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## 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 Power Dissipation Issues Transient Protection Issues PCB Issues Semiconductor Overstress Issues V-I Circuit “Recognize” Objectives**Provide Synthesis Techniques for Common Topologies**Provide Tools to Simplify Stability Analysis Provide Analysis Techniques for Power Dissipation Provide Solutions for Common Transient Problems Provide Tips for PCB Layouts Provide Tricks for Tina-TI Analysis V-I Circuit “Analyze, Synthesize, Tina-ize ” Objectives**Power Amplifiers Strategy for Markets**1. High Volume Growth Communications 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, Consumer High Speed Buffers, High Voltage, High Current OPAs**Power Amplifiers Applications in Markets**COMPETITION 1. Mostly Discrete 2. National Semiconductor, ST, Maxim, Allegro, ON-SEMI, International Rectifier,Infineon, Toshiba 1. Test, Particularly Automated ATE Analog Pin Driver, Power V & I Excitation 2. Power Line Communication High Pulse Current Drive Through Transformer or Capacitor Coupled ac Power Line (Residential & Commercial) 3. Displays High Current Driver for Dithering Projected Light Beam, High Voltage for Ink Jet Printers 4. Industrial, Medical, Scientific, Analytical, and Laboratory TEC Drivers, Electromechanical Linear Valve/Positioner Drivers, Motors, Power Supplies 5. Optical Networking / Gen Laser Systems TEC Drivers (Thermo-electric Coolers), Laser Pumps 6. Some Audio Headphone and Speaker Drivers 7. Some Automotive Power Steering Pumps, Window Motors**Poles, Zeros, Bode Plots**Op Amp Loop Gain Model Loop Gain Test β and 1/β Rate-of-Closure Stability Criteria Loop Gain Rules-of-Thumb for Stability RO and ROUT Review - Essential Principles**Commercial Break(Shameless Self-Promotion)**See 15 Part Series: “Operational Amplifier Stability” http://www.analogzone.com/acqt0704.htm**Poles and Bode Plots**• Pole Location = fP • Magnitude = -20dB/Decade Slope • Slope begins at fP and continues down as frequency increases • Actual Function = -3dB down @ fP • Phase= -45°/Decade Slope through fP • Decade Above fP Phase = -90° • Decade Below fP Phase = 0° • A(dB) = 20Log10(VOUT/VIN)**Zeros and Bode Plots**• Zero Location = fZ • Magnitude = +20dB/Decade Slope • Slope begins at fZ and continues up as frequency increases • Actual Function = +3dB up @ fZ • Phase = +45°/Decade Slope through fZ • Decade Above fZ Phase = +90° • Decade Below fZ Phase = 0° • A(dB) = 20Log10(VOUT/VIN)**Op Amp Loop Gain Model**1/b = Small Signal AC Gain b = feedback attenuation VOUT/VIN = Acl = Aol/(1+Aolβ) If Aol >> 1 then Acl ≈ 1/β Aol: Open Loop Gain β: Feedback Factor Acl: Closed Loop Gain**Traditional Loop Gain Test**Op Amp Loop Gain Model Op Amp is “Closed Loop” SPICE Loop Gain Test: Break the Closed Loop at VOUT Ground VIN Inject AC Source, VX, into VOUT Aolβ = VY/VX**β and 1/β**β is easy to calculate as feedback network around the Op Amp 1/β is reciprocal of β Easy Rules-Of-Thumb and Tricks to Plot 1/β on Op Amp Aol Curve**Loop Gain Using Aol & 1/β**Plot (in dB) 1/β on Op Amp Aol (in dB) Aolβ = Aol(dB) – 1/β(dB) Note how Aolβ changes with frequency Proof (using log functions): 20Log10[Aolβ] = 20Log10(Aol) - 20Log10(1/β) = 20Log10[Aol/(1/β)] = 20Log10[Aolβ]**Stability Criteria using 1/β & Aol**At fcl: Loop Gain (Aolb) = 1 Rate-of-Closure @ fcl = (Aol slope – 1/β slope) *20dB/decade Rate-of-Closure @ fcl = STABLE **40dB/decade Rate-of-Closure@ fcl = UNSTABLE**Loop Gain Bandwidth Rule: 45 degrees for f < fcl**Aolβ (Loop Gain) Phase Plot Loop Stability Criteria:<-180 degree phase shift at fcl Design for: <-135 degree phase shift at all frequencies <fcl Why?: Because Aol is not always “Typical” Power-up, Power-down, Power-transient Undefined “Typical” Aol Allows for phase shift due to real world Layout & Component Parasitics**Poles & Zeros Transfer: (1/β, Aol) to Aolβ**Aol & 1/β Plot Loop Gain Plot (Aolβ) To Plot Aolβ from Aol & 1/β Plot: Poles in Aol curve are poles in Aolβ (Loop Gain)Plot Zeros in Aol curve are zeros in Aolβ (Loop Gain) Plot Poles in 1/β curve are zeros in Aolβ (Loop Gain) Plot Zeros in 1/β curve are poles in Aolβ (Loop Gain) Plot [Remember: β is the reciprocal of 1/β]**Frequency Decade Rules for Loop Gain**• Loop 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**Op Amp Model for Derivation of ROUT**ROUT = RO / (1+Aolβ) From: Frederiksen, Thomas M. Intuitive Operational Amplifiers. McGraw-Hill Book Company. New York. Revised Edition. 1988.**Op Amp Model for Loop Stability Analysis**• RO is constant over the Op Amp’s bandwidth • ROis defined as the Op Amp’s 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) • ROis included when calculating b for Loop Stability analysis**Bipolar Power Op Amps**CMOS Power Op Amps Light Load vs Heavy Load RO & Op Amp Output Operation**RO Measure w/DC Operating Point: IOUT = 0mA**RO = VOA / AM1 RO = 9.61mVrms / 698.17μArms RO = 13.765Ω**RO Measure w/DC Operating Point IOUT = 4.45mA Sink**RO = VOA / AM1 RO = 3.45Vrms / 706.25µArms RO = 4.885Ω**RO Measure w/DC Operating Point IOUT = 5.61mA Source**RO = VOA / AM1 RO = 3.29mVrms / 700.98μArms RO = 4.693Ω**RO Measure w/DC Operating Point IOUT = 2.74A Source**RO = VOA / AM1 RO = 314.31uVrms / 550.1μArms RO = 0.571Ω**RO Measure w/DC Operating Point IOUT = 2.2A Sink**RO = VOA / AM1 RO = 169.92uVrms / 635.16μArms RO = 0.267Ω**RO Measure w/DC Operating PointIOUT = 0A**RO = VOA / AM1 RO = 4.42mVrms / 702.69μArms RO = 6.29Ω**RO Measure w/DC Operating PointIOUT = 1A Sink**RO = VOA / AM1 RO = 166.76μVrms / 540.19μArms RO = 0.309Ω**RO Measure w/DC Operating PointIOUT = 1A Source**RO = VOA / AM1 RO = 166.61μVrms / 540.34μArms RO = 0.308Ω**Basic Topology**Stability Analysis (w/effects of Ro) 1/b & Aol Test Loop Gain Test Transient Test Small Signal BW for Current Control Non-Inverting Floating Load V-I**Non-Inverting V-I Floating Load**VP +5V VP 3.03A -5V -3.03A -1V +1V VP Op Amp Point of Feedback is VRS Op Amp Loop Gain forces +IN (VP) = -IN = VRS IOUT = VP / RS IOUT = {(R2*VIN) / (R1A + R1B + R2)} / RS**Non-Inverting V-I Floating LoadRO Reflected Outside of Op**Amp**Non-Inverting V-I Floating LoadFB#1 1/b Data for RO No Load**& Full Load**Non-Inverting V-I Floating LoadFB#1 1/b Plot for RO No Load**& Full Load**Non-Inverting V-I Floating LoadFB#1 Loop Gain Tina SPICE**Results