1. Serial Powering - Protection Purpose Protect the stave Assure supply of power to a serial powered chain of modules when one member of the chain fails Control the stave Allow power to arbitrary selection of modules Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 1

2. Why add protection? 2 Wire bonding failure Power failure modes Noisy module Open circuit module Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 Without protection, one failed module can adversely affect the operation of all other modules on stave Demonstration staves are very reliable - Protection is not strictly necessary

3. How to add protection? 3 Short out affected module(s) -- Switch on -- Short out and disable this module One module out-of-service Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 The switch should respond to module over-voltage and to DCS control

4. Issues to address 4 How does the protection do its job? Is automatic protection required? How fast must the protection react? Is DCS control/reporting required? (yes) How is the protection controlled? Switching must not affect the rest of the SP chain? Where should the switch be placed? (hybrid) Quantitative estimate of failure rate? What extra complexity can we justify? Is protection needed for other powering configurations? But… C ircuit options default state connections Feedback from hybrid current/voltage Reaction time Implementation requirements AC coupling Automatic and/or DCS Transient effects on problem &/or power-up Bus-cable or hybrid Numerical failure analysis Switch failure modes, fail safe, mass, possibility of common mode failure, monitoring Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 Note that independent module voltage monitoring may be available through the shunt regulator device if using an “intelligent” component such as SPi, but this may not be possible if there is a an open-circuit module. However, it may be possible to identify a faulty module by switching all modules off, then each one on in turn.

5. Qualitative target specification 5 DCS should be able to switch off (short-out) selected modules Residual voltage (when ‘off’) < 100mV Minimise number of components, area of components and bus-cable lines Position on hybrid is acceptable Over-voltage & over-current automatic protection is desirable Switching a working module on/off must not affect the behaviour of other modules During normal operation (module working) protection draws no power Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009

6. Can we use just one transistor for the task of shorting and SR? Can we accept the risk of wire-bonds carrying power from bus-cable to hybrid or should protection be placed directly on the bus-cable? Can SR and protection be included in a single ASIC package? Examples 6 Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 OR Less material, but possibility of common mode failure OR Easier to implement, but depends on good wire bonding

7. a) Circuit option 7 No active protection This option has been sufficient for demonstration staves. This is a serious option for the ATLAS upgrade. +simple minimum mass, minimum lines engineered redundancy including thick wire bonds & several shunt transistors -Cannot switch modules off Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009

8. b) Circuit option 8 Bonn Each module has a single line to an off-detector controller. This can be used to switch the module off (short it) or to monitor the module voltage. +simple +control & monitor default state = OC -no fast auto- response -many bus-cable wires Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 OC = Open Circuit (ie switch is “off”, module powered) RefATLAS Tracker Upgrade Workshop, NIKHEF 3-7 Nov 2008 Powering, Wed 5 Nov 2008, 17:30 Laura Gonella http://indico.cern.ch/conferenceTimeTable.py?confId=32084

9. c) Circuit option 9 BNL A common data line fed to a one-wire controller output is latched and used on each module to switch the module off (short it). +latching control +single DCS wire +fast auto-response default state = OC -no monitor -low residual module- off voltage required to hold latch Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 RefATLAS Tracker Upgrade Workshop, NIKHEF 3-7 Nov 2008 Electronics Working Group, Tue 4 Nov 2008, 15:40 David Lynn http://indico.cern.ch/conferenceTimeTable.py?confId=32084 OC = Open Circuit (ie switch is “off”, module powered)

10. d) Circuit options 10 Villani Similar to the Bonn design, but power is delivered to the one- wire controller and latch by the data line. +latching control +“single” DCS wire +no trickle power default state = OC -no monitor -no auto-response Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 OC = Open Circuit (ie switch is “off”, module powered)

11. e) Circuit options 11 Extended As Villani design, but latch may also be set in the safe state using the shunt regulator alarm. Also consider depletion mode FET for fail-safe. +latching control +single DCS wire +no trickle power +auto-response default = SC -no monitor Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 SC = Short Circuit (ie switch is “on”, module un-powered)

12. Comparison 12 Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 Proposal Auto over-voltage protectionAuto over-current protectionLatchingMinimum ( ‘ off ’ ) voltage Circuit complexityExtra bus-cable linesExtra passive module componentsExtra active module componentsExtra module massExtra area mm 2 Demonstrated No protection NNNn/aL00000Y Bonn NNN0Ln21??? BNL YNY?M243? 100 Y Villani NNY0H2????½ Extended YYY0H2????N

13. Summary 13 …circuit options are being implemented and evaluated… Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009

14. End 14 …circuit designs follow… Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009

15. Bonn protection 15 Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 Copied from presentation by Laura Gonella ATLAS Tracker Upgrade Workshop, NIKHEF 3-7 Nov 2008 Powering, Wed 5 Nov 2008, 17:30 http://indico.cern.ch/conferenceTimeTable.py?confId=32084

16. BNL protection 16 Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 Copied from presentation by David Lynn ATLAS Tracker Upgrade Workshop, NIKHEF 3-7 Nov 2008 Electronics Working Group, Tue 4 Nov 2008 http://indico.cern.ch/conferenceTimeTable.py?confId=32084

17. Villani protection 17 Richard Holt – Rutherford Appleton Laboratory ATLAS SCT SP protection options January 2009 From Giulio Villani, RAL – personal communication