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EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Features
* Specified for +3V, +5V, or 5V Applications * Power Down to 0 A * 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/s * Low Offset Voltage = 4 mV max * Output Current = 100 mA * High Open Loop Gain = 80 dB * Differential Gain = 0.05% * Differential Phase = 0.05
General Description
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/s 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. The EL2257C/EL2357C have a high speed disable feature. Applying a low logic level to all ENABLE pins reduces the supply current to 0 A within 50 ns. Each amplifier has its own ENABLE pin. This is useful for both multiplexing and reducing power consumption. 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. The EL2257C/EL2357C are available in plastic DIP and SOIC packages. Both parts operate over the industrial temperature range of -40C to +85C. For single amplifier applications, see the EL2150C/EL2157C. For space saving, industry standard pin out dual and quad applications, see the EL2250C/EL2450C.
Applications
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. EL2257CN EL2257CS EL2357CN EL2357CS Temp. Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package 14 Pin PDIP 14 Pin SOIC 16 Pin PDIP 16 Pin SOIC Outline # MDP0031 MDP0027 MDP0031 MDP0027
Connection Diagrams
January 5, 2000
Top View Top View
(c) 1995 Elantec, Inc.
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Absolute Maximum Ratings (T
A
= 25 C)
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)
Power Dissipation Storage Temperature Range Ambient Operating Temperature Range Operating Junction Temperature
See Curves -65C to +150C -40C to +85C 150C
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 I II III IV V Test Procedure 100% production tested and QA sample tested per QA test plan QCX0002. 100% production tested at TA = 25C and QA sample tested at TA = 25C, TMAX and TMIN per QA test plan QCX0002. QA sample tested per QA test plan QCX0002. Parameter is guaranteed (but not tested) by Design and Characterization Data. Parameter is typical value at TA = 25C for information purposes only.
DC Electrical Characteristics
VS=+5V, GND=0V, TA=25C, VCM=1.5V, VOUT=1.5V, VCLAMP=+5V, VENABLE=+5V, unless otherwise specified. Parameter VOS TCVOS IB IOS TCIOS PSRR CMRR CMIR RIN CIN ROUT IS,ON IS,OFF PSOR AVOL Offset Voltage Offset Voltage Temperature Coefficient Input Bias Current Input Offset Current Input Bias Current Temperature Coefficient Power Supply Rejection Ratio Common Mode Rejection Ratio Common Mode Input Range Input Resistance Input Capacitance Output Resistance Supply Current - Enabled (per amplifier) Supply Current - Shut Down (per amplifier) Common Mode SOIC Package PDIP Package Av=+1 VS=VCLAMP=+12V, VENABLE=+12V VS=VCLAMP=+10V, VENABLE=+0.5V VS=VCLAMP=+12V, VENABLE=+0.5V Power Supply Operating Range Open Loop Gain VS=VCLAMP=+12V, VOUT=+2V to +9V, RL=1 k to GND VOUT=+1.5V to +3.5V, RL=1 k to GND VOUT=+1.5V to +3.5V, RL=150 to GND 2.7 65 80 70 60 Description EL2257C EL2357C Measured from Tmin to Tmax VIN=0V VIN=0V Measured from Tmin to Tmax VS=VENABLE=+2.7V to +12V, VCLAMP=OPEN VCM=0V to +3.8V VCM=0V to +3.0V 45 50 55 0 1 2 1 1.5 40 5 0 5 12.0 6.5 50 -1100 Test Conditions Min -4 -6 10 -5.5 150 50 70 65 70 VS-1.2 -10 +1100 Typ Max 4 6 Test Level I I V I I V I I I I I V V V I I V I I V V Units mV mV V/C A nA nA/C dB dB dB V M pF pF m mA A A V dB dB dB
2
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
DC Electrical Characteristics (Continued)
VS=+5V, GND=0V, TA=25C, VCM=1.5V, VOUT=1.5V, VCLAMP=+5V, VENABLE=+5V, unless otherwise specified. Parameter VOP Description Positive Output Voltage Swing Test Conditions VS=+12V, AV=+1, RL=1 k to 0V VS=+12V, AV=+1, RL=150 to 0V VS=5V, AV=+1, RL=1 k to 0V VS=5V, AV=+1, RL=150 to 0V VS=+3V, AV=+1, RL=150 to 0V VON Negative Output Voltage Swing VS=+12V, AV=+1, RL=150 to 0V VS=5V, AV=+1, RL=1 k to 0V VS=5V, AV=+1, RL=150 to 0V IOUT IOUT,OFF VIH-EN VIL-EN IIH-EN IIL-EN VOR-CL VACC-CL IIH-CL IIL-CL Output Current
[1]
Min
Typ 10.8
Max
Test Level V I V I I
Units V V V V V mV V V mA mA A V V A A V mV A A
9.6 3.4 1.8
10.0 4.0 3.8 1.95 5.5 -4.0 -3.7 -3.4 8
I V I I V
VS=5V, AV=+1, RL=10 to 0V VS=5V, AV=+1, RL=50 to 0V VENABLE=+0.5V Relative to GND Pin Relative to GND Pin VS=VCLAMP=+12V, VENABLE=+12V VS=VCLAMP=+12V, VENABLE=+0.5V Relative to GND Pin VIN=+4V, RL=1 k to GND VCLAMP=+1.5V and +3.5V VS=VCLAMP=+12V VS=+12V, VCLAMP=+1.2V
75
100 60 0 20 0.5 340 0 410 1 VOP 100 12 250 25
Output Current, Disabled ENABLE pin Voltage for Power Up ENABLE pin Voltage for Shut Down ENABLE pin Input Current-High Voltage Clamp Operating Range CLAMP Accuracy [4] CLAMP pin Input Current - High CLAMP pin Input Current - Low / Per Amplifier
[2]
I I I I I I I I I
2.0
ENABLE pin Input Current-Low [2]
[3]
1.2 -250
-30
-15
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
Closed Loop AC Electrical Characteristics
VS=+5V, GND=0V, TA=25C, VCM=+1.5V, VOUT=+1.5V, VCLAMP=+5V, VENABLE=+5V, AV=+1, RF=0, RL=150 to GND pin, unless otherwise specified [1] Test Level V V V V V V V V V V V I V V V V V V V V V V V V V
Parameter BW
Description -3 dB Bandwidth (Vout=400 mVp-p)
Test Conditions VS=+5V, AV=+1, RF=0 VS=+5V, AV=-1, RF=500 VS=+5V, AV=+2, RF=500 VS=+5V, AV=+10, RF=500 VS=+12V, AV=+1, RF=0 VS=+3V, AV=+1, RF=0
Min
Typ 125 60 60 6 150 100 25 30 20 60 55
Max
Units MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz V/s V/s ns % ns ns ns % nV/H z pA/H z ns ns ns
BW
0.1 dB Bandwidth (Vout=400 mVp-p)
VS=+12V, AV=+1, RF=0 VS=+5V, AV=+1, RF=0 VS=+3V, AV=+1, RF=0
GBWP PM SR tR,tF OS tPD tS dG dP eN iN tDIS tEN tCL
Gain Bandwidth Product Phase Margin Slew Rate Rise Time, Fall Time Overshoot Propagation Delay 0.1% Settling Time 0.01% Settling Time Differential Gain [2] Differential Phase [2] Input Noise Voltage Input Noise Current Disable Time [3] Enable Time
[3]
VS=+12V, @ AV=+10 RL=1 k, CL=6 pF VS=+10V, RL=150, Vout=0V to +6V VS=+5V, RL=150, Vout=0V to +3V 0.1V Step 0.1V Step 0.1V step VS=5V, RL=500, AV=+1, VOUT=3V VS=5V, RL=500, AV=+1, VOUT=3V AV=+2, RF=1 k AV=+2, RF=1 k f=10 kHz f=10 kHz 200
275 300 2.8 10 3.2 40 75 0.05 0.05 48 1.25 50 25 7
Clamp Overload Recovery
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
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
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
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
Closed Loop Output Impedance vs Frequency
6
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Large Signal Step Response, VS = +3V
Large Signal Step Response, VS = +5V
Large Signal Step Response, VS = +12V
Small Signal Step Response
Large Signal Step Response, VS = 5V
Slew Rate vs Temperature
Settling Time vs Settling Accuracy
Voltage and Current Noise vs Frequency
7
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
Output Current vs Die Temperature
8
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
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 = 150 to GND
Negative Output Voltage Swing vs Die Temperature, RL = 150 to GND
Clamp Accuracy vs Die Temperature
9
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
IClamp Accuracy RL = 150
Clamp Accuracy RL = 1 k
Clamp Accuracy RL = 10 k
Enable Response for a Family of DC Inputs
Disable Response for a Family of DC Inputs
Disable/Enable Response for a Family of Sine Waves
OFF Isolation
10
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257 Channel to Channel Isolation vs Frequency
EL2357 Channel to Channel Isolation vs Frequency
14-Lead Plastic SO Maximum Power Dissipation vs Ambient Temperature
14-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature
16-Lead Plastic SO Maximum Power Dissipation vs Ambient Temperature
16-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature
11
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Simplified Schematic (One Channel)
12
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Applications Information
Product Description
The EL2257C/EL2357C's, connected in voltage follower mode, -3 dB bandwidth is 125 MHz while maintaining a 275 V/s 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. 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.
Supply Voltage Range and Single-Supply Operation
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. 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. 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 k 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.
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 F tantalum capacitor in parallel with a 0.1 F 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 F tantalum capacitor in parallel with a 0.1 F ceramic capacitor from the VS+ pin to the GND pin will suffice. 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.
Choice Of Feedback Resistor, RF
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
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. For AV = +1, RF = 0 is optimum. For AV = -1 or +2 (noise gain of 2), optimum response is obtained with RF between 500 and 1 k. For AV = -4 or +5 (noise gain of 5), keep RF between 2 k and 10 k.
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 10 load, or 60 mA into 50. With this large output current capability, a 50 load can be driven to 3V with VS = 5V, making it an excellent choice for driving isolation transformers in telecommunications applications.
Driving Cables and Capacitive Loads
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 5 and 50) 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.
Video Performance
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 150, 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 150 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 =150, 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. 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 k, 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.
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.
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EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
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 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 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 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
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. 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. while Figure 6 is a graph of propagation delay vs. overdrive as a square wave is presented at the input.
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
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
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. 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.
Figure 9.
Figure 7.
Figure 10. Short Circuit Current Limit 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 75 video load. Three sinewaves of varying amplitudes and frequencies are applied to the three
17
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
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 x ( T JMAX - T AMAX ) 2 ---------------------------------------------------------------- + ( V OUT ) N x JA V S = ---------------------------------------------------------------------------------------------( I S x R L ) + V OUT
Power Dissipation
With the high output drive capability of the EL2257C/EL2357C, it is possible to exceed the 150C 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. The maximum power dissipation allowed in a package is determined by:
T JMAX - T AMAX PD MAX = -------------------------------------------- JA
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 = +85C and IS = 6.5 mA per amplifier.
EL2257 Single Supply Voltage vs. RLoad for Various VOUT and Packages
where: * * * * TJMAX = Maximum Junction Temperature TAMAX = Maximum Ambient Temperature JA = 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:
V OUT PD MAX = N x V S x I SMAX + ( V S - V OUT ) x --------------RL
Figure 11.
EL2357 Single Supply Voltage vs. RLoad for Various VOUT and Packages
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
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
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 250A i2 7 11 250A 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
.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.
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.
January 5, 2000
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.

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