Features

● Low power current: maximum value of 4μA/amplifier

● Single power operation: 2.7 V to 12 V [123 123 ]

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Wide input voltage range

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Low offset voltage: 1.5 MV

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No phase reversal Application

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comparator

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battery power supply meter

● Safety monitoring

● Remote sensor

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Low -voltage strain film amplifier Generally explained

OP281 and OP481 are dual -and four ultra -low -power single power supply amplifiers, which have rail transfers. The power supply voltage of each power supply is low to 2.0 V, and is specified to be +3 V and +5 V single power supply and ± 5 V dual power supply. OP281/OP481 uses the CBCMOS process of analog device, with accurate bipolar input and an output swinging in the millivolva area, continuously absorbing or source current to the same voltage as the power supply voltage.

The applications of these amplifiers include the interface of safety monitoring, portable equipment, battery and power control, signal adjustment, and sensors in extremely low power systems.

When the output is driven to a power supply voltage, the output can swing between the orbit and does not increase the power current, which allows OP281/OP481 to be used as a comparator in a very low power system. This is due to their fast saturation recovery time. The transmission delay is 250 μs.

OP281/OP481 specifies within the scope of the extended industrial temperature range ( 40 ° C to+85 ° C). The OP281 dual amplifier has 8 -line SOIC surface installation and TSSOP packaging. The OP481 four -way amplifier provides a narrow 14 -line SOIC and Tssop encapsulation.

引脚配置

典型性能特征

[123 ]

Application Operation Theory OPX81 series operation amplification amplification amplificationThe device consists of extremely low power and rail transition amplifier, and the required current is less than 4 μA's static current. Many other competitors may be promoted as low -power current discharge, but when the output of these devices is driven to the power supply rail, it will attract more current. Even if the output is driven to any power rail, the power supply current of OPX81 remains below 4μA. As long as the input and output remain within the range of the power supply, the power current should meet the requirements of the specifications. FIG. 36 shows the simplified schematic diagram of the OPX81 single channel. The input level adopts a bipolar differential pair. PNP transistors are used to keep the input level linear and extend the scope of the co -mode to the ground. This is an important consideration for the application of single power supply. The noise at the front end of the bipolar is also lower than the front end of the MOS with only Mia. The output of the computing amplifier consists of a pair of CMOS crystals with a conjugated structure. This setting allows the output of the amplifier to swing within the millivolva range of any power rail. The net empty height required for the output level is limited by the current driver of the load. The lower the output current, the closer to the distance from the power supply track. Figure 11, Figure 12, and 13 show the relationship between the output voltage and the load current. This behavior is a typical rail transition amplifier.

Enter overvoltage protection

OPX81 series operational amplifier input level consists of PNP differential pair. If the base voltage of these input transistors drops more than 0.6 volt of the negative power supply, the input ESD protective diode will become positive bias and start to generate large current. In addition to damaging the device, this will also produce phase reversal effects on the output end. To prevent this, the input current should be limited to less than 0.5 mAh.

This can be achieved by simply connecting a resistor with the input of the device. The size of the resistor should be proportional to the minimum possible input signal, and can be calculated using the following formulas:

In the formula:

vee is the The negative power of the amplifier.

VIN, Min is the expected minimum input voltage offset.

For example, if the input signal may be as low as 1 V, the single channel of OPX81 should be used with the single power supply voltage of +5 V. Because the amplifier is powered by a single power supply, VEE is ground; therefore, the necessary series resistance should be 2 kΩ.

Input offset voltage

OPX81 series operational amplifier design is designed for low offset voltage (less than 1MV).

Enter the co -mode voltage range

In the voltage range between the rated voltage x8 to 1, the OPV is 1. However, the operational amplifier can work in the case of the co -mode voltage slightly lower than the VEE. Figure 37 shows the matchingThe single OPX81 channel is placed as a differential amplifier, and the single power supply voltage is 3 V. Apply a negative DC voltage on the two input terminals to generate a co -mode voltage smaller than ground. The 400 MV P-P input signal is then applied to a non-conversion input. Figure 38 shows the input and output waveform generated. Please note how the output of the amplifier decreases slightly without fail.

Capacity load

Most low -power current discharge is difficult to drive the capacitance load because the output level of these loads requires higher current. The high -capacitor at the output end will increase the overwhelming and bell in the amplifier level jump response, and may affect the stability of the device. However, by carefully designing the output level and its high phase, the OPX81 series can withstand a certain degree of capacitor load. Figure 39 shows a single channel jump response to 10 NF capacitors connecting 10 NF capacitors at the output end. Note that under such a load, the output overput will not exceed 10%, even if the power supply voltage is only 3V.

Micro -power reference voltage generator

The circuit bias of many single power supply circuits is half of the power supply voltage. In these cases, the fake grounding benchmark can be created by using a sorter of the amplifier buffer. Figure 40 shows the schematic diagram of this circuit.

Two 1 MΩ resistors generate reference voltage, and at the same time, only 1.5 μA current is absorbed from the 3 V power supply. The capacitors connected from the inverter to the capacitor output end of the computing amplifier provide compensation to allow the bypass container to connect to the benchmark output end. This bypass container helps to establish communication ground for reference output. The entire reference generator is less than 5 μA from the 3V power supply.

Window comparator

OPX81 series of extremely low power current requirements to make it very suitable for the application of battery supply with long service life, such as monitoring systems. Figure 41 shows a circuit using OP281 as a window comparator.

The threshold limit of the window is set by VH and VL, provided that VH u0026 GT; VL. As long as the input voltage is less than VH, the output of the first OP281 (A1) will be kept negative, and in this case, it is grounded. Similarly, as long as the input voltage is higher than VL, the output of the second OP281 (A2) will remain on the ground. As long as VIN keeps between VL and VH, the output of the two computing amplifiers will be 0 V. In the case of no current flow in D1 or D2, the base of Q1 will be kept on the ground, causing the transistor to be cut off, and forcing VOUT to enter the positive power rail. If the input voltage rises above the VH, the output of A2 remains on the ground, but the output of A1 to the track, D1 transmission current. This generates a base voltage, turn on Q1 and make VOUT becomes lower. If VIN is lower than VL, the output of A2 becomes higher, and the conduction current of D2 will also occur. Therefore, if the input voltage is between VL and VH, VOUT is high, but if the input voltage exceeds this range, VOUT is low.

R1 and R2 separators set up the upper part of the window, and the R3 and R4 divisors set the lower part of the window. In order to make the window comparator work normally, VH must be larger than VL's voltage.

2 KΩ resistor connects the input voltage of the input terminal to the operation amplifier. This can protect OP281 and make it unwilling to be affected by over -current at the input level of the device. D1 and D2 are small signal switch diode (1N4446 or equivalent device), Q1 is 2N2222 or equivalent NPN transistor.

Low -voltage side current monitor

In the design of the power control circuit, a large number of design work is concentrated in ensuring the long -term reliability of the augmented crystal tube under extensive load current conditions. Therefore, in these designs, monitoring and restricting equipment power consumption are the most important. FIG. 42 shows an example of a 5V single power current monitor, which can be merged into the design of a voltage regulator with a folding current limit or a large current power supply with a pilot protection. The design uses the co -mode range of OPX81 to the ground. Monitor the current in the power circuit, where the 0.1Ω parallel resistance RSENSE generates a very small voltage drop. Through the feedback of Q1, the voltage of the inverter end is equal to the non -inverter voltage. Q1 is a 2N2222 or an equivalent NPN transistor. This reduces the voltage on R1 equals the voltage on RSense. Therefore, the current through Q1 is proportional to the current through the RSENSE, and the output voltage is given from the following formula:

The voltage on R2 decreases with the increase of i by I increased. ; Therefore, if a higher power current is detected, VOUT will be reduced. For the component value, VOUT transmission characteristics are 2.5 v/a, which will be reduced from VEE.

Low -voltage semi -wave and full wave rectifier

Due to its fast driving recovery time, OP281 can be configured to be configured with a full wave of low -frequency (u0026 lt; 500Hz) applications. Rectifier. Figure 43 shows the schematic diagram.

The amplifier A1 is used as a voltage follower, and the voltage is tracked only when the input voltage is greater than 0 V. This provides semi -wave rectification for the non -switching terminal of the amplifier A2. When the output of A1 follows the input, the inverter terminal of the A2 also follows the input of the virtual ground between the A2 and the virtual ground between the non -inverter terminal. Because there is no potential difference between R1, there is no current flowing through R1 or R2; therefore, the output of A2 also follows the transmissionenter. When the input voltage is lower than 0 V, the non -fall phase of A2 becomes 0 V. This allows A2 to work as a inverter amplifier with a gain of 1 and provides a full -wave rectifier version of the input signal. When the input signal is smaller than the ground, a 2kΩ resistor and the non -switch of A1 are connected in series to protect the device.

Battery power supply phone headset amplifier

FIG. 45 shows how to use OP281 as a two -way amplifier in the phone headset. One end of the OP281 can be used as a amplifier of a microphone, and the other end can be used to drive the speaker. A typical telephone headset uses a 600Ω speaker and an polar microphone that requires a power supply voltage and a partial pressure resistor.

OP281-A operational amplifier provides about 29 decibel gains from the audio signal from the microphone. The gain is set by 300 kΩ and 11 kΩ resistors. The gain bandwidth of the amplifier is 95 kHz. In the case of setting the gain to 28, at the attenuation of 3 dB at 3.4 kHz. This is acceptable, because the frequency band of telephone audio is limited to 300 kHz to 3 kHz signals. If the microphone requires a higher gain, an additional gain level should be used because the increase in OP281 will limit the audio bandwidth. A 2.2kΩ resistor is used to biased the polar microphone. This resistance value may vary from the microphone specifications. The output of the microphone is the non -conversion terminal of the AC coupling to the computing amplifier. Two 1 MΩ resistors are used to provide DC offset for single power supply. OP281-B amplifier (see Figure 45) can provide the earphone speaker with a gain of up to 15 decibels. The input audio signal is coupled with the 10kΩ potential meter used to regulate the volume. Similarly, the two 1 MΩ resistors provide 1 μF capacitors for DC offset to establish AC grounding for volume control potential meter. Because OP281 is a rail -to -rail loss amplifier, it is difficult to directly drive the 600Ω speaker. Here, the AB buffer is used to isolate the load of the amplifier and provides the current required to drive the speaker. By placing a buffer in the feedback loop of the computing amplifier, the cross distortion can be minimized. The minimum value of Q1 and Q2 should be 100. 600Ω speakers communicate with the transmitter to prevent static current from flowing into the speaker. 1 μF coupled electric container cut off the equivalent high -pass filter at 265 Hz when adding a 600Ω load. Similarly, this will not cause problems because it exceeds the frequency range of the phone audio signal.

The circuit in FIG. 45 consumes about 250 μA. The static current of the AB buffer is 140 μA, and the current of about 100 μA is consumed by the microphone itself. The expected life of CR20323V lithium battery is 160mA hours, which means that the circuit can run continuously for 640 hours on a single battery.

Dimensions