Serial Powering vs. DC-DC Conversion - A First Comparison

heartlustElectronics - Devices

Nov 2, 2013 (3 years and 10 months ago)

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Serial Powering vs. DC
-
DC Conversion
-

A First Comparison

Tracker Upgrade Power WG Meeting

October 7
th
, 2008

Katja Klein

1. Physikalisches Institut B

RWTH Aachen University

Katja Klein

Serial Powering vs. DC
-
DC Conversion

2

Outline


Compare Serial Powering & DC
-
DC conversion under various aspects


Power loss in cables


Local efficiency


Compatibility with services


Power supplies


Bias voltage


Safety


Slow control


Start
-
up


Scalability


Flexibility


Potential to deliver different voltages


Process considerations & radiation hardness


Interplay with FE
-
chip


Interplay with readout & controls


Noise


Material budget


Space


Test systems


Discussion


The Basic Ideas

Katja Klein

Serial Powering vs. DC
-
DC Conversion

3

Conversion
ratio r:

r

=
V
out

/
V
in

! <<
1





P
drop

= R

I
0
2

n
2

r
2

V
drop

= R

I
0

P
drop

= R

I
0
2

Serial powering



Powered from constant
current
source



Each module is on different ground


potential


AC
-
coupled communication



Shunt regulator and transistor to take


excess current and stabilize voltage



Voltages are created locally via shunt


and linear regulators

Parallel powering with DC
-
DC conversion



Need radiation
-
hard magnetic field tolerant


DC
-
DC converter



One converter per module or parallel scheme



1
-
step or 2
-
step conversion

Katja Klein

Serial Powering vs. DC
-
DC Conversion

4

The Buck Converter

Convertion ratio g > 1
:

g = V
in

/ V
out

Switching frequency f
s
:

f
s

= 1 / T
s

The
“buck
converter“ is simplest inductor
-
based step
-
down converter:

Katja Klein

Serial Powering vs. DC
-
DC Conversion

5

The Charge Pump



Capacitor
-
based design



Step
-
down: capacitors charged in series and discharged in parallel



Conversion ration = 1 / number of parallel capacitors



Low currents

Implementation Examples

Katja Klein

Serial Powering vs. DC
-
DC Conversion

6

PP with DC
-
DC conversion:

Serial powering:

Atlas pixels, Tobias Stockmanns

Stefano Michelis, TWEPP2008



Two
-
stage system



Diff. technologies proposed for the two stages



Analogue and digital power fully separated



Power for optical links ~ integrated



HV not integrated



Regulators on
-
chip or on the hybrid



AC
-
coupled communication with off
-
module


electronics



Power for optical links not integrated



HV not integrated

What Conversion Ratio do we need?

Katja Klein

Serial Powering vs. DC
-
DC Conversion

7



Total tracker current estimate



Current strip tracker: 15kA; current pixel: 1.5kA



Geoffs strawman: strips: 25kW/1.2V = 21kA; pixels: 3.2kA; trigger layers: 10kA



Currents increase roughly by factor of 2 in this strawman



Power loss in cables



Goes with I
2


increase by factor of 4 for same number of cables (2000)



Total power loss inverse proportional to number of power groups



Can compensate with (conversion ratio)
2



Material budget



Saving in cable x
-
section scales with I



Total material independent of segmentation



Of course want to reduce as much as possible

Conversion ratio needed for parallel powering with DC
-
DC converters?

With conversion ratio of ¼ we would be as good as or better than today.

SP: current fixed; cable material & power loss depends only on # of cables!

Power Losses in Cables

Katja Klein

Serial Powering vs. DC
-
DC Conversion

8



Consider system with n modules:


P
det

= n

I
0

V
0



Voltage drop on cables & power loss P
cable



calculated within each scheme



Efficiency = P
det

/ P
total

= P
det

/ (P
det

+ P
cable
)



Power losses in cables lead to decrease of overall power efficiency



expensive



... increase the heat load within the cold volume


cooling capacity must be higher

SP

DC
-
DC,

r = 1/10

DC
-
DC, r = 1/5

Serial powering



Eff. increases with n. Since 10
-
20


modules can be chained, efficiency


can be very high!

PP with DC
-
DC conversion



E
ff. goes down with n. Need more cables


or lower conversion ratio



Equal to SP if conversion ratio = 1/n

Local Efficiency

Katja Klein

Serial Powering vs. DC
-
DC Conversion

9

Serial powering



Constant current source



total power consumption is contant!



Current of chain is fixed to highest


current needed by any member



Current not used by a module flows


through shunt regulator



Linear regulator: voltage difference


between dig. & analog drops across it



Local power consumption is


increased!



Estimated increase for


-

Atlas pixels (NIM A557): 35%


-

Atlas strips (NIM A579, ABCD): 18%

PP with DC
-
DC conversion



All DC
-
DC converters have inefficiencies



switching losses



ESR of passive components



R
on

of transistor etc.



Typical values (e.g. comm. buck): 80
-
95%



Efficiency goes down for low conv. ratio!



Trade
-
off betw. eff. & switching frequency



In two
-
step schemes, efficiencies multiply



Estimates (St. Michelis, TWEPP2008):



Step
-
1: 85
-
90%



Step
-
2: 93%



Total: 80
-
85%



This needs to be demonstrated

Compatibility with LIC Cables

Katja Klein

Serial Powering vs. DC
-
DC Conversion

10

PP with DC
-
DC conversion



30V is largely enough



For any reasonable segmentation and


conv. factor currents should be lower


e.g. 20 chips a 53mA per module


1.2A / module


20 modules per rod


24A /rod


r = ¼


I = 6A



looks compatible

Serial powering



Current is small



30V allows for chains with more than


20 modules



looks compatible

Constraints from recycling of current services:



2000 LICs with two LV conductors & common return each




Not realistic to split return to obtain 4000 lines




Stay with 2000 LV power lines (“power groups“)



LV conductors certified for 30V and 20A



Twisted pairs (HV/T/H/sense) certified for 600V



256 PLCC control power cables



Adapt at PP1 to (lower mass) cables inside tracker

Power Supplies

Katja Klein

Serial Powering vs. DC
-
DC Conversion

11

PP with DC
-
DC conversion



Standard PS: ~15V, ~10A


(radiation & magnetic field tolerant?)



Any sensitivity of converter to input


voltage ripple?



No sensing needed (local regulation)?

Serial powering



Constant current source



Not so common in industry (e.g. CAEN)



Atlas: PSs developed by Prague group


(developed already their current PSs)



No sensing



Assume that power supplies will be exchanged after 10 years

Bias Voltage

Katja Klein

Serial Powering vs. DC
-
DC Conversion

12

PP with DC
-
DC conversion



Same options as for SP


Serial powering



Not yet well integrated into concept



Derive on
-
module via step
-
up converters?


In Atlas, piezo
-
electric transformers are


discussed.



Or independent delivery using todays


cables



Power is not a problem (currents are very low)



Up to now: independent bias lines for 1
-
2 modules



Might not be possible anymore when current cables are re
-
used



Note: T/H/sense wires are equal to HV wires

Safety (I)

Katja Klein

Serial Powering vs. DC
-
DC Conversion

13

PP with DC
-
DC conversion



Open connections



Converter itself can break



Shorts between converter and module



If PP of several mod.s by one converter:


risk to loose several modules at once

Serial powering



Open leads to loss of whole chain



Shunt regulators/transistors to cope


with this



Several concepts are on the market


(next page)



Connection to module can break




bypass transistor on mothercable


-

high V, high I


rad.
-
hardness?


-

must be controlable from outside



Real
-
time over
-
current protection?



Real time over
-
voltage protection?



Fermilab expressed interest to perform a systematic failure analysis

Safety (II)

Katja Klein

Serial Powering vs. DC
-
DC Conversion

14

2.
One shunt regulator + transistor per module

+ no matching issue

-

no redundany

-

needs high
-
current shunt transistor

-

must stand total voltage


3.
One reg. per module + distributed transistors

+ no matching issue

+ some redundancy

-

feedback more challenging


1.
Shunt regulators + transistors parallel on
-
chip
(Atlas pixels)

+ redundancy

-

matching issue at start
-
up


Regulator with lowest threshold voltage


conducts first




all current goes through this regulator




spread in threshold voltage and


internal resistance must be small

Slow Control

Katja Klein

Serial Powering vs. DC
-
DC Conversion

15

PP with DC
-
DC conversion



Slow control IC or block on hybrid



For on
-
chip charge pump:


would be useful to have SC information


from individual chips



Could be used to set converter output


voltage and switch on/off converters

Serial powering



Slow control IC or block on hybrid



Could be used to communicate with


linear regulator and turn to stand
-
by



Ideas to sense module voltage in


Atlas pixels:


-

sense potential through HV return


-

sense through AC
-
coupled data
-
out


termination


-

sense from bypass transistor gate



Module voltage(s)



Module current(s)?



Bias current

Start
-
up & Selective Powering

Katja Klein

Serial Powering vs. DC
-
DC Conversion

16

PP with DC
-
DC conversion



If converter output can be switched


on/off, then easy and flexible:



-

controls can be switched on first


-

bad modules (chips?) can be switched off


-

groups of chips/modules can be switched


on/off for tests



This should be a requirement!

Serial powering



If controls powered from separate line,


it can be switched on first



Devices in chain switched on together


(both module controller and FE
-
chips)



Can take out modules only by closing


bypass transistor from outside

Scalability

Katja Klein

Serial Powering vs. DC
-
DC Conversion

17

Serial powering



Current is independent on # of modules



Number of modules reflected in maximal


voltage within chain; relevant for



capacitors for AC
-
coupling



constant current source



bypass / shunt transistors

PP with DC
-
DC conversion



If one converter per module:


perfect scalability



PP of several mod. by one converter:


current depends on # of modules,


must be able to power largest group



Should specify soon what we need



current per chip



# of chips per module



# of modules per substructure



Otherwise we will be constraint by


currents that devices can provide



Consequences if more modules are powered per chain or in parallel?


E.g. barrel vs. end caps: different # of modules per substructure

Flexibility

Katja Klein

Serial Powering vs. DC
-
DC Conversion

18

PP with DC
-
DC conversion



If one converter per module:


very flexible, do not care!



If PP of several modules by one converter:


distribution between modules arbitrary

Serial powering



Current of chain is equal to highest


current needed by any member




chains with mixed current


requirements are inefficient!



Flexibility with respect to combination of devices with different currents


E.g. trigger vs. standard module (or 4 / 6
-
chips)

Potential to Provide Different Voltages

Katja Klein

Serial Powering vs. DC
-
DC Conversion

19

PP with DC
-
DC conversion



With charge pumps, only integer


conversion ratios are possible



With inductor
-
based designs, arbitrary


V
out

< V
in

can be configured


(but feedback circuit optimized for a


certain range)



Only hard requirement: V
in

>= V
opto



Analogue and digital voltage can be


supplied independently




no efficiency loss

Serial powering



Needed voltage created by regulators



~1.2V by shunt regulator



Lower voltage derived from this via


linear regulator


efficiency loss



Technically could power opto
-
electronics


and controls via own regulators, but


inefficient to chain devices with different


current consumption



Decouple from chain


(Atlas: plan to power separately from


dedicated cables)



Chip supply voltage(es): ~ 1.2V (Atlas: 0.9V for digital part to save power)



Opto
-
electronics supply voltage: 2.5


3V

Process Considerations & Radiation Hardness

Katja Klein

Serial Powering vs. DC
-
DC Conversion

20

Serial powering



Regulators must be rad.
-
hard



Standard CMOS process can be used;


but...



HV tolerant components (up to n

U
0
):


-

capacitors for AC
-
coupling


-

bypass transistor



Shunt transistors must stand high


currents (~2A) if one per module

PP with DC
-
DC conversion



Commercial devices are not rad.
-
hard



Apparent exception: Enpirion EN5360


(S. Dhawan, TWEPP2008)



Standard 130nm CMOS: 3.3V maximal



For high conversion ratio transistors


must tolerate high V
in

, e.g. 12V



Several “high voltage“ processes exist



Rad.
-
hard HV process not yet identified



This is a potential show stopper



For r = ½ (e.g. charge pump) can use


3.3V transistors
-

radiation hardness?

Interplay with FE
-
Chip

Katja Klein

Serial Powering vs. DC
-
DC Conversion

21

Serial powering



Several options for shunt


-

Regulator and transistor on
-
chip


-

Only shunt transistor on
-
chip


-

Both external



Linear regulators typically on
-
chip



Next Atlas strip FE
-
chip (ABCnext):


-

linear regulator


-

shunt regulator circuit


-

shunt transistor circuit



Next Atlas pixel chip (FE
-
I4):


-

Shunt regulator


-

LDO




DC
-
balanced protocol

PP with DC
-
DC conversion



Ideally fully decoupled



Not true anymore in two
-
step approach with


on
-
chip charge pump



Next Atlas strip FE
-
chip (ABCnext):


-

linear regulator to filter switching noise



Next Atlas pixel chip (FE
-
I4):


-

LDO


-

Charge pump (r = ½)



No influence on protocol

Readout & Controls

Katja Klein

Serial Powering vs. DC
-
DC Conversion

22

PP with DC
-
DC conversion



Nothing special: electrical transmission of


data and communication signals to


control ICs



No DC
-
balanced protocol needed

Serial powering



Modules are on different potentials




AC
-
coupling to off
-
module


electronics needed



Decoupling either on the hybrid


(needs space for chips & capacitors)


or at the end of the rod


(Atlas strips, P. Phillips, TWEPP08)



Needs DC
-
balanced protocol




increase of data volume

Atlas pixels, NIM A557

Noise

Katja Klein

Serial Powering vs. DC
-
DC Conversion

23

Serial powering



Intrinsically clean


-

current is kept constant


-

voltages generated locally



Main concerns:


-

pick
-
up from external source


-

pick
-
up from noisy module in chain



Tests by Atlas pixels (digital) and strips


(binary) revealed no serious problems


-

noise injection


-

modules left unbiased


-

decreased detection thresholds


-

external switchable load in parallel to one


module (changes potential for all modules):


some effect (Atlas pixels, NIM A557)


PP with DC
-
DC conversion



Switching noise couples conductively


into FE



Radiated noise (actually magnetic


near
-
field) is picked up by modules



Details depend on FE, distances,


filtering, coil type & design, switching


frequency, conversion ratio, ...



Shielding helps against radiated noise,


but adds material, work and cost



LDO helps against conductive noise,


but reduces efficiency



Surprises might come with bigger


systems



Not good to start already with shielding


and system
-
specific fine
-
tuning

Material Budget

Katja Klein

Serial Powering vs. DC
-
DC Conversion

24

Serial powering



Regulators ~ one add. chip per hybrid



Components for AC
-
coupling


-

HV
-
safe capacitors (might be big!)


-

LVDS chip



Flex for discrete components



Cable cross
-
section from PP1 to


detector (rest stays) scales with current


-

One cable must carry I
0


-

Total mass depends on modules / cable



Motherboard/
-
cable: power planes can


be narrow, small currents & voltages


created locally


PP with DC
-
DC conversion



Converter chip(s)



Discrete components


-

air
-
core inductor (D = 1
-
2cm!)


-

output filter capacitor(s)



Flex for discrete components



One cable must carry I
0
nr


t
otal


mass depends only on conv. ratio



Motherboard/
-
cable


-

buck converter can tolerate certain


voltage drop since input voltage must


not be exact


low mass


-

charge pumps have no output


regulation: need exact V
in



Shielding?

Space

Katja Klein

Serial Powering vs. DC
-
DC Conversion

25

Serial powering



Different options are discussed, but


regulators + shunt transistors are either


in readout chip or in a separate chip




~ one additional chip per hybrid



Components for AC
-
coupling


-

LVDS buffers


-

HV
-
safe capacitors (might be big)



Bypass transistor?

PP with DC
-
DC conversion



Charge pump in readout chip or in a


separate chip



Buck converter:


-

controller chip


-

discrete air
-
core inductor (D = 1
-
2cm!)


-

discrete output filter capacitor(s)


-

more?




very unlikely to be ever fully on
-
chip



In all other inductor
-
based topologies


more components (inductors!) needed

Test Systems for Construction Phase

Katja Klein

Serial Powering vs. DC
-
DC Conversion

26

PP with DC
-
DC conversion



Electrical readout of single modules


possible with adapter PCB

Serial powering



If AC
-
coupling at end of stave, a


decoupling board is necessary to read


out single modules



Adapter PCB needed anyway for


electrical readout


RWTH Aachen (L. Feld)



proposal accepted


System test measurements with commercial and custom
DC
-
DC (buck) converters


Simulation of material budget of powering schemes


Rad.
-
hard magnetic
-
field tolerant buck converter in collaboration with CERN group


Bristol university (C. Hill)



proposal accepted



Development of PCB air
-
core toroid



DC
-
DC converter designs
with air
-
core transformer


PSI (R. Horisberger)



no proposal, but private communication


Development of on
-
chip CMOS step
-
down converter (
charge pump
)


IEKP Karlsruhe (W. de Boer)


proposal under review


Powering via cooling pipes


Fermilab / Iowa / Mississippi (S. Kwan)


proposal under review



System test measurements focused on pixel modules
(DC
-
DC conversion & SP)



Power distribution simulation software





Katja Klein

Serial Powering vs. DC
-
DC Conversion

27

Work on Powering within CMS Tracker


Both schemes have their pros and cons


how to weigh them?


SP is complicated, but I do not see a real show stopper


DC
-
DC conversion is straightforward, but two potential show stoppers


noise, radiation
-
hardness of HV
-
tolerant process


Need to understand SP better


In particular safety, slow controls


Up to now, we focus on DC
-
DC conversion


should we start on SP? Who?


Both Atlas pixels and strips integrate power circuitry in their new

FE
-
chips: shunt regulators, charge pump, LDO


Seems to be a good approach
-

can we do the same?


Katja Klein

Serial Powering vs. DC
-
DC Conversion

28

Summary