Features

Excellent sound quality characteristics

Low noise: 6 nv/Hz

Low distortion: 0.0006%

High conversion rate: 22 V/3S

Broadband: 9 MHz

Low power current: 5 ma

Low offset voltage: 1 mv

Low offset current: 2 na

The unit gain stable

SOIC-8 package

PDIP-8 package

Application

High-performance audio

Active filter

Fast amplifier

Pointer

OP275

is the first to use Bart to use Bart The front -end amplifier of the bulb. This new front -end design combines bipolar transistors and JFET transistors to obtain a amplifier with accuracy and low noise performance of bipolar crystal tube and the speed and sound quality of JFET. Total harmonic distortion and noise are equal to previous audio amplifiers, but at lower power currents. The extremely low L/F angle below 6 Hz is kept a flat noise density response. Whether the noise is measured at 30 Hedz or 1 kilo, it only has 6 millishalzzz. The input -level JFET part provides a high conversion rate for OP275 to maintain low distortion. Even when the large output swing is required, the 22V/μs conversion rate of OP275 is the fastest among any standard audio amplifier. The best thing is that this low noise and high speed are achieved by using a power current below 5 mA, which is lower than any standard audio amplifier.

The improved DC performance also provides bias and offset currents that greatly reduce pure dual -pole design. The input offset voltage is guaranteed to be 1MV, usually less than 200 μV. This allows OP275 to be used in many DC coupling or application and applications without special choices or additional offset adjustments.

The output can drive the 600Ω load to 10V valid value, while maintaining low distortion. At 3V RMS, THD+noise is low, 0.0006%.

OP275 is specified in the extended industrial temperature range (-40 ° C to+85 ° C). OP275 has two encapsulation forms: plastic impregnation and SOIC-8. SOIC-8 packaging has 2500 rolls. For various reasons, the SOIC-8 surface paste packaging does not provide many audio amplifiers; however, the design of the OP275 allows it to provide complete performance in the surface packaging packaging.

pin connection

OP275 -typical performance characteristics [

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Application Circuit protection OP275 has inherent short -circuit protection. The internal 30Ω resistor inside the output line restricted the output current at room temperature at ISC+ 40 mAh and ISC - - 90 mAh. Usually, the power supply voltage is ± 15 volts.

However, when an excessive voltage or current is applied, any power supply may damage the device. As shown in Figure 1, if the user can be shortened to the power supply, the output current of the OP275 should be designed to ± 30 mA.

Total harmonic distortion

OP275's total harmonic distortion+noise (THD+n) is far below 0.001%, and the load is reduced to 600Ω. However, this depends on the peak output. In Figure 2, the THD+noise output by 3V RMS is less than 0.001%. In Figure 3, THD+noise is lower than 0.001%under 10K and 2K loads, but increased to more than 0.1%under 600 load conditions. This is the result of OP275 output swing capacity. Note that the results in Figure 4 show THD and VIN (VRMS). This figure shows that before the output reaches 9.5 V RMS, THD+noise is still very low. This performance is similar to competitive products.

The output design of OP275 to maintain low harmonic distortion when driving 600Ω load. However, the driving 600Ω load and very high output swing cause higher distortion, if the editing occurs. A common example is to try to drive 10 V RMS into any load with ± 15 V power. The editing will occur and distortion will be very high. In order to obtain low harmonic distortion when the output oscillation is large, the power supply voltage can be increased. Figure 5 shows the performance of the OP275 driver 600Ω load, and the power supply voltage is between ± 18 v and ± 20 v. Please note that when using the ± 18 V power supply, the distortion is quite high. When using the ± 20 V power supply, the distortion is very low at 0.0007%.

Noise

The voltage noise density of OP275 decreases from 30Hz to 7nv/¨Hz. This makes the low noise design has good performance throughout the audio range. Figure 6 shows a typical OP275, and its 1/F corner is 2.24 Hz.

Noise test

For audio applications, noise density is usually the most important noise parameter. To characterize, OP275 uses the audio accuracy system to test. The input signal of the audio accuracy must be enlarged to the degree of accurate measurement.For OP275, the noise is about 1020 in the circuit shown in Figure 7. Any readings of audio accuracy must be divided by gain. When implementing the test fixture, good power bypass is essential.

Enter over current protection

The maximum input differential voltage that can be applied to OP275 is determined by a pair of Qina diode connected to its input end. They limit the maximum differential input voltage to ± 7.5V. This is to prevent the emission polar beam penetration occur at the input level of OP275 when it is applied to a very large differential voltage. However, in order to keep the OP275 low input noise voltage, the internal resistance with the input series is not used to limit the current in the diode. In a small signal application, this is not a problem; however, in applications that may accidentally apply large differential voltage to devices, large transient currents can flow through these diode. Although the design of these diode can carry ± 5 mAh current, the external resistor shown in Figure 8 should be used in Figure 8 in the absence of ± 5 mAh in the absence of ± 7.5 V.

The output voltage phase reversed

Because the input stage of OP275 combines bipolar crystal (for low noise) and P -channel JFET (for for it High -speed performance), so if the input of OP275 exceeds its negative co -mode input voltage, the output voltage of the OP275 may appear phase reversal. This may occur in very serious industrial applications, and sensors or system faults may apply very large voltage to the input of OP275. Although the input voltage range of OP275 is ± 10.5 V, the input voltage of about -13.5 V will cause the output voltage phase to reverse. In the reversal amplifier configuration, OP275's internal 7.5V input clamp diode will prevent phase reversal; however, they will not prevent this effect from occurring in non -conversion applications. For these applications, the repair is very simple, as shown in Figure 9. A 3.92kΩ resistor and the non -reversible input of OP275 solve this problem.

Overload or speeding

The overload or driving recovery time of the operation amplifier refers to the time required for the output voltage from saturated to the rated output voltage Essence This recovery time is important in applications that can quickly recover after the amplifier must recover quickly after a large abnormal transient event. The circuit shown in Figure 10 is used to evaluate the overload recovery time of OP275. OP275 is recovered to VOUT +10 V about 1.2 milliseconds, and it takes about 1.5 micrists to recover to VOUT - 10 V.

Measurement settlement time

OP275 design combines high conversion rates and wide increase benefits, to generate fast for 8 and 12 -bit applications Stability (TS u0026 LT; 1 μs) amplifier. The test circuit used to measure the stable time of OP275 is shown in Figure 11. Compared with fake and node technology, the advantage of this test method is to measure the actual output of the amplifier, rather than measure the error voltage at the node. In addition to the conversion rate and bandwidth effect measured by fake and node methods, the circuit also uses the common mode stability effect. Of course, a reasonable flat -top pulse is needed as stimulation.

The output waveform of OP275 was tested by the Schottky diode, and the JFET source was buffer. The signal was amplified by OP260 10 times, and Schottky was clawed at the output end to prevent the oscilloscope from entering the amplifier overload. OP41 is configured to be a fast integral device to provide the overall DC offset zero.

High -speed operation

Like most high -speed amplifiers, you should pay attention to the power supply decoupling, the lead of the lead, and the component placing. Figure 12 and 13 show the recommendation circuit configuration of inverter and non -inverse applications.

In inverter and non -inverter applications, feedback resistors and source resistance and capacitors (RS and CS) and OP275 input capacitors (CIN CIN ) Form a pole, as shown in Figure 14. When RS and RF are within the Kilohm range, this pole will generate too much phase shift or even oscillation. A small capacitor, CFB, parallel and RFB eliminate this problem. By setting RS (CS+CIN) RFBCFB, the impact of feedback poles is completely eliminated.

Note that the source impedance can minimize distortion

Since OP275 is a very low distortion amplifier, you should pay close attention to the source impedance of the two inputs. Like many FET amplifiers, the P channel JFET in the OP275 input level shows the grid capacitance with changes in the input voltage. In the inverse configuration, the inverter input is kept on the virtual ground, so the input voltage is not changed. Therefore, because the voltage of the grid to the source is constant, it will not cause distortion due to the input capacitor model. However, in non -easy -to -use applications, the voltage from the gate to the source is not constant. If the input impedance is greater than 2K and unbalanced, the capacitance modulation can cause distortion of more than 1 kHz.

FIG. 15 shows some guidance principles to maximize OP275 distortion performance in non -reversal applications. The best way to prevent unnecessary distortion is to ensure that the parallel combination of feedback and gain setting resistance (RF and RG) is less than 2kΩ. Keeping the value of these resistors is small to help reduce the circuit thermal noise and DC offset error. If the parallel combination of RF and RG is greater than 2kΩ, a additional resistor RS should be used in series without switching. The RS value is determined by the parallel combination of RF and RG to maintain the low distortion performance of OP275.

Drive capacitance load

oP275 is designed to drive the resistor load to 600Ω, the capacitor load exceeds 1000 PF, and maintains stability. When the bandwidth is reduced when the capacitance load is driven, the designer does not have to worry about the stability of the device. The chart in FIG. 16 shows the 0 DB bandwidth of OP275 from 10 PF to 1000 PF capacitor load.

High -speed and low noise differential line drive

The circuit in FIG. 17 is a unique line drive widely used in industrial applications. In the case of ± 18 volt power, the route driver can provide a 30 -volts of differential signals to 2.5 kV load. The combination of the high conversion rate of OP275 and the width width can produce a full power bandwidth of 130 kHz, while the reference input noise voltage spectrum generated by the low noise front end is 10 NV/¨Hz.

This design is a transformer, and the output co -modular noise suppression of the output of the transmission system is crucial. As with the design of a transformer -based, without changing the circuit gain 1, any output can be used for a short circuit for the application of an unbalanced circuit drive. Other circuit gains can be set according to the formulas in the figure. This makes it easy to set as non -reversing, reversal or differential operations.

A 3rd pole, 40 kHz low -pass filter

The tight matching and uniform communication characteristics of OP275 make it GIC (broad impedance converter) and FDNR (frequency related negative resistance) filtering The ideal choice of device application. The circuit in FIG. 18 illustrates a linear phase, 3 poles, 40 kHz low -pass filters, and uses OP275 as an inductive simulator (rotor). The circuit uses an OP275 (A2 and A3) as FDNR, and an OP275 (A1 and A4) input buffer and bias current source for A3. The amplifier A4 is configured to the gain to 2 to set the band amplitude response to 0 dB. Compared with the traditional method, the advantage of this filter topology is that the computing amplifier used in FDNR is not in the signal path, and the performance of the filter is relatively not sensitive to component changes. In addition, this configuration can process a large signal level without any internal nodes of the filter. As shown in Figure 19, the symmetrical conversion rate and low distortion of the OP275 have a clean and good transient response.

The size of the shape