125 MHz Single Supply, Clamping Op Amps Features General Description • Specified for +3V, +5V, or ± 5V Applications • Power Down to 0 µA • Output Voltage Clamp • Large Input Common Mode Range 0V < VCM < VS - 1.2V • Output Swings to Ground Without Saturating • -3 dB Bandwidth = 125 MHz • ± 0.1 dB Bandwidth = 30 MHz • Low Supply Current = 5 mA • Slew Rate = 275 V/µs • Low Offset Voltage = 4 mV max • Output Current = ±100 mA • High Open Loop Gain = 80 dB • Differential Gain = 0.05% • Differential Phase = 0.05° The EL2257C/EL2357C are supply op amps. Prior single supply op amps have generally been limited to bandwidths and slew rates 1/4 that of the EL2257C/EL2357C. The 125 MHz bandwidth, 275 V/µs slew rate, and 0.05%/0.05° differential gain/differential phase makes this part ideal for single or dual supply video speed applications. With its voltage feedback architecture, this amplifier can accept reactive feedback networks, allowing them to be used in analog filtering applications. The inputs can sense signals below the bottom supply rail and as high as 1.2V below the top rail. Connecting the load resistor to ground and operating from a single supply, the outputs swing completely to ground without saturating. The outputs can also drive to within 1.2V of the top rail. The EL2257C/EL2357C will output ±100 mA and will operate with single supply voltages as low as 2.7V, making them ideal for portable, low power applications. Applications The EL2257C/EL2357C also have an output voltage clamp feature. This clamp is a fast recovery (<7 ns) output clamp that prevents the output voltage from going above the preset clamp voltage. This feature is desirable for A/D applications, as A/D converters can require long times to recover if overdriven. • • • • • • • Video Amplifier PCMCIA Applications A/D Driver Line Driver Portable Computers High Speed Communications RGB Printer, FAX, Scanner Applications • Broadcast Equipment • Active Filtering • Multiplexing Ordering Information Part No. Temp. Range Package The EL2257C/EL2357C have a high speed disable feature. Applying a low logic level to all ENABLE pins reduces the supply current to 0 µA within 50 ns. Each amplifier has its own ENABLE pin. This is useful for both multiplexing and reducing power consumption. The EL2257C/EL2357C are available in plastic DIP and SOIC packages. Both parts operate over the industrial temperature range of -40°C to +85°C. For single amplifier applications, see the EL2150C/EL2157C. For space saving, industry standard pin out dual and quad applications, see the EL2250C/EL2450C. Connection Diagrams Outline # EL2257CN -40°C to +85°C 14 Pin PDIP MDP0031 EL2257CS -40°C to +85°C 14 Pin SOIC MDP0027 EL2357CN -40°C to +85°C 16 Pin PDIP MDP0031 EL2357CS -40°C to +85°C 16 Pin SOIC MDP0027 Top View January 5, 2000 Top View © 1995 Elantec, Inc. EL2257C/EL2357C EL2257C/EL2357C EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps Absolute Maximum Ratings (T A = 25 °C) Power Dissipation Storage Temperature Range Ambient Operating Temperature Range Operating Junction Temperature Supply Voltage between VS and GND 12.6V Input Voltage (IN+, IN-, ENABLE, CLAMP) GND–0.3V, VS+0.3V Differential Input Voltage ±6V Maximum Output Current 90 mA Output Short Circuit Duration (see note [1] DC Electrical Characteristics) See Curves -65°C to +150°C -40°C to +85°C 150°C Important Note: All parameters having Min/Max specifications are guaranteed. The Test Level column indicates the specific device testing actually performed during production and Quality inspection. Elantec performs most electrical tests using modern high-speed automatic test equipment, specifically the LTX77 Series system. Unless otherwise noted, all tests are pulsed tests, therefor TJ = TC = TA. Test Level Test Procedure I 100% production tested and QA sample tested per QA test plan QCX0002. II 100% production tested at TA = 25°C and QA sample tested at TA = 25°C, TMAX and TMIN per QA test plan QCX0002. III QA sample tested per QA test plan QCX0002. IV Parameter is guaranteed (but not tested) by Design and Characterization Data. V Parameter is typical value at TA = 25°C for information purposes only. DC Electrical Characteristics VS=+5V, GND=0V, TA=25°C, VCM=1.5V, VOUT=1.5V, VCLAMP=+5V, VENABLE=+5V, unless otherwise specified. Parameter VOS Description Offset Voltage Test Conditions Min Typ Max Test Level Units EL2257C -4 4 I mV EL2357C -6 6 I mV TCVOS Offset Voltage Temperature Coefficient Measured from Tmin to Tmax 10 V µV/°C IB Input Bias Current VIN=0V -5.5 -10 I µA IOS Input Offset Current VIN=0V 150 +1100 I nA TCIOS Input Bias Current Temperature Coefficient Measured from Tmin to Tmax 50 V nA/°C PSRR Power Supply Rejection Ratio VS=VENABLE=+2.7V to +12V, VCLAMP=OPEN 70 I dB CMRR Common Mode Rejection Ratio -1100 45 VCM=0V to +3.8V 50 65 I dB VCM=0V to +3.0V 55 70 I dB CMIR Common Mode Input Range RIN Input Resistance Common Mode 0 CIN Input Capacitance VS-1.2 I V 2 I MΩ SOIC Package 1 V pF PDIP Package 1.5 V pF Av=+1 40 V mΩ mA 1 ROUT Output Resistance IS,ON Supply Current - Enabled (per amplifier) VS=VCLAMP=+12V, VENABLE=+12V 5 6.5 I IS,OFF Supply Current - Shut Down (per amplifier) VS=VCLAMP=+10V, VENABLE=+0.5V 0 50 I µA VS=VCLAMP=+12V, VENABLE=+0.5V 5 V µA PSOR Power Supply Operating Range AVOL Open Loop Gain 2.7 I V 80 I dB VOUT=+1.5V to +3.5V, RL=1 kΩ to GND 70 V dB VOUT=+1.5V to +3.5V, RL=150Ω to GND 60 V dB VS=VCLAMP=+12V, VOUT=+2V to +9V, RL=1 kΩ to GND 2 65 12.0 DC Electrical Characteristics (Continued) VS=+5V, GND=0V, TA=25°C, VCM=1.5V, VOUT=1.5V, VCLAMP=+5V, VENABLE=+5V, unless otherwise specified. Parameter VOP Description Test Conditions Positive Output Voltage Swing Min VS=+12V, AV=+1, RL=1 kΩ to 0V VS=+12V, AV=+1, RL=150Ω to 0V 9.6 VS=±5V, AV=+1, RL=1 kΩ to 0V VON Negative Output Voltage Swing [1] V V 10.0 I V 4.0 V V V 3.4 3.8 I VS=+3V, AV=+1, RL=150Ω to 0V 1.8 1.95 I V I mV V V VS=+12V, AV=+1, RL=150Ω to 0V 5.5 VS=±5V, AV=+1, RL=1 kΩ to 0V -4.0 VS=±5V, AV=+1, RL=150Ω to 0V -3.7 Output Current IOUT,OFF Output Current, Disabled VENABLE=+0.5V VIH-EN ENABLE pin Voltage for Power Up Relative to GND Pin VIL-EN ENABLE pin Voltage for Shut Down Relative to GND Pin IIH-EN ENABLE pin Input Current-High IIL-EN ENABLE pin Input Current-Low [2] VOR-CL Voltage Clamp Operating Range VACC-CL VS=±5V, AV=+1, RL=10Ω to 0V ±75 VS=±5V, AV=+1, RL=50Ω to 0V [3] Units 10.8 Max VS=±5V, AV=+1, RL=150Ω to 0V IOUT [2] Test Level Typ 8 -3.4 ±100 ±60 0 20 2.0 VS=VCLAMP=+12V, VENABLE=+12V 340 VS=VCLAMP=+12V, VENABLE=+0.5V 0 I V I mA V mA I µA I V 0.5 I V 410 I µA µA 1 I VOP I V 100 250 I mV 12 25 Relative to GND Pin 1.2 CLAMP Accuracy [4] VIN=+4V, RL=1 kΩ to GND VCLAMP=+1.5V and +3.5V -250 IIH-CL CLAMP pin Input Current - High VS=VCLAMP=+12V IIL-CL CLAMP pin Input Current - Low / Per Amplifier VS=+12V, VCLAMP=+1.2V -30 -15 I µA I µA 1. Internal short circuit protection circuitry has been built into the EL2257C/EL2357C. See the Applications section. 2. If the disable feature is not desired, tie the ENABLE pins to the VS pin, or apply a logic high level to the ENABLE pins. 3. The maximum output voltage that can be clamped is limited to the maximum positive output Voltage, or VOP. Applying a Voltage higher than VOP inactivates the clamp. If the clamp feature is not desired, either tie the CLAMP pin to the VS pin, or simply let the CLAMP pin float. 4. The clamp accuracy is affected by VIN and RL. See the Typical Curves Section and the Clamp Accuracy vs. VIN and RL curve. 3 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps Closed Loop AC Electrical Characteristics VS=+5V, GND=0V, TA=25°C, VCM=+1.5V, VOUT=+1.5V, VCLAMP=+5V, VENABLE=+5V, AV=+1, RF=0Ω, RL=150Ω to GND pin, unless otherwise specified [1] Parameter BW BW Description -3 dB Bandwidth (Vout=400 mVp-p) ±0.1 dB Bandwidth (Vout=400 mVp-p) Test Conditions Min Typ Max Test Level Units VS=+5V, AV=+1, RF=0Ω 125 V MHz VS=+5V, AV=-1, RF=500Ω 60 V MHz VS=+5V, AV=+2, RF=500Ω 60 V MHz VS=+5V, AV=+10, RF=500Ω 6 V MHz VS=+12V, AV=+1, RF=0Ω 150 V MHz VS=+3V, AV=+1, RF=0Ω 100 V MHz VS=+12V, AV=+1, RF=0Ω 25 V MHz VS=+5V, AV=+1, RF=0Ω 30 V MHz VS=+3V, AV=+1, RF=0Ω 20 V MHz MHz GBWP Gain Bandwidth Product VS=+12V, @ AV=+10 60 V PM Phase Margin RL=1 kΩ, CL=6 pF 55 V ° SR Slew Rate VS=+10V, RL=150Ω, Vout=0V to +6V 275 I V/µs VS=+5V, RL=150Ω, Vout=0V to +3V 300 V V/µs tR,tF Rise Time, Fall Time ±0.1V Step 2.8 V ns OS Overshoot ±0.1V Step 10 V % tPD Propagation Delay ±0.1V step 3.2 V ns tS 200 0.1% Settling Time VS=±5V, RL=500Ω, AV=+1, VOUT=±3V 40 V ns 0.01% Settling Time VS=±5V, RL=500Ω, AV=+1, VOUT=±3V 75 V ns dG Differential Gain [2] AV=+2, RF=1 kΩ 0.05 V % dP Differential Phase [2] AV=+2, RF=1 kΩ 0.05 V ° eN Input Noise Voltage f=10 kHz 48 V nV/ÐH z iN Input Noise Current f=10 kHz 1.25 V pA/ÐH z tDIS Disable Time [3] 50 V ns tEN Enable Time [3] 25 V ns tCL Clamp Overload Recovery 7 V ns 1. All AC tests are performed on a “warmed up” part, except slew rate, which is pulse tested. 2. Standard NTSC signal = 286 mVp-p, f=3.58 MHz, as VIN is swept from 0.6V to 1.314V. RL is DC coupled. 3. Disable/Enable time is defined as the time from when the logic signal is applied to the ENABLE pin to when the supply current has reached half its final value. 4 Typical Performance Curves Non-Inverting Frequency Response (Gain) Non-Inverting Frequency Response (Phase) 3 dB Bandwidth vs Temperature for Non-Inverting Gains Inverting Frequency Response (Gain) Inverting Frequency Response (Phase) 3 dB Bandwidth vs Temperature for Inverting Gains Frequency Response for Various RL Frequency Response for Various CL Non-Inverting Frequency Response vs Common Mode Voltage 5 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps 3 dB Bandwidth vs Supply Voltage for Non-Inverting Gains Frequency Response for Various Supply Voltages, AV = + 1 PSSR and CMRR vs Frequency 3 dB Bandwidth vs Supply Voltage for Inverting Gains Frequency Response for Various Supply Voltages, AV = + 2 PSRR and CMRR vs Die Temperature Open Loop Gain and Phase vs Frequency Open Loop Voltage Gain vs Die Temperature 6 Closed Loop Output Impedance vs Frequency Large Signal Step Response, VS = +3V Large Signal Step Response, VS = +5V Large Signal Step Response, VS = ±5V Small Signal Step Response Slew Rate vs Temperature Large Signal Step Response, VS = +12V Settling Time vs Settling Accuracy Voltage and Current Noise vs Frequency 7 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps Differential Gain for Single Supply Operation Differential Phase for Single Supply Operation Differential Gain and Phase for Dual Supply Operation 2nd and 3rd Harmonic Distortion vs Frequency 2nd and 3rd Harmonic Distortion vs Frequency 2nd and 3rd Harmonic Distortion vs Frequency Output Voltage Swing vs Frequency for THD < 0.1% Output Voltage Swing vs Frequency for Unlimited Distortion 8 Output Current vs Die Temperature Supply Current vs Supply Voltage (per amplifier) Supply Current vs Die Temperature (per amplifier) Input Resistance vs Die Temperature Offset Voltage vs Die Temperature (4 Samples) Input Bias Current vs Input Voltage Input Offset Current and Input Bias Current vs Die Temperature Positive Output Voltage Swing vs Die Temperature, RL = 150Ω to GND Negative Output Voltage Swing vs Die Temperature, RL = 150Ω to GND Clamp Accuracy vs Die Temperature 9 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps IClamp Accuracy RL = 150Ω Clamp Accuracy RL = 1 kΩ Clamp Accuracy RL = 10 kΩ Disable Response for a Family of DC Inputs Enable Response for a Family of DC Inputs Disable/Enable Response for a Family of Sine Waves OFF Isolation 10 EL2257 Channel to Channel Isolation vs Frequency 14-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature EL2357 Channel to Channel Isolation vs Frequency 16-Lead Plastic SO Maximum Power Dissipation vs Ambient Temperature 11 14-Lead Plastic SO Maximum Power Dissipation vs Ambient Temperature 16-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps Simplified Schematic (One Channel) 12 Applications Information Product Description Supply Voltage Range and Single-Supply Operation The EL2257C/EL2357C’s, connected in voltage follower mode, -3 dB bandwidth is 125 MHz while maintaining a 275 V/µs slew rate. With an input and output common mode range that includes ground, these amplifiers were optimized for single supply operation, but will also accept dual supplies. They operate on a total supply voltage range as low as +2.7V or up to +12V. This makes them ideal for +3V applications, especially portable computers. The EL2257C/EL2357C have been designed to operate with supply voltages having a span of greater than 2.7V, and less than 12V. In practical terms, this means that the EL2257C/EL2357C will operate on dual supplies ranging from ±1.35V to ±6V. With a single-supply, the EL2257C/EL2357C will operate from +2.7V to +12V. Performance has been optimized for a single +5V supply. While many amplifiers claim to operate on a single supply, and some can sense ground at their inputs, most fail to truly drive their outputs to ground. If they do succeed in driving to ground, the amplifier often saturates, causing distortion and recovery delays. However, special circuitry built into the EL2257C/EL2357C allows the output to follow the input signal to ground without recovery delays. Pins 11 and 4 (14 and 3) are the power supply pins on the EL2257C (EL2357C). The positive power supply is connected to pin 11 (14). When used in single supply mode, pin 4 (3) is connected to ground. When used in dual supply mode, the negative power supply is connected to pin 4 (3). As supply voltages continue to decrease, it becomes necessary to provide input and output voltage ranges that can get as close as possible to the supply voltages. The EL2257C/EL2357C have an input voltage range that includes the negative supply and extends to within 1.2V of the positive supply. So, for example, on a single +5V supply, the EL2257C/EL2357C have an input range which spans from 0V to 3.8V. Power Supply Bypassing And Printed Circuit Board Layout As with any high-frequency device, good printed circuit board layout is necessary for optimum performance. Ground plane construction is highly recommended. Lead lengths should be as short as possible. The power supply pins must be well bypassed to reduce the risk of oscillation. The combination of a 4.7 µF tantalum capacitor in parallel with a 0.1 µF ceramic capacitor has been shown to work well when placed at each supply pin. For single supply operation, where the GND pin is connected to the ground plane, a single 4.7 µF tantalum capacitor in parallel with a 0.1 µF ceramic capacitor from the VS+ pin to the GND pin will suffice. The output range of the EL2257C/EL2357C is also quite large. It includes the negative rail, and extends to within 1V of the top supply rail with a 1 kΩ load. On a +5V supply, the output is therefore capable of swinging from 0V to +4V. On split supplies, the output will swing ±4V. If the load resistor is tied to the negative rail and split supplies are used, the output range is extended to the negative rail. Choice Of Feedback Resistor, RF For good AC performance, parasitic capacitance should be kept to a minimum. Ground plane construction should be used. Carbon or Metal-Film resistors are acceptable with the Metal-Film resistors giving slightly less peaking and bandwidth because of their additional series inductance. Use of sockets, particularly for the SO package should be avoided if possible. Sockets add parasitic inductance and capacitance which will result in some additional peaking and overshoot. The feedback resistor forms a pole with the input capacitance. As this pole becomes larger, phase margin is reduced. This increases ringing in the time domain and peaking in the frequency domain. Therefore, RF has some maximum value which should not be exceeded for optimum performance. If a large value of RF must be used, a small capacitor in the few picofarad range in parallel with RF can help to reduce this ringing and peaking at the expense of reducing the bandwidth. 13 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps As far as the output stage of the amplifier is concerned, RF + RG appear in parallel with RL for gains other than +1. As this combination gets smaller, the bandwidth falls off. Consequently, RF has a minimum value that should not be exceeded for optimum performance. Output Drive Capability In spite of their moderately low 5 mA of supply current, the EL2257C/EL2357C are capable of providing ±100 mA of output current into a 10Ω load, or ±60 mA into 50Ω. With this large output current capability, a 50Ω load can be driven to ±3V with VS = ±5V, making it an excellent choice for driving isolation transformers in telecommunications applications. For AV = +1, RF = 0Ω is optimum. For AV = -1 or +2 (noise gain of 2), optimum response is obtained with RF between 500Ω and 1 kΩ. For AV = -4 or +5 (noise gain of 5), keep RF between 2 kΩ and 10 kΩ. Driving Cables and Capacitive Loads Video Performance When used as a cable driver, double termination is always recommended for reflection-free performance. For those applications, the back-termination series resistor will de-couple the EL2257C/EL2357C from the cable and allow extensive capacitive drive. However, other applications may have high capacitive loads without a back-termination resistor. In these applications, a small series resistor (usually between 5Ω and 50Ω) can be placed in series with the output to eliminate most peaking. The gain resistor (RG) can then be chosen to make up for any gain loss which may be created by this additional resistor at the output. For good video performance, an amplifier is required to maintain the same output impedance and the same frequency response as DC levels are changed at the output. This can be difficult when driving a standard video load of 150Ω, because of the change in output current with DC level. Differential Gain and Differential Phase for the EL2257C/EL2357C are specified with the black level of the output video signal set to +1.2V. This allows ample room for the sync pulse even in a gain of +2 configuration. This results in dG and dP specifications of 0.05% and 0.05° while driving 150Ω at a gain of +2. Setting the black level to other values, although acceptable, will compromise peak performance. For example, looking at the single supply dG and dP curves for RL =150Ω, if the output black level clamp is reduced f r o m 1 . 2 V t o 0 .6 V d G / d P w i l l i n c r e a s e f r o m 0.05%/0.05° to 0.08%/0.25°. Note that in a gain of +2 configuration, this is the lowest black level allowed such that the sync tip doesn’t go below 0V. Disable/Power-Down Each amplifier in the EL2257C/EL2357C can be individually disabled, placing each output in a highimpedance state. The disable or enable action takes only about 40 ns. When all amplifiers are disabled, the total supply current is reduced to 0 mA, thereby eliminating all power consumption by the EL2257C/EL2357C. The EL2257C/EL2357C amplifier’s power down can be controlled by standard CMOS signal levels at each ENABLE pin. The applied CMOS signal is relative to the GND pin. For example, if a single +5V supply is used, the logic voltage levels will be +0.5V and +2.0V. If using dual ±5V supplies, the logic levels will be -4.5V and -3.0V. Letting all ENABLE pins float will disable the EL2257C/EL2357C. If the power-down feature is not desired, connect all ENABLE pins to the V S+ pin. The guaranteed logic levels of +0.5V and +2.0V are not standard TTL levels of +0.8V and +2.0V, so care must be taken if standard TTL will be used to drive the ENABLE pins. If your application requires that the output goes to ground, then the output stage of the EL2257C/EL2357C, like all other single supply op amps, requires an external pull down resistor tied to ground. As mentioned above, the current flowing through this resistor becomes the DC bias current for the output stage NPN transistor. As this current approaches zero, the NPN turns off, and dG and dP will increase. This becomes more critical as the load resistor is increased in value. While driving a light load, such as 1 kΩ, if the input black level is kept above 1.25V, dG and dP are a respectable 0.03% and 0.03°. For other biasing conditions see the Differential Gain and Differential Phase vs. Input Voltage curves. 14 Output Voltage Clamp The EL2257C/EL2357C amplifiers have an output voltage clamp. This clamping action is fast, being activated almost instantaneously, and being deactivated in < 7 ns, and prevents the output voltage from going above the preset clamp voltage. This can be very helpful when the EL2257C/EL2357C are used to drive an A/D converter, as some converters can require long times to recover if overdriven. The output voltage remains at the clamp voltage level as long as the product of the input voltage and the gain setting exceeds the clamp voltage. For example, if the EL2257C/EL2357C is connected in a gain of 2, and +3V DC is applied to the CLAMP pin, any voltage higher than +1.5V at the inputs will be clamped and +3V will be seen at the output. Each amplifier of the EL2257C have their own CLAMP pin, so individual clamp levels may be set, whereas a single CLAMP pin controls the clamp level of the EL2357C. Figure 2. Figure 3 shows the output of amplifier A of the same circuit being driven by a 0.5V to 2.75V square wave as the clamp voltage is varied from 1.0V to 2.5V, as well as the unclamped output signal. The rising edge of the signal is clamped to the voltage applied to the CLAMP pin almost instantaneously. The output recovers from the clamped mode within 5–7 ns, depending on the clamp voltage. Even when the CLAMP pin is taken 0.2V below the minimum 1.2V specified, the output is still clamped and recovers in about 11 ns. Figure 1 below is the EL2257C with each amplifier unity gain connected. Amplifier A is being driven by a 3 Vp-p sinewave and has 2.25V applied to CLAMPA, while amplifier B is driven by a 3 Vp-p triangle wave and 1.5V is applied to CLAMPB. The resulting output waveforms, with their outputs being clamped is shown in Figure 2. Figure 3. The clamp accuracy is affected by 1) the CLAMP pin voltage, 2) the input voltage, and 3) the load resistor. Depending upon the application, the accuracy may be as little as a few tens of millivolts up to a few hundred millivolts. Be sure to allow for these inaccuracies when choosing the clamp voltage. Curves of Clamp Accuracy vs. VCLAMP and VIN for 3 values of RL are included in the Typical Performance Curves Section. Figure 1. 15 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps Unlike amplifiers that clamp at the input and are therefore limited to non-inverting applications only, the EL2257C/EL2357C output clamp architecture works for both inverting and non-inverting gain applications. There is also no maximum voltage difference limitation between VIN and VCLAMP which is common on input clamped architectures. while Figure 6 is a graph of propagation delay vs. overdrive as a square wave is presented at the input. The voltage clamp operates for any voltage between +1.2V above the GND pin, and the minimum output voltage swing, V OP . Forcing the CLAMP pin much below +1.2V can saturate transistors and should therefore be avoided. Forcing the CLAMP pin above VOP simply de-activates the CLAMP feature. In other words, one cannot expect to clamp any voltage higher than what the EL2257C/EL2357C can drive to in the first place. If the clamp feature is not desired, either let the CLAMP pin float or connect it to the VS+ pin. Figure 4. EL2257C/EL2357C Comparator Application The EL2257C/EL2357C can be used as a very fast, single supply comparator by utilizing the clamp feature. Most op amps used as comparators allow only slow speed operation because of output saturation issues. However, by applying a DC voltage to the CLAMP pin of the EL2257C/EL2357C, the maximum output voltage can be clamped, thus preventing saturation. Figure 4 is amplifier A of an EL2257C implemented as a comparator. 2.25V DC is applied to the CLAMP pin, as well as the IN- pin. A differential signal is then applied between the inputs. Figure 5 shows the output square wave that results when a ±1V, 10 MHz triangular wave is applied, Figure 5. Propagation Delay vs Overdrive EL2257/EL2357 as a Comparator Figure 6. 16 inputs. Logic signals are applied to each of the ENABLE pins to cycle through turning each of the amplifiers on, one at a time. Figure 10 shows the resulting output waveform at VOUT. Switching is complete in about 50 ns. Notice the outputs are tied directly together. Decoupling resistors at each output are not necessary. In fact, adding them approximately doubles the switching time to 100 ns. Video Sync Pulse Remover Application All CMOS Analog to Digital Converters (A/Ds) have a parasitic latch-up problem when subjected to negative input voltage levels. Since the sync tip contains no useful video information and it is a negative going pulse, we can chop it off. Figure 7 shows a unity gain connected amplifier A of an EL2257C. Figure 8 shows the complete input video signal applied at the input, as well as the output signal with the negative going sync pulse removed. Figure 9. Figure 7. Figure 10. Short Circuit Current Limit The EL2257C/EL2357C have internal short circuit protection circuitry that protect it in the event of its output being shorted to either supply rail. This limit is set to around 100 mA nominally and reduces with increasing junction temperature. It is intended to handle temporary shorts. If an output is shorted indefinitely, the power dissipation could easily increase such that the part will be destroyed. Maximum reliability is maintained if the output current never exceeds ±90 mA. A heat sink may be Figure 8. Multiplexing with the EL2257C/EL2357C The ENABLE pins on the EL2257C/EL2357C allow for multiplexing applications. Figure 9 shows an EL2357C with all 3 outputs tied together, driving a back terminated 75Ω video load. Three sinewaves of varying amplitudes and frequencies are applied to the three 17 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps required to keep the junction temperature below absolute maximum when an output is shorted indefinitely. curves for various loads and output voltages according to: R L × ( T JMAX – T AMAX ) 2 ----------------------------------------------------------------- + ( V OUT ) N × θ JA V S = ----------------------------------------------------------------------------------------------( I S × R L ) + V OUT Power Dissipation With the high output drive capability of the EL2257C/EL2357C, it is possible to exceed the 150°C Absolute Maximum junction temperature under certain load current conditions. Therefore, it is important to calculate the maximum junction temperature for the application to determine if power-supply voltages, load conditions, or package type need to be modified for the EL2257C/EL2357C to remain in the safe operating area. Figures 11 and 12 below show total single supply voltage VS vs. RL for various output voltage swings for the PDIP and SOIC packages. The curves assume WORST CASE conditions of TA = +85°C and IS = 6.5 mA per amplifier. The maximum power dissipation allowed in a package is determined by: EL2257 Single Supply Voltage vs. RLoad for Various VOUT and Packages T JMAX – T AMAX PD MAX = --------------------------------------------θ JA where: • • • • TJMAX = Maximum Junction Temperature TAMAX = Maximum Ambient Temperature θJA = Thermal Resistance of the Package PDMAX = Maximum Power Dissipation in the Package. The maximum power dissipation actually produced by an IC is the total quiescent supply current times the total power supply voltage, plus the power in the IC due to the load, or: Figure 11. EL2357 Single Supply Voltage vs. RLoad for Various VOUT and Packages V OUT PD MAX = N × V S × I SMAX + ( V S – V OUT ) × ---------------RL where: • • • • • N = Number of amplifiers VS = Total Supply Voltage ISMAX = Maximum Supply Current per amplifier VOUT = Maximum Output Voltage of the Application RL = Load Resistance tied to Ground If we set the two PDMAX equations, [1] and [2], equal to each other, and solve for VS , we can get a family of Figure 12. 18 EL2257C/EL2357C Macromodel (one channel) * Revision A, October 1995 * Pin numbers reflect a standard single opamp. * When not being used, the clamp pin, pin 1, * should be connected to Vsupply, pin 7 * Connections: +input * | -input * | | +Vsupply * | | | -Vsupply * | | | | output * | | | | | clamp * | | | | | | .subckt EL2257/el 3 2 7 4 6 1 * * Input Stage * i1 7 10 250µA i2 7 11 250µA r1 10 11 4K q1 12 2 10 qp q2 13 3 11 qpa r2 12 4 100 r3 13 4 100 * * Second Stage & Compensation * gm 15 4 13 12 4.6m r4 15 4 15Meg c1 15 4 0.36pF * * Poles * e1 17 4 15 4 1.0 r6 17 25 400 c3 25 4 1pF r7 25 18 500 c4 18 4 1pF * * Connections:IN+IN+IN+IN+IN+IN+IN+INININININ * Output Stage & Clamp * i3 20 4 1.0mA q3 7 23 20 qn q4 7 18 19 qn q5 7 18 21 qn q6 4 20 22 qp q7 7 23 18 qn d1 19 20 da d2 18 1 da r8 21 6 2 r9 22 6 2 r10 18 21 10k r11 7 23 100k d3 23 24 da d4 24 4 da d5 23 18 da * * Power Supply Current * ips 7 4 3.2mA * * Models * 19 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps .model .model .model .model .ends qn npn(is800e-18 bf150 tf0.02nS) qpa pnp(is810e-18 bf50 tf0.02nS) qp pnp(is800e-18 bf54 tf0.02nS) da d(tt0nS) 20 EL2257C/EL2357C EL2257C/EL2357C 125 MHz Single Supply, Clamping Op Amps General Disclaimer Specifications contained in this data sheet are in effect as of the publication date shown. Elantec, Inc. reserves the right to make changes in the circuitry or specifications contained herein at any time without notice. Elantec, Inc. assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. January 5, 2000 WARNING - Life Support Policy Elantec, Inc. products are not authorized for and should not be used within Life Support Systems without the specific written consent of Elantec, Inc. Life Support systems are equipment intended to support or sustain life and whose failure to perform when properly used in accordance with instructions provided can be reasonably expected to result in significant personal injury or death. Users contemplating application of Elantec, Inc. Products in Life Support Systems are requested to contact Elantec, Inc. factory headquarters to establish suitable terms & conditions for these applications. Elantec, Inc.’s warranty is limited to replacement of defective components and does not cover injury to persons or property or other consequential damages. Elantec, Inc. 1996 Tarob Court Milpitas, CA 95035 Telephone: (408) 945-1323 (800) 333-6314 Fax: (408) 945-9305 European Office: 44-71-482-4596 21 Printed in U.S.A.