8/11/2006 FPIX TB meeting L. Perera 1

Pixel Power Supply Response MeasurementLalith Perera - Univ. of Iowa

Carlos Florez , Simon Kwan, Charles Newsom, Christian Veelken

• Response of the CAEN power supply to transient currents

• Response of the power supply to remote shut down.

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CAEN Power supply overview

• SY2527 system mainframe• Can install six A1676A branch control

cards• A1676A branch control card

– Controls one E4000 crate• E4000 crate

– Accommodates 8 power modules• CAEN E4603 power module

– Each unit has two independent power units

• Two low voltages 2.5V, 1.75V (remotely sensed voltage control, up

to 6V at the supply)• Two high voltages.

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Objective

• Preliminary testing to get familiar with using the power supply with the MSC cable for the system test

• Make sure that power supply meet system requirements and behave well with remote sensing:

– Current fluctuations changes the voltage drop across the supply cable resulting fluctuating voltage at the load.

CAENA4603

48V

Pulse generator

CAENSY2527

LoadCable ~40m

scope

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CMS pixel power cable (MSC)

• We used a 40m length of MSC cable

• Six 4mm2 cables for LV– 4 for 2.5 V– 2 for 1.75

• Resistance of each cable m

• Cables for sense wires and HV

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Test Setup

switching transistors

resistor elements

Jumper switches

Test Load • Six resistors ~1.6 (connected through jumper switches - up to 8A current)

• Two 0.1 connected through switching transistors (FET) (2A pulse current)

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Results

pulse current

voltage at the load

control pulse

• No observed oscillations• Voltage drops by ~ 0.5V when load change by 2A.• recovery time of the power supply

– 2.5V ~50 s, 1.75V 100 s

• There are small (50mV) spikes at ~ 80kHz likely to be coming from from switching in the power supply

2.5V 1.75V

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response to 1s pulse after adding 13F capacitor

•Voltage fluctuation can be lowered by adding decoupling capacitors near the load

•However in the real detector load is distributed, so capacitors at each ROC should take care of the fluctuation

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Remote Shut Down• CAEN power supply is controlled by the DCS computer so

can be turned on/off through DCS. It is software controlled so would to be too slow for an emergency shut down.

There are two control inputs to SY2527 to turn off all channels.

•KILL: input for a TTL/NIM signal “ The KILL input signal, sent through the relevant connector, allows to switch the channels off at the maximum rate available, regardless of the Ramp-Down or other parameters.”

•INTERLOCK: close/open circuit input “The INTERLOCK condition allows to switch off simultaneously all the channels, similar to the KILL command”

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Shut Down Response Time Measurement

power supplyPulse generator

load

scope

KILL

power supply

load

scope

INTERLOCKrelay

From PLC

Test setup to measure KILL response time

Test setup to measure INTERLOCK response time

5v

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Results: KILL

KILL

Power Digital

Power Ana.

Response time

68ms 18ms 36ms

40ms 96ms 27ms

Response time to KILL changes from few ms to ~100ms

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INTERLOCK Response Time

36ms 42ms 68ms

•Measured INTERLOCK response time is tens of ms and varies

•It could be that both KILL and INTERLOCK is activated by software

So depending on where it occurs in the control loop of the

power supply it gives a different response time.

This needs to be verified with CAEN.

INTERLOCK

Power Ana.

Power Digital

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Conclusions• Power supply behaves well to transient currents with the CMS

MSC cable. No oscillations observed.

• Remote sensing time constant of the supply voltage is about 25 s.

• There are two remote hardware shut down modes (INTERLOCK, KILL) available. Both have response times in the order of tens of ms