Compilation of Dis-/Advantages of DC-DC Conversion Schemes Katja Klein 1. Physikalisches Institut B RWTH Aachen University Power Task Force Meeting December 16th, 2008

Advantages: Grounding Standard grounding scheme Module ground potentials are all the same Common ground reference for bias, analogue and digital voltage for whole substructure (rod, petal) Bias voltage ground reference is the same for all modules Easier for slow controls (difficult in SP to sense voltages) Katja Klein Discussion of DC-DC Conversion

Advantages: Communication Readout and control scheme is very standard AC-coupling of communication not needed Control chips can be supplied independently of modules Katja Klein Discussion of DC-DC Conversion

Advantages: Start-Up & Selective Powering Easy start-up Control chips can be powered on first If one converter per module, single modules can be powered on/off In scenario w/ charge pump per chip, single chips can be powered on/off Katja Klein Discussion of DC-DC Conversion

Advantages: Different Voltages Different voltages can be provided Buck-type converters: the same converter chip can be configured for different output voltages Via a resistive bridge Two conversion steps can be combined No efficiency loss (in contrast to linear regulation in SP) Can cope with Vopto > Vchip Can cope with Vana ≠ Vdig Charge pumps: only integer conversion ratios, defined by configuration Katja Klein Discussion of DC-DC Conversion

Advantages: Flexibility Great flexibility with respect to combination of modules with different load Different numbers of readout chips Trigger modules vs. standard modules power groups with different number of modules TEC vs. barrel In contrast, with SP current is fixed to highest current needed by any chain member  chains must be uniform to avoid burning power in regulators Katja Klein Discussion of DC-DC Conversion

Advantages: Changing Loads Compatibility with changing loads, relevant for pixel detector load is driven by occupancy trigger modules SP: the highest current potentially needed must always be provided  inefficiency Katja Klein Discussion of DC-DC Conversion

Disadvantages: Chip Technology Need for a “high voltage“ tolerant process (10-12V) Good candidate identified, radiation hardness still to be proven Strong dependency on foundry: support of process over years? Any changes in process must be followed closely and irradiation tests be repeated Katja Klein Discussion of DC-DC Conversion

Disadvantages: Converter Efficiency Converter efficiency will be around 80% (ESR of passive components, Ron of transistors, switching losses) Local generation of heat  cooling of DC-DC converters needed Local efficiency decreases with lower conversion factor (Uout/Uin) Local efficiency decreases with higher switching frequency In two-step schemes efficiencies multiply Katja Klein Discussion of DC-DC Conversion

Disadvantages: Currents in Cables Cannot compete with Serial Powering Currents in power group with DC-DC conversion = I0nr I0 = current of a single module n = number of parallely powered modules in the power group r = conversion ratio = Uout/Uin Current in Serial Powering chain = I0, independent of n E.g. for 20 modules in power group need r = 20 to compensate Higher efficiency in SP (at least up to FE)  less cooling needed Cables inside tracker volume can be thinner with SP Katja Klein Discussion of DC-DC Conversion

Discussion of DC-DC Conversion Disadvantages: Risks We have to stick with parallel powering Multiplicity (modules per cable) as today or higher Open connections (e.g. at PP1, PP0) lead to loss of power group Short on module leads to loss of power group Protection needed? Use DC-DC converter to switch off module? Converter can break: can imagine isolated failures (loss of regulation...) and failures that lead to loss of power group (short) More risky if one converter powers several modules Do we need redundancy? This adds mass Katja Klein Discussion of DC-DC Conversion

Disadvantages: Material & Space Material budget and space considerations Amount of copper in cables scales with current = I0nr I0 = current of a single module n = number of modules in the power group r = conversion ratio = Uout/Uin Air-core inductor (even if integrated into PCB, it needs a lot of copper) Filter capacitors, maybe other filter components With regulation (buck etc.), PCB traces can be narrow Without regulation (charge pumps), input voltage must be exact Linear regulator or rather solid input traces Is shielding needed? How to design good low mass shielding? Katja Klein Discussion of DC-DC Conversion

Disadvantages: Material Budget Simulated components: Kapton substrate with 4 copper layers Copper wire toroid Resistors & capacitors Chip TEC 1 converter / module Mother- boards Analog Opto-Hybrids Kapton circuits FE-hybrids Katja Klein Discussion of DC-DC Conversion

Disadvantages: Material Budget Total gain for strip tracker with 1 converter per module and a conversion ratio of 8; with power cables and motherboards modified accordingly: Strip tracker Katja Klein Discussion of DC-DC Conversion

Discussion of DC-DC Conversion Disadvantages: Noise DC-DC converters are undoubtedly noise sources (by design) Conductive noise through cables Ripple on output voltage: switching frequency (1-5MHz) + higher harmonics are in the bandpath of the amplifier Switching leads to high frequency noise (tens of MHz, not so critical) Both CM and DM contributions Radiated noise From inductor near field via inductive (and capacitive?) coupling From cables Has to be taken into account for all aspects of electronics system design: readout chip, FE-hybrid, grounding & shielding, motherboard, layout ... Not clear what to prepare for: noise depends on implementation For same chip, noise emission can be rather different depending on PCB etc. Scalability from lab system to complete detector not obvious PS noise requirements to be understood Katja Klein Discussion of DC-DC Conversion