OP162GSZ datasheet(12/20 Pages) AD

12 / 20 page

OP162/OP262/OP462

Data Sheet

Rev. H | Page 12 of 20

APPLICATIONS

FUNCTIONAL DESCRIPTION

The OPx62 family is fabricated using Analog Devices’ high

speed complementary bipolar process, also called XFCB. This

process trench isolates each transistor to lower parasitic capaci-

tances for high speed performance. This high speed process has

been implemented without sacrificing the excellent transistor

matching and overall dc performance characteristic of Analog

Devices’ complementary bipolar process. This makes the OPx62

family an excellent choice as an extremely fast and accurate low

voltage op amp.

Figure 30 shows a simplified equivalent schematic for the OP162.

A PNP differential pair is used at the input of the device. The

cross connecting of the emitters lowers the transconductance of

the input stage improving the slew rate of the device. Lowering

the transconductance through cross connecting the emitters has

another advantage in that it provides a lower noise factor than if

emitter degeneration resistors were used. The input stage can

function with the base voltages taken all the way to the negative

power supply, or up to within 1 V of the positive power supply.

Figure 30. Simplified Schematic

Two complementary transistors in a common-emitter

configuration are used for the output stage. This allows the

output of the device to swing to within 50 mV of either supply

rail at load currents less than 1 mA. As load current increases,

the maximum voltage swing of the output decreases. This is due

to the collector-to-emitter saturation voltages of the output

transistors increasing. The gain of the output stage, and conse-

quently the open-loop gain of the amplifier, is dependent on the

load resistance connected at the output. Because the dominant pole

frequency is inversely proportional to the open-loop gain, the

unity-gain bandwidth of the device is not affected by the load

resistance. This is typically the case in rail-to-rail output

devices.

OFFSET ADJUSTMENT

Because the OP162/OP262/OP462 have an exceptionally low

typical offset voltage, adjustment to correct offset voltage may

not be needed. However, the OP162 has pinouts to attach a

nulling resistor. Figure 31 shows how the OP162 offset voltage

can be adjusted by connecting a potentiometer between Pin 1

and Pin 8, and connecting the wiper to VCC. It is important to

avoid accidentally connecting the wiper to VEE, as this can damage

the device. The recommended value for the potentiometer is

20 kΩ.

Figure 31. Offset Adjustment Schematic

RAIL-TO-RAIL OUTPUT

The OP162/OP262/OP462 have a wide output voltage range

that extends to within 60 mV of each supply rail with a load

current of 5 mA. Decreasing the load current extends the output

voltage range even closer to the supply rails. The common-mode

input range extends from ground to within 1 V of the positive

supply. It is recommended that there be some minimal amount

of gain when a rail-to-rail output swing is desired. The minimum

gain required is based on the supply voltage and can be found as

−

V,min

where VS is the positive supply voltage. With a single-supply

voltage of 5 V, the minimum gain to achieve rail-to-rail output

should be 1.25.

OUTPUT SHORT-CIRCUIT PROTECTION

To achieve a wide bandwidth and high slew rate, the output of

the OP162/OP262/OP462 are not short-circuit protected. Shorting

the output directly to ground or to a supply rail may destroy the

device. The typical maximum safe output current is ±30 mA.

Steps should be taken to ensure the output of the device will not

be forced to source or sink more than 30 mA.

In applications where some output current protection is needed,

but not at the expense of reduced output voltage headroom, a

low value resistor in series with the output can be used. This is

shown in Figure 32. The resistor is connected within the feed-

back loop of the amplifier so that if VOUT is shorted to ground

VCC

VEE

+IN

–IN

VOUT

–5V

20k

Ω

OP162

+5V

VOS

OP162GSZ Folha de dados(PDF) 12 Page - Analog Devices

OP162GSZ Folha de dados(HTML) 12 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

Folha de dados Download

Ligação URL