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Gamma-ray Large Area Space Telescope. GLAST Large Area Telescope: Electronics, Data Acquisition & Flight Software TEM Power Supply Part 1 Gunther Haller Stanford Linear Accelerator Center Manager, Electronics, DAQ & FSW LAT Chief Electronics Engineer [email protected]

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Gamma-ray Large Area Space Telescope

GLAST Large Area Telescope:

Electronics, Data Acquisition & Flight Software

TEM Power Supply

Part 1

Gunther Haller

Stanford Linear Accelerator Center

Manager, Electronics, DAQ & FSW

LAT Chief Electronics Engineer

[email protected]

(650) 926-4257

Lat electronics physical
LAT Electronics Physical

TKR Front-End Electronics (MCM)

16 Tower Electronics Modules

  • DAQ electronics module (DAQ-EM)

  • Power-supplies for tower electronics

ACD Front-End Electronics (FREE)


CAL Front-End Electronics (AFEE)


Global-Trigger/ACD-EM/Signal-Distribution (GAS) Unit*

3 Event-Processor Units (2+1 spare)

  • Event processing CPU

  • LAT Communication Board (LCB)

  • Storage Interface Board (SIB)

Spacecraft Interface Unit

  • Storage Interface Board (SIB): EEPROM

    SC MIL1553 control & data

  • LAT control CPU

  • LAT Communication Board (LCB): LAT command and data interface

Power-Distribution Unit (PDU)*

  • Spacecraft interface, power

  • LAT power distribution

  • LAT health monitoring

* Primary & Secondary Units shown in one chassis

Lat power distribution
LAT Power Distribution

  • SIU’s are powered directly by spacecraft on dedicated feeds

  • Rest of LAT electronics is powered via SC main feed to PDU

    • Prime and redundant SC feeds connected to prime and redundant PDU circuits

  • PDU controls power to towers, to GASU, and to EPU’s

    • Either PDU circuit can supply power to clients

  • GASU switches power to ACD

    • Prime and redundant GASU circuit can supply power to ACD

  • TEM’s switch power to TKR/CAL

    • No redundancy in tower power system

  • Heater power circuit not shown


  • Requirements are in LAT-SS-01281

  • Supply power to Calorimeter, Tracker, TEM-DAQ systems

    • Main drivers are

      • Low output noise, down to 100 uV RMS, 1 mV p-p

        • Powers input amplifiers of CAL and TKR front-end electronics

      • Low output voltage, down to 1.5 V

        • TKR input amplifier runs of 1.5V to meet power/thermal requirements for 850k channels

      • High overall efficiency

        • Total LAT power limited, also thermal limits because of radiator area

      • Adjustable high-voltage supply up to 150V

        • Silicon strip TKR detectors (up to 150V) and CAL Si-diodes (up to 100V) need remotely adjustable depletion voltages

Detailed requirements
Detailed Requirements

  • See LAT-SS-1281,

    (display the requirement pages in that document for discussion)

Tower power supply module
Tower Power Supply Module


Ana-1.5V-A (~1A)

Ana-1.5V-B (~1A)

Tracker Voltages

Ana-2.5V-A (~1A)

Ana-2.5V-B (~1A)

Dig-2.5V-A (~0.3A)

Dig-2.5V-B (~0.3A)

HV-150Vadj- (~1uA)

28V from PDU



Ana-3.3V (~0.4A)

Calorimeter Voltages

Dig-3.3V (~0.96A)

HV-100Vadj- (~1uA)



Dig-3.3V-del (~0.6A)

TEM-DAQ Voltages

Dig-2.5V (~0.4 A)

Currents are measured values


Temp, 3.3V TEM-V Sensors

I-Total MON

Tracker electronics
Tracker Electronics

  • TKR sub-system electronics

    • Si-Strip Detectors

    • 24 GTFE (GLAST Tracker Front-End) ASICs (1,536 signal channels)

    • 2 GTRC (GLAST Tracker Readout Controller) ASICs

    • MCM (Multi-Chip Module)

    • Flex-cables

  • Total of 36 (4 sides, 9 each) MCM’s per tower power supply module

    • Power is routed via TEM DAQ board from TEM-PS to TKR



    Calorimeter electronics
    Calorimeter Electronics

    • CAL sub-system electronics

      • Diodes

      • 48 GCFE (GLAST Calorimeter Front-End) ASICs

      • 4 GCRC (GLAST Calorimeter Readout Controller) ASICs

      • AFEE (Analog Front-End Electronics) board

  • Total of 4 (4 sides, 1 each) AFEE’s per tower power supply module

    • Power is routed via TEM DAQ board from TEM-PS to CAL



    Daq electronics
    DAQ Electronics

    • Tower Electronics Module DAQ board

    • Total of 1 TEM DAQ per tower power supply module


    • Tower Power Supply interface via two connectors to

      • Power Distribution Unit

        • Incoming 28V +/- 1V

        • Monitoring to PDU

        • For EGSE desire to be able to remotely adjust front-end voltages

      • Tower Electronics Module

        • Supply voltages to TKR, CAL, and TEM

        • HV currents and total current monitoring

        • Enable signals for CAL and TKR system

        • Analog set voltage for HV supplies

      • LAT-SS-1281



    Tower Electronics Module

    TEM – PSU Stack


    • When SLAC electronics group started getting involved in LAT electronics (at approval of project)

      • Efficiency of power supplies of tower was supposed to be about 70% overall to meet power numbers

      • Tried to get more power, but denied

        • SC interface issue

        • Problem with getting rid of heat (radiator areas)

      • Worked to even more optimizing CAL, TKR, DAQ power (ASIC’s and other components),

        • Reduced power supply efficiency required to 62% (still very challenging, but that was it)

    • Standard solution with “catalog” 28V/3.3V DC/DC converter and linear regulators were explored but not realistic

      • At tower load of ~25W, needed at least 40W (at 3.3V!) converter, (no 1.5V or 2.5V converter available at that time)

        • At LAT load: efficiency is 65% to 70%. just for 28->3.3V part

        • Need to generate 2.5V and 1.5V via linear regulators from 3.3V

        • Results in 47-50% overall efficiency (including HV supplies)

        • Over allocation: between 88W and 126W

    Development con t
    Development (Con’t)

    • First solution

      • Pursued full-custom vendor design

        • Proof-of-principle prototype was designed and built, based on synchronous rectification

        • Measured 87% efficiency of 28V/1.5V supply!

        • Met power requirement (status at CDR)

        • Went out for bids (Responses came in after CDR)

        • Bid returned were not affordable, by a lot

        • Not a working solution

    Development con t1
    Development (Con’t)

    • Beginning of 04

      • International Rectifier proposed new Z-series converter, based on synchronous rectification

      • 28V/3.3V converter with up to 82% efficiency at full load, great device compared to others on the market

      • New Device (no flight heritage yet), assembly of two PC-boards and controller hybrid

    Development con t2
    Development (Con’t)

    • Needed to be optimized for LAT load (Z-series is optimized for 20A/3.3V (~82%), LAT only needs 40% of that -> efficiency drops considerably)

    • Put contract in place late spring 03 (as back-up)

    • However still does not meet power allocation by > 30W

    • Prototypes to be delivered late Fall 03

    • On order, but cancelable (need to decide end of 9/03 with penalty of 10%)

    • Risk that calorimeter 3.3V analog is connected to DAQ TEM 3.3V, very hard to filter low frequency noise from DAQ

  • Need to decide by end of 9/03 to avoid further penalty

  • Development con t3
    Development (Con’t)

    • Spring 03:

    • Surveyed commercial DC/DC converters and evaluated for potential radiation performance (CMOS versus bipolar technology, IC feature sizes)

    • Radiation tested several DC/DC integrated circuit devices at Legnaro and TAMU (in Summer 03)

    • Selected MAX724/726 devices as base-line

    • Designed circuit board for low-voltage circuits using MAX726

    • Designed high-voltage circuit (all along needed to be full-custom since nothing available as a catalog item)

      • Received also proof-of-principle HV design from vendor (at CDR)

      • Went out for bids

      • Was not affordable, by a lot

      • Got previous flight design from Art Ruitberg (GSFC)

      • Started new design at SLAC (Dieter Freytag), eliminating transformers

    Development con t4
    Development (Con’t)

    • Designed/simulated high-voltage circuit by 7/03

    • Laid out HV-only PC board, fabricate/loaded by 8/03

    • Designed/laid-out/fabricated full TEM-PS by end of August 03

    • Started testing 9/03

    • Review 9/22/03