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Deciphering Electrical Characteristics in an Op Amp Datasheet Tim Green Linear Applications Manager Tucson Division [email protected] Op Amp Basics Ideal Operational Amplifier • • • • • Zero input current Infinite input resistance Infinite open loop gain Zero output resistance Infinite Slew Rate Ideal Op Amp +IN + -IN - Input Current = 0A +IN Rin Infinite -IN Input Current = 0A OUT Open Loop Gain Infinite + + - - Rout 0 ohms Ideal Op Amp OUT Op Amp Loop Gain Model network RF network RI =VFB/VOUT VOUT VFB VOUT RF + + VFB VIN RI - VOUT/VIN = Acl = Aol/(1+Aolβ) If Aol >> 1 then Acl ≈ 1/β Aol: Open Loop Gain VIN + Aol VOUT β: Feedback Factor Acl: Closed Loop Gain Ideal Operational Amplifier VINM VINP + Aol VOUT = (VINP – VINM) * Aol VOUT / Aol – VINP = -VINM If Aol = ∞ (for an Ideal Op Amp) then: -VINP = -VINM or VINP = VINM VOUT Ideal Operational Amplifier Irf = (Vout - Vin) / RF Iri = Vin / RI Iin- = 0A Non-Inverting Configuration Irf = Iri (Vout - Vin) / RF = Vin / RI Vout / Vin = 1 + RF/RI For Ideal Op Amp With Feedback and High Open Loop Gain: +IN is forced to equal -IN Ideal Op Amp + Vin 1 Vin 1V Vout 10V - Iin- = 0A RI 10k RF 90k Iri Irf Ideal Operational Amplifier Irf = (Vout - 0V) / RF Iri = (0V-Vin) / RI Iin- = 0A Inverting Configuration For Ideal Op Amp With Feedback and High Open Loop Gain: +IN is forced to equal -IN Irf = Iri (Vout - 0V) / RF = (0V-Vin) / RI Vout / Vin = -RF/RI Ideal Op Amp + Gnd 0V Vout -9V - Iin- = 0A RI 10k Vin 1 RF 90k Iri Irf Intuitive AC Op Amp Model VO RO K(f) IN+ x1 RIN IN- + - VDIFF VOUT Input Specifications Input Bias Current (Ib) & Input Offset Current (Ios) Input Offset Voltage (Vos) Power Supply Rejection Ratio (PSRR): Referred-To-Input Vos Common Mode Voltage Range (Vcm) Common Mode Rejection Ratio (CMRR): Referred-To-Input Vos Small Signal Input Parasitics: Input Capacitance, Input Resistance Input Noise: Current, Voltage (in, en) Input Bias Current (Ib), Input Offset Current (Ios) Ib- 3p Ib = Ideal Op Amp - Ib = Vout Ib+ + Ib2 7pA + 3pA 2 = 5pA + Ios = Ib+ - IbIos = 7pA - 3pA = 4pA Ib+ 7p Ib = 5pA Ios = 4pA Polarity is + or – Current into or out of inputs Input Bias Current (Ib), Input Offset Current (Ios) 25C Specs in Table Often Curves for Temperature Specs Polarity is + or – Input Bias Current (Ib) Vout Error 2 Vinm = 1.5uV Vinm 1 RF 1M RF 1M Vout Ib- 3p Ib- 3p RI 1M Ideal Op Amp Idelal Op Amp RI 1M - Rs 1M Vout Rs 1M Vout + + + Vin Ib+ 7p Vin Ib causes errors at Vout Ib+ 7p Vinp Vinp =7uV 3 Ib flow s through feedback and input resistors View Vout and Vin as low impedance Vinm = Ib- (RF // RI) Vinp = Ib+ (Rs) VIb- 1.5u RI 1M Ideal Op Amp Ideal Op Amp R3 1M + VIb+ 7u Ib flow s through feedback and input resistors Model as VIb+ and VIbInverting and Non-Inverting Gains create Vout error Vout R1 1M Vout error = 11uV + + Vout Rs 1M Vin 4 R2 1M RF 1M Vin + Vout error = 11uV VIb 5.5u Simplified VIb Model VIb = VIb+ - VIbNon-Invverting Gain Creates Vout error Input Offset Voltage (Vos) Vout Error 25C Specs in Table Often Histograms show distribution of Vos Polarity is + or – RF 1M Ideal Op Amp RI 1M Vout + Vos 25u Input Offset Voltage Creates Vout error Vout error = 50uV Input Offset Voltage (Vos) Drift Vout Error Vos Drift Specs in Table Often Histograms show distribution of Vos Drift Polarity is + or - RF 1M Ideal Op Amp RI 1M Vout Vos_drift 60u Vos 25u + Vout error = 170uV Initial Vos + Vos Drift creates Vout error Operating Temperatue = 25C to 85C T = 85C - 25C = 60C dVos Vos_drift = T dT Vos_drift = 60C 1uV/C = 60uV Power Supply Rejection Ratio (PSRR) Vout Error RF 1M DC PSRR in Table DC PSRR Drift in Table Polarity is + or PSRR is an RTI (Referred-To-Input) specification Appears as Input Offset Voltage Ideal Op Amp RI 1M + Vout + Vout error = 20uV Vos_PSRR 10u delta_Vcc 500m PSSR DC = 20uV/V delta_Vcc = 500mV (DC change in Vcc) Vos_PSRR = PSSR DC delta_Vcc Vos_PSRR = 20uV/V 500mV = 10uV Vcc 5 PSSR reflects as Vos_PSRR & creates Vout error Power Supply Rejection Ratio (PSRR) Vout Error AC PSRR in Curve Frequency of analysis = 20kHz PSRR AC @ 20kHz = 80dB Convert PSRR (dB) to PSRR (Linear Gain): (80dB/20) 10 = 10,000 PSRR is an attenuation so 1V gets attenuated by x10,000 1/10,000 = 1e-4V/V Now convert numerator to uV: (1e-4V) (1uV/1e-6V) = 1e-4uV / 1e-6 = 100uV: PSRR AC @ 20kHz = 100uV/V 20kHz R4 1M Ideal Op Amp R5 1M PSRR AC reflects as Vos_PSRR_ac & creates Vout error PSRR is an RTI (Referred-To-Input) specification Appears as Input Offset Voltage + Vos_PSRR_ac 10uVpp @ 20kHz + Vout Vout error = 20uVpp @ 20kHz + + PSSR AC @ 20kHz = 100uV/V delta_Vcc_ac = 100mVpp (AC change in Vcc @ 20kHz) Vos_PSRR_ac = PSSR AC delta_Vcc_ac Vos_PSRR_ac = 100uV/V 100mVpp = 10uVpp - delta_Vcc_ac 100mVpp @ 20kHz Vcc 5 Common Mode Voltage Range (Vcm) Vin_CM = Voltage Common to Vinp & Vinm Vcm Same for DC & AC AC peak voltage < Vcm Vinm Vee 15 V = 2V max Ideal Op Amp - Vinp + Vout + + Common Mode Voltage Range For: Non-Inverting Gain Vinp = Vinm So: Vin_CM = Vin From Vcm spec Vin must stay 2V aw ay from either supply for op amp to operate as a linear gain block RF 1M Vin -13V < Vin < +13V V = 2V max Vcc 15 Common Mode Rejection Ratio (CMRR) Vout Error CMRR DC in Table Polarity is + or - CMRR DC reflects as Vos_CMRR & creates Vout error CMRR DC = 130dB Convert CMRR (dB) to CMRR (Linear Gain): RF 1M (130dB/20) 10 = 3.16e+6 CMRR is an attenuation so 1V gets attenuated by x3.16e+6 1/3.16e+6 = 3.16e-7V/V Now convert numerator to uV: (31.6e-7V) (1uV/1e-6V) = 3.16e-7uV / 1e-6 = 0.316uV: CMRR DC = 0.316uV/V CMRR DC = 0.316uV/V Vin = 5V for Non-Inverting Gain Vin =Vcm Vcm = 5V Vos_CMRR = CMRR DC Vcm Vos_CMRR = 0.316uV/V 5V = 1.58uV CMRR is an RTI (Referred-To-Input) specification Appears as Input Offset Voltage V2 15 Ideal Op Amp RI 1M + Vin 5 Vos_CMRR 1.58u Vout + Vout error = 3.16uV V1 15 Common Mode Rejection Ratio (CMRR) Vout Error AC CMRR in Curve Frequency of Analysis = 1kHz CMRR AC = 100dB @ 1kHz Convert CMRR (dB) to CMRR (Linear Gain): (100dB/20) 10 = 100,000 CMRR is an attenuation so 1V gets attenuated by x100,000 1/100,000 = 1e-5V/V Now convert numerator to uV: (1e-5V) (1uV/1e-6V) = 1e-5uV / 1e-6 = 10uV: CMRR AC = 10uV/V @ 1kHz RF 1M RI 1M CMRR AC reflects as Vos_CMRR_ac & creates Vout error CMRR is an RTI (Referred-To-Input) specification Appears as Input Offset Voltage Vee 15 Ideal Op Amp 200uVpp @ 1kHz Vos_CMRR_ac + + CMRR AC = 10uV/V @1kHz Vin = 20Vpp for Non-Inverting Gain Vin =Vcm_ac Vcm_ac = 20Vpp Vos_CMRR_ac = CMRR AC Vcm_ac Vos_CMRR_ac = 10uV/V 20Vpp = 200uVpp Vin 20Vpp @ 1kHz + Vout + Vout error = 400uVpp @ 1kHz Vcc 15 Cin Small Signal Input Parasitics RF 1M Vee RI 1M Ccm, Cdiff in Table Rcm, Rdiff in Table if specified Ccm Rcm Cdiff Rdiff + +In Ccm Rdiff > 200GW for Bipolar Inputs Rcm > 40MW for Bipolar Inputs Even greater for JFET or MOSFET inputs Ideal Op Amp - -In Vout + Rcm Small Signal Input Parasitics Vcc Ccm and Cdiff can be a problem: Ccm and Cdiff form Cin Cin & RF form a Loop Gain pole unwanted oscillations depending upon UGBW and value of RF. Input Noise: Current, Voltage (in, en) Op Amp Noise Model Noise Model OPA277 Data (IN+ and IN- are not correlated) VN IN+ IN- IOP1 Tina Simplified Model U1 nV * VN - fA IN * + Understanding The Spectrum: Total Noise Equation (Current or Voltage) 1/f Noise Region (Pink Noise Region) White Noise Region (Broadband Noise Region) Voltage Noise (nV/ Hz ) 100k enT = √[(en1/f)2 + (enBB)2] 10k 1k 100 10 1 0.1 fL where: enT = Total rms Voltage Noise in volts rms en1/f = 1/f voltage noise in volts rms enBB = Broadband voltage noise in volts rms 1 10 100 1k 10k Frequency (Hz) enBB calculation en1/f calculation fH Real Filter Correction vs Brickwall Filter where: fP = roll-off frequency of pole or poles fBF = equivalent brickwall filter frequency Noise BW Small Signal BW 0 Filter Attenuation (dB) Skirt of 1-Pole Filter Response Skirt of 2-Pole Filter Response -20 Skirt of 3-Pole Filter Response -40 Brickwall -80 0.1fP fP fBF Frequency (f) 10fP AC Noise Bandwidth Ratios for nth Order Low-Pass Filters BWn = (fH)(Kn) Effective Noise Bandwidth Real Filter Correction vs Brickwall Filter Number of Poles in Filter Kn AC Noise Bandwidth Ratio 1 1.57 2 1.22 3 1.16 4 1.13 5 1.12 Broadband Noise Equation eBB BWn = (fH)(Kn) where: BWn = noise bandwidth for a given system fH = upper frequency of frequency range of operation Kn = “Brickwall” filter multiplier to include the “skirt” effects of a low pass filter enBB = (eBB)(√[BWn]) where: enBB = Broadband voltage noise in volts rms eBB = Broadband voltage noise density ; usually in nV/√Hz BWn = Noise bandwidth for a given system 1/f Noise Equation e1/f@1Hz e1/f@1Hz = (e1/f@f)(√[f]) where: e1/f@1Hz = normalized noise at 1Hz (usually in nV) e1/f@f = voltage noise density at f ; (usually in nV/√Hz) f = a frequency in the 1/f region where noise voltage density is known en1/f = (e1/f@1Hz)(√[ln(fH/fL)]) where: en1/f = 1/f voltage noise in volts rms over frequency range of operation e1/f@1Hz = voltage noise density at 1Hz; (usually in nV) fH = upper frequency of frequency range of operation (Use BWn as an approximation for fH) fL = lower frequency of frequency range of operation Example Noise Calculation R2 1k Given: OPA627 Noise Gain of 101 R1 100k V1 15 - + + VG1 VF1 + U1 OPA627/BB V2 15 Find (RTI, RTO): Voltage Noise Current Noise Resistor Noise Voltage Noise Spectrum and Noise Bandwidth 50nV/rt-Hz 5nV/rt-Hz Unity Gain Bandwidth = 16MHz Closed Loop Bandwidth = 16MHz / 101 = 158kHz Example Voltage Noise Calculation Voltage Noise Calculation: Broadband Voltage Noise Component: BWn ≈ (fH)(Kn) (note Kn = 1.57 for single pole) BWn ≈ (158kHz)(1.57) =248kHz enBB = (eBB)(√BWn) enBB = (5nV/√Hz)(√248kHz) = 2490nV rms 1/f Voltage Noise Component: e1/f@1Hz = (e1/f@f)(√f) e1/f@1Hz = (50nV/√Hz)(√1Hz) = 50nV en1/f = (e1/f@1Hz)(√[ln(fH/fL)]) Use fH = BWn en1/f = (50nV)(√[ln(248kHz/1Hz)]) = 176nV rms Total Voltage Noise (referred to the input of the amplifier): enT = √[(en1/f)2 + (enBB)2] enT = √[(176nV rms)2 + (2490nV rms)2] = 2496nV rms Example Current Noise Calculation Note: This example amp doesn’t have 1/f component for current noise. en-in= (in)x(Req) R1 1k en-out= Gain x (in)x(Req) Rf 3k Gain IOP1 U2 - fA * VF1 Req = R1 || Rf + * Example Current Noise Calculation Broadband Current Noise Component: BWn ≈ (fH)(Kn) BWn ≈ (158kHz)(1.57) =248kHz inBB = (iBB)(√BWn) inBB = (2.5fA/√Hz)(√248kHz) = 1.244pA rms Req = Rf || R1 = 100k || 1k = 0.99k eni = (In)( Req) = (1.244pA)(0.99k) = 1.23nV rms Since the Total Voltage noise is envt = 2496nV rms the current noise can be neglected. neglect Resistor Noise – Thermal Noise The mean- square open- circuit voltage (e) across a resistor (R) is: en = √ (4kTKRΔf) where: TK is Temperature (ºK) R is Resistance (Ω) f is frequency (Hz) k is Boltzmann’s constant (1.381E-23 joule/ºK) en is volts (VRMS) To convert Temperature Kelvin to TK = 273.15oC + TC 0 1 10 468.916 1000 3 en density = √ (4kTKR) 1 10 468.916 3 100 23 ( 25 273.15 ) X 10 9 23 ( 125 273.15 ) X 10 9 23 ( 55 273.15 ) X 10 9 nV/rt-Hz 0 Noise Spectral Density vs. Resistance Noise Spectral Density vs. Resistance 0 Resistor Noise – Thermal Noise 100 10 23 4 1.3806510 9 ( 25 273.15) X 10 25C 23 9 4 1.3806510 ( 125 273.15) X 10 10 125C 1 23 9 4 1.3806510 ( 55 273.15) X 10 -55C 0.347 1 0.1 10 10 100 1 10 3 1 10 X 4 1 10 5 Resistance (Ohms) 1 10 6 1 10 7 10 7 0.347 0.1 10 10 Example Resistor Noise Calculation enr = √(4kTKRΔf) where: R = Req = R1||Rf Δf = BWn enr = √(4 (1.38E-23) (273 + 25) (0.99k)(248kHz)) = 2010nV rms * U1 en-out= Gain x (√(4kTRΔf)) Gain nV R1Rf 2k nV R2R1 1k * U1 en-in= √(4kTRΔf) IOP1 - VF1 Req = R1 || Rf + * Total Noise Calculation Voltage Noise From Op-Amp RTI: env = 2510nV rms Current Noise From Op-Amp RTI (as a voltage): eni = 1.24nV rms Resistor Noise RTI: enr = 2020nV rms Total Noise RTI: en in = √((2510nV)2 + ((1.2nV)2 + ((2010nV)2) = 3216nV rms Total Noise RTO: en out = en in x gain = (3216nV)(101) = 325uV rms Calculating Noise Vpp from Noise Vrms Relation of Peak-to-Peak Value of AC Noise Voltage to rms Value Peak-to-Peak Amplitude Probability of Having a Larger Amplitude 2 X rms 32% 3 X rms 13% 4 X rms 4.6% 5 X rms 1.2% 6 X rms * 0.3% 6.6 X rms 0.1% *Common Practice is to use: Peak-to-Peak Amplitude = 6 X rms Voltage Noise (f = 0.1Hz to 10Hz) Low Frequency Low frequency noise spec and curve: Over specific frequency range: 0.1Hz < f < 10Hz Given as Noise Voltage in pp units Measured After Bandpass Filter: 0.1Hz Second−Order High−Pass 10Hz Fourth−Order Low−Pass Frequency Response Specifications Open Loop Gain (Aol) & Phase Slew Rate (SR) Total Harmonic Distortion + Noise (THD+N) Settling Time (ts) Open Loop Gain & Phase Open-Loop Voltage Gain at DC Linear operation conditions NOT the same as Voltage Output Swing to Rail Gain-Bandwidth Product = UGBW (Unity Gain Bandwidth) G=1 Stable Op Amps 5.5MHz Vout/Vin: Gain Accuracy & Frequency Response R2 9k Real Op Amp R3 1k - + Vout + Vin fcl Aol at any Frequency: Aol_f = UGBW / f 1/Beta Vout/Vin Aol @ 1kHz = 5.5MHz / 1kHz = 5500 Aol @ 1kHz = 20LOG10(5500) = 74.8dB Gain Accuracy at any frequency: Vout/ Vin Frequency Response Frequency of analysis for Gain Accuracy = 1kHz 1/ = 10 20LOG10(10) = 20dB Vout / Vin = Aol 1+Aol fcl is w here Aol = 1 f > fcl: Loop Gain < 1 so Vout/Vin = Aol Vout / Vin = Aol 1+Aol Vout / Vin = 5500 / (1+ 5500 0.1) Vout/ / Vin = 9.98185 Vout / Vin ideal = 10 Gain Error = ((10 - 9.98185) / 10) 100 = 0.18% Slew Rate Slew Rate Measurement: 10% to 90% of Vout Slew Rate & Full Power Bandwidth or Maximum Output Voltage vs Frequency Maximum Rate of change of sinew ave is at zero cross Highest Frequency Op Amp can track sinew ave limited by: Frequency, Output Voltage, Slew Rate SR (V/us) = 2 f Vop (1e-6) w here: SR = Slew Rate in V/us f = frequency of interest Vop = Vout peak voltage Given Slew Rate = 2V/us What is max f for sinew ave of 2.5Vpp? SR (V/us) = 2 f Vop (1e-6) 2 = 2 f (2.5Vpp/2) (1e-6) Solving for f: fmax = 254.6kHz THD + Noise Larger Closed Loop Gain Loop Gain to correct for Op Amp Non-Linearities and Noise THD + Noise = 1% Example Fundamental f = Input Frequency Fundamental f = 99% Vout Amplitude Harmonics due to Op Amp non-linearities Noise due to Op Amp Input Noise (en, in) Harmonics + Noise < 1% of Vout Settling Time Slew Rate Note: Settling Time includes Slew Rate time Settling Time Settling Time Large Signal effects: Slew Rate Small Signal effects Large Gain = Less closed loop Bandwidth Large Gain = Less Loop Gain (AolB) to correct for errors Large Gain = Longer Settling Time Output Specifications Voltage Output Swing from Rail Short Circuit Current (Isc) Open Loop Output Impedance (Zo) Closed Loop Output Impedance (Zout) Capacitive Load Drive Voltage Output Swing From Rail Loaded Vout swing from Rail Higher Current Load Farther from Rail Higher Current Load Larger Vsat Vsat = Vs - Vout +25C Curve: Op Amp Aol is degraded if on curve 1 Op Amp Aol is okay if left of curve 2 2 1 Short Circuit Current (Isc) Output shorted Current Limit engaged For Graph shown TJ max is okay If using larger voltages (i.e. +5V, Gnd) use Short-Circuit Current values & analyze power dissipation and TJ max Open Loop Output Impedance (Zo) Closed Loop Output Impedance (Zout) Capacitive Load Drive Op Amp Model for Derivation of ROUT Definition of Terms: RO = Op Amp Open Loop Output Resistance ROUT = Op Amp Closed Loop Output Resistance ROUT = RO / (1+Aolβ) RF RI RO -IN RDIFF VFB VE xAol + VO IOUT - 1A + +IN VOUT Op Amp Model From: Frederiksen, Thomas M. Intuitive Operational Amplifiers. McGraw-Hill Book Company. New York. Revised Edition. 1988. ROUT = VOUT/IOUT ROUT vs RO • RO does NOT change when Closed Loop feedback is used • ROUT is the effect of RO, Aol, and β controlling VO – Closed Loop feedback (β) forces VO to increase or decrease as needed to accommodate VO loading – Closed Loop (β) increase or decrease in VO appears at VOUT as a reduction in RO – ROUT increases as Loop Gain (Aolβ) decreases Note: Some op amps have ZO characteristics other than pure resistance (RO) – consult data sheet / manufacturer. RO & CL: Modified Aol Model RI RF 100kW 100kW OPA452 - Da + fpo1 = 1/(2∙П∙RO∙CL) fpo1 = 5.545kHz Create a new “Modified Aol” Plot RO + 28.7W ol et A + ta She Extra Pole in Aol Plot due to RO & CL: fpo1 = 1/(2∙П∙28.7Ω∙1μF) - VIN - VOUT CL 1F RO & CL: OPA542 Modified Aol First Order 120 OPA452 Aol 100 80 Gain (dB) 60 fpo1 40 STABLE 40dB/Decade Rate-Of-Closure 20 fcl 1/ 0 -20 Modified Aol due to CL -40 -60 1 10 100 1K 10K Frequency (Hz) 100k 1M 10M Zo (Open Loop Output Impedance) Cap Load Drive As Cap Load increases Loop Gain Phase Margin decreases and we see the transient response for Cap Load increase in overshoot for OPA376 OPA376 and many other Single Supply Op Amps Open Loop Output Impedance is not Purely Resistive For about 500pF Load Capacitance Small-Signal Overshoot is 50% From: Dorf, Richard C. Modern Control Systems. Addison-Wesley Publishing Company. Reading, Massachusetts. Third Edition, 1981. 2nd Order Transient Curves Signal overshoot of 50% or normalized signal output of 1.5 yields a Damping ratio ( z) of 0.2 From: Dorf, Richard C. Modern Control Systems. Addison-Wesley Publishing Company. Reading, Massachusetts. Third Edition, 1981. 2nd Order Damping Ratio vs Phase Margin Damping ratio ( z) of 0.2 yields 23.5 degrees of phase margin for AC Loop Stability 23.5o Closed Loop Output Impedance Closed Loop Output impedance gives an indication of what source impedance the closed loop op amp will have to drive loads over frequency For Bipolar, Emitter-Follower Output Op amps like OPA177, open loop output impedance = RO (purely resistive inside UGBW) Since ROUT = RO/(1+Aol) and RO is resistive ROUT looks opposite of Aol and increase at higher frequencies Power Supply Specifications Specified Voltage Range (VS) Operating Voltage Range (VS) Quiescent Current (IQ) Specified and Operating Voltage Range (VS) For 2.2V < VS < 5.5V data sheet specifications will be met For 2 < VS < 2.2V the op amp will still function but all data sheet specifications may not be met i.e. Output Swing to Rail, Aol, etc may be degraded Quiescent Current (IQ) +Vs IQ + + Vout Real Op Amp IQ -Vs Quiescent Current: Supply Current to operate the op amp Does NOT include load current Temperature Range Specifications Specified Range Operating Range Thermal Resistance (QJA) Specified and Operating Temperature Range For -40C < TA < +125C data sheet specifications will be met For +125C < TA < +150C the op amp will still function but all data sheet specifications may not be met i.e. Output Swing to Rail, Aol, etc may be degraded Thermal Resistance (QJA) Thermal Resistance (QJA) QJA will be used with ambient temperature TA and internal total power dissipation PD to compute maximum op amp junction temperature TJ Thermal Model PD = PIQ + POUT PD = Total Power Dissipated PIQ = Power Dissipated due to IQ POUT = Power Dissipated in Output Stages TJ Thermal model with no heat sink Analogous to an electrical circuit PD RθJA TJ= PD( RθJA) + TA T – is analogous to voltage R – is analogous to resistance TA TA P – is analogous to current IQ Power Dissipation (PIQ) PIQ = [+Vs - (-Vs) ] IQ +Vs IQ + + Vout Real Op Amp IQ -Vs DC Normal Maximum Power Dissipation in Output Stage (POUT) +Vs Vout = IQ + Real Op Amp + 1 2 Vs Iout_DC Vout Vin IQ RL -Vs RI RF POUT_DC = Vs 2 4 RL DC Short Circuit Maximum Power Dissipation in Output Stage (POUT) +Vs IQ + + Real Op Amp + POUT_SHORT = Vs Isc Isc VF1 VG1 IQ -Vs RI RF AC Normal Maximum Power Dissipation in Output Stage (POUT) For AC Sinusoidal Signals +Vs IQ Vout peak = POUT_AC = 2 Vs 2 + + 2 Vs 2 Real Op Amp + Iout_AC Vout Vin RL IQ RL -Vs Pc(Push-Pull) vs Vload for an AC Sinusoidal Signal RI P(Push Pull Output Transistors) 0.3 0.25 0.2 0.15 POUT_AC = 0.1 Vout peak = 2 Vs 2 Vs 2 2 RL 0.05 0 0 1 2 3 V(load) peak AC Sinusoidal Voltage 4 5 RF AC Normal Maximum Power Dissipation in Output Stage (POUT) For AC Sinusoidal Signals AC Maximum Power Dissipation Formula based on symmetrical dual supplies Vcc Vcc 5 To use formula for single supply circuits set +Vs = +(Vcc/2) and -Vs = -(Vcc/2) as shown. IQ + + Real Op Amp Iout_AC + Vout Vin IQ RL +Vs 2.5 +Vs = (Vcc/2) IQ + RF + RI Real Op Amp + Iout_AC Vout Vin IQ RL POUT_AC = 2 Vs 2 2 RL -Vs 2.5 RI RF -Vs = -(Vcc/2) Absolute Maximum Rating Absolute Maximum Rating For Long-Term Reliable Operation use Op Amp below the Absolute Maximum Ratings Heat is semiconductor’s worst enemy – Keep TJ at least 25C less than TJ Max For this op amp be sure to limit current into the input terminals to 10mA during electrical overstress conditions. Op Amp Selection Tip Choosing an Op Amp? Focus on Key Concerns for Application to Narrow Search Voltage? Current? Speed? Cu rre SSBW @ G=? Slew Rate? SR(V/us)=2pifVOP1e-6 where: f=Hz Speed? - nt? Supply Current? Output Current? Input Bias Current? + ? e g a t l o V Supply Voltage? Input Offset Voltage? Output Swing Voltage? References References Jim Karki, Senior Applications Engineer, Texas Instruments “Understanding Operational Amplifier Specifications” White Paper: SLOA011 John Brown, Strategic Marketing Engineer (Retired), Texas Instruments “How to Use TI/BB Data Sheet Specs for Op Amps and IAs” Internal White Paper Art Kay, Senior Applications Engineer, Texas Instruments “Analysis and Measurement of Intrinsic Noise in Op Amp Circuits: Parts 1-7” http://www.en-genius.net/site/zones/audiovideoZONE/technical_notes/avt_022508 Tim Green, Senior Applications Engineer, Texas Instruments “Operational Amplifier Stability: Parts 1-9 of 15” http://www.en-genius.net/site/zones/acquisitionZONE/technical_notes/acqt_121106