John Brown Art Kay Tim Green Tina-TI

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High Current V-I Circuits. The Four Musketeers of HPL. Recognize. Analyze. Synthesize. Tina-ize. John Brown Art Kay Tim Green Tina-TI. Potential Applications, End Equipment, Markets Circuit Topologies Circuit Stability Issues - PowerPoint PPT Presentation

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  • John Brown Art Kay Tim Green Tina-TISynthesizeTina-izeThe Four Musketeers of HPLAnalyzeRecognizeHigh Current V-I Circuits

  • V-I Circuit Recognize ObjectivesPotential Applications, End Equipment, MarketsCircuit TopologiesCircuit Stability IssuesPower Dissipation IssuesTransient Protection IssuesPCB IssuesSemiconductor Overstress Issues

  • V-I Circuit Analyze, Synthesize, Tina-ize ObjectivesProvide Synthesis Techniques for Common TopologiesProvide Tools to Simplify Stability AnalysisProvide Analysis Techniques for Power DissipationProvide Solutions for Common Transient ProblemsProvide Tips for PCB LayoutsProvide Tricks for Tina-TI Analysis

  • Power Amplifiers Strategy for Markets1. High Volume GrowthCommunications Optical Networking ONET (TECs, Laser Diode Pumps, Avalanche Photodiode Bias HV)DLP Digital Light Projectors (high voltage OPA)Industrial Electromechanical (OPA, PWM)Automotive Electromechanical (OPA, PWM)2. Gen Std Catalog Products Steady Growth Industrial, Medical, Lab, ATE, Some Audio, ConsumerHigh Speed Buffers, High Voltage, High Current OPAs

  • Power Amplifiers Applications in Markets1. Test, Particularly Automated ATEAnalog Pin Driver, Power V & I Excitation2. Power Line CommunicationHigh Pulse Current Drive Through Transformeror Capacitor Coupled ac Power Line (Residential & Commercial)3. Displays High Current Driver for Dithering Projected Light Beam, High Voltage for Ink Jet Printers4. Industrial, Medical, Scientific, Analytical, and Laboratory TEC Drivers, Electromechanical Linear Valve/Positioner Drivers, Motors, Power Supplies5. Optical Networking / Gen Laser SystemsTEC Drivers (Thermo-electric Coolers), Laser Pumps 6. Some AudioHeadphone and Speaker Drivers7. Some AutomotivePower Steering Pumps, Window MotorsCOMPETITION1. Mostly Discrete2. National Semiconductor, ST, Maxim, Allegro, ON-SEMI, International Rectifier, Infineon, Toshiba

  • Review - Essential Principles Poles, Zeros, Bode Plots Op Amp Loop Gain Model Loop Gain Test and 1/ Rate-of-Closure Stability Criteria Loop Gain Rules-of-Thumb for Stability RO and ROUT

  • Commercial Break(Shameless Self-Promotion)See 15 Part Series: Operational Amplifier Stabilityhttp://www.analogzone.com/acqt0704.htm

  • Poles and Bode PlotsPole Location = fPMagnitude = -20dB/Decade SlopeSlope begins at fP and continues down as frequency increasesActual Function = -3dB down @ fPPhase = -45/Decade Slope through fPDecade Above fP Phase = -90Decade Below fP Phase = 0A(dB) = 20Log10(VOUT/VIN)

    AC

    R

    C

    VIN

    VOUT

    A = VOUT/VIN

    Single Pole Circuit Equivalent

    X100,000

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    Frequency (Hz)

    A (dB)

    +90

    -90

    +45

    +-45

    10

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    1k

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    100k

    1M

    10M

    Frequency (Hz)

    0

    q

    (degrees)

    -20dB/Decade-6dB/Octave

    -45o @ fP

    -45o/Decade

    fP

    -90o

    0o

    G

    0.707G = -3dB

    Straight-Line Approximation

    Actual Function

  • Zeros and Bode PlotsZero Location = fZMagnitude = +20dB/Decade SlopeSlope begins at fZ and continues up as frequency increasesActual Function = +3dB up @ fZPhase = +45/Decade Slope through fZDecade Above fZ Phase = +90Decade Below fZ Phase = 0A(dB) = 20Log10(VOUT/VIN)

    AC

    R

    C

    VOUT

    A = VOUT/VIN

    Single Zero Circuit Equivalent

    X100,000

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    Frequency (Hz)

    A (dB)

    +90

    -90

    +45

    +-45

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    10M

    Frequency (Hz)

    0

    q

    (degrees)

    +90o

    0o

    +45o/Decade

    +45o @ fZ

    fZ

    +20dB/Decade+6dB/Octave

    Straight-Line Approximation

    G

    1.414G = +3dB(1/0.707)G = +3dB

    Actual Function

  • Op Amp: Intuitive Model

    +

    -

    K(f)

    VDIFF

    IN+

    IN-

    RIN

    RO

    VO

    VOUT

    x1

  • Op Amp Loop Gain ModelVOUT/VIN = Acl = Aol/(1+Aol)If Aol >> 1 then Acl 1/Aol: Open Loop Gain: Feedback FactorAcl: Closed Loop Gain1/b = Small Signal AC Gainb = feedback attenuation

    +

    -

    +

    -

    S

    VOUT

    b network

    b

    RF

    RI

    VIN

    Aol

    S

    +

    -

    VOUT

    VIN

    VFB

    VFB

    RF

    RI

    b =VFB/VOUT

    VOUT

    b network

  • Stability Criteria

  • Traditional Loop Gain TestOp Amp Loop Gain ModelOp Amp is Closed LoopSPICE Loop Gain Test:Break the Closed Loop at VOUTGround VINInject AC Source, VX, into VOUTAol = VY/VX

    +

    -

    +

    -

    b network

    RF

    RI

    VIN

    VFB

    VOUT

    +

    -

    +

    -

    RF

    RI

    VIN

    b network

    VFB

    VOUT

    VX

    VY

    1GF

    1GH

    Short for ACOpen for DC

    Open for ACShort for DC

  • and 1/ is easy to calculate as feedback network around the Op Amp1/ is reciprocal of Easy Rules-Of-Thumb and Tricks to Plot 1/ on Op Amp Aol Curve

    +

    -

    +

    -

    VOUT

    b network

    RF

    RI

    VIN

    VFB

    VFB

    RF

    RI

    b =VFB/VOUT

    VOUT

    b network

  • Loop Gain Using Aol & 1/Plot (in dB) 1/ on Op Amp Aol (in dB)Aol = Aol(dB) 1/(dB)Note how Aol changes with frequency

    Proof (using log functions): 20Log10[Aol] = 20Log10(Aol) - 20Log10(1/) = 20Log10[Aol/(1/)] = 20Log10[Aol]

    0

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    Frequency (Hz)

    Aol (dB)

    fcl

    1/b

    Acl

    Aol

    Aol b(Loop Gain)

    Closed Loop Response

    Open Loop Response

  • Stability Criteria using 1/ & AolAt fcl: Loop Gain (Aolb) = 1

    Rate-of-Closure @ fcl =(Aol slope 1/ slope)*20dB/decade Rate-of-Closure @ fcl = STABLE**40dB/decade Rate-of-Closure@ fcl = UNSTABLE

    0

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    Frequency (Hz)

    Aol (dB)

    Aol

    1/b1

    1/b2

    1/b3

    1/b4

    fcl1

    fcl4

    fcl3

    fcl2

    *

    *

    **

    **

  • Loop Gain Bandwidth Rule: 45 degrees for f < fclAol (Loop Gain) Phase PlotLoop Stability Criteria:
  • Poles & Zeros Transfer: (1/, Aol) to Aol

    Aol & 1/ PlotLoop Gain Plot(Aol)To Plot Aol from Aol & 1/ Plot:

    Poles in Aol curve are poles in Aol (Loop Gain)PlotZeros in Aol curve are zeros in Aol (Loop Gain) Plot

    Poles in 1/ curve are zeros in Aol (Loop Gain) PlotZeros in 1/ curve are poles in Aol (Loop Gain) Plot[Remember: is the reciprocal of 1/]

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    Frequency (Hz)

    A (dB)

    Aol

    fcl

    1/b

    fp1

    fp2

    fz1

    Aol

    b

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    Frequency (Hz)

    A (dB)

    fp1

    fz1

    fp2

    fcl

  • Frequency Decade Rules for Loop GainLoop Gain View: Poles: fp1, fp2, fz1; Zero: fp3

    Rules of Thumb for Good Loop Stability:

    Place fp3 within a decade of fz1 fp1 and fz1 = -135 phase shift at fz1 fp3 < decade will keep phase from dipping further

    Place fp3 at least a decade below fcl Allows Aol curve to shift to the left by one decade

    +

    -

    +

    -

    VIN

    RI

    RF

    VOUT

    CL

    Cn

    Rn

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    Frequency (Hz)

    A (dB)

    fcl

    fp1

    fp2

    fz1

    fp3

    Aol

    1/Beta

    VOUT/VIN

  • Op Amp Model for Derivation of ROUT From: Frederiksen, Thomas M. Intuitive Operational Amplifiers. McGraw-Hill Book Company. New York. Revised Edition. 1988.ROUT = RO / (1+Aol)

    +

    -

    RDIFF

    xAol

    RO

    -IN

    +IN

    -

    +

    VE

    Op Amp Model

    1A

    VOUT

    VO

    RF

    RI

    IOUT

    VFB

    ROUT = VOUT/IOUT

  • Op Amp Model for Loop Stability AnalysisRO is constant over the Op Amps bandwidth RO is defined as the Op Amps Open Loop Output Resistance RO is measured at IOUT = 0 Amps, f = 1MHz (use the unloaded RO for Loop Stability calculations since it will be the largest value worst case for Loop Stability analysis)RO is included when calculating b for Loop Stability analysis

  • RO & Op Amp Output Operation Bipolar Power Op Amps CMOS Power Op Amps Light Load vs Heavy Load

  • RO Measure w/DC Operating Point: IOUT = 0mA

  • RO Measure w/DC Operating Point: IOUT = 0mARO = VOA / AM1RO = 9.61mVrms / 698.17Arms RO = 13.765

  • RO Measure w/DC Operating Point IOUT = 4.45mA Sink

  • RO Measure w/DC Operating Point IOUT = 4.45mA SinkRO = VOA / AM1RO = 3.45Vrms / 706.25Arms RO = 4.885

  • RO Measure w/DC Operating Point IOUT = 5.61mA Source

  • RO Measure w/DC Operating Point IOUT = 5.61mA SourceRO = VOA / AM1RO = 3.29mVrms / 700.98Arms RO = 4.693

  • RO Measure w/DC Operating Point IOUT = 2.74A Source

  • RO Measure w/DC Oper