Features

● Low noise: 2.3NV/√Hz

● Low difference gain gain/phase error

● High output current: 150mA

● Quick settlement: 25ns (0.01%)

● gain bandwidth: 500MHz

● Equipment stable: ≥2V/v

● Low offset voltage: ± 100 μV [123 [123 ]

● Conversion rate: 500V/μs

● 8 -pin DIP, SOIC packaging

Application

Low noise differential disappear

● High -resolution video

● Line driver

● High -speed signal processing

● ADC/DAC buffer

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123] ● Ultrasonic

● pulse/radio frequency amplifier

● Active filter

Instructions

OPA621 is a precise broadband single -piece operator It has a very fast stable time, low differential gain, phase error, and high output current driving capacity.

OPA621 stable under ± 2V/V or higher gain. Due to its ""classic"" computing amplifier circuit structure, the amplifier has a very low offset and completely symmetrical differential input. Unlike the design of the ""current feedback"" amplifier, OPA621 can be used in the application of all high -speed and accuracy operations amplifiers.

Low noise, low distortion, broad band width, and high lineivity make the amplifier apply to radio frequency and video applications. Short -circuit protection is provided by internal current limit circuits.

OPA621 has DIP and SO-8 packaging.

Typical performance curve

Unless there are other instructions, otherwise VCC u003d ± 5VDC, RL u003d 100 , TA u003d+25 ° C.

Application information

] Performance Discussion

OPA621 provides speed and accuracy that could not be achieved in the form of a single film. Unlike current feedback amplifiers, the design of OPA621 adopts the ""classic"" computing amplifier architecture, so it can be used for all traditional operational amplifiers applications. Although current feedback amplifiers can indeed provide wider bandwidth at higher gains, they have many shortcomings. Current feedback amplifier is wrongThe input characteristics (that is, one input is low impedance) so that it cannot be used for various applications. In addition, unbalanced inputs make it difficult to correct the input bias current error. Because the input bias current is irrelevant, it is impossible to eliminate the bias current by matching the inverter and non -inverter input resistance. The current noise is also asymmetric, usually significantly higher in the inverter input. Perhaps the most important thing is that due to the weighing internal design, the stability time of 0.01%is usually very poor. Many current feedback design shows that even if the stability time of 0.1%is reasonable, the stability time is 0.01%in more than 10 microseconds. This amplifier is not suitable for fast and stable 12 applications.

OPA621's ""classic"" computing amplifier architecture uses real differences and completely symmetrical inputs to eliminate these troublesome issues. All traditional circuit configuration and computing amplifiers are suitable for OPA621. The use of low drift film resistance allows the internal working current to fine -tune the chip -level to optimize the communication performance, such as bandwidth and stability time, and DC parameters, such as input offset voltage and drift. As a result, a broadband, high -frequency single -piece operational amplifier, the width accumulation of the gain band is 500MHz, the stable time of 0.01%is 25ns, and the input bias voltage is 200 μV.

Note for wiring

Maximum improvement of OPA621's performance requires some wiring prevention measures and high -frequency layout technology. Oscillation, ringing, low bandwidth and stability, peak and unstable gain and instability are typical problems that plague all high -speed amplifiers. Generally speaking, the conductors of all printing circuit boards should be wide to provide a signal path with low resistance and low impedance. They should also be as short as possible. The entire physical circuit should be as small as possible. Miscellaneous capacitors should minimize, especially at high impedance nodes, such as the input terminal of the amplifier. To minimize the coupling from the output or power to the input signal. The length of all circuit components should not exceed 1/4 inches (6mm) to reduce the induction of the lead and should use low resistance. This will minimize the time constant of circuit capacitors and eliminate bruises and parasitic circuits.

Like all high -frequency circuits, grounding is the most important application consideration of OPA621. If you do not use good grounding technology, vibrations with a frequency of 500MHz and above are prone to occur. All unused areas on the side of the component of the heavy floor (recommended to use 2 ounce copper). A good ground floor can reduce the pickup of strange signals, provide a low -resistant, low -induced public return path for signals and power, and transmit the heat of the active circuit packaging foot to the environment air by the stream.

The power sources are very important and must be used always, especially when driving a large current load. Both power cords should bypass ground and get closer to the amplifier pin as much as possible. It is recommended to use extremely short -drawn capacitor (1 μF to 10 μF). Parallel 0.1 μF ceramics should be added to the power pins. Side stickerThe road electric container will produce good results because their low lead inductors. In addition, inhibitory filters can be used for isolation noise power supply lines. Appropriate bypass and non -adjustment power cords allow the output of the full placement and the best stable time performance.

The main points to be remembered

1) Do not use the point -to -point wiring, because the increase in wiring inductance will be unfavorable to the communication performance. However, if it is necessary, a very short direct signal path is required. Input signal grounding circuits, load ground circuits, and power public lines should be connected to the same physical point to eliminate ground circuits that may cause unnecessary feedback.

2) Good component selection is very important. The capacitors used in key positions should be low -induced, with high -quality dielectric materials. Similarly, the diodes used in key positions should be Schottki, such as HP50822835 for rapid recovery and minimum charge storage. Ordinary diode is not suitable for radio frequency circuits.

3) Do not use the socket as much as possible to weld OPA621 directly to the PC board. The socket will increase parasitic capacitors and inductors, which will seriously reduce the communication performance or produce oscillation. If you have to use a socket, consider using the zero-section without welding sockets, such as the Augat part number 8134-HC-5P2. Alternatively, TEFLON #174; positioner near the amplifier pins can be used to install feedback elements.

4) The resistance value used in the feedback network should be hundreds of ohms to get the best performance. The connected capacitance problem limits the acceptable resistance range at the high -end approximately 1k and the low -end restrictions within the output driving limit of the amplifier. The metal film and carbon resistance are satisfactory, but the wire -wound resistor (even the ""inductive"" type) is absolutely unacceptable in high -frequency circuits.

5) Surface paste components (chip resistors, capacitors, etc.) have a low lead inductor, so it is highly recommended. The circuit with all OPA621AU (SO-8 packaging) on u200bu200bthe surface installation element will provide the best AC performance. SO8's parasitic encapsulation inductance and capacitors are lower than Cerdip and 8 -drawing plastic DIP.

6) Avoid the output overload. Remember that the output current must be provided by the amplifier to drive its own feedback network and drive its load. High impedance load can achieve minimum distortion.

7) Don't forget that these amplifiers use ± 5V power. Although they run well at+5V and -5.2V, the use of ± 15V power will damage parts.

8) Standard business test equipment has not been designed for testing equipment within the speed range of OPA621. The desktop computing amplifier tester and ATE system need a special test head to successfully test these amplifiers.

9) Termination of the transmission line load. Undolved lines, like axis cables, may be capacitance or perceptual loads for the amplifier. Use it by itA transmission line is connected to the sexual impedance end, and the load of the amplifier looks pure as a resistance.

10) Insert prototype board and wound board will not be satisfactory. A clean layout is necessary to use radio frequency technology; there is no shortcut.

The offset voltage adjustment

The input bias voltage of OPA621 is laser fine -tuning, which does not need to be adjusted for most applications. However, if additional adjustments are needed, the circuit in FIG. 1 can be used without reduced offset with temperature changes. Avoid external noise at any time, because such external power adjustment can avoid external noise. Remember, the additional offset error can be generated by the input bias current of the amplifier. Two input impedances are matched as possible, as shown in R3. This will reduce the input bias current error of the amplifier's offset current, usually only 0.2 μA.

Input protection

For MOSFET devices, static damage has been well recognized, but any semiconductor device should be subject to this potential damage Source protection. OPA621 integrates the ESD protection diode in the film, as shown in Figure 2. This does not require users to add external protection diode, which will increase the capacitance and reduce the communication performance.

All feet on OPA621 internal protection of any power supply through a pair of back -to -back bias diodes to prevent static discharge. When the input voltage exceeds any power of about 0.7V, these diode will start to turn on. When the signal source still exists, this may occur in the power supply of the amplifier. The diode can usually bear the continuous current of 30mA without damage. However, in order to ensure long -term reliability, the current of the diode should be limited to about 10mA as much as possible.

The design of the internal protection diode can withstand 2.5kV (using human models) and will provide sufficient ESD protection for most normal operating procedures. However, static damage may cause subtle changes in the input characteristics of the amplifier, not necessarily damaged the device. In the precision operational amplifier, this may lead to a significant decrease in offset voltage and drift. Therefore, when dealing with OPA621, it is strongly recommended to take anti -static measures.

Output driving capacity

The design of OPA621 uses a large output device, and has been optimized to drive 50 and 75 resistance load. This device can easily drive 6VP-P to a load of 50 This high output driver capacity makes OPA621 an ideal choice for extensive radio frequency, intermediate frequency and video applications. In many cases, no additional buffer is needed.

The internal current limiting circuit limits the output current at about 150 mA at 25 ° C. This prevents short accidents due to accidentsDestruction caused by roads does not require external current limiting circuits. Although the device can withstand the instantaneous short circuit of any power supply, it is not recommended.

Many high -speed applications with high requirements, such as ADC/DAC buffer, need to have a low -width output impedance computing amplifier. For example, when the signal -related capacitance of the input terminal of the driver Flash A/D converter, low output impedance is essential. As shown in Figure 3, OPA621 maintains a very low closed -loop output impedance in the frequency. The closed -loop output impedance increases with frequency, because the frequency of the circuit gain is reduced.

Thermal factors

OPA621 does not need a radiator in most environments. However, the use of heat sinks will reduce internal heat rise and will lead to colder and more reliable operation. Under extreme temperature and full load conditions, radiator is needed. See the ""maximum power consumption"" curve, Figure 4.

The internal power consumption is given by the formula PD u003d PDQ+PDL. The PDQ is static power consumption and the PDL is the power consumption caused by the load. (For ± VCC u003d ± 5V, PDQ u003d 10V x 28ma u003d 280MW, maximum value). For the case where the amplifier is driven by DC voltage (± VOUT), the maximum value of the PDL appears at ± vout u003d ± VCC/2, and it is equivalent to PDL, MAX u003d (± VCC) 2/4rl. Note that the output -level power consumption is the voltage on the output transistor, not the load.

When the output is short -circuit, PDL u003d 5V x 150mA u003d 750MW. Therefore, PD u003d 280MW+750MW u003d 1W. Please note that short -circuit conditions represent the maximum internal power consumption that can be generated. Therefore, the ""maximum power consumption"" curve starts from 1W, and is reduced according to the thermal resistance θja of each packaging environment of each package according to the maximum condensation of 175 ° C. The short -circuit current is shown in Figure 5 with the temperature change.

Capacity load

OPA621 output level is optimized to drive as low as 50 resistance load. However, capacitive loads reduce the phase habits of the amplifier, which may cause high -frequency peak or oscillation. The capacitance load greater than 15PF shall be buffered by connecting a small resistor (usually 5 to 25 ) with the output shown in Figure 6. This is especially important when driving high -capacitor loads (such as flash memory A/D converters).

Generally speaking, the capacitance load should minimize to obtain the best high -frequency performance. If the cable is connected correctly, the coaxial cable can be driven. When the coaxial cable or transmission line is connected to the inner end of its characteristic impedance, the capacitor (RG-58 is 29pf/feet) of the coaxial cable does not load the amplifier.

Compensation

OPA621 is stable when the reversal gain ≥-2V/V and non-reversal gain ≥ 2V/V. The phase of the two configurations is about 50 °. A unified reversal and non -reversal income should be avoided. The minimum stable gain of +2V/V and -2V/V is the circuit configuration with the highest requirements for the stability of the ring, and it is most likely to oscillate in these gains. If possible, the device is used when the noise gain is greater than 3 to improve the phase margin and reduce the sensitivity to oscillation. (Please note that from the perspective of stability, the reverse gain of -2V/V is equivalent to the noise gain of 3.) The gain and phase response of other gains are shown in the typical performance curve.

OPA621's high -frequency response under good layout and the frequency of high -gain circuits are flat. However, the use of low -gain circuits and configuration with large feedback resistors can generate high -frequency increase peaks. This peak can be minimized by connecting a small capacitor with feedback resistance. The capacitor compensation is zero -loop, high -frequency, and transmitting function zero point generated by the input capacitor of the amplifier (usually 2PF after PC is installed) and the time constant of input and feedback resistors. The selected compensator can be a PC board electric container for fine -tuning, fixed capacitors or plans. The capacitor value is closely related to the circuit layout and the closed -loop gain. The use of small resistance values u200bu200bwill maintain phase margin and avoid peak values u200bu200bby maintaining zero disconnection frequency. When a high closed -loop gain is required, it is recommended to use a three -resistor fade (TEE network) to avoid large value resistors with large amounts of use time constant.

Settlement time

Stable time refers to the total time required from the specified error range from the input signal to the output of the output. This error zone represents the percentage of the output conversion value, 2V steps. Therefore, the stability time is 0.01%requiring the error band to ± 200 μV, and the center of the center is 2V.

At the stable time specified in the reverse gains of 2 times, the 2V jump only occurred between 25ns and 0.01%, making OPA621 one of the fastest single -piece amplifiers. As described in the typical performance curve, the stable time increases with the changes in the closed -loop gain and the output voltage. Keep strict attention to the details mentioned in ""Wiring Care"". The amplifier can also be recovered quickly from the input overload. The overload recovery time from 50%overload to linear operation is usually only 30ns.

In fact, it is very difficult to measure the settlement time on OPA621. Except for the best laboratory, accurate measurement is almost impossible. In addition, a fast flat top generator and high -speed oscilloscope need to be needed. Unfortunately, fast flat -top generators can stabilize to 0.01%in enough time, but they are scarce and expensive. However, fast oscilloscope is more common. In order to obtain the best results, the sampling oscilloscope is recommended. The sampling range usually hasBandwidth greater than 1GHz and very low capacitor input. They also show a faster stable time. With a response signal, a real -time oscilloscope is often loaded.

FIG. 7 shows the test circuit for stable time used to measure OPA621. This method uses 16 -bit sampling oscilloscope to monitor the input and output pulse. These waveforms are captured by the sampling range, on average, and then subtracted in the software to generate error signals. This technology eliminates the needs of traditional ""fake and knots"