AD8055/AD8056

Rev. J | Page 13 of 16

FREQUENCY (MHz)

5

4

–5

1

–2

–3

–4

3

2

–1

0

0.3

1

10

100

500

402Ω

100Ω

402Ω

50Ω

POWER DISSIPATION LIMITS

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

while the quiescent power dissipation of the AD8056 in the

MSOP-8 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

MSOP-8 package.

The power dissipated under heavy load conditions is

approximately equal to the supply voltage minus the output

voltage, times the load current, plus the quiescent power

previously computed. The 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.

Figure 39. Capacitive Load Drive

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

larger values of capacitive loads, a small series resistor, R

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

while the AD8056 in the MSOP-8 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. However, because

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.

S

, can

C

RESISTOR SELECTION

Table 3 is a guide for resistor selection for maintaining gain

flatness vs. frequency for various values of gain.

Table 3.

Gain

−3 dB Bandwidth (MHz)

+1

0

300

+2

402

402

160

+5

1 k

249

45

+10

909

100

20

DRIVING CAPACITIVE LOADS

When driving a capacitive load, most op amps exhibit peaking

in the frequency response just before the frequency rolls off.

Figure 39 shows the responses for an AD8056 running at a gain

of +2, with an 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.

L

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

approximately 25 Ω.

50Ω

AD8055

+5V

–5V

402Ω

402Ω

6

7

2

3

4

FET PROBE

0.1µF

10µF

0.1µF

10µF

Figure 40. Setup for R vs. C

S

L

40

0

35

20

15

10

5

30

25

0

1020

3040

5060

270

Figure 41. R vs. C

S

L