AD8560 Просмотр технического описания (PDF) - Analog Devices

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AD8560

16 V Rail-to-Rail Buffer Amplifier

Analog Devices 

AD8560

APPLICATIONS

Theory of Operation

These buffers are designed to drive large capacitive loads in LCD

applications. Each has a high output current drive and rail-to-

rail input/output operation and can be powered from a single 16

V supply. They are also intended for other applications where low

distortion and high output current drive are needed.

Input Overvoltage Protection

As with any semiconductor device, whenever the input exceeds

either supply voltage, attention needs to be paid to the input

overvoltage characteristics. As an overvoltage occurs, the amplifier

could be damaged depending on the voltage level and the magnitude

of the fault current. When the input voltage exceeds either supply

by more than 0.6 V, internal pin junctions will allow current to

flow from the input to the supplies.

This input current is not inherently damaging to the device as

long as it is limited to 5 mA or less. If a condition exists using

the buffers where the input exceeds the supply by more than 0.6 V,

a series external resistor should be added. The size of the resistor

can be calculated by using the maximum overvoltage divided by

5 mA. This resistance should be placed in series with the input

exposed to an overvoltage.

Output Phase Reversal

The buffer family is immune to phase reversal. Although the device’s

output will not change phase, large currents due to input overvoltage

could damage the device. In applications where the possibility exists

of an input voltage exceeding the supply voltage, overvoltage protec-

tion should be used as described in the previous section.

Total Harmonic Distortion (THD+N)

The buffer family features low total harmonic distortion. The total

harmonic distortion plus noise for the buffer over the entire

supply range is below 0.08%. When the device is powered from

a 16 V supply, the THD + N stays below 0.03%. Figure 1 shows

the AD8560’s THD + N versus the frequency performance.

10

Short Circuit Output Conditions

The buffer family does not have internal short circuit protection

circuitry. As a precautionary measure, do not short the output

directly to the positive power supply or to the ground.

It is not recommended to operate the AD8560 with more than

35 mA of continuous output current. The output current can be

limited by placing a series resistor at the output of the amplifier

whose value can be derived using the following equation:

RX

≥

VS

35 mA

For a 5 V single-supply operation, RX should have a minimum

value of 143 Ω.

Recommended Land Pattern for the AD8560

Figure 2 is a recommended land pattern for the AD8560 PCB

design. The recommended thermal pad size for the PCB design

matches the dimensions of the exposed pad on the bottom of

the package. The solder mask design for improved thermal pad

contact to the exposed pad and reliability uses a stencil pattern

for approximately 85% solder coverage. A minimum clearance

of 0.25 mm is maintained on the PCB between the outer edges

of the thermal pad and the inner edges of the pattern for the

land to avoid shorting. For better thermal performance, thermal

vias should also be used. Since the AD8560 is relatively a low

power part, just soldering the exposed package pad to the PCB

thermal pad should provide sufficient electrical performance.

SYMM CL

0.28 ؋ 0.75

TYP 16 PL

2.1 1.95 0.65

0.9

0.4

SYMM CL

0.05

0.1

1

0.875



0.1

VS = ؎2.5V

VS = ؎8V

0.01

20

100

1k

FREQUENCY – Hz

10k 30k

Figure 1. THD + N vs. Frequency

0.20

0.25

SOLDER MASK

BOARD METALLIZATION

Figure 2. 16-Lead 4 x 4 Land Pattern

REV. 0

–9–

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