Features

Unit gain bandwidth: 5.5MHz

Low -voltage offset: 1.0 mv

conversion rate: 7.5V/μs

Single power operation operation : 5 V to 18 V

High -output current: 70mA

Low power current: 800 μA/amplifier

When the capacitance load is large

Rail pair pair pair Rail input and output

Application

LCD GAMMA and VCOM Driver

modem

Portable instrument

Direct access arrangement

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General description

AD8614 (single channel) and AD8644 (four sounds) are single -power supply, 5.5 MHz bandwidth rail bars, and optimized the LCD display application.

XFCB and XFCB are processed by high -voltage complementary processes. This patent process includes a groove isolation transistor, which reduces the internal parasitic capacitance, thereby increasing the gain bandwidth, phase margin, and capacitor load driving. The low power current of each amplifier 800 μA (typical value) is essential for portable or dense packaging design. In addition, the railway to the railway output swing provides a larger dynamic range and control ratio of the standard video amplifier.

The working voltage of these products ranges from 5 to 18 volts. The unique combination of 70 mAh output drive, high conversion rate and high capacitor -driven capacity makes AD8614/AD8644 an ideal choice for LCD applications.

The temperature range of AD8614 and AD8644 is -20 ° C to+85 ° C. They have 5-line SOT-23, 14 line Tssop and 14-line SOIC surface installation and packaging, and use tapes and rolls.

pin configuration

Typical performance features

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Operation theory AD8614/AD8644 uses analog device high -voltage, super fast complement bipolar (HV XFCB) process for processing. This process includes a groove isolation transistor, which can reduce parasitic capacitors.

FIG. 26 shows a simplified schematic diagram of AD8614/AD8644. The input level is the rail, consisting of two complementary differential pairs, a NPN pair and a PNP pair. The input level is from two back -to -diodes to prevent the avalanche from being penetrated. Each input has a 1.5 kΩThe resistor restricts the input current during the overvoltage event, and provides a reverse rotation protection when exceeding the input value. Two differential pairs are connected to a dual folding co -source grid. This is the most gain in the amplifier. Dual -folding the co -source grids of the common source of the output -class circuit. Two complementary co -emission polar transistors are used as output. This allows the output to swing from each guide to within 125 millivols under the load of 10 mia. The output -level gain and the opening gain of the computing amplifier depends on the load resistance.

AD8614/AD8644 has no built -in short -circuit protection. The short -circuit limit is a function of the voltage drop on the high current attenuation and output -level schematic diagram of the output -class transistor. In a short -circuit voltage event, the voltage on the resistor is fixed on a diode.

Short -circuit protection of the output

In order to achieve the broad bandwidth and high conversion rate, the output of AD8614/AD8644 did not have short circuit protection. The output is short -circuited to the ground or the power rail may damage the device. The typical maximum safety output current is 70 mAh.

In applications that need to be protected by some output current, but not at the cost of reducing the output voltage, the low -value resistor can be used in series with the output. As shown in Figure 25. The resistor is connected to the feedback circuit of the amplifier. Therefore, if VOUT is short -circuited on the ground and VIN swing to 18 V, the output current does not exceed 70 mA.

For the application of 18 V single power supply, it is not recommended to use a resistor less than 261Ω.

Enter overvoltage protection

Like any semiconductor device, as long as there is a condition that enters exceeding any power supply voltage, you need to pay attention Voltage characteristics. When a voltage occurs, the amplifier may be damaged, depending on the voltage level and the size of the fault current. When the input voltage exceeds 0.6V, the internal pin connection will be powered on, and the permitted current allows the current from the input flow to the power supply. As shown in Figure 26, the AD8614/AD8644 connects 1.5 kΩ resistor in each input end, which helps limit the current. As long as the input current is limited to 5 mAh or less, the input current does not cause inherent damage to the device. If the voltage is large enough and the current exceeds 5 mAh, an external series resistor should be added. Divide the maximum overvoltage at 5 mA, and then subtract the internal 1.5 kΩ resistor to calculate the size of the resistor. For example, if the input voltage can reach 100 V, the external resistance should be (100 V ÷ 5 ma) –1.5 kΩ u003d 18.5 kΩ. If both inputs are affected by overvoltage, or both inputs are affected by overvoltage.

The output phase reversal

As long as the input voltage is limited in the power rail, AD8614/AD8644 will not occur.change. Although the output of the device does not change the phase, the large current generated by the input voltage will cause the device to damage. In the application where the input voltage may exceed the power supply voltage, the overvoltage protection described in the previous section should be used.

Power loss

AD8614/AD8644 The maximum power that can be securely dissipated is limited by the increase in related knot temperature. The maximum safety knot temperature is 150 ° C, and it must not exceed the temperature, otherwise it will affect the performance of the device. If this maximum value is temporarily exceeded, once the mold temperature is reduced, the circuit will return to normal work. Make the equipment for a long time in the overheating state and cause permanent damage to the equipment.

To calculate the internal knot temperature of AD8614/AD8644, the following formulas can Nerring temperature.

PDiss is the power consumption of AD8614/AD8644.

θja is the thermal resistance of AD8614/AD8644 to the environment packaging.

TA is the ambient temperature of the circuit.

The power consumed by the device can be calculated as:

In the formula:

ILOAD is AD8614/AD8644 output load current.

VS is AD8614/AD8644 power supply voltage.

Vout is the output voltage of AD8614/AD8644.

FIG. 27 provides a simple way to determine whether the device is overheating. Based on the type of encapsulation and the environmental temperature around the packaging, the maximum safety power consumption can be found graphically. By using the previous equations, it is easy to see whether the PDISS exceeds the power reduction curve of the device. In order to ensure the correct operation, the recommendation reduction curve shown in Figure 27 must be observed.

Unused amplifier

It is recommended to configure any unused amplifier in the four -yuan package to a unit gain follower. Non -turning input is connected to the ground layer.

Capacitor load driver

AD8614/AD8644 has excellent capacitor load driving capabilities. Although the device is stable under the large capacitor load, as the capacitor load increases, the bandwidth of the amplifier will decrease.

When the AD8614/AD8644 outputs a large capacity load, the buffer network can be used to improve the transient response. The network consists of a series of R-C, which connects from the output of the amplifier to the ground to connect it with the capacitance. The configuration is shown in Figure 28. Although this kind of network does not increase the bandwidth of the amplifier, But it does significantly reduce the amount of overwhelming.

The best value of the buffer network should be determined according to the experience of the capacitance load. Table 4 shows several buffer network values u200bu200bof a given load capacitor.

Direct arrangement

FIG. 29 shows a 5V single power transfer/receiving telephone line interface diagram of the 600Ω transmission system. It allows full dual -time transmission of signals on the transformer coupling 600Ω line. The amplifier A1 provides a adjustable gain to meet the output driving requirements of the modem. Both A1 and A2 are configured to apply the maximum possible differential signal to the transformer. The maximum available signal of a single 5V power supply is about 4.0V P-P, which connects the 600Ω transmission system. The amplifier A3 is configured to the differential amplifier to extract the receiving information from the transmission line to enlarge it through A4. A3 also prevents transmitting signal interference from receiving signals. The gain of A4 can be adjusted in the same way as A1 to meet the requirements of the modem input signal. The standard resistance value allows the resistance array in a single -line encapsulation (SIP) format. It combines it with AD8644 14 line SOIC or Tssop packaging, which can provide a compact solution.

Single -chip headset/microphone front placing large -scale solution

Due to its high output current performance, AD8644 is an excellent amplifier for driving computer applications The audio output jack. Figure 30 shows how to connect AD8644 to the AC codec to drive the headset or speaker.

If you need to gain gain from the output amplifier, four additional resistors should be added, as shown in Figure 31.

The gain of AD8644 can be set to:

both circuits do not need to input coupling capacitors, because the reference voltage Provided by AD1881A.

Resistance R4 and R5 help protect the AD8644 output, in order to prevent the output jack or earphone cable unexpectedly short -circuit. The output coupling capacitor C1 and C2 block the DC current from the headset, and generate a high -pass filter with an angular frequency

. The RL is the resistance of the headset.

The remaining two amplifiers can be used as a low -pressure microphone front amplifier. A single AD8614 can be used as an independent microphone front placed. Figure 32 shows this implementation.

The size of the shape

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