Protect Your Device Against Power-Related Damage Understand and Make Best Use of Protection Features in System DC Power Supplies

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1 Protect Your Device Against Power-Related Damage Understand and Make Best Use of Protection Features in System DC Power Supplies August 20 th, 2014 Edward Brorein Power and Energy Division 1

2 Agenda The need for protecting against power-related damage 1 st line of defense: voltage and current limits 2 nd line of defense: current and voltage shutdown protection Considerations for being an integral part of the test system: Properly sequencing power for DUT safety Remote controls for test system integration Status subsystem and DUT protection Special considerations for long-duration tests Summary Page 2

The Need for Protecting Against Power-Related Damage Common Causes for Different Types of Voltage-Related Fault Events Voltage-Related Fault Event Causes: Operator/programming/controller error

3 The Need for Protecting Against Power-Related Damage Common Causes for Different Types of Voltage-Related Fault Events Voltage-Related Fault Event Causes: Operator/programming/controller error Voltage sense leads misconnected Over-riding external voltage source DC source internal circuit failure Predominantly series-regulated linear sources Load induced transient voltages Most voltage-related fault events are over-voltage but under-voltage fault events also exist Page 3

The Need for Protecting Against Power-Related Damage Common Causes for Different Types of Current-Related Fault Events Current-Related Fault Event

applied voltage slew rate Excessive current from DUT problems induced from incorrect bias sequencing DC source over-voltage protect trip drawing large

4 The Need for Protecting Against Power-Related Damage Common Causes for Different Types of Current-Related Fault Events Current-Related Fault Event Causes: Excessive current from overloading DUT s output Excessive current from DUT failure Excessive DUT inrush current Problem with DUT Too high of applied voltage slew rate Excessive current from DUT problems induced from incorrect bias sequencing DC source over-voltage protect trip drawing large DUT discharge current A large variety of mechanisms are incorporated into modern system DC power supplies to avoid as well as quickly act on fault events! Page 4

5 Agenda The need for protecting against power-related damage 1 st line of defense: voltage and current limits 2 nd line of defense: current and voltage shutdown protection Considerations for being an integral part of the test system: Properly sequencing power for DUT safety Remote controls for test system integration Status subsystem and DUT protection Special considerations for long-duration tests Summary Page 5

6 Protecting DUT with Voltage and Current Limits + Voltage CV setting = 5V R L > 5Ω CV Operation. Normal operating point R L = 5Ω Crossover pt. R L < 5Ω CL Operation + Voltage V limit = 5V V out R L > 5Ω VL Operation R L = 5Ω Crossover pt.. R L < 5Ω CC Operation Normal operating point + Current + Current 0 I out I limit = 1A 0 CC setting = 1A Constant Voltage Operation Constant Current Operation Current limit protects against excess current with increased loading Voltage limit protects against excess voltage with decreased loading On general purpose power supplies settings and limits are usually the same Page 6

Multi-Quadrant DC Source Settings and Limits 2 quadrant and 4 quadrant models Single constant voltage setting Separate + and current limits Limit restricted to

restricted to respective quadrants Keysight N678xA SMU in current priority 2 quadrant and 4 quadrant models Single constant current setting Separate + and voltage

7 Multi-Quadrant DC Source Settings and Limits 2 quadrant and 4 quadrant models Single constant voltage setting Separate + and current limits Limit restricted to respective quadrant Keysight N678xA SMU in voltage priority 2 quadrant and 4 quadrant models Single constant voltage setting Separate + and current limits Limits restricted to respective quadrants Keysight N678xA SMU in current priority 2 quadrant and 4 quadrant models Single constant current setting Separate + and voltage limits voltage limit is zero for 2 quadrant Limits restricted to respective quadrants Limits and settings are often uniquely different in multi-quadrant DC sources Page 7

Practical Considerations for Current Limits 2ms/ 2A/ gross limit (~5A) ~5.5ms 0 to 10A load step applied gross limit (~5A) ~0.5ms Current limit starts working 1A limit setting 0.

8 Practical Considerations for Current Limits 2ms/ 2A/ gross limit (~5A) ~5.5ms 0 to 10A load step applied gross limit (~5A) ~0.5ms Current limit starts working 1A limit setting 0.1A limit setting 3-Amp general performance DC power supply current limit response characteristics Larger difference between rating and limit setting produces greater overshoot Use reasonably-sized DC power supply for application Smaller difference between load and limit setting gives slower response Evaluate for application, keep expectations realistic or look for faster power supply Response characteristics vary greatly depending on conditions Page 8

9 Practical Considerations for Current Limits 5ms/ 2A/ ~5 ms ~0.7ms General purpose vs. N7951A Advanced Power System current limit response characteristics Comparable rated high performance DC power supply typically has 5~10X faster response speed Consider evaluating higher performance DC power supplies when faster current limit response is absolutely needed Response characteristics vary greatly between power supplies Page 9

10 Agenda The need for protecting against power-related damage 1 st line of defense: voltage and current limits 2 nd line of defense: current and voltage shutdown protection Considerations for being an integral part of the test system: Properly sequencing power for DUT safety Remote controls for test system integration Status subsystem and DUT protection Special considerations for long-duration tests Summary Page 10

Greater DUT Protection Using Over Current Protect (OCP) Problem: Many devices cannot take sustained current Solution: OCP provides greater level of currentrelated fault event damage Works together

11 Greater DUT Protection Using Over Current Protect (OCP) Problem: Many devices cannot take sustained current Solution: OCP provides greater level of currentrelated fault event damage Works together with current limit When current limit is reached output shuts down with OCP turned on Programmable hold-off delay avoids nuisance tripping Common cause is turn-on inrush current Delay is in addition to current limit response time OCP fault condition is latched Needs to be cleared to restart 12A Current limit active 2A/ 0.5ms/ Output quickly shuts down Keysight N7951A Advanced Power System (APS) output response with OCP enabled Page 11

Two-tier OCP Example Tailored for Current-Sensitive DUTs Problem: DUT requires time limit for inrush current as well as fast protection against excess peak Requires two OCPs, not generally

routing in the N6900A / N7900A series Advanced Power System (APS) In this example: Standard OCP acts immediately at 14A limit Signal routing adds 13.

12 Two-tier OCP Example Tailored for Current-Sensitive DUTs Problem: DUT requires time limit for inrush current as well as fast protection against excess peak Requires two OCPs, not generally available Solutions: External custom hardware (complex) Routine that executes within DC source Some advanced DC sources feature internally executable programming capabilities Expression signal routing in the N6900A / N7900A series Advanced Power System (APS) In this example: Standard OCP acts immediately at 14A limit Signal routing adds 13.5 A OCP with 300 ms delay Set to 300 ms delay Graphically configuring a second OCP for APS using the N7906A software Immediate OCP >14A Delayed OCP 13.5A to 14A No OCP <13.5A 14585A 10A/d 100 ms/d Two-tier OCP response for different loads Page 12

13 Protecting DUTs with Over Voltage Protect (OVP) Problem: DUTs need protection against voltage in excess of voltage setting or limit OV damage is virtually immediate Solution: OVP provides fast-acting shutdown on excess voltage above a set threshold Operates independent from voltage control Typical implementation depends on topology and potential failure mode: Linear: SCR crowbar creates hard short on output High-performance switch-mode: Turn output off and down-programmer full-on Basic-performance switch-mode: Turn output off Protect fault is latched Needs to be cleared to restart Voltage DUT OV damage. OVP setting V max setting 0 Operating point Load Line R L OVP variations :. I out OVP trip point I limit Current Voltage soft limit setting Tracking OVP Front panel lock-out Page 13

14 Practical Considerations for Over Voltage Protect (OVP) Margins and Response Time Prevent false tripping: Need sufficient margin over V max operating condition Transient voltage amplitude is load and set up dependent Adequately protect DUT: Voltage DUT OV damage OVP setting V max setting Leave margin Load transients Need sufficient margin below DUT OV damage level Factor in response delay (10 s to 100 s of µs) vs. DC power supply slew rate Example: 10 V/ms slew rate and 50 µs delay yields 0.5 V overshoot High performance DC power supply have up to 10X faster response Leave margin Start of OV condition Example: Keysight N6900A/N7900A series Advance Power System < 30 µs.. OVP response delay OVP act point OVP trip point Time (µs) Page 14

15 Practical Considerations for Over Voltage Protect (OVP) OVP Sense Point Power supply + SENSE + OUT OVP is traditionally sensed here V OVP SET > V DUT + V LEADS - OUT - SENSE Load lead voltage drop + - Load lead resistance Load lead resistance - + Load lead voltage drop DUT Using sense leads for OVP moves the OVP sense point right at the DUT OVP sensing at +/- OUT: Protects DUT and power supply for open, shorted, or reversed sense leads Protects power supply for open load leads Accuracy problematic for low voltages / large load lead voltage drops. OVP sensing at +/- SENSE: Accurate OV protection for any voltage level / any load lead voltage drops Does not protect in event of open, shorted, or reversed sense leads Keysight N6900A/N7900A APS OVP monitors both OUT and SENSE: Falls back to sensing at +/- OUT for open, shorted, or reversed sense leads Further augmented by sense lead fault detect system Page 15

16 Assuring Voltage Integrity at DUT When Remote Sensing Sense Protection Power supply + SENSE + OUT Load lead voltage drop + - Load lead resistance DUT - OUT - SENSE Load lead resistance - + Load lead voltage drop Sense Lead Protect: Passively reverts to local sense connection for open sense lead Prevents runaway output for open sense lead condition Sense Fault Detect: Actively checks for open sense leads Feature of 663xxB/D, and N6900A/N7900A series Advanced Power System (APS) Sets flag and displays annunciator indicating sense fault 663xxB/D triggers shutdown. N6900A/N7900A can be configured to trigger shutdown Sense Fault Detect assures a higher level of voltage integrity during test Page 16

17 Under Voltage Protection (UVP) Problem: Too low of voltage can damage certain DUTs Over-discharge batteries Reverse polarity on junctions in semiconductors Solutions: Some DC sources feature under voltage limits Custom hardware (complex, fast response) or software routine (easier, slow response) Some advanced DC sources feature internally executable programming capabilities Expression signal routing in the N6900A / N7900A series Advanced Power System (APS) In this example: Threshold comparator triggers protection shutdown for voltage dropping below 3V Challenge in use: Needs to be disabled prior to powering up and powering down to prevent undesired triggering Graphically creating a custom UVP for APS using the N7906A software Page 17

18 Agenda The need for protecting against power-related damage 1 st line of defense: voltage and current limits 2 nd line of defense: current and voltage shutdown protection Considerations for being an integral part of the test system: Properly sequencing power for DUT safety Remote controls for test system integration Status subsystem and DUT protection Special considerations for long-duration tests Summary Page 18

19 Properly Sequencing and Ramping DUT Bias Voltages Problem: Improper/imprecise sequencing of multiple bias voltages can cause DUT problems: Malfunction Excessive current draw Latch-up failure Solutions: Use test system controller for sequencing: Imprecise timing due to priority interrupts Good for ~100 ms sequence time delays Does not control slew rate Create custom hardware for sequencing: Costly and time consuming to develop Slew rate control complex to implement Use sequencing capabilities in system power supplies: Should include slew control and span separate units Supply A Supply B Delay sequence Supply A Supply B Simultaneous sequence ratio-metric ramp Supply A Supply B Simultaneous sequence simultaneous ramp Sequencing Examples Page 19

off-couple trigger connections extends precise sequencing to stand-alone Keysight N6900A and N7900A

20 Properly Sequencing and Ramping DUT Bias Voltages Delays, coupling, and slew (not shown) provides precise on/off sequencing on Keysight N6705B and N6700A/B series multiple output products On- and off-couple trigger connections extends precise sequencing to stand-alone Keysight N6900A and N7900A series single output units Controls built into power supplies resolves sequencing and ramping needs Page 20

21 Problem: Remotely Disabling Power Supply with Inhibit (INH) A remote shutdown is often needed: Panic switch on test system or fixture Fault issued by: Power distribution unit (PDU) Another power supply Another piece of test equipment By DUT itself Solution: Inhibit (INH) input on system power supply: Compatible with open collector or switch No intervention needed by controller Typical latency of just microseconds Can be set to off, latched, or live If latched, protection fault must be cleared before resuming INH control input on Keysight N6700A/B, N6900A, or N7900A series DC sources Page 21

22 Disabling Multiple Power Supply Outputs on a Fault Event Problem: Often all bias voltages need to be disabled on the event a fault: Leaving other bias voltages on can damage DUT Not brining all biases down as a group can damage DUT Solution: Fault event signal (FLT) used to group multiple power supplies: FLT true when protect status is true Includes over voltage, over current, over temperature, inhibit, and other fault conditions Chaining FLT outputs and INH inputs groups multiple units together for faults No need for controller intervention Latency of just microseconds Daisy chaining FLT and INH signals on Keysight N6700A/B, N6900A, or N7900A series DC sources for all to react on a fault on any one unit Page 22

Determining Operating Conditions Status Subsystem Tracks Operational Conditions Operation status group tracks normal operating conditions Determine if DUT is in expected operating condition (CC, CV,

23 Determining Operating Conditions Status Subsystem Tracks Operational Conditions Operation status group tracks normal operating conditions Determine if DUT is in expected operating condition (CC, CV, etc.) Condition register tracks current status Bits are live, not latched Event register tracks past status Bits are latched, cleared when read Detect occurrence of transient conditions Enable register allows select status to request service from test controller Voltage limit and current limit are considered questionable conditions, not operational conditions N6900A/N7900A series Advanced Power System operation status group registers Page 23

Determining Questionable Conditions Status Subsystem Tracks Questionable Conditions Questionable status group tracks abnormal operating conditions If DUT is in a fault (OV, OC, etc.

24 Determining Questionable Conditions Status Subsystem Tracks Questionable Conditions Questionable status group tracks abnormal operating conditions If DUT is in a fault (OV, OC, etc.) If power supply is in a fault (PF, CP, OT, etc.) If test system is in a fault (INH, PROT, etc.) Condition register tracks current status Bits are live, not latched Event register tracks past status Bits are latched, cleared when read Detect occurrence of transient conditions Fault conditions that shut down power supply are latched prior to questionable status group Fault needs to be cleared to restart N6900A/N7900A series Advanced Power System questionable status group registers Page 24

25 Determining Events to Avoid Possible Faults in the Making Status Subsystem Tracks Standard Event Conditions Event register tracks standard events: Bits are latched and cleared when read DDE flags self-test, calibration, or other device-specific errors Can identify subjecting DUT to an erroneous or miscalibrated condition EXE and CMD flag execution and command syntax errors Setting an important value, limit, or other critical setting could be ignored if errors are not checked PON flags AC power has been cycled Detect loss and recovery of AC power N6900A/N7900A series Advanced Power System standard event status group registers Page 25

26 Tracking Overall Status Status Byte Register Summarizes Information from Status Groups Enable registers in event groups pass selected status along to status byte register ERROR QUEUE NOT EMPTY Enable registers need to be set to pass status of individual bits Per IEEE SCPI standards Also includes error queue status Service request can be generated from status SRQ Enable register needs to be set accordingly N6900A/N7900A series Advanced Power System questionable status byte register Page 26

27 Diagnosing Faults After the Fact (and Failure) Post-Mortem Root Cause Analysis Failures do still occur! Random vs. systemic failures Often unique combination of factors Hard/impossible to reproduce Lack of info: cause is speculative / often incorrect Tracking key factors yields insights Power supply status and conditions DUT status and conditions I.D. if random or systemic I.D. combination of factors leading to failure Resource-intensive to track factors Need to continually query DC power supply Need independent thread to log factors N7906A utility displaying contents of optional black box recorder on N6900A/N7900A series APS 1. Time scale 2. Voltage 3. Current 4. Status signals 5. Output power cycled 6. User defined tag Page 27

28 Agenda The need for protecting against power-related damage 1 st line of defense: voltage and current limits 2 nd line of defense: current and voltage shutdown protection Considerations for being an integral part of the test system: Properly sequencing power for DUT safety Remote controls for test system integration Status subsystem and DUT protection Special considerations for long-duration tests Summary Page 28

29 Protecting DUTs During Long-Term Testing Loss of Test System Controller Problem: Loss of system controller can damage or destroy DUTs in long-term tests Burn-in testing Power cycling Battery charging and discharging Solution: Monitoring interface bus activity detects loss of test system controller: Stand-alone system or integrated into power supply Disables power supply output after set period of time Referred to as a watchdog timer Test system controller Interface bus Bus activity monitor System DC power supply Activity Watchdog timer Reset in Timed out Trigger fault / shut down Conceptual block diagram of watchdog timer on Keysight N6700A/B, N6900A, and N7900A series DC power supplies Page 29

30 Protecting Against Disruption of AC Power Setting Power-up State after AC Power Recovers Recover in an unpowered wake-up state: Standard for power-on reset state Generally preferred choice for conventional short-term testing Prevents re-powering DUT when in an un-initiated state Recover to prior state and settings: Recall state 0 (pre-assigned) at power-on on many power supplies Auto-reset at power-on (last state and settings) on some power supplies (feature in Keysight N5700 and N8700 series) Often a preferred choice for some long-term testing Prevents loss of test time after AC power recovers Identifying AC power was disrupted: Query PON flag in status subsystem Page 30

31 Summary The need for device protection against power-related damage during test Variety of causes for power-related events Voltage-related or current-related events are most common Limits provide a first line of defense Protect against excessive voltage or current Shutdown protection provides a second line of defense When all voltage or current needs to be removed Power-related protection needs to be integral to the test system Other power supplies in test system Test fixture, test rack, and other test equipment Monitoring status with test system software Background logging of DUT and power supply Long-duration tests have unique considerations Loss of controller, AC power, recovery state Page 31

note 5991-3093EN Reducing Device-Failure

32 Useful References Protect Against Power-Related DUT Damage During Test: App note EN Reducing Device-Failure Risk with a Black-Box Recorder: App note EN Page 32

More Useful References Learn more about the 9 test challenges the APS can help you overcome www.keysight.

33 More Useful References Learn more about the 9 test challenges the APS can help you overcome Check out Watt s Up? Keysight Power Blog Page 33

34 Thank You for Your Time! Page 34

Protect Against Power-Related DUT Damage During Test

Protect Against Power-Related DUT Damage During Test Our thanks to Keysight Technologies for allowing us to reprint this article. An over-voltage or over-current event can occur for a variety of reasons,