AD8565/AD8566/AD8567
Output Phase Reversal
THD + N
The AD856x family is immune to phase reversal. Although
the device鈥檚 output will not change phase, large currents due
to input overvoltage could damage the device. In applications
where the possibility of an input voltage exceeding the supply
voltage exists, overvoltage protection should be used as described
in the previous section.
Power Dissipation
The AD856x family features low total harmonic distortion. Figure
4 shows a graph of THD + N versus frequency. The Total Harmonic
Distortion plus Noise for the AD856x over the entire supply range
is below 0.008%. When the device is powered from a 16 V supply,
the THD + N stays below 0.003%. Figure 4 shows the AD8566
in a unity noninverting configuration.
10
The maximum allowable internal junction temperature of 150擄C
limits the AD856x family Maximum Power Dissipation. As the
ambient temperature increases, the maximum power dissipated
by the AD856x family must decrease linearly to maintain the
maximum junction temperature. If this maximum junction
temperature is exceeded momentarily, the part will still operate
properly once the junction temperature is reduced below 150擄C.
If the maximum junction temperature is exceeded for an extended
period of time, overheating could lead to permanent damage of
the device.
The maximum safe junction temperature, T
JMAX
, is 150擄C. Using
the following formula, we can obtain the maximum power that
the AD856x family can safely dissipate as a function of temperature.
P
DISS
=
T
J
MAX
鈥?/div>
T
A
/胃
J
A
where:
P
DISS
= AD856x power dissipation
T
J
MAX
= AD856x maximum allowable junction temp (150擄C)
T
A
= Ambient Temperature of the circuit
胃
J
A
= AD856x package thermal resistance, junction-to-ambient
The power dissipated by the device can be calculated as;
P
DISS
= (V
S
鈥?/div>
V
OUT
)
where:
V
S
= supply voltage
V
OUT
= output voltage
I
LOAD
= output load current
Figure 3 shows the maximum power dissipation versus temperature.
To achieve proper operation, use the previous equation to calculate
P
DISS
for a specific package at any given temperature, or use the
chart below.
1.25
14-LEAD SOIC
1
THD + N 鈥?%
0.1
V
S
=
V
S
=
2.5V
8V
0.01
20
100
1k
FREQUENCY 鈥?Hz
10k
30k
Figure 4. THD + N vs. Frequency Graph
Short Circuit Output Conditions
The AD856x family does not have internal short circuit protection
circuitry. As a precautionary measure, it is recommended not to
short the output directly to the positive power supply or to ground.
It is not recommended to operate the AD856x with more than
35 mA of continuous output current. The output current can be
limited by placing a series resistor at the output of the amplifier
whose value can be derive using the following equation:
R
X
鈮?/div>
V
S
35
mA
I
LOAD
For a 5 V single supply operation,
R
X
should have a minimum
value of 143
鈩?
LCD Panel Applications
MAXIMUM POWER DISSIPATION 鈥?W
1.00
The AD856x amplifier is designed for LCD panel applications
or applications where large capacitive load drive is required. It
can instantaneously source/sink greater than 250 mA of current.
At unity gain, it can drive 1
碌F
without compensation. This
makes the AD856x ideal for LCD V
COM
driver applications.
To evaluate the performance of the AD856x family, a test circuit
was developed to simulate the V
COM
Driver application for an
LCD panel.
0.75
14-LEAD TSSOP
8-LEAD MSOP
0.50
5-LEAD SOT-23
0.25
0
鈥?5
鈥?5
5
25
45
AMBIENT TEMPERATURE 鈥?C
65
85
Figure 3. Maximum Power Dissipation vs. Temperature
for 5-, 8-, and 14-Lead Packages
REV. A
鈥?鈥?/div>
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