Datasheet

AD8605/AD8606/AD8608 Data Sheet
Rev. N | Page 16 of 24
APPLICATIONS 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
can 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.
MAXIMUM POWER DISSIPATION
Power dissipated in an IC causes the die temperature to
increase, which 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
damage or destroy the device.
The maximum power dissipation of the amplifier is calculated
according to
JA
A
J
DISS
TT
P
θ
−
=
where:
T
J
is the junction temperature.
T
A
is the ambient temperature.
θ
JA
is the junction-to-ambient thermal resistance.
Figure 45 compares the maximum power dissipation with
temperature for the various AD860x family packages.
INPUT OVERVOLTAGE PROTECTION
The AD860x has internal protective circuitry. However, if the
voltage applied at either input exceeds the supplies by more
than 0.5 V, external resistors should be placed in series with
the inputs. The resistor values can be determined by
mA5≤
−
S
S
IN
R
VV
The remarkable low input offset current of the AD860x (<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 AD860x has a low total harmonic distortion. Figure 46 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.
TIME (4µs/DIV)
VO
LT
AGE (2V/DIV)
V
OUT
V
IN
V
S
= ±2.5V
V
IN
= 6V p-p
A
V
= 1
R
L
= 10kΩ
02731-043
Figure 44. No Phase Reversal
AMBIENT TEMPERATURE (°C)
1.0
0.8
0
–45
130–20
POWER DISSI
PA
TION (W)
30 80 105
0.6
0.4
0.2
1.7
1.8
1.6
1.4
1.2
02731-044
TSSOP-14
5 55
1.5
1.3
1.1
0.9
0.7
0.5
0.3
0.1
5-LEAD SO
T
-23
MSOP-8
SOIC-14
WLCSP-5
SOIC-8
Figure 45. Maximum Power Dissipation vs. Ambient Temperature
FREQUENC
Y (Hz)
0.1
0.01
0.0001
20 20k100
THD + NOISE (%)
1k
0.001
10k
V
SY
= ±2.5V
A
V
= 1
B
W
= 80kHz
02731-045
Figure 46. THD + Noise vs. Frequency