AD8055/AD8056

–10–

REV. B

Power Dissipation Limits

pation of the AD8055 in the SOT-23-5 package is 65 mW,

while the quiescent power dissipation of the AD8056 in the

microSOIC is 120 mW. This translates into a 15.6

°C rise above

the ambient for the SOT-23-5 package and a 24

°C rise for the

microSOIC package.

The power dissipated under heavy load conditions is approxi-

mately equal to the supply voltage minus the output voltage,

times the load current, plus the quiescent power computed above.

This total power dissipation is then multiplied by the thermal

resistance of the package to find the temperature rise, above

ambient, of the part. The junction temperature should be kept

below 150

°C.

The AD8055 in the SOT-23-5 package can dissipate 270 mW

while the AD8056 in the microSOIC package can dissipate

325 mW (at 85

°C ambient) without exceeding the maximum

die temperature. In the case of the AD8056, this is greater than

1.5 V rms into 50

Ω, enough to accommodate a 4 V p-p sine-wave

signal on both outputs simultaneously. But since each output of

the AD8055 or AD8056 is capable of supplying as much as

110 mA into a short circuit, a continuous short circuit condition

will exceed the maximum safe junction temperature.

Resistor Selection

The following table is provided as a guide to resistor selection

for maintaining gain flatness vs. frequency for various values of

gain.

–3 dB

Bandwidth

Gain

(MHz)

+1

0

—

300

+2

402

402

160

+5

1k

249

45

+10

909

100

20

Driving Capacitive Loads

When driving a capacitive load, most op amps will exhibit peak-

ing in the frequency response just before the frequency rolls off.

Figure 36 shows the responses for an AD8056 running at a gain

of +2, with a 100

Ω load that is shunted by various values of

capacitance. It can be seen that under these conditions, the part

is still stable with capacitive loads of up to 30 pF.

FREQUENCY – MHz

5

4

–5

0.3

500

1

10

100

1

–2

–3

–4

3

2

–1

0

402

100

402

50

Figure 36. Capacitive Load Drive

In general, to minimize peaking or to ensure the stability for

chosen to produce less than 1 dB of peaking in the frequency

about 25

Ω.

50

AD8055

+5V

–5V

402

402

6

7

2

3

4

0.1 F

10 F

0.1 F

10 F

FET PROBE

0

270

10

20

30

40

50

60

40

0

35

20

15

10

5

30

25