Features

Low noise: 3NV/√Hz

Broadband:

—OPA227: 8 MM, 2.3 volts/microseconds

—OPA228: 33 MM, 10 volts/microseconds

Settling time: 5μs (significantly improved than OP-27)

High -co -model suppression ratio: 138 db

High -Open Ring gain: 160 db

Low input bias current: maximum 10 na

# 8226; low offset voltage: maximum 75 μV

Wide power supply range: ± 2.5 v to ± 18 v

OPA227 replaced OP-27, LT1007, MAX427 [ 123]

OPA228 replaced OP-37, LT1037, MAX437

single, double and four versions

# 8226; Data collection

Telecom equipment

Earth physical analysis

vibration analysis

#8226 Spectral analysis

Professional audio equipment

active filter

123]

The OPAX2X series operational amplifier combines low noise, broad band width and high precision, making it an ideal choice for the application of communication and precision DC performance.

OPA227 has the characteristics of unit gain stability, with a high conversion rate (2.3V/μS) and wide band width (8MHz). OPAX228 optimizes 5 or higher closed -loop gains and provides higher speeds. The conversion rate is 10V/μs and the bandwidth is 33MHz.

OPAX227 and OPAX228 series operational amplifiers are ideal choices for professional audio equipment. In addition, low static current and low cost make it an ideal choice for high -precision portable applications.

OPAX227 and OPAX228 series operations amplifiers are industrial standards OP-27 and OP-37-by-alternatives, which have comprehensive substantial improvements. The dual -channel and four -channel versions can be used to save space and reduce the cost of each channel.

OPA227, OPA228 There are two packaging: DIP-8 and SO-8. OPA4227 and OPA4228 have DIP-14 and SO-14 packaging, and are configured with standard pins. The working temperature is -40 ° C to 85 ° C.

Equipment information

(1), please refer to the appointment appendix at the end of the data table.

Typical features

Unless there are other instructions, otherwise TA u003d 25 ° C, RL u003d 10kΩ, vs u003d ± 15V.

Detailed explanation Overview OPAX2X series operational amplifier combines low noise, broad band width and high precision, making it an ideal choice for applications that need to communicate and precise DC performance. OPAX227 unit is stable and has a high conversion rate (2.3V/μS) and broadband (8MHz). OPAX228 optimizes 5 or higher closed -loop gains and provides higher speeds. The conversion rate is 10V/μs and the bandwidth is 33MHz. Function box diagram

Feature description

OPAX22X series is the unit gain stable, without unexpected output phase reversal, so that to make the It is easy to use in wide applications. In the application of noise or high impedance power supply, decoupling capacitors that are close to the device pins may be needed. In most cases, 0.1-μF capacitors are enough.

The offset voltage and drift

The OPAX2X series has very low offset voltage and drift. In order to achieve the highest DC accuracy, the circuit layout and mechanical conditions should be optimized. The connection of heterogeneous metals will generate heat potential at the input terminal of the computing amplifier, thereby reducing the disorders and drift. These thermocouple effects will exceed the inherent drift of the amplifier and eventually reduce their performance. By ensuring that the thermal power of the two inputs is equal, they can eliminate them. In addition:

keep the thermal quality connected to the two input terminals is similar.

The thermal source should stay away from the key input circuit as much as possible.

Shielding the computing amplifier and input circuit to prevent it from the impact of airflows such as cooling fans.

Working voltage

OPAX22X series operational amplifier works in the voltage range of ± 2.5 volts to ± 18 volts, which has excellent performance. Point with most of the power supply voltageDifferent operational amplifiers are different, the OPA227 series is designed for practical applications; a set of specifications are suitable for the range of power supply range from ± 5-v to ± 15-v. Specifications are guaranteed to ± 5-V to ± 15-V power supply. Some applications do not require equal positive and negative output voltage. The power supply voltage does not need to be equal. The maximum voltage between the power of the OPAX22X series is 5 volts, and the voltage between the power supply is 36 volts. For example, the positive power supply can be set to 25 V, and the negative power supply is set to -5 V, and vice versa. In addition, key parameters are guaranteed within the specified temperature range (-40 ° C to 85 ° C). The typical feature shows the parameters that significantly changes with the working voltage or temperature.

The offset voltage adjustment

OPAX22X series is a very low offset and drift of laser fine -tuning, so most applications do not require external adjustment. However, OPA227 and OPA228 (single type) provide bias voltage connection on pinna 1 and 8. As shown in Figure 36, the offset voltage can be adjusted by the connection potential meter. This adjustment can only be used to zero the displacement of the computing amplifier. This adjustment is not used in the offset generated in other places in the compensation system, as this will cause additional temperature drift.

Input protection

Back -to -back diode (see Figure 37) for input protection on OPAX22X. The opening threshold of these diode is exceeded. If the limited conversion rate of the amplifier is under the pulse conditions, the current flow will cause the current to protect the diode. If there is no external flow resistance, the input device may be destroyed. High input current source causes subtle damage to the amplifier. Although the device may still work normally, important parameters, such as input offset voltage, drift, and noise may occur.

When using OPA227 as a unit gain buffer (follower), the input current should be limited to 20 mAh. This can be achieved by inserting a feedback resistor or a connected source of a resistance. Use Formula 1 to calculate a sufficient resistor size.

Among them: rx connecting or inserting feedback path with the source series.

For example, for 10 V pulse (vs u003d 10 V), the total circuit resistance must be 500Ω. If the source impedance is large enough to limit the current alone, no additional resistance is required. The size of any external resistor must be carefully selected because they increase noise. For more information about noise calculation, see the noise performance part of this data table. Figure 37 shows an example of a current -limiting feedback resistor.

Input bias current eliminates

The input bias current of the OPAX2X series is excessive and opposite to offset current for internal compensation. The input bias current generated is input biasThe difference between current and offset current. The remaining input bias current can be positive or negative.

When the bias current is eliminated in this way, the input bias current is similar to that of the input bias current. The increased resistance (as shown in Figure 38) in order to eliminate the impact of the input bias current may actually increase the offset and noise, so it is not recommended.

Noise performance

Figure 39 shows that in the unit gain configuration (no feedback resistance network, so no additional noise contribution), different sources of impedance in different sources of impedance in different sources of impedance Total circuit noise. Two different operational amplifiers display and general circuit noise calculation. OPA227 has extremely low voltage noise, which is an ideal choice for low source impedance (less than 20 kΩ). A similar precision computing amplifier, OPA277, has some higher voltage noise, but lower current noise. It provides excellent noise performance under medium source impedance (10 kΩ to 100 kΩ). Above 100kΩ, FET input computing amplifier, such as OPA132 (very low current noise) can provide better performance. Use the formula in Figure 39 to calculate the general circuit noise. EN u003d voltage noise, in u003d current noise, RS u003d source impedance, K u003d Bolzman constant u003d 1.38 × 10–23 J/K, T is temperature (unit: K). For detailed information about calculating noise, see the basic noise calculation.

Basic noise calculation

The design of the low noise computing amplifier circuit needs to carefully consider various possible noise factors: noise from the signal source, in the operation amplifier The noise generated and noise from the feedback network resistor. The total noise of the circuit is a square root and combination of all noise components.

The resistance part of the source impedance generates the heat noise of proportion to the square root of the resistance. This function is shown in Figure 39. Because the source impedance is usually fixed, the computing amplifier and feedback resistance are selected to minimize their contribution to total noise.

FIG. 39 shows the total noise of different sources of impedance in the unit gain configuration (no feedback resistance network, so there is no additional noise contribution). The computing amplifier itself provides voltage noise components and current noise components. Voltage noise is usually modified as a part of the bias voltage. The current noise is modeled to the time variable in the input bias current, and the voltage component of the noise is generated with the source resistance reaction. Therefore, the minimum noise computing amplifier of the given application depends on the source impedance. For low -source impedance, current noise can be ignored, and voltage noise usually dominates. For high -source impedance, current noise may dominate.

FIG. 40 shows the configuration of the inverter and non -inverter calculation amplifier circuit. In the configuration of the gains, the feedback network resistance will also produce noise. The current noise and feedback resistance reaction of the amplifier and the feedback resistance is generated.Noise component. The feedback resistance value can usually be selected so that these noise sources can be ignored. The total noise equation of the two configurations is shown in the figure below.

FIG. 41 shows 0.1 HZ 10 HZ with a filter for testing OPA227 and OPA228 noise. Filter circuit uses the FilterPro software of Texas Instrument Company. Figure 42 shows the configuration of OPA227 and OPA228 used for noise testing.

EMIRR (Emirr)

Electromagnetic interference inhibitory ratio (EMI) describes the EMI antipness of the operation amplifier. For many operational amplifiers, a common adverse effect is changes in the offset voltage caused by the rectification of RF signals. A computing amplifier, if it can more effectively inhibit changes in offset caused by EMI, has a higher EMIR and quantitatively quantitatively quantified. There are many ways to measure Emirr, but this section provides EMIRR IN+, which specifically describes the EMIRR performance when applying the RF signal to the non -reversed input foot of the operation amplifier. Generally speaking, due to the following three reasons, only Emirr tests for non -conversion input:

1. As we all know, the input pins of the operation amplifier are the most sensitive to electromagnetic interference, usually more capable than the power supply or output pin. Correct RF signal. 2. The input of non -exchanges and inverter computing amplifiers has a symmetrical physical layout, and it shows almost matching EMIRR properties.

3.emirr is easier to measure on the feet of non -conversion tube than other tube feet, because non -conversion inputs can be isolated on the print circuit board (PCB). This isolation allows the radio frequency signal to directly apply to the input terminal that does not be converted without requiring complex interaction or connecting PCB lines from other components.

For more formal discussions about EMIRR IN+definition and test methods, please refer to the application report sBOA128, the EMI suppression ratio of the operation amplifier. The relationship between Emirr in+of OPA227 is shown in Figure 43.

If available, any dual and four -way computing amplifier equipment versions have almost similar Emirr IN+performance. OPA227 unit gain bandwidth is 8MHz. The EmirR performance below this frequency indicates a interference signal in the bandwidth of the operational amplifier.

Table 1 shows the emir in+value of OPA227 in actual applications. The applications listed in Table 1 can be concentrated on the specific frequency or near it. This information may be particularly interested in designers engaged in such applications, or designers working in other fields may be particularly interested, such as industry, industry,Science and Medical (ISM) wireless radio wave band.

Emirr in+Test configuration

Figure 44 shows the circuit configuration of the test Emirr IN+. The radio frequency source is connected to the non -conversion input terminal of the computing amplifier through the transmission line. The computing amplifier is configured in the unit gain buffer topology, and the output is connected to a low -pass filter (LPF) and a digital multimeter (DMM). The large impedance loss of the input end of the computing amplifier will cause voltage reflex; however, when determining Emirr IN+, this impact is described and explained. The resulting DC offset voltage is sampled and measured by a multimeter. LPF isolates the remnant radio frequency signal that is possible to interfere with the accuracy of the multimeter. For more details, see SBOA128.

Equipment function mode

OPAX22x has a single function mode. When the power supply voltage is greater than 5 v (± 2.5 V)), it can be run. OPA2X's maximum power supply voltage is 36 V (± 18 V).

Application and implementation

Note: The information in the following application chapters is not part of the TI component specification, TI does not guarantee its accuracy or integrity. TI's customers are responsible for determining the applicability of the component. Customers should verify and test their design implementation to confirm the system function.

Application information

OPAX2X series is a precision operational amplifier with low noise. The OPAX227 series has a stable unit gain, the conversion rate is 2.3V/μs, and the bandwidth is 8MHz. The OPAX228 series is optimized for higher speed applications, with a gain of 5 or higher, with a conversion rate of 10V/μs and a bandwidth of 33MHz. In the application of noise or high impedance power supply, decoupling capacitors that are close to the device pins may be needed. In most cases, 0.1-μF capacitors are enough.

Triversar, 20 kHz low, 0.5-DB Cat Bibi Snow Filter

Long wave infrared detector amplifier

]

High -performance synchronous demodulator

Three -band active sound control control (Bass, Middle Yin and treble)

Typical application

Design requirements

1. Operation OPAX228 gain is less than 5 v/v

2. The capacity load runs stable operation

[12]3] Detailed design program

Use OPA228

OPAX228 series in low -gain, which is applicable to applications with a signal gain of 5 or higher, but can use its high speed at a lower gain. In the absence of external compensation, OPA228 has sufficient phase margin to maintain the stability of the unit gain and have a pure resistance load. However, the increase in load capacitors will reduce phase margin and make the operational amplifier unstable.

Various compensation technologies have been evaluated and used for OPA228. The recommended configuration includes an additional capacitor (CF) to connect with feedback resistance, as shown in Figure 51 and Figure 52. This feedback capacitor is used to compensate the two purposes. The input capacitance and feedback resistance of the computing amplifier causes phase shift and causes unstable. CF compensation input capacitance to minimize peak values. In addition, in high frequencies, the ratio of input capacitors to feedback capacitors has a great impact on the closed -loop gain of the amplifier. Therefore, you can choose CF to produce good stability while maintaining high speed.

In the absence of external compensation, the noise specifications of OPA228 are the same as OPA227, and the gain is 5 or larger. With additional external compensation, OPA228's output noise will be higher. The increase in noise is directly related to the increase in high -frequency closed -loop gain established by the ratio of CIN/CF.

FIG. 51 and Figure 52 show a recommendation circuit with gain to 2 and –2, respectively. The approximate value of CF is given in the figure. Because the compensation is highly dependent on circuit design, circuit board layout and load conditions, CF should be optimized through experiments to obtain the best results. Figures 53 and Figure 55 show the large signal and small signal level response capacitance of G u003d 2 configuration under the 100 PF load 54 and Figure 56 to show the large signal and small signal of G u003d -2 configuration of 100 pF Step response.

Application curve

Power suggestion

OPAX22X series specified working voltage is to be the working voltage of aspect 5 V to 36 V (± 2.5 V to ± 18 V); many specifications are suitable for -40 ° C to 85 ° C. See the electrical characteristics that can be displayed with significant changes related to working voltage or temperature: OPAX227 series (vs u003d ± 5 v to ± 15 v).

Pay attention to safety

The power supply voltage greater than 36 V permanently damaged the device; please refer to the absolute maximum rated value. The 0.1-μF bypass electric container closer to the power supply foot to reduce the coupling error of noise or high impedance power supply. For more information on the side electric container places, please refer to the layout guide.

Layout

layout guide

In order to obtain the best operating performance of the device, please use good PCB layout practice, including:

noise can spread to the analog circuit through the power pins and operational amplifiers of the entire circuit. The barrier container is used to reduce the coupling noise by providing a low -impedance power supply of an analog circuit.

-Colin the low ESR and 0.1-μF ceramic side electric container between each power supply foot and ground, and as close to the device as much as possible. Single -width capacitors from V+to the ground are suitable for single power applications.

Circuit simulation and the individual grounding of the digital part are one of the simplest and most effective noise suppression methods. Usually on one or more multi -layer PCB layers. The floor helps to distribute heat and reduce the noise of electromagnetic interference. Ensure that the number of numbers and simulation of the ground is separated, and the flowing current flows. For more details, see the circuit board layout technology (Sloa089).

In order to reduce parasitic coupling, the input trajectory should be as far away from the power supply or output trajectory as much as possible. If these record channels cannot be separated, it is much better than parallel to the noise recorder.

The external components are as close to the device as possible. As shown in the layout example, keeping RF and RG approach the inverter input, which can minimize the parasitic capacitance.

The length of the input record should be as short as possible. Always remember that the input trajectory is the most sensitive part of the circuit.

Consider setting a driver's low impedance protection ring around the key line. The protective ring can significantly reduce the leakage current of different potentials nearby.

It is recommended to clean the PCB after assembly to obtain the best performance.

Any precision set circuit may change performance changes due to water entering plastic packaging. After any water -based PCB cleaning process, it is recommended to bake PCB components to remove the water packaging water during the cleaning process. In most cases, it is enough to bake for 30 minutes after low temperature at 85 ° C.

layout example