OPA549T

® OPA 549 OPA549 For most current data sheet and other product information, visit www.burr-brown.com High-Voltage, High-Current OPERATIONAL AMPLIFIER FEATURES q HIGH OUTPUT CURRENT: 8A Continuous 10A Peak q WIDE POWER SUPPLY RANGE: Single Supply: +8V to +60V Dual Supply: ±4V to ±30V q WIDE OUTPUT VOLTAGE SWING q FULLY PROTECTED: Thermal Shutdown Adjustable Current Limit q OUTPUT DISABLE CONTROL q THERMAL SHUTDOWN INDICATOR q HIGH SLEW RATE: 9V/µs q CONTROL REFERENCE PIN q 11-LEAD POWER ZIP PACKAGE DESCRIPTION The OPA549 is a low-cost, high-voltage/high-current operational amplifier ideal for driving a wide variety of loads. This laser-trimmed monolithic integrated circuit provides excellent low-level signal accuracy, and high output voltage and current. The OPA549 operates from either single or dual supplies for design flexibility. The input common-mode range extends below the negative supply. The OPA549 is internally protected against overtemperature conditions and current overloads. In addition, the OPA549 provides an accurate, user-selected current limit. Unlike other designs which use a “power” resistor in series with the output current path, the OPA549 senses the load indirectly. This allows the current limit to be adjusted from 0A to 10A with a resistor/potentiometer, or controlled digitally with a voltage-out or current-out DAC. The Enable/Status (E/S) pin provides two functions. It can be monitored to determine if the device is in thermal shutdown, and it can be forced low to disable the output stage and effectively disconnect the load. The OPA549 is available in an 11-lead power ZIP package. Its copper tab allows easy mounting to a heat sink for excellent thermal performance. Operation is specified over the extended industrial temperature range, –40°C to +85°C. APPLICATIONS q VALVE, ACTUATOR DRIVER q SYNCHRO, SERVO DRIVER q POWER SUPPLIES q TEST EQUIPMENT q TRANSDUCER EXCITATION q AUDIO POWER AMPLIFIER V+ OPA549 ILIM Ref RCL ES Pin E/S Forced Low: Output disabled Indicates Low: Thermal shutdown V– VO RCL sets the current limit value from 0A to 10A. (Very Low Power Dissipation) International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 ® © 1999 Burr-Brown Corporation PDS-1450A 1 Printed in U.S.A. November, 1999 OPA549 SPECIFICATIONS: VS = ±2.25V to ±18V Boldface limits apply over the specified temperature range, TA = –40°C to +85°C At TCASE = +25°C, VS = ±30V, Ref = 0V, and E/S pin open, unless otherwise noted. OPA549T PARAMETER OFFSET VOLTAGE Input Offset Voltage vs Temperature vs Power Supply INPUT BIAS CURRENT(1) Input Bias Current(2) vs Temperature Input Offset Current NOISE Input Voltage Noise Density Current Noise Density VOS dVOS/dT PSRR IB IOS en in VCM = 0V, IO = 0 TCASE = –40°C to +85°C VS = ±4V to ±30V, Ref = V – VCM = 0V TCASE = –40°C to +85°C VCM = 0V f = 1kHz f = 1kHz Linear Operation Linear Operation VCM = (V–) – 0.1V to (V+) – 3V (V+) – 3 (V–) – 0.1 80 CONDITION MIN TYP ±1 MAX ±5 100 –500 ±50 UNITS mV µV/°C µV/V nA nA/°C nA nV/√Hz pA/√Hz V V dB Ω || pF Ω || pF dB dB MHz V/µs µs % V V V V V A Arms A A mA ±20 25 –100 ±0.5 ±5 70 1 (V+) – 2.3 (V–) – 0.2 95 107 || 6 109 || 4 INPUT VOLTAGE RANGE Common-Mode Voltage Range: Positive VCM Negative VCM Common-Mode Rejection Ratio CMRR INPUT IMPEDANCE Differential Common-Mode OPEN-LOOP GAIN Open-Loop Voltage Gain FREQUENCY RESPONSE Gain Bandwidth Product Slew Rate Full Power Bandwidth Settling Time: ±0.1% Total Harmonic Distortion + Noise(3) AOL VO = ±25V, RL = 1kΩ VO = ±25V, RL = 4Ω 100 110 100 0.9 9 See Typical Curve 20 0.015 GBW SR G = 1, 50Vp-p Step, RL = 4Ω G = –10, 50V Step f = 1kHz,RL = 4Ω,G = +3, Power = 25W IO = 2A IO = –2A IO = 8A IO = –8A RL = 8Ω to V– Waveform Cannot Exceed 10A peak (V+) – 3.2 (V–) + 1.7 (V+) – 4.8 (V–) + 4.6 (V–) + 0.3 ±8 8 THD+N OUTPUT Voltage Output, Positive Negative Positive Negative Negative Maximum Continuous Current Output: dc(4) ac(4) Output Current Limit Current Limit Range Current Limit Equation Current Limit Tolerance(1) Capacitive Load Drive (Stable Operation) CLOAD Output Disabled Leakage Current Output Capacitance OUTPUT ENABLE /STATUS (E/S) PIN Shutdown Input Mode VE/S High (output enabled) VE/S Low (output disabled) IE/S High (output enabled) IE/S Low (output disabled) Output Disable Time Output Enable Time Thermal Shutdown Status Output Normal Operation Thermally Shutdown Junction Temperature, Shutdown Reset from Shutdown Ref (Reference Pin for Control Signals) Voltage Range Current(2) POWER SUPPLY Specified Voltage Operating Voltage Range, (V+) – (V–) Quiescent Current Quiescent Current in Shutdown Mode TEMPERATURE RANGE Specified Range Operating Range Storage Range Thermal Resistance, θJC Thermal Resistance, θJA VS (V+) – 2.7 (V–) + 1.4 (V+) – 4.3 (V–) + 3.9 (V–) + 0.1 RCL = 7.5kΩ (ILIM = ±5A), RL = 4Ω 0 to ±10 ILIM = 15800 • 4.75V/(7500Ω + RCL) ±200 ±500 See Typical Curve See Typical Curve 750 Output Disabled Output Disabled pF E/S Pin Open or Forced High E/S Pin Forced Low E/S Pin Indicates High E/S Pin Indicates Low (Ref) + 2.4 (Ref) + 0.8 –50 –55 1 3 (Ref) + 2.4 (Ref) + 3.5 (Ref) + 0.2 +160 +140 V V µA µA µs µs V V °C °C V mA V V mA mA °C °C °C °C/W °C/W Sourcing 20µA Sinking 5µA, TJ > 160°C (Ref) + 0.8 V– –3.5 ±30 8 IQ ILIM Connected to Ref IO = 0 ILIM Connected to Ref –40 –40 –55 No Heat Sink 1.4 30 ±26 ±6 (V+) – 8 60 ±35 +85 +125 +125 NOTES: (1) High-speed test at TJ = +25°C. (2) Positive conventional current is defined as flowing into the terminal. (3) See “Total Harmonic Distortion + Noise vs Frequency” in the Typical Performance Curves section for additional power levels. (4) See “Safe Operating Area” (SOA) in the Typical Performance Curves section. ® OPA549 2 ABSOLUTE MAXIMUM RATINGS(1) Output Current ................................................ See SOA Curve (Figure 6) Supply Voltage, V+ to V– ................................................................... 60V Input Voltage Range ....................................... (V–) – 0.5V to (V+) + 0.5V Input Shutdown Voltage ................................................... Ref – 0.5 to V+ Operating Temperature .................................................. –40°C to +125°C Storage Temperature ..................................................... –55°C to +125°C Junction Temperature ...................................................................... 150°C Lead Temperature (soldering, 10s) ................................................. 300°C ESD Capability (Human Body Model) ............................................. 2000V NOTE: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. PACKAGE/ORDERING INFORMATION PACKAGE DRAWING NUMBER 242 TEMPERATURE RANGE –40°C to +85°C PRODUCT OPA549T PACKAGE 11-Lead Power ZIP ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. CONNECTION DIAGRAM Tab connected to V–. Do not use to conduct current. 2 1 3 –In VO 4 +In 5 6 Ref 7 8 ILIM 9 E/S 10 11 V– V+ Connect both pins 1 and 2 to output. Connect both pins 5 and 7 to V–. Connect both pins 10 and 11 to V+. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. ® 3 OPA549 TYPICAL PERFORMANCE CURVES At TCASE = +25°C, VS = ±30V and E/S pin open, unless otherwise noted. OPEN-LOOP GAIN AND PHASE vs FREQUENCY 120 100 80 0 –20 –40 –130 –120 INPUT BIAS CURRENT vs TEMPERATURE –IB +IB Input Bias Current (nA) –110 –100 –90 –80 –70 –60 –50 –40 –60 –40 –20 0 20 40 60 80 100 120 140 Gain (dB) 40 20 0 –20 –40 1 10 100 1k 10k 100k 1M Frequency (Hz) –80 –100 –120 –140 –160 10M Phase (°) 60 –60 Temperature (°C) CURRENT LIMIT vs TEMPERATURE 9 8 7 8A 9 8 7 CURRENT LIMIT vs SUPPLY VOLTAGE +ILIM, 8A –ILIM, 8A Current Limit (A) Current Limit (A) 6 5 4 3 2 1 0 –75 –50 –25 0 25 5A 6 5 4 3 2 1 0 0 5 +ILIM, 5A –ILIM, 5A 2A +ILIM, 2A –ILIM, 2A 50 75 100 125 10 15 20 25 30 Temperature (°C) Supply Voltage (V) INPUT BIAS CURRENT vs COMMON-MODE VOLTAGE –200 –180 Quiescent Current (mA) 30 QUIESCENT CURRENT vs TEMPERATURE VS = ±30V 25 20 15 10 IQ Shutdown (output disabled) 5 0 –75 VS = ±5V Input Bias Current (nA) –160 –140 –120 –100 –80 –60 –40 –20 –0 –30 –20 –10 0 10 20 30 –50 –25 0 25 50 75 100 125 Common-Mode Voltage (V) Temperature (°C) ® OPA549 4 TYPICAL PERFORMANCE CURVES (Cont.) At TCASE = +25°C, VS = ±30V and E/S pin open, unless otherwise noted. COMMON-MODE REJECTION RATIO vs FREQUENCY 100 90 80 70 60 50 40 10 100 1k Frequency (Hz) 10k 100k POWER SUPPLY REJECTION RATIO vs FREQUENCY 120 Power Supply Rejection Ratio (dB) Common-Mode Rejection (dB) 100 80 –PSRR 60 +PSRR 40 20 0 10 100 1k 10k 100k 1M Frequency (Hz) VOLTAGE NOISE DENSITY vs FREQUENCY 300 250 OPEN-LOOP GAIN, COMMON-MODE REJECTION RATIO AND POWER SUPPLY REJECTION RATIO vs TEMPERATURE 120 AOL, CMRR, PSRR (dB) Voltage Noise (nV/√Hz) 110 AOL 100 PSRR 90 CMRR 200 150 100 50 0 1 10 100 1k 10k 100k Frequency (Hz) 80 –75 –50 0 50 100 125 Temperature (°C) GAIN-BANDWIDTH PRODUCT AND SLEW RATE vs TEMPERATURE 1 16 GBW 15 14 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 –75 –50 –25 0 25 SR– SR+ TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY G = +3 RL = 4 Ω Gain-Bandwidth Product (MHz) 75W 10W Slew Rate (V/µs) 13 12 11 10 9 8 7 6 50 75 100 125 Temperature (°C) THD+N (%) 0.1 1W 0.1W 0.01 0.001 20 100 1k Frequency (Hz) 10k 20k ® 5 OPA549 TYPICAL PERFORMANCE CURVES (Cont.) At TCASE = +25°C, VS = ±30V and E/S pin open, unless otherwise noted. OUTPUT VOLTAGE SWING vs OUTPUT CURRENT 5 (V+) –VO 5 OUTPUT VOLTAGE SWING vs TEMPERATURE IO = +8A VSUPPLY – VOUT (V) VSUPPLY– VOUT (V) 4 (V–) –VO 3 4 IO = –8A 3 IO = +2A 2 2 IO = –2A 1 1 0 0 2 4 6 8 10 Output Current (A) 0 –75 –50 –25 0 25 50 75 100 125 Temperature (°C) MAXIMUM OUTPUT VOLTAGE SWING vs FREQUENCY 30 25 Output Voltage (Vp) OUTPUT LEAKAGE CURRENT vs APPLIED OUTPUT VOLTAGE 5 4 Leakage current with output disabled. Leakage Current (mA) Maximum output voltage without slew rate-induced distortion. 3 2 1 0 –1 –2 –3 –4 RCL = 0 RCL = ∞ 20 15 10 5 0 1k 10k 100k Frequency (Hz) 1M –5 –40 –30 –20 –10 0 10 20 30 40 Output Voltage (V) OFFSET VOLTAGE PRODUCTION DISTRIBUTION 25 25 OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION Percent of Amplifiers (%) 15 Percent of Amplifiers (%) –4.7 –4.23 –3.76 –3.29 –2.82 –2.35 –1.88 –1.41 –0.94 –0.47 0 0.47 0.94 1.41 1.88 2.35 2.82 3.29 3.76 4.23 4.7 20 20 15 10 10 5 5 0 0 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 Offset Voltage (mV) Offset Voltage (µV/°C) ® OPA549 6 TYPICAL PERFORMANCE CURVES (Cont.) At TCASE = +25°C, VS = ±30V and E/S pin open, unless otherwise noted. SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE 70 60 50 Overshoot (%) 40 30 20 G = –1 10 0 0 5k 10k 15k 20k 25k 30k 35k G = +1 10V/div LARGE-SIGNAL STEP RESPONSE G = 3, CL = 1000pF 5µs/div Load Capacitance (pF) SMALL-SIGNAL STEP RESPONSE G = 1, CL = 1000pF SMALL-SIGNAL STEP RESPONSE G = 3, CL = 1000pF 2.5µs/div 100mV/div 50mV/div 2.5µs/div ® 7 OPA549 APPLICATIONS INFORMATION Figure 1 shows the OPA549 connected as a basic noninverting amplifier. The OPA549 can be used in virtually any op amp configuration. Power supply terminals should be bypassed with low series impedance capacitors. The technique shown, using a ceramic and tantalum type in parallel, is recommended. Power supply wiring should have low series impedance. Be sure to connect both output pins (pins 1 and 2). CONTROL REFERENCE (Ref) PIN The OPA549 features a reference (ref) pin to which the ILIM and the Enable/Status (E/S) pin are referred. Ref simply provides a reference point accessible to the user that can be set to V–, ground, or any reference of the user’s choice. Ref cannot be set below the negative supply or above (V+) – 8V. If the minimum VS is used, Ref must be set at V–. ADJUSTABLE CURRENT LIMIT The OPA549’s accurate, user-defined current limit can be set from 0A to 10A by controlling the input to the ILIM pin. Unlike other designs, which use a power resistor in series with the output current path, the OPA549 senses the load indirectly. This allows the current limit to be set with a 0µA to 633µA control signal. In contrast, other designs require a limiting resistor to handle the full output current (up to 10A in this case). Although the design of the OPA549 allows output currents up to 10A, it is not recommended that the device be operated continuously at that level. The highest rated continuous current capability is 8A. Continuously running the OPA549 at output currents greater than 8A will degrade long-term reliability. V+ 10µF + 0.1µF(2) R1 10, 11 R2 E/S 3 9 1, 2 OPA549 8 VO ILIM(1) ZL G = 1+ R2 R1 VIN 4 5, 7 Ref 6 0.1µF(2) 10µF + Operation of the OPA549 with current limit less than 1A results in reduced current limit accuracy. Applications requiring lower output current may be better suited to the OPA547 or OPA548. Resistor-Controlled Current Limit Figure 2a shows a simplified schematic of the internal circuitry used to set the current limit. Leaving the ILIM pin open programs the output current to zero, while connecting ILIM directly to Ref programs the maximum output current limit, typically 10A. With the OPA549, the simplest method for adjusting the current limit uses a resistor or potentiometer connected between the ILIM pin and Ref according to Equation 1: V– NOTE: (1) ILIM connected to Ref gives the maximum current limit, 10A (peak). (2) Connect capacitors directly to package power supply pins. FIGURE 1. Basic Circuit Connections. R CL = POWER SUPPLIES The OPA549 operates from single (+8V to +60V) or dual (±4V to ±30V) supplies with excellent performance. Most behavior remains unchanged throughout the full operating voltage range. Parameters that vary significantly with operating voltage are shown in the Typical Performance Curves. Some applications do not require equal positive and negative output voltage swing. Power supply voltages do not need to be equal. The OPA549 can operate with as little as 8V between the supplies and with up to 60V between the supplies. For example, the positive supply could be set to 55V with the negative supply at –5V. Be sure to connect both V– pins (pins 5 and 7) to the negative power supply and both V+ pins (pins 10 and 11) to the positive power supply. Package tab is internally connected to V–, however, do use the tab to conduct current. 75kV – 7.5kΩ I LIM (1) Commonly used values are shown in Figure 2. Digitally-Controlled Current Limit The low-level control signal (0µA to 633µA) also allows the current limit to be digitally controlled by setting either a current (ISET) or voltage (VSET). The output current ILIMcan be adjusted by varying ISET according to Equation 2: ISET = ILIM/15800 (2) Figure 2b demonstrates a circuit configuration implementing this feature. The output current ILIM can be adjusted by varying VSET according to Equation 3: VSET = (Ref) + 4.75V – (7500Ω)(ILIM)/15800 (3) Figure 11 demonstrates a circuit configuration implementing this feature. ® OPA549 8 (a) RESISTOR METHOD (b) DAC METHOD (Current or Voltage) Max IO = ILIM ±ILIM = 4.75V 7500Ω (4.75) (15800) 7500Ω + RCL 4.75V ISET 8 RCL 0.01µF (optional, for noisy environments) 6 Ref D/A 7500Ω Max IO = ILIM ±ILIM =15800 ISET 8 6 Ref RCL = = 15800 (4.75V) ILIM 75kΩ ILIM – 7500Ω – 7.5kΩ OPA549 CURRENT LIMIT: 0A to 10A DESIRED CURRENT LIMIT 0A(2) 2.5A 3A 4A 5A 6A 7A 8A 9A 10A RESISTOR(1) (RCL) ILIM Open 22.6kΩ 17.4kΩ 11.3kΩ 7.5kΩ 4.99kΩ 3.24kΩ 1.87kΩ 845Ω ILIM Connected to Ref ISET = ILIM/15800 VSET = (Ref) + 4.75V – (7500Ω) (ILIM)/15800 CURRENT (ISET) 0µA 158µA 190µA 253µA 316µA 380µA 443µA 506µA 570µA 633µA VOLTAGE (VSET) (Ref) + 4.75V (Ref) + 3.56V (Ref) + 3.33V (Ref) + 2.85V (Ref) + 2.38V (Ref) + 1.90V (Ref) + 1.43V (Ref) + 0.95V (Ref) + 0.48V (Ref) NOTES: (1) Resistors are nearest standard 1% values. (2) Offset in the current limit circuitry may introduce approximately ±0.25A variation at low current limit values. FIGURE 2. Adjustable Current Limit. ENABLE/STATUS (E/S) PIN The Enable/Status Pin provides two unique functions: 1) output disable by forcing the pin low and 2) thermal shutdown indication by monitoring the voltage level at the pin. Either or both of these functions can be utilized in an application. For normal operation (output enabled), the E/S pin can be left open or driven high (at least 2.4V above Ref). A small value capacitor connected between the E/S pin and CREF may be required for noisy applications. Output Disable To disable the output, the E/S pin is pulled to a logic low (no greater than 0.8V above Ref). Typically the output is shut down in 1µs. To return the output to an enabled state, the E/S pin should be disconnected (open) or pulled to at least 2.4V above Ref. It should be noted that driving the E/ S pin high (output enabled) does not defeat internal thermal shutdown; however, it does prevent the user from monitoring the thermal shutdown status. See Figure 3 for an example implementing this function. This function not only conserves power during idle periods (quiescent current drops to approximately 6mA) but also allows multiplexing in multi-channel applications. Figure 12 OPA549 E/S Ref CMOS or TTL Logic Ground FIGURE 3. Output Disable. shows two OPA549s in a switched amplifier configuration. The on/off state of the two amplifiers is controlled by the voltage on the E/S pin. Under these conditions, the disabled device will behave like a 750pF load. Slewing faster than 3V/µs will cause leakage current to rapidly increase in devices that are disabled, and will contribute additional load. At high temperature (125°C), the slewing threshold drops to approximately 2V/µs. Input signals must be limited to avoid excessive slewing in multiplexed applications. ® 9 OPA549 Thermal Shutdown Status The OPA549 has thermal shutdown circuitry that protects the amplifier from damage. The thermal protection circuitry disables the output when the junction temperature reaches approximately 160°C and allows the device to cool. When the junction temperature cools to approximately 140°C, the output circuitry is automatically re-enabled. Depending on load and signal conditions, the thermal protection circuit may cycle on and off. The E/S pin can be monitored to determine if the device is in shutdown. During normal operation, the voltage on the E/S pin is typically 3.5V above Ref. Once shutdown has occurred, this voltage drops to approximately 200mV above Ref. See Figure 4 for an example implementing this function. The Safe Operating Area (SOA curve, Figure 6) shows the permissible range of voltage and current. The safe output current decreases as VS – VO increases. Output short circuits are a very demanding case for SOA. A short circuit to ground forces the full power supply voltage (V+ or V–) across the conducting transistor. Increasing the case temperature reduces the safe output current that can be tolerated without activating the thermal shutdown circuit of the OPA549. For further insight on SOA, consult Application Bulletin AB-039. 20 10 PD Output Current (A) OPA549 Ref E/S 1 Output current can be limited to less than 8A—see text. PD PD =9 TC = 25°C =4 =1 0W 7W 8W HCT E/S pin can interface with standard HCT logic inputs. Logic ground is referred to Ref. TC = 85°C Pulse Operation Only (Limit rms current to ≤ 8A) 1 2 5 10 TC = 125°C Logic Ground 0.1 20 50 100 FIGURE 4. Thermal Shutdown Status. External logic circuitry or an LED can be used to indicate if the output has been thermally shutdown, as demonstrated in Figure 10. Output Disable and Thermal Shutdown Status As mentioned earlier, the OPA549’s output can be disabled and the disable status can be monitored simultaneously. Figure 5 provides an example of interfacing to the E/S pin. VS – VO (V) FIGURE 6. Safe Operating Area. POWER DISSIPATION Power dissipation depends on power supply, signal, and load conditions. For dc signals, power dissipation is equal to the product of output current times the voltage across the conducting output transistor. Power dissipation can be minimized by using the lowest possible power supply voltage necessary to assure the required output voltage swing. For resistive loads, the maximum power dissipation occurs at a dc output voltage of one-half the power supply voltage. Dissipation with ac signals is lower. Application Bulletin AB-039 explains how to calculate or measure power dissipation with unusual signals and loads. THERMAL PROTECTION Power dissipated in the OPA549 will cause the junction temperature to rise. Internal thermal shutdown circuitry shuts down the output when the die temperature reaches approximately 160°C and resets when the die has cooled to 140°C. Depending on load and signal conditions, the thermal protection circuit may cycle on and off. This limits the dissipation of the amplifier but may have an undesirable effect on the load. Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable operation, junction temperature should be limited to 125°C maximum. To estimate the margin of safety OPA549 E/S Ref Open-drain logic output can disable amplifier's output with logic low. HCT logic input monitors thermal shutdown status during normal operation. Open Drain (Output Disable) HCT (Thermal Status Shutdown) Logic Ground FIGURE 5. Output Disable and Thermal Shutdown Status. SAFE OPERATING AREA Stress on the output transistors is determined both by the output current and by the output voltage across the conducting output transistor, VS – VO. The power dissipated by the output transistor is equal to the product of the output current and the voltage across the conducting transistor, VS – VO. ® OPA549 10 in a complete design (including heat sink) increase the ambient temperature until the thermal protection is triggered. Use worst-case load and signal conditions. For good reliability, thermal protection should trigger more than 35°C above the maximum expected ambient condition of your application. This produces a junction temperature of 125°C at the maximum expected ambient condition. The internal protection circuitry of the OPA549 was designed to protect against overload conditions. It was not intended to replace proper heat sinking. Continuously running the OPA549 into thermal shutdown will degrade reliability. AMPLIFIER MOUNTING AND HEAT SINKING Most applications require a heat sink to assure that the maximum operating junction temperature (125°C) is not exceeded. In addition, the junction temperature should be kept as low as possible for increased reliability. Junction temperature can be determined according to the Equations: TJ = TA + PD θJA where (4) (5) screw torque, insulating material used (if any), and thermal joint compound used (if any) also affect θCH. A typical θCH for a mounted 11-lead power ZIP package is 0.5°C/W. Now we can solve for θHA: θHA = [(TJ – TA)/ PD] – θJC – θCH θHA = [(125°C – 40°C)/10W] – 1.4°C/W – 0.5°C/W θHA = 6.6°C/W To maintain junction temperature below 125°C, the heat sink selected must have a θHA less than 6.6°C/W. In other words, the heat sink temperature rise above ambient must be less than 66°C (6.6°C/W • 10W). For example, at 10W Thermalloy model number 6396B has a heat sink temperature rise of 56°C (θHA = 56°C/10W = 5.6°C/W), which is below the required 66°C required in this example. Thermalloy model number 6399B has a sink temperature rise of 33°C (θHA = 33°C/10W = 3.3°C/W), which is also below the required 66°C required in this example. Figure 7 shows power dissipation versus ambient temperature for a 11-lead power ZIP package with the Thermalloy 6396B and 6399B heat sinks. θJA = θJC + θCH + θHA TJ = Junction Temperature (°C) TA = Ambient Temperature (°C) PD = Power Dissipated (W) 30 PD = (TJ (max) – TA)/ θJA (TJ (max) – 150°C) θJC = Junction-to-Case Thermal Resistance (°C/W) θHA = Heat Sink-to-Ambient Thermal Resistance (°C/W) θJA = Junction-to-Air Thermal Resistance (°C/W) Figure 7 shows maximum power dissipation versus ambient temperature with and without the use of a heat sink. Using a heat sink significantly increases the maximum power dissipation at a given ambient temperature as shown. The challenge in selecting the heat sink required lies in determining the power dissipated by the OPA549. For dc output, power dissipation is simply the load current times the voltage developed across the conducting output transistor, PD = IL (VS – VO). Other loads are not as simple. Consult Application Bulletin AB-039 for further insight on calculating power dissipation. Once power dissipation for an application is known, the proper heat sink can be selected. Heat Sink Selection Example—An 11-lead power ZIP package is dissipating 10 Watts. The maximum expected ambient temperature is 40°C. Find the proper heat sink to keep the junction temperature below 125°C (150°C minus 25°C safety margin). Combining Equations (4) and (5) gives: TJ = TA + PD ( θJC + θCH + θHA ) (6) TJ, TA, and PD are given. θJC is provided in the Specifications Table, 1.4°C/W (dc). θCH can be obtained from the heat sink manufacturer. Its value depends on heat sink size, area, and material used. Semiconductor package type, mounting Power Dissipation (W) θCH = Case-to-Heat Sink Thermal Resistance (°C/W) 20 with Thermalloy 6399B Heat Sink, θJA = 5.2°C/W 10 with Thermalloy 6396B Heat Sink, θJA = 7.5°C/W θJA = 30°C/W with No Heat Sink, 0 0 25 50 75 100 125 Ambient Temperature (°C) Thermalloy 6396B assume OPA549 θ HA θ CH θ JC θ JA θ HA θ CH θ JC θ JA = = = = = = = = 5.6°C/W 0.5°C/W 1.4°C/W 7.5°C/W 3.3°C/W 0.5°C/W 1.4°C/W 5.2°C/W Thermalloy 6396B assume OPA549 FIGURE 7. Maximum Power Dissipation vs Ambient Temperature. Another variable to consider is natural convection versus forced convection air flow. Forced-air cooling by a small fan can lower θCA (θCH + θHA ) dramatically. Some heat sink manufacturers provide thermal data for both of these cases. Heat sink performance is generally specified under idealized conditions that may be difficult to achieve in an actual application. For additional information on determining heat sink requirements, consult Application Bulletin AB-038. ® 11 OPA549 As mentioned earlier, once a heat sink has been selected, the complete design should be tested under worst-case load and signal conditions to ensure proper thermal protection. Any tendency to activate the thermal protection circuitry may indicate inadequate heat sinking. The tab of the 11-lead power ZIP package is electrically connected to the negative supply, V–. It may be desirable to isolate the tab of 11-lead power ZIP package from its mounting surface with a mica (or other film) insulator. For lowest overall thermal resistance, it is best to isolate the entire heat sink/OPA549 structure from the mounting surface rather than to use an insulator between the semiconductor and heat sink. OUTPUT STAGE COMPENSATION The complex load impedances common in power op amp applications can cause output stage instability. For normal operation, output compensation circuitry is typically not required. However, for difficult loads or if the OPA549 is intended to be driven into current limit, an R/C network may be required. Figure 8 shows an output R/C compensation (snubber) network which generally provides excellent stability. A snubber circuit may also enhance stability when driving large capacitive loads (>1000pF) or inductive loads (motors, loads separated from the amplifier by long cables). Typically, 3Ω to 10Ω resistors in series with 0.01µF to 0.1µF capacitors is adequate. Some variations in circuit values may be required with certain loads. OUTPUT PROTECTION Reactive and EMF-generating loads can return load current to the amplifier, causing the output voltage to exceed the power supply voltage. This damaging condition can be avoided with clamp diodes from the output terminal to the power supplies as shown in Figure 8. Schottky rectifier diodes with a 8A or greater continuous rating are recommended. VOLTAGE SOURCE APPLICATION Figure 9 illustrates how to use the OPA549 to provide an accurate voltage source with only three external resistors. First, the current limit resistor, RCL , is chosen according to the desired output current. The resulting voltage at the ILIM pin is constant and stable over temperature. This voltage, VCL, is connected to the non-inverting input of the op amp and used as a voltage reference, thus eliminating the need for an external reference. The feedback resistors are selected to gain VCL to the desired output voltage level. PROGRAMMABLE POWER SUPPLY A programmable source/sink power supply can easily be built using the OPA549. Both the output voltage and output current are user-controlled. Figure 10 shows a circuit using potentiometers to adjust the output voltage and current while Figure 11 uses digital-to-analog converters. An LED connected to the E/S pin through a logic gate indicates if the OPA549 is in thermal shutdown. R1 R2 V+ V+ R1 5kΩ VIN R2 20kΩ G=– R2 = –4 R1 4.75V VO = VCL (1 + R2/R1) Ref ILIM IO = 15800 (4.75V) 7500Ω + RCL D1 OPA549 7500Ω VCL D2 10Ω (Carbon) 0.01µF Motor V– V– D1, D2 : Schottky Diodes 0.01µF (Optional, for noisy environments) For Example: If ILIM = 7.9A, RCL = 2kΩ VCL = 2kΩ • 4.75V (2kΩ + 7500Ω) = 1V 10 1 = 10 RCL Uses voltage developed at ILIM pin as a moderately accurate reference voltage. FIGURE 8. Motor Drive Circuit. Desired VO = 10V, G = R1 = 1kΩ and R2 = 9kΩ FIGURE 9. Voltage Source. ® OPA549 12 1kΩ +5V 9kΩ 9kΩ G=1+ = 10 1kΩ V+ = +30V V– = 0V 10.5kΩ Output Adjust 0.12V to 2.5V 3 OPA549 4 6 9 E/S 10kΩ VO = 1V to 25V IO = 0 to 10A 74HCT04 R ≥ 250Ω 499Ω V– +5V ILIM 8 Ref 1kΩ Current Limit Adjust 0V to 4.75V Thermal Shutdown Status (LED) 20kΩ 0.01µF FIGURE 10. Resistor-Controlled Programmable Power Supply. V+ = +30V V– = 0V 1kΩ –5V VREF +5V VREF A RFB A 10pF 1/2 DAC7800/1/2(3) DAC A AGND A ILIM 8 Thermal Shutdown Status (LED) IOUT A 1/2 OPA2336 4 6 Ref +5V 3 1, 2 OUTPUT ADJUST G = 10 9kΩ OPA549 9 E/S 74HCT04 VO = 7V to 25V IO = 0A to 10A R ≥ 250Ω VREF B RFB B 10pF 1/2 DAC7800/1/2 DAC B DGND AGND B IOUT B 1/2 OPA2336 0.01µF CURRENT LIMIT ADJUST Choose DAC780X based on digital interface: DAC7800 - 12-bit interface, DAC7801 - 8-bit interface + 4 bits, DAC7802 - serial interface. FIGURE 11. Digitally-Controlled Programmable Power Supply. ® 13 OPA549 R1 VIN1 R2 OPA549 E/S OPA549 ILIM Ref VO R3 VE/S VIN2 R4 RCL1 RCL2 Close for high current (could be open drain output of a logic gate). OPA549 E/S Limit output slew rates to ≤ 3V/µs (see text). FIGURE 12. Switched Amplifier. FIGURE 13. Multiple Current Limit Values. R1 1kΩ R2 4kΩ Master OPA549 VIN Ref ILIM 0.1Ω 20A Peak VO G=5 Slave 0.1Ω OPA549 ILIM Ref FIGURE 14. Parallel Output for Increased Output Current. ® OPA549 14