

• Assume

only 1 000 LICs

can be used to power the modules (reason: links) • Spec of LICs: U max = 30V, I max = 20A (return) • Calculate mean number of modules per LIC • Calculate mean current per LIC • Estimate necessary conversion ratio • In reality, could try to level out (but then granularity becomes an issue)

Layout Long barrel double stack Hybrid strawman

tracking trigger

# of Modules

20 000 10 040 1 568

Power per module

4 - 9W

# Modules per LIC

20

Current per LIC (worst case)

200A

Conv. ratio

1/10 0.9 - 1.9W

up to 9W 12 12 19A 120A 1 1/6 Katja Klein 5

First Conclusion

• Buck converters are needed at least for trigger layers • Charge pumps are no option for some approaches (max. current ~ 1A)  Currents to be provided too big for a single charge pump per module  Charge pump per chip not feasible (90nm, no space for capacitors, ...) • Discuss in the following the integration of buck converters • Come back to charge pumps later Katja Klein 6

Dimensions and Weight of Buck PCBs

Smallest Aachen PCB (V1):

Area: 2.3cm

2 Height: 10mm Weight: 1.0g

12mm 19mm Aachen PCB with lowest noise (V3):

Area: 3.2cm

2 Height: 10mm Weight: 1.1g

Numbers are without connectors

Katja Klein

27mm 12mm

7

Dimensions and Weight of Buck PCBs

CERN PCB

(proposal): INDUCTOR ASIC SMD SMD SMD SMD 1.5-2 cm 1.5-2 cm 

Area (currently) needed per buck converter PCB: 2-4cm

2

• Some further minimization probably possible (e.g. remove connectors) • But filter capacitors are necessary • Coil must have a certain inductance (  noise) and low DC resistance (  efficiency) Katja Klein 8

Material Budget

• TEC, conversion ratio 1/8, eff. = 80%, current power consumption, 1.2V only (Aachen) • One buck converter per module, located close to module

Total MB of: TEC modules TEC Converters TEC electronics & cables: - 29% Original TEC TEC with buck converters r = 1/8



With above assumptions, buck converter close to module saves material

(caveat: savings are half due to DC-DC conversion, half due to methodology) Katja Klein 9

Buck converters with r = 1/8, located at petal rim:

TEC electronics & cables: - 18%

Material Budget

Buck converters with r = ¼ at petal rim, one charge pump with r = ½ per chip

TEC electronics & cables: - 24%



Buck converter close to module gives largest saving for TEC

 Desirable to repeat study for barrel geometry and two operation voltages Katja Klein 10

Cooling Requirements

• Converter efficiency ~ 80% • Heat to be dissipated ranges from 150mW (outer tracker module with 1 hybrid) to ~ 2W (3D-integrated stacked module, inner layers) • A contact to the cooling system should be foreseen Katja Klein 11

Shielding Requirements

Measurements with solenoid coil (worst case) • Measurements show that shielding the whole converter helps against EMI from coil  Shielding

only the coil

was not so efficient (reason not completely understood) • New Aachen boards need

not

be shielded anymore in our system test set-up • Requirements depend strongly

on distance to FE-electronics

(plus technical details of converter and coil...) • Recommendation at this point: a DC-DC converter

on the module

should be shielded  30  m of Aluminium worked fine (no improvement with thicker shields)  Details would have to be worked out and tested Katja Klein 12

Integration of Buck Converter (I)

Arguments for buck converter on separate PCB, close to module:

• Very limited space on most proposed hybrids  size less critical • Larger distance preferred for EMI anyway (also damping of ripple?) • Converter development completely decoupled from hybrid and module development  No common deadlines, can optimize converter design as needed (even late) • Different hybrids for different module proposals  avoid involvement of many groups • PCB could be developed, manifactured and tested standalone • Easier for cooling? (module cooling is difficult enough without converters)

Arguments for buck converter on the module/hybrid:

• Less mass (avoid connectors & connection between converter and module) • Power regulation closer to FE-ASICs (only relevant if no LDO) • Could have pluggable PCB on hybrid, but then connectors are needed (mass) • Noise effects can be tested more easily (don‘t need additional PCB) Katja Klein 13

Outer Tracker Module Proposal

TCS I/O PLL 2 x 4-MUX + LCDS driver each output 160Mbit/s DC-DC shielded micro-twisted pairs I /O DC-DC out 2.5V

Sensor HV • CBC-power ~ 0.75W per hybrid; i.e. 0.75W or 1.5W per module • Plus DCU, PLL, DC-DC inefficiency, GBT-port, MUX, LCDS-driver • No motherboards • Upper part of hybrid ~ 2.5cm x 1cm, no space for buck on this hybrid • Some space between hybrids; but routing of input & output?

• Integration of buck on rod level looks more practical and elegant 2.5cm

DCU Sensor with 4x2.5cm strips 2x 1024 @95um pitch integrated pitch adaptor 8x CBC 2x 128ch wire bonded 40Mbit/s out each Katja Klein 14

Outer Tracker Module Proposal

• Indeed the buck converter must be able to provide several Amps (as anyway needed by pT-modules) • Could save material by combining two one-hybrid modules into one unit • Could even consider to power two two-hybrid modules (3W) with one converter • Loose two modules if converter fails • No other drawbacks from power point of view Katja Klein 15

Katja Klein

Vertically Integrated Hybrid Module

• 130 or 90nm • Communication through vias in ROC and interposer (3D-integration) • No motherboards • FE-power 4-9W per stacked module • Up to 10A per stacked module • Need at least two buck converters per stack (better more)  module needs to be “partitioned“ • No space on module; no hybrid • Modules integrated onto “beams“ • Buck converters must be integrated into beam structure • Shielded space already foreseen • Discussions between Fermilab & Aachen started 16

1 Modul:

Katja Klein

Trigger Module (Sandro)

• 90nm • Sensor size = 4.8cm x 4.8cm

• Hybrid ~ 1cm x 4.8cm

• Power per p T -module = 2.6W

• I per modul ~ 3A • No space for buck converter (unless hybrid is considerably increased) • Practical issues (fabrication?) • Again, integration into support structure seems more feasible • How would support structure look like?

1 Chip

17

Trigger Module (Geoff et al.)

data out control in 26mm 80mm • Sensor size ~ 2.6cm x 8.0cm

• Hybrid ~ 1cm x 4cm • 130nm • Power per p T -module ~ 1.3W (similar to outer tracker module) • No space for buck converters, unless hybrid is considerably increased Katja Klein 18

Integration of Buck Converter (II)

• There is a tendency to avoid motherboards at all  Outer tracker module, vertically integrated double-stack proposal, others?

• This goes hand in hand with rather minimalistic hybrids of a few cm 2 • All existing or planned buck converter PCBs need an area of 2 - 4cm 2 •

Suggestion: a separate buck converter PCB close to the module, e.g. inside the beam (for double-stack approach) or on the rod/stave

 converter needs cooling contact – probably not too dificult then  need short power cable between converter PCB and module  Could/should be designed such that it fits with all proposals/applications:  Version with 1.2V and 0.9V for CBC  Version with two (or three) buck converters for very high-power trigger modules  Version with 1.2V and 2.5V for GBT, for PP1 or bulkhead Katja Klein 19

Provision of two Operating Voltages for CBC

• V ana = 1.2V, possibility to have V dig • P = 64mW per Chip with 1.2V

< V ana (~ 0.9V) (26mW analog power, digital power would be halved with U = 0.9V) • Both analog and digital currents ~ 20-30mA per chip • How to provide the two voltages? Options:

1.

Use the two LV conductors in LICs and two separate buck converters

 Same conversion ratio for both bucks  Power supplies must provide two voltages

2.

3.

4.

Provide one common input voltage, use two separate buck converters

  Different conversion ratios for bucks Lower power losses than option 1.

Derive V dig



from V ana with linear regulator

Method with lowest efficiency

Derive V dig



from V ana with charge pump (ratio 4:3)

Option with lowest mass and space requirements  Brings us to more general question: do we want to use charge pumps, and how?

Katja Klein 20

Option 1: Only Buck Converters

• Conversion in one step • Assume buck converter close to the modules with r = 1/6 or smaller (as needed) • If the necessary conversion ratio can be realized in one step for all proposals must be studied with new ASIC prototypes! (issue of switching losses) • Do not use charge pumps  no additional chips on the FE-hybrid or inside CBC •

Must find space for 1 or 2 buck converters (as many as operating voltages) either on your module/hybrid or (preferred!) on your support structure

• If decided to put buck on support structure, module design can proceed completely independently • Could fit with all proposals • Maximal current per buck converter to be understood, of the order of 4A  Looks tight for double-stack proposal, must find reasonable partitioning Katja Klein 21

Option 2: Buck + Charge Pump per Module

• Could be necessary if conversion ratio cannot be provided in one step  Buck converter with r  ¼ close to module; charge pump with r = ½ per module • Is however NOT compatible with any pT-module (due to current requirements) • (Only) Possible useful application: provision of U dig  conversion ratio 4:3, current ~ 300mA for CBC for one FE-hybrid  less material than two buck converters (but not half!)  on cost of higher complexity •

Space for buck converter: see option 1

•

In addition need space for 1 chip plus capacitors (details to be worked out)

 on FE-hybrid  or even on buck PCB?

• Such a chip is currently not being developed Katja Klein 22

Option 3: Buck + Charge Pump On-Chip

• Assume charge pump is integrated

into read-out ASIC

• Concerns raised by Mark: substrate noise, constraints on layout, space for passives • Could be necessary if conversion ratio cannot be provided in one step  Buck converter with r  ¼ close to module; charge pump with r = ½ per module • Seems NOT compatible with some pT-modules (technology, space for passives) • Possible useful application: provision of U dig  conversion ratio 4:3, current ~ 20mA for CBC  less material than two buck converters (but not half!) • Alternative: derive both voltages with charge pumps  conversion ratio 1:2  one capacitor per voltage (100nF, 0201?)  need LDO for analogue power  can switch on/off single read-out ASICs  how to power auxiliary ASICs (PLL, MUX, LCDS driver, ...)?

•

Space for buck converter: see option 1

•

In addition need space for capacitor(s) close to CBC on FE-hybrid

• Design block for 60mA in 130nm being developed by CERN/Atlas Katja Klein 23

Option 4: Buck + Sep. Charge Pump per Chip

• Assume now

separate charge pump chip per readout-ASIC

• No substrate noise, no constraints on CBC layout • Space for passives still needed,

plus

space for charge pump chips • Very small chips to be integrated onto hybrid – possible but cumbersome?

• Looks NOT compatible with some pT-modules (technology, space) • Possible useful application: provision of U dig  conversion ratio 4:3, current ~ 20mA for CBC  less material than two buck converters, but more than option 3 • Alternative: derive both voltages with charge pumps  conversion ratio 1:2  one capacitor per voltage (100nF, 0201?)  need LDO for analogue power  can switch on/off single read-out ASICs •

Space for buck converter: see option 1

•

In addition need space for 1 or 2 chips plus capacitor(s) close to CBC

Katja Klein 24

Conclusion & Recommendation (my opinion)

• Buck converters cannot be avoided (but charge pumps can) • No motherboards and no or very small hybrids  integrate buck converter onto separate small PCB • Cannot decide today if charge pumps are needed, keep option open • Abandon option 4 (separate charge pump chip per read-out ASIC) •

Prepare for option 1 with buck on support structure

• Explore and do not exclude options 2 & 3  Allow some space for charge pump chip plus caps on hybrid  Allow some space for caps close to CBC  Integrate charge pump block offered by CERN group into CBC  in a way that it can be bypassed  would learn a lot about option 3  this is an opportunity to make real progress!

Katja Klein 25