Design of the Internal Power Supply Boardfor the Digital Optical Module

of the KM3NeT Neutrino Telescope

by E. Anassontzis, A. Belias , E. Kappos, K. Manolopoulos, P. Rapidis

on behalf of the KM3NeT Collaboration

Potential neutrino sources

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Supernova Remnants

Pulsar Wind Nebula

Gamma-Ray Burst

?Dark

Matter ? ?

? ? ?

?

?

? ?

Active Galactic Nuclei

Cosmogenicneutrinos

Micro Quasars

Detection principle

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Active Galactic Nuclei

Neutrino-induced muons in the deep sea

Picture from ANTARESup-going neutrino

µ

CherenkovNeutrinoTelescope

43°

water/

rock

charge currentinteractions

KM3NeT Artistic Impression

TIPP’14 K. ManolopoulosELECTRO-OPTICAL CABLE TO SHORE

~100m

~ 700m

6 Building Blocks (BBs) ~ 6 km3

1 BB = 115 Detection Units (DU)1 DU = 18 Digital Optical Modules

KM3NeT- Where & When

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200 People40 Institutes10 Countries

2 BBs in each site ~2km3

KM3NeT-France: Toulon (~ 2500m)

KM3NeT-Italy: Capo Passero (~ 3500m)

KM3NeT-Greece: Pylos (depth ~ 4500m)

Common hardware, data handling and operation control

Centrally managed Nodes for marine

science at each site

Digital Optical Module (DOM)

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Upper Hemisphere12 PMTs

Lower Hemisphere19 PMTs

Central Logic Board(CLB)

PMT Base:High Voltage SupplyAnalog Front-End

Power-Board

Digital Optical Module (DOM)

Receives power from external 400V/12V power supply.Uses internal power supply board (DOM-PB) to

generate 7 power rails at various voltages as required by its electronic modules, e.g.Central logic (FPGA) board.Photomultiplier (PMT) bases.Optical communications.Instrumentation boards inside the DOM, e.g.

Acoustic piezo sensor for the DOM positioning system. Compasses and tiltmeters to monitor the orientation of PMTs. Temperature and humidity sensors. LED nanobeacons for timing calibration.

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DOM Power Supply Board (DOM-PB)

Design considerationsMultiple power rails derived from 12V input.High power conversion efficiency desirable.Power up sequencing requirements to adhere to (strictly

sequential).Strict form factor constraints imposed by DOM mechanical

design. Not easily accessible or serviceable inside the DOM.

Attached directly to DOM heat conductor to improve cooling. DOM uses an internal mushroom-shaped aluminium heat conductor to

improve heat flow to its environment (sea water).Shielded against EMI and acoustic noise to other DOM

modules.Reliability – operating lifetime > 10 years.

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Design optionsPre-production version, to be used only during DOM

electronic systems development for power evaluation purposes, with capabilities forCurrent and voltage sensing of all power rails.I2C communication for data acquisition by

FPGA firmware. PC software.

Dynamic power profiling tool for DOM electronic modules.Reduced power efficiency due to:

Extra ICs (ADCs, buffers, …) Current sensing resistors.

Production version.Without the above capabilities, to increase power efficiency.

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Implementation considerations

Use readily available off-the-shelf components (ICs).

Modular design for flexibility in implementing future changes in case of component obsolescense or procurement problems.

Low costComponent costs

2 power connectors, 1 mixed power/signal connector. Input DC power filter, output ferrite (LC) filters. Switching/linear regulator ICs, magnetics, other ICs

PCB costs Use max 4 layers.

No blind or buried vias.TIPP14 K.MANOLOPOULOS.

Power rail specifications with current (power) estimates Step down: 12V → 1.0V 2.3A (FPGA board) 12V → 1.8V 0.9A 12V → 2.5V 0.9A 12V → 3.3V 0.7A (digital) 12V → 3.3V 0.3A (analog, PMT bases, low noise/ripple required) 12V → 5.0V 0.4A Step up: 12V → 0V .. 30V 5mA (programmable via I2C) Power sequencing:

Power-up: Low voltages precede higher voltages. Power-down: Not specified. Power-good output asserted when all step-down rails are good. Separate power-good output for the PMT rail required. Step-up rail: no need for power-good. Activated when 5.0V rail is good.

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Implementation decisionsFor efficiency, use switching regulators due to high

step-down ratio.

For reduced noise/ripple and higher efficiency on the PMT rail: Use linear regulator preceded by step-down 12V → 3.8V

to reduce linear dropout.

Avoid using power sequencer IC:Use the ENABLE input and POWER_GOOD outputs of

switching regulators in a daisy-chain (i.e. domino-like) configuration, where each regulator is enabled by the power good output of the previous (lower) rail.

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Voltage Rising Time

Implementation options for step-down switching regulatorsRegulator IC with external magnetics.

Flexibility in selecting switching frequency and component values. Longer development for tests & qualification of each switcher design. Less flexibility in modifying the Power Board design.

Modular point-of load (POL) switching regulator. Regulator IC with magnetics supplied as a single module.

Encapsulated modules (expensive, but EMC qualified). Module on mini PCB (low cost).

Speeds up development. Flexibility in upgrading and modifying the Power Board design. Guaranteed electrical and EMC specifications. Optimized PCB design by manufacturer, own GND plane. Widely available by several manufacturers, low cost.

No flexibility in selecting switching frequency.

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DOM Vout Settings

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Power Board Overview

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ConclusionsPower efficiency of pre-production version approx.

80%.Estimated power efficiency of production version

approx. 85%.

Further workUse power profiling capability of pre-production version

to provide precise figures on current consumption of all DOM electronic modules.

Optimise power efficiency by replacing POL modular converters with bespoke switching regulators with own magnetics to achieve at least 90% efficiency on each rail.

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Thank you for your attention.Questions?

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