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High Current V-I Circuits

High Current V-I Circuits. Tim Green Art Kay John Brown November 2006. Potential Applications, End Equipment, Markets Circuit Topologies Circuit Stability Issues Power Dissipation Issues Transient Protection Issues PCB Issues Semiconductor Overstress Issues.

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High Current V-I Circuits

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  1. High Current V-I Circuits Tim Green Art Kay John Brown November 2006

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Commercial Break(Shameless Self-Promotion) See 15 Part Series: “Operational Amplifier Stability” http://www.analogzone.com/acqt0704.htm

  8. 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)

  9. 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)

  10. Op Amp: Intuitive Model

  11. 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

  12. Stability Criteria

  13. 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

  14. 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

  15. 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]

  16. 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

  17. 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

  18. 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]

  19. 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

  20. 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.

  21. 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

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

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

  24. RO Measure w/DC Operating Point: IOUT = 0mA RO = VOA / AM1 RO = 9.61mVrms / 698.17μArms RO = 13.765Ω

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

  26. RO Measure w/DC Operating Point IOUT = 4.45mA Sink RO = VOA / AM1 RO = 3.45Vrms / 706.25µArms RO = 4.885Ω

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

  28. RO Measure w/DC Operating Point IOUT = 5.61mA Source RO = VOA / AM1 RO = 3.29mVrms / 700.98μArms RO = 4.693Ω

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

  30. RO Measure w/DC Operating Point IOUT = 2.74A Source RO = VOA / AM1 RO = 314.31uVrms / 550.1μArms RO = 0.571Ω

  31. RO Measure w/DC Operating Point IOUT = 2.2A Sink

  32. RO Measure w/DC Operating Point IOUT = 2.2A Sink RO = VOA / AM1 RO = 169.92uVrms / 635.16μArms RO = 0.267Ω

  33. RO Measure w/DC Operating Point IOUT = 0A

  34. RO Measure w/DC Operating PointIOUT = 0A RO = VOA / AM1 RO = 4.42mVrms / 702.69μArms RO = 6.29Ω

  35. RO Measure w/DC Operating PointIOUT = 1A Sink

  36. RO Measure w/DC Operating PointIOUT = 1A Sink RO = VOA / AM1 RO = 166.76μVrms / 540.19μArms RO = 0.309Ω

  37. RO Measure w/DC Operating PointIOUT = 1A Source

  38. RO Measure w/DC Operating PointIOUT = 1A Source RO = VOA / AM1 RO = 166.61μVrms / 540.34μArms RO = 0.308Ω

  39. 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

  40. 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

  41. Non-Inverting V-I Floating LoadRO Reflected Outside of Op Amp

  42. Non-Inverting V-I Floating LoadFB#1 DC 1/b Derivation

  43. Non-Inverting V-I Floating LoadFB#1 1/b Derivation

  44. Non-Inverting V-I Floating LoadFB#1 1/b Data for RO No Load & Full Load

  45. OPA548 Data Sheet Aol

  46. Non-Inverting V-I Floating LoadFB#1 1/b Plot for RO No Load & Full Load

  47. Non-Inverting V-I Floating LoadFB#1 1/b Tina SPICE

  48. Non-Inverting V-I Floating LoadFB#1 1/b Tina SPICE Results

  49. Non-Inverting V-I Floating LoadFB#1 1/b Tina SPICE Results

  50. Non-Inverting V-I Floating LoadFB#1 Loop Gain Tina SPICE Results

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