AD8605/AD8606/AD8608

Rev. D | Page 13 of 20

APPLICATION INFORMATION

OUTPUT PHASE REVERSAL

Phase reversal is defined as a change in polarity at the output of

the amplifier when a voltage that exceeds the maximum input

common-mode voltage drives the input.

Phase reversal can cause permanent damage to the amplifier; it

may also cause system lockups in feedback loops. The AD8605

does not exhibit phase reversal even for inputs exceeding the

supply voltage by more than 2 V.

TIME (4

µs/DIV)

Figure 43. No Phase Reversal

MAXIMUM POWER DISSIPATION

Power dissipated in an IC causes the die temperature to

increase. This can affect the behavior of the IC and the

application circuit performance.

The absolute maximum junction temperature of the AD8605/

AD8606/AD8608 is 150°C. Exceeding this temperature could

cause damage or destruction of the device. The maximum

power dissipation of the amplifier is calculated according to

the following formula:

JA

A

J

DISS

T

T

P

θ

−

=

where:

Figure 44 compares the maximum power dissipation with

temperature for the various AD8605 family packages.

TEMPERATURE (°C)

1.0

0.8

0

0

100

20

40

60

80

0.6

0.4

0.2

SOIC-14

2.0

1.8

1.6

1.4

1.2

SOIC-8

SOT-23

MSOP

TSSOP

Figure 44. Maximum Power Dissipation vs. Temperature

INPUT OVERVOLTAGE PROTECTION

The AD8605 has internal protective circuitry. However, if the

voltage applied at either input exceeds the supplies by more

than 2.5 V, external resistors should be placed in series with the

inputs. The resistor values can be determined by the formula

(

)

R

V

V

S

S

IN

5

200

≤

Ω

+

−

The remarkable low input offset current of the AD8605 (<1 pA)

allows the use of larger value resistors. With a 10 kΩ resistor at

the input, the output voltage has less than 10 nV of error

voltage. A 10 kΩ resistor has less than 13 nV/√Hz of thermal

noise at room temperature.

THD + NOISE

Total harmonic distortion is the ratio of the input signal in V

rms to the total harmonics in V rms throughout the spectrum.

Harmonic distortion adds errors to precision measurements

and adds unpleasant sonic artifacts to audio systems.

The AD8605 has a low total harmonic distortion. Figure 45

shows that the AD8605 has less than 0.005% or −86 dB of THD

+ N over the entire audio frequency range. The AD8605 is

configured in positive unity gain, which is the worst case, and

with a load of 10 kΩ.