ADA4084-2ARMZ-R7 datasheet(30/36 Pages) AD

30 / 36 page

ADA4084-1/ADA4084-2/ADA4084-4

Data Sheet

Rev. I | Page 30 of 36

START-UP CHARACTERISTICS

The ADA4084-1/ADA4084-2/ADA4084-4 are specified to operate

from 3 V to 30 V (±1.5 V to ±15 V) under nominal power

supplies. During power-up as the supply voltage increases from

0 V to the nominal power supply voltage, the supply current (ISY)

increases as well, to the point at which it stabilizes and the amplifier

is ready to operate. The stabilization varies with temperature, as

shown in Figure 103. For example, at −40°C, it requires a higher

voltage and stabilizes at a lower supply current than at hot

temperatures. At hot temperatures, it requires a lower voltage but

stabilizes at a higher current. In all cases, the ADA4084-1/

ADA4084-2/ADA4084-4 are specified to start up and operate at

a minimum of 3 V under all temperature conditions.

INPUT PROTECTION

As with any semiconductor device, if conditions exist where the

applied input voltages to the device exceed either supply voltage,

the input overvoltage I-to-V characteristic of the device must be

considered. When an overvoltage occurs, the amplifier may be

damaged, depending on the magnitude of the applied voltage

and the magnitude of the fault current.

The D1, D2, D4, and D5 diodes conduct when the input common-

mode voltage exceeds either supply pin by a diode drop. This

diode drop voltage varies with temperature and is in the range

of 0.3 V to 0.8 V. As shown in the simplified equivalent input

circuit of Figure 106, the ADA4084-1/ADA4084-2/ADA4084-4

do not have any internal current limiting resistors; thus, fault

currents can quickly rise to damaging levels.

This input current is not inherently damaging to the device,

provided that it is limited to 5 mA or less. If a fault condition

causes more than 5 mA to flow, add an external series resistor at

the expense of additional thermal noise. Figure 108 shows a

typical noninverting configuration for an overvoltage protected

amplifier, where the series resistance (R1) is chosen, such that

(

)

SUPPLY

MAX

−

For example, a 1 kΩ resistor protects the ADA4084-1/ADA4084-2/

ADA4084-4 against input signals up to 5 V above and below the

supplies. Note that the thermal noise of a 1 kΩ resistor at room

temperature is 4 nV/√Hz, which exceeds the voltage noise of the

ADA4084-1/ADA4084-2/ADA4084-4. For other configurations

in which both inputs are used, add a series resistor to limit the

input current. To ensure optimum dc and ac performance,

balance the source impedance levels.

VIN

VOUT

1/2

ADA4084-1/

ADA4084-2/

ADA4084-4

Figure 108. Resistance in Series with the Input

Limits Overvoltage Currents to Safe Values

To protect the Q1/Q2 and Q3/Q4 pairs from large differential

voltages that may result in Zener breakdown of the emitter-base

junction, D100 and D101 are connected between the two inputs.

This precludes operation as a comparator. For a more complete

description, see the MT-035 Tutorial, Op Amp Inputs, Outputs,

Single-Supply, and Rail-to-Rail Issues; the MT-083 Tutorial,

Comparators; the MT-084 Tutorial, Using Op Amps as

Comparators; and the AN-849 Application Note, Using Op

Amps as Comparators.

OUTPUT PHASE REVERSAL

Some operational amplifiers designed for single-supply operation

exhibit an output voltage phase reversal when their inputs are

driven beyond their useful common-mode range. Typically, for

single-supply bipolar op amps, the negative supply determines

the lower limit of their common-mode range. With these devices,

external clamping diodes, with the anode connected to ground

and the cathode to the inputs, prevent input signal excursions

from exceeding the negative supply of the device (that is, GND),

preventing a condition that causes the output voltage to change

phase. JFET input amplifiers can also exhibit phase reversal, and, if

so, a series input resistor is usually required to prevent it.

The ADA4084-1/ADA4084-2/ADA4084-4 are free from

reasonable input voltage range restrictions, provided that input

voltages no greater than the supply voltages are applied (see

Figure 38, Figure 69, and Figure 100).

Although device output does not change phase, large currents can

flow through the input protection diodes. Therefore, apply the

technique recommended in the Input Protection section to

those applications where the likelihood of input voltages

exceeding the supply voltages is high.

ADA4084-2ARMZ-R7 数据表(PDF) 30 Page - Analog Devices

ADA4084-2ARMZ-R7 数据表(HTML) 30 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

数据表下载